WO2018085739A1 - Heat treatment method and apparatus - Google Patents

Abstract

The invention is a method of and apparatus for in-situ heat treatment for re-solutionizing β-phase in sensitized aluminum-magnesium alloy structures and, in particular, a method of and apparatus for in-situ heat treatment for re-solutionizing β-phase in sensitized aluminum-magnesium alloy structures comprising naval vessels. The invention also relates to a method for maximizing the absorption of radiant energy on a substrate. The invention also relates to an apparatus for securing a heat treatment device to a substrate having an irregular surface.

Description

Heat Treatment Method and Apparatus

RELATED APPLICATIONS

[0001] This application claims the benefit of commonly owned US Provisional patent application 62/418,150 filed on 04 November 2016, and commonly owned US Provisional patent application 62/451,662, filed on 28 January 2017. This application is related to commonly owned US Provisional patent application 62/360,372, filed 09 July 2016. The heater support device of this invention is similar to the support device in commonly owned US Patent application 13/561,032, filed on 28 July 2012. This application incorporates by reference the disclosure of the following commonly US patent applications: 62/418,150 filed on 04 November 2016, 62/451.662, filed on 28 January 2017, 62/360,372, filed on 09 July 2016 and 13/561,032, filed on 28 July 2012.

GOVERNMENT SUPPORT

[0002] Not applicable.

SEQUENCE LISTING

[0003] Not applicable.

FIELD OF THE INVENTION

[0004] The present invention relates generally to the field of localized heat treatment of sensitized metallic compounds and, in particular, to the in-situ de-sensitization heat treatment of sensitized aluminum-magnesium alloys in naval vessels. The present invention also relates to a method for maximizing the absorption of infrared energy on a target. The present invention also relates to an apparatus for heat treating a substrate having an irregular surface.

BACKGROUND

[0005] Aluminum has been used in the construction of naval vessels for more than a century.

Experimental small craft were constructed of aluminum as long ago as the 1890's and, at that time, further use seemed promising. The first sizable craft constructed of aluminum was the sloop-rigged yacht Vendenesse, built at St. Denis in France in 1892. Aluminum plate was used for the shell plating, decks and bulkheads, although the frames, keel and stringers were steel. Within four months after launch, corrosion was observed over 20 square meters ( ~ 200 square feet) of her bottom, where the bottom paint had failed. Corrosion was a continuing problem for the Vendenesse. The first use of aluminum in the United States for a sizable craft occurred in 1895 when Herrshoff designed and built the America's Cup yacht Defender which was to be the pride of American technology. The side shell plating and some of the frames were of an aluminum-nickel alloy. The portion of the Defender below the waterline was bronze, as were the rivets for the aluminum portions. This combination of aluminum with bronze led to rapid corrosion of the aluminum but not before the Cup was won by Defender. The experience with these vessels was not promising, leading Scientific American in an article published in 1894 to state that this experience "does not present a very encouraging prospect for the introduction of aluminum boats."¹

[0006] Aluminum was first used in the U.S. Navy for some topside fittings for the torpedo boats intended for the battleship USS Maine. These stanchions, sockets and decklight frames quickly corroded and were replaced with steel. A similar experiment with the same results was made with the torpedo boats Foote, Rodgers, and Winslow, which were built in Baltimore between 1895 and 1898. The first aluminum deckhouses for U.S. Navy ships were for the torpedo boats Dahlgren and Craven, which were designed and built by Bath Iron Works in 1898. Possibly, the use of aluminum for the hulls by French yards interested the Bath Iron Works, and they used this new technology. However, the aluminum in these boats evidently fared no better than it had in other applications, for aluminum was not used again in structural applications for forty years.

[0007] In the 1930s, lightweight topside structure was becoming important for destroyers. In 1935, aluminum was reintroduced to deckhouse and was used extensively for many other nonstructural purposes, including furniture and joiner bulkheads. With the DD-409 class, designed in 1936, came the greatest use of aluminum for exposed deckhouse structure. Plating was mixed, some of aluminum, some of mild steel, with the framing of mild steel. This application of aluminum plate was apparently successful, because the next class designed, the DD-423, used aluminum for plating throughout the entire deckhouse, except where thick steel was used for fragment protection.

[0008] Design of deckhouse structure became rather standardized with mild steel transverse frames spaced 21 inches supporting aluminum plating that was 4.8 mm (3/16 inches) thick everywhere except in way of gun blast, where it was 6.3 mm (1/4 inches) thick. The next major design, the Fletcher (DD-445) class destroyers, used this configuration from the beginning of the class in 1940. However, with the onset of World War II, all uses of aluminum except for aircraft came under

¹ NTIS-PB2009101032 ; Aluminum Structure Design and Fabrication Guide; Sielski, R. A.; 796 pages; 2007 careful scrutiny because of shortages, and the use of aluminum in Navy ships was temporarily discontinued. The DD-445 class was thus a mixture of steel and aluminum.

[0009] With the USS Gearing (DD-692) and USS Sommer (DD-710) class destroyers, riveted aluminum came back, being used for about half of the deckhouse sides and decks, although the transversely framed stiffeners were welded steel. Following the war, the development of aluminum welding had an effect, and in 1948 the new destroyer leaders, the USS Mitcher (DL-2) class had aluminum deckhouses that were entirely welded, including the transversely oriented frames. From about 1953 on, all new U.S. Navy combatants (destroyers, destroyer escorts, frigates and cruisers) had aluminum for the majority of their deckhouses. In addition, aluminum is used for the deckhouse in landing ships, and for the islands of aircraft carriers and amphibious assault ships.

[0010] The use of aluminum for the hulls of high-speed merchant vessels began in the 1990s with increased construction of high-speed ferries. These vessels have become so technologically advanced that they have surpassed the capabilities of many naval vessels; many navies today are adapting derivatives of these high speed vessels to combatant craft.

[0011] The U.S. Navy is using 5XXX aluminum alloys as a critical construction material in the design and construction of state-of-the-art Navy ships. As noted above, aluminum had long been used in the construction of naval vessels. In order to maximize the stability and, in some cases, speed of naval vessels, aluminum-magnesium [5XXX] alloys have been used to construct ship superstructures. More recently, the current U.S. Navy shipbuilding plan is to grow the size of the fleet with significant aluminum structural components to approximately 170 vessels by 2040, including 32 Littoral Combat Ships [LCS], 20 Future Frigates [FF], 22 Guided Missile Cruisers [CG], 12 Aircraft Carriers [CVN], 11 Joint High Speed Vessels [JHSV], and 73 Ship to Shore Connectors [SSC] to replace the 91 Landing Craft Air Cushion [LCAC] Vehicles.²

[0012] The primary alloying element in 5XXX series aluminum alloys is magnesium. During production, highly controlled heat treatments are used to evenly distribute magnesium in the aluminum

² "Quantitative Nondestructive 5XXX Aluminum Material Assessments to Reduce Total Ownership Costs," Dunn, Ryan, Naval Engineering Journal, March 2016, Vol. 128, No.l, pp 23-34 matrix. Different alloys in the 5XXX series contain different amounts of magnesium ranging from ~ 3.5% in 5086 to ~ 4% in 5083 and up to ~5 % in 5046. These alloys are popular for marine applications because they combine a wide range of strength, good forming and welding characteristics, and high resistance to general corrosion. 5XXX alloys with greater than 3.0% magnesium content may be susceptible to stress corrosion cracking [SCC] . In service, limitations should be placed on the amount of cold work and maximum permissible operating temperature for the higher magnesium content alloys to avoid increased susceptibility to stress corrosion cracking and intergranular corrosion [IGC]. For these reasons, such alloys should not be used at operating temperatures greater than approximately 65°C

[149°F].

[0013] Ships and vessels constructed of 5XXX aluminum alloys are susceptible to a metallurgical phenomenon known as sensitization. The evenly distributed state of the magnesium within the

Aluminum matrix is thermodynamically metastable and exposure to even mildly elevated temperatures for extended periods of time can cause the magnesium to form beta-phase [Mg₂Al₃] precipitates. The formation of these beta-phase precipitates along the grain boundaries as a connected network is called sensitization. Welding on existing 5XXX aluminum structures that have become sensitized in support of repair, maintenance and/or modification may require specific critical welding procedures and, in some cases, the application of cold working technologies or wholesale material replacement depending on the degree of sensitization (DoS).

[0014] As noted above, sensitization is the formation of magnesium rich beta-phase precipitates at material grain boundaries as the result of exposure to elevated temperatures for extended periods of time. These beta-phase precipitates are anodic to the surrounding aluminum matrix, and when exposed to a corrosive environment, sensitized material will experience intergranular corrosion [IGC] . When tensile stress is applied to material that has experienced IGC, stress corrosion cracking [SCC] can result.

[0015] At a high level, the rate of sensitization is primarily a function of four factors: thermal exposure, alloy composition (% magnesium), material temper and the material grain size and microstructure. Assuming equivalent thermal exposures, tempers, grain sizes, and microstructures, 5XXX aluminum alloys containing higher amounts of magnesium will sensitize faster than 5XXX aluminum alloys with lesser amounts of magnesium. For example, 5046 (- 5% magnesium) will sensitize faster than an equivalent 5083 (~ 4% magnesium) sample, and 5083 will sensitize faster than an equivalent 5086 (~ 3.5% magnesium) sample when exposed to the same thermal conditions.

[0016 ] The beta-phase [Mg₂Al₃] precipitates contain approximately 38% magnesium which is significantly higher than the aluminum matrix , which for 5456 Aluminum alloy is approximately 5% magnesium. Elemental magnesium is thermodynamically less stable and kinetically more active than elemental aluminum. These characteristics make magnesium more susceptible to dissolution in low and neutral pH environments. The beta-phase [Mg₂Al₃] behaves more like magnesium than aluminum and will dissolve rapidly in seawater environments. This difference in dissolution behavior, combined with the fact that beta-phase forms preferentially on grain boundaries during service, leads to the preferred corrosion of those grain boundaries. In other words, these beta-phase preferential grain boundaries are susceptible to intergranular corrosion [ IGC ].

[0017] Stress Corrosion Cracking [SCC] will occur if a specific set of material properties and environmental conditions are present. As illustrated in Figure 1 , sensitized material is one of the conditions that contributes to SCC of aluminum alloys. The sensitized material then needs to be exposed to a corrosive environment and intergranular corrosion [IGC] needs to initiate corrosion along grain boundaries. Lastly, a tensile stress needs to be applied to the IGC affected material to form a stress- corrosion crack.

[0018] Aluminum-magnesium alloys can become sensitized in different ways. Heating and holding the alloy for even a relatively short period of time at an elevated temperature may produce the sensitized condition. However, it is not always necessary to heat to elevated temperatures to produce the condition.

[0019] The Naval Surface Warfare Center Carderock Division [NSWCCD] has an ongoing effort to predict sensitization rates of various 5XXX aluminum alloys in the fleet. As part of this effort, two sample racks holding six samples each were mounted on a deployed Navy vessel. The temperature of each test specimen was measured and recorded by an attached thermocouple every 20 minutes. The collected temperature data was fed into a predictive model developed by NSWCCD to predict sensitization rates for different 5XXX aluminum alloys based on the recorded thermal exposures. Based on this data it is estimated that recrystallized 5083 aluminum alloy will reach sensitization levels above 25mg/cm² after approximately 7 to 10 years of normal operating fleet exposure and 5456 aluminum alloy is estimated to become sensitized after approximately 4 years of normal operating fleet exposure. The 25mg/cm² test result quoted above was obtained using the industry standard Nitric Acid Mass Loss Test (hereinafter "NAMLT"). The U.S. Navy considers 5XXX alloys which have a NAMLT test result above 25 mg/cm² to be sensitized.

[0020] Ships and vessels with aluminum superstructures made from 5XXX aluminum alloys have experienced cracking due to the effects of corrosion. Surface ship structures made of 5456 and/or 5083 aluminum will become sensitized from long-term [4 - 10 years] exposure to normal fleet operating conditions. In addition, heat from welding processes, for example Friction welding or Gas Metal Arc [GMA welding] , used in ship fabrication and repair may also contribute to the sensitization of these ship structures. Once the ship superstructure has become sensitized, it is more prone to inter granular corrosion [IGC] and also to stress corrosion cracking [SCC] .

[0021] The importance of implementing innovative approaches to reduce total ownership costs associated with the repair, maintenance, and modernization of vessels constructed using 5XXX aluminum alloys is best exemplified by the problems and significant increases in total ownership costs associated with the repair of a significant number of sensitization and fatigue related superstructure cracks across the 22-ship Ticonderoga class guided missile cruisers. The high cost of aluminum crack repair and significant number of CG superstructure cracks in addition to the difficulties associated with working on sensitized aluminum has added several hundred million dollars to the total ownership costs of the CG class ships. With an additional 20 years of service life remaining for many of the CG class ships, it is conservative to estimate that stress corrosion cracking and the difficulties associated with performing work on sensitized aluminum will continue to significantly increase total ownership costs.

BRIEF SUMMARY OF THE INVENTION

[0022] Once portions of ship structure made from 5XXX alloys have become sensitized it was not thought that this condition was easily reversible. The normal practice to deal with this situation was, often, wholesale replacement of the sensitized aluminum. However, it has been discovered that it is possible to de-sensitize these portions of ship structure m-situ by re-dissolving the beta-phase into the alloy matrix via the proper type of anneal heat treatment. Note the teachings of Kramer et al., in U.S. Patent 9,394,596. This de-sensitization process is similar to the types of mill stabilization heat treatments used for many years in aluminum production. Once an area of the ship structure has been determined to be sensitized, an in-situ heat treatment using a portable heater is applied to de-sensitize the affected area. One of the disadvantages of this type of treatment is that it tends to anneal the structure. Because the 5456 aluminum-magnesium alloy commonly used in naval ship construction derives its strength from work hardening, the treated, annealed plate is softer than, for example, the HI 16 or H321 marine grade plate. Thus, close control of the anneal heat treatment is critical.

[0023] This invention is a method for in-situ de-Sensitization of a 5XXX alloy structure by applying a localized heat treatment. The heat treatment is similar to a mill stabilization treatment used to reverse sensitization and to restore corrosion resistance and shape fixability in existing Aluminum-magnesium products. Such a treatment is disclosed in Zhao et al. US Patent 6,248,193 B l which reference teaches heating a continuously cast and rolled aluminum-magnesium alloy sheet with from 3% - 6% magnesium to a temperature of 240°C to 340 °C and holding that temperature for one hour or more. As taught in Zhao et al. this heat and hold treatment followed by a slow cooling ensures that magnesium segregated through continuous casting may be reliably precipitated in the form of particles along the grain boundaries. Of course, in a mill setting, such heat treatments are fairly easily carried out. Doing a de- sensitization heat treatment on an existing structure such as a ship is another matter entirely.

[0024] Another portion of the invention is a new method for more efficient heat transfer during the in- situ heat treatment process for aluminum, other metals and of non-metallic compounds. One of the heat sources envisioned for use in providing heat to the sensitized aluminum substrate is an infrared emitter. This heat source is well-known in the art. What is new is the concept of tuning the frequency of the infrared emitter to match the absorption spectrum of the material being heated. For example, with the sensitized aluminum of the current invention, the aluminum reflects over 90% of the infrared energy impacting it over a wide range of impacting energy wavelengths. Except if the frequency of the impacting radiation is in the 600 - 900 nm range, there is a pronounced dip in the energy reflected. At approximately 825nm wavelength of impacting infrared radiation, the aluminum only reflects about 86% of the energy impacting it. In other words, the aluminum absorbs more of the impacted energy if the energy is coming in at these frequencies. This means that the in-situ heat treatment may be performed more efficiently.

[0025] Another way to achieve a more efficient heat transfer during the in-situ heat treatment process for sensitized aluminum, other metals and of non-metallic compounds is to coat the sensitized aluminum, other metal or non-metallic compound with a coating which will absorb more of the infrared energy than the bare substrate would absorb. It is envisaged that this coating would either be able to withstand the temperatures involved and be removed at a later time, or be a sacrificial coating and designed to burn off during the treatment.

[0026] Another portion of the invention involves the provision of a heat treatment apparatus which is capable of applying a closely controlled heat treatment to a substrate of interest which substrate may have an irregular surface. The apparatus comprises a support device and a heating unit. The support device supports the heating unit directly over the substrate of interest and permits the system to be secured to one surface of the substrate of interest in a removable and non-destructive manner. The support device has legs which have securing means on the bottom thereof to secure the system to one surface of the substrate of interest in a releasable and non- destructible way. Normally the support device will have at least three (3) legs [although there may be more or less as desired and/or necessary]. Typically, these securing means comprise powerful suction cups, but they may be magnetic if the substrate is ferrous or they could be any other suitable means to secure the device to a substrate in a releasable and non-destructible way . The support device also permits the heating unit to be biased towards the substrate of interest. Removable, as used herein, means that the system may be placed upon a surface of the substrate of interest and then removed. The idea is that the legs permit the device to be secured to and removed from a substrate in a manner that does not damage the substrate. It is to be understood that not damaging the substrate may still permit a cleaning or light abrasion of the substrate to remove a protective coating in the area where the treatment is desired. The support device also has an adjustment means that permits each leg to independently extend/retract as necessary to accommodate a substrate of interest with an irregular [non-planar] surface. The legs permit the device to be biased against the surface and the design of the heater assures that the surface directly under the heater will receive the correct treatment and the area even immediately outside the heater will receive minimal heat. In certain applications, the heating unit will be thermally sealed against the surface.

[0027] The substrate will most often be a metal, often aluminum, and may have an irregular surface. To provide the best contact possible with such an irregular substrate, each leg of the device is independently adjustable [as noted above] in order to move the heater body closer or farther away from the substrate surface. Each leg has a two stage adjustment system, a coarse adjustment and a fine adjustment. As mentioned above, the support device comprises means to secure the device to the substrate of interest and permits the device to be biased against the substrate. This feature, in combination with the above mentioned independently adjustable legs permits the device to be used on substrates with irregular surfaces. If the means to adhere is a suction cup, it is even possible to removably secure the device to an vertical surface using vacuum-powered suction cups. These are suction cups powered by air being forced through a vacuum producing venturi closely associated with the suction cup. Using this type of design, it has been found that the device can be used successfully on substrates that actually are inclined slightly beyond the vertical.

[0028] There are several significant problems inherent in performing such a heat treatment on an existing aluminum - magnesium structure. First of all is the problem of detecting just exactly which portions of the existing structure are sensitized and would thus need to be de-sensitized. Secondly, it is important when working on the sensitized portion of an existing structure that the surrounding, non- sensitized areas not become sensitized by the heat treatment applied to the sensitized areas. This situation can occur if the surrounding, non-sensitized areas receive too much heat from the de-sensitization process. Thirdly, it is important to make sure that the de-sensitizing treatment not reduce the strength of the existing, sensitized structure below acceptable levels. Lastly, it is important to make sure that the structure being treated [and surrounding structures] have the absolute minimum deformation as a result of the de-sensitization heat treatment.

[0029] The industry standard test for determining the degree of sensitization of aluminum-magnesium alloy structures is the NAMLT test [Nitric Acid Mass Loss Test]. The NAMLT test requires cutting sample coupons from areas of the structure that are suspected of being sensitized and then performing the NAMLT test on them. This test essentially destroys the sample coupons and harvesting the sample coupons leaves holes in the aluminum structure. Cutting numerous holes in the structure of a billion dollar ship is not going to win anyone a popularity contest. Since it is extremely difficult, if not outright impossible, to determine sensitization by merely looking at a suspect area, harvesting sample coupons is definitely a hit-or-miss affair. Experience with repair of previous cracks on similar ships in the fleet might at least suggest which portions of the structure are likely to be sensitized— but this is still a less than satisfactory method for directing sample coupon harvesting. Fortunately, the recent development of the DoS-Probe [note the article by Ryan C. Dunn (one of the inventors of this application) "Quantitative Nondestructive 5XXX Aluminum Material Assessments to Reduce Total Ownership Costs," Dunn, Ryan, Naval Engineering Journal, March 2016, Vol. 128, No. l, pp 23-34] makes this detecting step vastly easier. Using a DoS-Probe to perform a non-destructive sensitization test of various portions of the existing structure permits a rapid determination of exactly which portions of the structure are sensitized. There are also other sensors which can be used to determine the degree of sensitization [DoS] of an aluminum-magnesium structure, for example the microwave sensor developed by AlphaSense, Inc.

[0030] Figure 2³ illustrates the effect of temperature on susceptibility of various aluminum-magnesium alloys to stress corrosion cracking. The x-axis represents the weight % of magnesium in the aluminum- magnesium alloy. The y-axis represents temperature in °C. Area 1 is the boundary of the sensitized range. Area 3 is the β-phase solid stability limit or the annealed range. Area 2 is the stabilization range. A sensitized structure made of aluminum-magnesium alloy with ~ 4 wt % magnesium [say 5083 alloy] can be de-sensitized by a heat treatment which heats the structure to a temperature of about 190 °C.

[0031] It is important to control the heat treatment closely to prevent surrounding non-sensitized areas from becoming sensitized by the de-sensitization treatment. This could occur, for example, if a non- sensitized area of the 4% wt magnesium structure close to the sensitized area was heated to a temperature ~ 160 °C by waste heat from the de-sensitization treatment. Figure 3 illustrates the forward portion of a Ticonderoga class CG cruiser. Let us say [for example] that area A as shown in Figure 3 represents an area of interest on the deckhouse of the ship made from 5083 aluminum-magnesium alloy. Let us further say that this is an area where stress cracks were known to have been a problem in the past. Figure 4 is a close-up view of area A. Let us further assume that it has been determined that portion B of area A

³ E. H. Dix, Jr., W. A. Anderson, M. B. Shumaker, "Influence of Service Temperature on the Resistance of Wrought Aluminum-Magnesium Alloys to Corrosion," CORROSION, Vol. 15, No. 2, pp. 55t - 62t, February, 1959. is sensitized, but that the remaining portions of area A are not sensitized. Heat treatment of portion B to de-sensitize it, for example as disclosed in the above noted Kramer et al patent U.S. 9,394,596, may require a controlled heating of portion B of area A to, say, approximately 240 °C for ~ 30 minutes. It is quite possible that other portions of area A [for example, immediately adjacent the boundaries of portion B] will be heated to approximately 160 °C because of the de-sensitization treatment of portion B. This could put these portions of area A into the sensitization portion 1 as shown in figure 3. Thus, in desensitizing portion B, portions of area A could become sensitized. Obviously, this is not a desirable outcome. In order to prevent this situation, it is known to use thermal dams to protect surrounding areas when a particular area is being de-sensitized. A typical thermal dam might be water-cooled or, perhaps, air-cooled. Any type of thermal dam which is robust enough to handle the necessary handling and temperature issues will suffice.

[0032] It should be noted that it generally takes more time to have aluminum-magnesium alloys become sensitized than it does to desensitize them— thus heating an area of an unsensitized or moderately sensitized aluminum-magnesium alloy to the sensitization range [for example, Area 1 in Figure 2] for short periods of time [ 5 - 10 minutes or so] will not impart significant amounts of sensitization, while heating a sensitized aluminum-magnesium alloy to approximately 260 °C for a short period of time [4 minutes or less] can cause the sensitized aluminum-magnesium alloy to become de-sensitized.

[0033] It is also important to prevent the structure being de-sensitized [and surrounding areas as well] from losing too much strength through annealing. It is obvious that the use of thermal dams could be an important tool in controlling this undesirable side effect.

[0034] Of course, it is also important to prevent the structure being de-sensitized [and surrounding areas as well] from undesirable deformation during a de-sensitization treatment. The use of thermal dams could also be an important tool in controlling deformation.

[0035] The heat treatment method of this invention involves an in-situ heat treatment of a sensitized area of an existing structure using a portable heating device. The gist of the invention is to use the minimum amount of heat effective to achieve the desired result for the minimum amount of time. Once the desired heat has been applied for the desired time, the heat source is turned off and the affected area is allowed to air-cool. This reduces unwanted sensitization of surrounding material, reduces unwanted annealing and undesirable deformation of the structure. Having stated these principles, minimum heat for the minimum time, it should be recognized that there might be times where more heat than the bare minimum necessary may be desirable in order to avoid undesirable collateral damage as will be further explained below in §

[0037]. [0036] In order to achieve this treatment, a protocol is determined for the specific aluminum-magnesium alloy comprising the sensitized structure. This protocol is determined using the relationships shown in figure 2. A target de-sensitization DoS value is determined for the sensitized structure. Based upon the wt % of Mg in the 5XXX aluminum-magnesium structure, a minimum temperature range and minimum hold time necessary to de-sensitize the structure is determined. A portable heater [ such as that shown in Figures 8 - 17 [18] or a heater such as shown in Figures 1 [321] - 7 [38]] with any necessary thermal dams is applied to the structure and the in-situ treatment is initiated. Once the sensitized material is in the desired temperature range and has been held there for the desired amount of time, the application of heat is discontinued and the structure allowed to air cool.

[0037] A heat treatment protocol with very short hold times is used to de-sensitize a sensitized structure. Once the structure has reached the desired temperature, it is not maintained at that desired temperature for long periods of time. For example temperature maintenance time periods of 5 to 60 minutes [as stated in the aforementioned Kramer et al. patent [U.S. 9,394,596] are not used. This method uses temperature maintenance times in the order of 0 to 4 minutes. For example, it might be determined that for a particular sensitized 5XXX structure with that the minimum temperature - minimum hold time protocol to de-sensitize the structure is 230 °C, with a hold time of zero [0] minutes. The structure could then be heated to 230 °C and allowed to immediately air-cool with essentially zero [0] minutes hold time. This process is illustrated in figure 5. For another sensitized 5XXX structure it might be determined that the minimum temperature - minimum hold time protocol is heating to 230 °C with a minimum hold time of 3 minutes. This process is illustrated in figure 6. For another sensitized 5XXX structure it might be determined that the minimum temperature - hold time protocol is heating to 230 °C with a minimum hold time of two [2] minutes. However, it may be desirable to have a shorter hold time [i.e. less than two minutes] in this instance because of concerns over "collateral damage" to surrounding portions of the structure due to sensitization, deformation and/or annealing issues. In this instance it may be decided to heat to a higher temperature [say 280 °C ] so that a zero [0] minute hold time may be used in order to address these collateral damage issues. This process is illustrated in figure 7.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 illustrates the process by which 5XXX aluminum alloy can become sensitized and is discussed supra in paragraph [0017].

[0039] Figure 2 illustrates the effect of temperature on the susceptibility of various aluminum- magnesium alloys to stress corrosion cracking and is discussed supra in paragraph [0030].

[0040] Figure 3 is a drawing of the forward portion of a Ticonderoga class CG cruiser. [0041] Figure 4 is a drawing of an area of interest "A" on the deckhouse of a Ticonderoga class CG cruiser.

[0042] Figure 5 illustrates a first embodiment of a process for the in situ heat treatment to de-sensitize a sensitized aluminum structure.

[0043] Figure 6 illustrates a second embodiment of a process for the in situ heat treatment to de-sensitize a sensitized aluminum structure.

[0044] Figure 7 illustrates a third embodiment of a process for the in situ heat treatment to de-sensitize a sensitized aluminum structure.

[0045] Figure 8 illustrates a first embodiment of an apparatus 100 particularly adapted to perform the processes for the in situ heat treatment to de-sensitize a sensitized aluminum structure illustrated in figures 5 - 7.

[0046] Figure 9 illustrates the water-cooled thermal dam portion 104 of apparatus 100.

[0047] Figure 10 illustrates a cross-section of the water-cooled thermal dam portion 104 of apparatus 100 along plane C - C of figure 9.

[0048] Figure 11 illustrates a cross-section of the water-cooled thermal dam portion 104 of apparatus 100 along plane D - D of figure 9.

[0049] Figure 12 illustrates a vortex tube.

[0050] Figure 13 illustrates a second embodiment of an apparatus particularly adapted to perform the processes for the in situ heat treatment to de-sensitize a sensitized aluminum structure illustrated in figures 5 - 7.

[0051] Figure 14 illustrates a cross-section of the thermal dam portion 104' of apparatus being cooled by vortex tube 120.

[0052] Figure 15 shows an end view of a first embodiment of a heater unit for the in situ heat treatment apparatus of the invention.

[0053] Figure 16 shows a plan view of the heater unit shown in figure 15.

[0054] Figure 17 shows an end view of a second embodiment of a heater unit for the in situ heat treatment apparatus of the invention.

[0055] Figure 18 shows a plan view of the heater unit shown in figure 17. [0056] Figure 19 shows a side view of a third embodiment of a heater unit for the in situ heat treatment apparatus of the invention.

[0057] Figure 20 shows a plan view of the heater unit shown in figure 19.

[0058] Figure 21 illustrates a heat treatment process as performed by the heater unit shown in figures 19 and 20.

[0059] Figure 22 also illustrates the heat treatment process performed by the heater unit shown in figures 19 and 20.

[0060] Figure 23 also illustrates the heat treatment process performed by the heater unit shown in figures 19 and 20.

[0061] Figure 24 illustrates another embodiment of the heat treatment process performed by the heater unit shown in figures 19 and 20.

[0062] Figure 25 illustrates an Alpha sensor which gives a more or less continuous readout of the degree of sensitization of an aluminum plate.

[0063] Figure 26 illustrates a heat treatment apparatus with four independently adjustable mounting means.

[0064] Figure 27 illustrates a single independently adjustable mounting means and the fine height adjustment means of same from the heat treatment apparatus of figure 24.

[0065] Figure 28 illustrates the coarse height adjustable mounting means of the heat treatment apparatus of figure 24.

[0066] Figure 29 shows an alternate embodiment of the adjustable mounting means which permits removably mounting of a heating means to a non-planar surface.

[0067] Figure 30 is a graph illustrating a typical spectral profile for aluminum of percentage reflectance of radiation impacting the aluminum verses the wavelength of the impacting radiation.

[0068] Figure 31 is a graph illustrating a spectral profile of percentage reflectance of radiation impacting a sample verses the wavelength of the impacting radiation for an Ag coated sample and an Al coated sample.

[0069] Figure 32 is a graph of the Spectral dependence of the spectral, normal absorptivity a ^„ and reflectivity p „ of selected opaque materials including an Aluminum evaporated film and black paint.

[0070] Figure 33 shows a side elevation a first embodiment of the second heat treatment device of the invention. [0071] Figure 34 shows a bottom view of the device from the perspective of arrows A in Figure 33

[0072] Figure 35 shows a top or plan view of the device of Figure 33.

[0073] Figure 36 illustrates the heating unit of the device of Figures 33 - 35 with heat shields attached.

[0074] Figure 37 shows a partial cross-section of the heating unit of Figure 35.

[0075] Figure 38 illustrates the coarse height adjustment means of the embodiment of Figures 33 -

[0076] Figure 39 illustrates a second embodiment of the second heat treatment device of the invention mounted on a non-planar surface.

DETAILED DESCRIPTION OF THE INVENTION

[0077] Since Figures 1 - 7 have been discussed supra, this section begins with a description of Figure 8.

[0078] A heating apparatus 100 suitable for performing these processes is shown in figure 8. Apparatus 100 comprises a prism-shaped heater shroud 102 surrounded at its lower border with a water-cooled thermal dam 104. Carrying handles 106, 106', 106" and 106"' are placed at the corners of apparatus 100 to aid in carrying and positioning apparatus 100. Power cord 110 provides any necessary electrical power to the heating elements inside heater shroud 102.

[0079] Figure 9 shows the water-cooled thermal dam 104 of figure 8. The water-cooled thermal dam 104 comprises solid aluminum blocks 112, 112', 112" and 112"' arranged in a generally rectangular fashion about the lower portion of heating shroud 102. Blocks 112, 112', 112" and 112"' are joined together at joints 114, 114', 114" and 114"' by welding or any other suitable joining means. Internal water conduit 116 runs through each block 112, 112', 112" and 112"'. In block 112 cooling water is fed in at inlet 118 [shown in figure 10], flows through the conduit 116 in thermal dam 104 and exits block 112 at outlet 118'.

[0080] Figure 10 shows a cross-section of water-cooled thermal dam 104 at plane C - C of figure 9. Block 112 contains an internal water pipe 116 [not illustrated in figure 10] which ends in outlet conduit 118' which conduit permits the cooling water to exit thermal dam 104 after absorbing waste heat. Figure 11 shows a cross-section of thermal dam 104 as shown at plane D - D of figure 9.

[0081] It is possible to construct thermal dam 104 with types of cooling devices other than internal water pipes. For example air vortex tube coolers may be used. The vortex tube was discovered in 1928 by George Ranque. The device uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of these two airstreams are adjustable with a valve built into the hot air exhaust. Temperatures as low as -50°F (-46°C) and as high as +260°F (127°C) are possible. Figure 12 illustrates a vortex tube 120. Compressed air is fed into vortex tube 120 at inlet nozzle 125 [usually at from 80 to 100 PSIG] and hot air flows out of outlet nozzle 123 while cold air flows out of outlet nozzle 124.

[0082] A generally accepted explanation of how a vortex tube works is as follows. Compressed air is supplied to the vortex tube and passes through nozzles that are tangent to an internal counterbore. These nozzles set the air in a vortex motion. The air may well be spinning at up to 1 ,000,000 rpm in this vortex. This spinning stream of air turns 90° and passes down the hot tube in the form of a spinning shell, similar to a tornado. A valve at one end of the tube allows some of the hot air to escape. What does not escape, heads back down the tube as a second vortex inside the low-pressure area of the larger vortex. This inner vortex loses heat to the larger vortex and exhausts through the other end as cold air.

[0083] Figure 13 shows a heating apparatus 100' similar to that shown in figure 8 except the apparatus 100' uses a thermal dam 104' which is cooled by multiple vortex tubes 120. Power cord 110' provides any necessary electrical power. Twelve (12) vortex tube coolers are shown in figure 13, but the exact number of vortex tubes used will vary depending upon the specific heating and cooling requirements encountered in the field and more than 12 or fewer than 12 may be used as necessary. Each vortex tube 120 is fed compressed air from a suitable source [not shown in figure 13 for clarity] as indicated by the curved arrows in figure 13 near the lower portions of vortex tubes 120. The warm air is exhausted at the upper portion of each vortex tube 120 while the cold air is exhausted through the lower portion of the tubes 120 into thermal dam 104' as shown in figure 14. As noted above, this air may be at a temperature as low as - 46 °C and can be quite useful for cooling purposes. Also as noted above, the air exhausted from the upper portions of tubes 120 may be at temperatures as high as ~ 127 °C. Rather than simply exhaust this hot air and waste the thermal energy therein, it is envisaged that this air will be collected and used as an energy source in the heating process. For example, in heating apparatus 100', hot air collection tubes 124 [not all of which are numbered in figure 13] extend from each vortex tube 120 to a central collection plenum 126. The collected air is then passed over the material being heated by heating apparatus 100'.

[0084] Figure 14 shows how a single vortex tube 120 would be mounted on thermal dam 104'. Cold air outlet 124 of vortex tube 120 is fastened within bore 150 in thermal dam 104'. Bore 150 communicates with cooling air conduit 116' within thermal dam 104'. It is noted that cooling air conduit 116' is shown somewhat larger than water pipe 116 [of figure 11], however this is explained by the different thermal capacities of water and of air. Cold air flows out of outlet 124 into and through air conduit 116' as shown by the arrows in figure 14. The air flow exits through bore 152 in the side of thermal dam 104' after absorbing heat.

[0085] Figures 15 and 16 show a heater 100" comprising a prism-shaped heating shroud 122 without a thermal dam. Six (6) resistive wire heating elements 126 are secured inside shroud 122 in a position where they can heat a substrate which shroud 122 is positioned upon. Obviously, other types of heating devices could be used to provide the heat necessary for the inventive heat treatment process—such as induction coils or radiant heaters or any suitable heat source. It should be noted that certain applications of this inventive method may not need a thermal dam and that the heating shroud 122 might be used as shown herein [i.e., without an attached thermal dam] to perform a heat treatment according to the inventive method.

[0086] Figures 17 and 18 show a heater 100"' comprising a prism-shaped heating shroud 132 without a thermal dam. Fifteen (15) radiant heating elements 130 are secured to the outside of shroud 132 in a position where they can heat a substrate which shroud 132 is positioned upon. Not all of the radiant heaters shown in figures 17 and 18 have lead lines going to them for the sake of clarity. Obviously, fifteen (15) radiant heaters 130 are shown in figures 17 and 18, but the exact number of radiant heaters 130 used will vary depending upon the specific heating and cooling requirements encountered in the field and more than 15 or fewer than 15 may be used as necessary and desirable. It should be noted that certain applications of this inventive method may not need a thermal dam and that the heating shroud 132 might be used as shown herein to perform a heat treatment [i.e., without an attached thermal dam] according to the inventive method.

[0087] Figures 19 and 20 show a heater 100"" comprising a point heat source 136 without a shroud or a thermal dam. Point heat source 136 is centrally positioned on one side of plate 160. Point heat source 136 could be infra-red, radiant, induction, a laser or any other suitable type of point heat source. Point heat source 136 should be capable of being pulsed or cycled [i.e., operated in an intermittent manner]. Point heat source 136 is mounted on plate 160 by means of stand 138 and right angle support rod 137. As is illustrated in figures 21 and 22, heat source 136 operates as a point source of heat and is focused essentially in the middle of plate 160 as shown in figure 21 by reference numeral 152. Figures 21 and 22, will be further described below.

[0088] Figure 23 is a plot of temperature verses distance on the sensitized 5XXX plate 160 where the β- phase in the sensitized aluminum is being re-solutionized. Let us assume that the treatment protocol calls for heating to a temperature range of from 250 °C to 300 °C with a three and one half (3.5) minute hold time. Point heat source 136 is used to heat substrate 160 and it is used in a pulsed or intermittent fashion - - that is, it is not on all the time. The point heat source 136 is used to heat the center point 152 of the sensitized 5XXX plate 160 to between 250 °C and 300 °C and impinges on the center of the plate 160; however, the heat flux flows outwardly from the central point 152 as shown by the arrows in figure 21. As the heat flux flows away from the center of plate 160, the plate temperature will drop. In this example, the plate temperature at a distance approximately 4.2 inches away from central point 152 will drop to 250 °C . Thus the circular area G shown in figure 20a will be heated to between 250 °C and 300 °C . Further cooling will occur as the distance increases from central point 152 until the portion of plate 160 10 inches out from the center is only at 100 °C. When the temperature in circular area G reaches 250 °C the application of heat is continued for the proper hold time [in this example 3.5 minutes] and then the application of heat is discontinued and plate 160 is allowed to air-cool back to ambient temperature.

[0089] With proper selection of the cycling of the intermittent heat source 136, this situation can be maintained as long as desired with no thermal dam or other structure being necessary to keep the temperature of area G of plate 160 between 250 °C and 300 °C and still maintain the portion of plate 160 outside of circular area H at or below 100 °C. The advantages of this system are obvious, the pulsed or intermittent heat source is cheaper to operate than one which is on all of the time, and doing away with the necessity of a thermal dam eliminates most of the structure [shroud, etc.] of the heat treatment device. This is clearly a great simplification of the heat treatment process.

[0090] As noted above in § [0032] it generally takes more time to have aluminum-magnesium alloys become sensitized than it does to desensitize them— thus heating an area of a unsensitized or moderately sensitized aluminum-magnesium alloy to the sensitization range [for example, Area 1 in Figure 2] for short periods of time [ 5 - 10 minutes or so] will not impart significant amounts of additional sensitization. Thus, in the treatment example discussed above in §§ [0087] - [0088] even though the area of plate 160 between circular area G and circular area H will be heated to a temperature between 250 °C and 100 °C for a short period of time [5 - 10 minutes or so] it will not become sensitized.

[0091] Figure 21 shows how the heat flux flows on treatment plate 160 when the device shown in figures 19 and 20 is used to apply heat to plate 160. As noted above in §[0087] and [0088] the heat from point heat source 136 impinges on plate 160 at point 152. The heat flux then flows outwardly as shown by the arrows in figure 21. As also noted above, the temperature of the treatment plate 160 decreases with distance from center point 152.

[0092] Figure 24 illustrates a second method of heat treatment according to the invention. Figure 24 illustrates the same basic situation and treatment protocol as that shown in figure 23. In figure 23 the heat source is turned on and run intermittently until the central portion of sensitized plate 160 reaches 300 °C and then the heater is shut off. The treatment protocol called for a temperature of 300 °C and a hold time of zero (0) minutes. In figure 24 , a DoS sensor 168 is utilized to give a more or less continuous readout of the degree of sensitization of plate 160. This type of reading can be done with the newly developed Alpha sensor as shown in figure 25. The device uses a cavity perturbation technique to non- destructively measure the degree of sensitization [DoS] of a sensitized aluminum-magnesium plate within approximately one (1) minute. The Alpha-sensor will even measure the DoS value of a coated plate. The sensor probe 168 is connected to the hand-held electronics and control package 174 by cable 170.

[0093] Figure 24 illustrates how the Alpha sensor can be used as a feedback control for the entire heat treatment process according to the invention. Probe 168 is emplaced on the surface of 5XXX plate 160 inside the heating zone. Electronics and control package 172 is placed safely outside the heating zone and the two are connected by cable 170. With this type of set-up, once it has been determined that plate 160 is sensitized [and this can be done by the Alpha sensor] the heat source 165 can be energized and a heat treatment for re-solutionizing β-phase in sensitized aluminum can be initiated on plate 160 without determining a minimum temperature -minimum heating time protocol. A target de-sensitization DoS value for plate 160 will need to be determined and a target treatment temperature range will also need to be determined. The control package 172 can take the DoS values from plate 160 on a more or less continuous predetermined schedule and use these values to control the heat treatment in a feedback manner. When the DoS values measured by probe 168 reach the desired target level, the application of heat can be discontinued and the plate allowed to air cool.

[0094] Figure 26 illustrates a heat treatment device 300 with independently adjustable mounting means 200, 200', 200" and 200"' attached to each of the four sides of heating device 300 and attached to thermal dam 305. The mounting means are essentially similar to those shown in commonly owned U.S. Patent Application 13/561,032. One of these independently adjustable mounting means 200 is further illustrated in figure 27 and is described below

[0095] Base mount 312 is securely mounted to thermal dam 305 or such other portion of heating shroud 302 as is desired in order to orient the independently adjustable mounting means 200 as is shown in figure 27. Independently adjustable mounting means 200 comprises a mounting means for a large, bellows-type suction cup 303 powered by a coaxial venturi 302 mounted to the upper portion of suction cup 303.

Venturi mount assembly 308 attaches coaxial venturi 302 to height adjustment screw 304 which provides a fine height adjustment for mounting means 200.

[0096] This fine height adjustment is achieved by means of adjustment nut 306 which is captured in the fork 309 of adjustment screw mount 310. Adjustment nut 306 is threaded onto adjustment screw 304 [the threads on adjustment screw 304 are not shown in the drawings for clarity] but is captured in fork 309 of adjustment screw mount 310. Using this construction, rotation of adjustment nut 306 moves adjustment screw 304 upwardly or downwardly and thus moves suction cup 303, which is attached to the lower end of screw 304, upwardly or downwardly as shown by the double-headed arrow next to suction cup 303. Thus suction cup 303 can be moved up or down.

[0097] Adjustment screw mount 310 is attached to heating device 300 by leg base mount 312. The means attaching the adjustment screw mount to the leg base mount permits a coarse height adjustment of adjustment screw mount 310 with respect to leg base mount 312 as will be further described below in regard to figure 28 . Adjustment screw mount 310 is shown with five linearly spaced holes 340, 340', 340", 340"' and 340"" bored into the right side of adjustment screw mount 310. Each hole 340, 340', 340", 340"' and 340"" has a smaller perpendicular hole bored there through to permit a push pin [not shown] to be inserted into the holes. Base mount 312 has a corresponding number of linearly spaced holes [not shown] bored therein. Pins 342, 342' are removably secured in two of the corresponding holes bored in base mount 312. Pins 342, 342' have transverse bores 344, 344' bored there through. In operation, base mount 312 would be assembled to adjustment screw mount 310 with pins 342, 342' being inserted into the corresponding holes in adjustment screw mount 310. When assembled, the

perpendicular holes in adjustment screw mount 310 align with the transverse bores 344, 344' of pins 342, 342'. Push pins [not shown] are inserted through the aligned perpendicular holes and transverse bores 344, 344' to secure the assembly. In order to adjust the relative position of adjustment screw mount 310 and base mount 312, the push pins would be removed, adjustment screw mount 310 and base mount 312 would be separated, and pins 342, 342' could then be inserted into different holes 340. This would give a different relative position between adjustment screw mount 310 and base mount 312. In addition, pins 342, 342' could be removed from their holes in base mount 312 and placed in other holes in base mount 312 to achieve different relative positioning of adjustment screw mount 310 and base mount 312.

[0098] Figure 29 shows an alternative independently adjustable mounting means 200" for heating shroud 302'. Base mount 312' is attached to thermal dam 305' of heater shroud 302'. Generally horizontal rod 1001 is movably mounted toleg base mount 312'. As shown by the arrows in Figure 28a, these rods can move up or down on leg base mounts 312'. Generally perpendicular upper leg

1002 is attached to horizontal rod 1001 as shown. Lower leg 1003 is attached to upper legs

1002 by universal joint 1004. Thus, lower leg 1003 has a large range of motion with respect to upper leg 1002. This arrangement permits suction cup assembly 1005 a considerable amount of movement such that it can be aligned with uneven surfaces.

[0099] When the suction cups are all properly positioned, and heating device 300 secured to the sensitized portion of the structure, the air is turned on and a sizable suction drawn in each suction cup. By these means the heat treatment device 300 may be held on just about any type of surface, including a more than vertical wall, to accomplish a de-sensitization heat treatment.

[0100] Since the in situ heat treatment process of the instant invention is intended to be performed upon large structures such as portions of a Ticonderoga class CG cruiser or any other vessel comprising sensitized aluminum. With this in mind, it is clear that when performing the in situ heat treatment processes described above, a considerable amount of heat energy must be generated by the heat-treatment apparatus, transmitted to the substrate material and then absorbed by the substrate material— usually 5XXX aluminum. Obviously, if there is any way to improve the heat transfer efficiency of this process, it would be a very desirable addition to the processes described above.

[0101] When radiant energy is directed onto an aluminum surface, the aluminum surface tends to reflect over 90% of the radiant energy impacting it over a wide range of impacting radiant energy wavelengths. This is illustrated in figure 30 which shows a typical aluminum spectral profile of percentage reflectance of energy verses the energy wavelength. Note that with 250 nm wavelength radiation, the aluminum percentage reflectance is about 89%. This increases to about 92% at 500 nm wavelength radiation. In the range of wavelengths from about 1000 nm to 2500 nm the percentage reflectance is about 94% to 97+%. Oddly enough, there is a pronounced dip in the percentage of reflectance in the 600 to 900 nm wavelength range. As shown in figure 30 , the percentage of reflectance for aluminum "bottoms out" at approximately 86% at a wavelength of approximately 825 nm. Obviously, to at least a limited extend, the portion of radiant energy reflected back from an aluminum surface depends upon the wavelength of the impacting radiation. As discussed supra , this portion is greater than 90% for a wide range of impacting energy wavelengths, but it dips to about 86% for impacting energy in the 825% nm

wavelength. Of course, the showing of figure 30 also means that when the impacting radiant energy has a wavelength of about 825nm the aluminum is absorbing more energy than when the impacting radiant energy has a wavelength of, say, 500 nm or 1000 nm or 2000 nm.

[0102] As shown in figure 31 , aluminum coated substrates also show this marked dip in reflectance of radiant energy at the 600-900nm wavelength. Thus, the radiant energy apparatus of the invention could be used on an aluminum coated substrate for more efficient heat transfer. As is also shown in figure 31 , Gold and Silver coated materials also show pronounced dips in reflectance depending upon the wavelength of the impacting radiant energy. Therefore, the inventive process could be used on Au or Ag coated materials to achieve a more efficient heat transfer.

[0103] In view of the discussion above in paragraph [0101], it should be possible to have a more efficient radiant energy transfer to an aluminum substrate if the impacting radiant energy has a wavelength in the 600 to 900nm range and even more efficiency is obtained when the impacting energy has a wavelength of approximately 825nm. To this end, the heat treatment apparatus used in performing the in situ heat treatment processes of the instant invention would be tuned to generate radiant energy in the wavelengths which would insure the maximum absorption of energy depending upon the substrate being treated. If the substrate was aluminum, the emitter wavelength would be in the 600 to 900 nm range and most particularly, approximately 825nm. For other materials, the emitter wavelength would be tuned to the most favorable absorption range for the particular target material.

[0104] Another way to achieve more efficient energy transmission would be to adjust the radiant energy absorption of the substrate in a pre -determined wavelength range of the emitter instead of fine-tuning the emitter wavelength. For example, the substrate surface could be treated to absorb more energy in the pre -determined wavelength range of the emitter. One method of treatment for the substrate might be to sand or abrade the surface of the substrate. Another acceptable method for treating might be polishing the surface of the substrate. Or, a coating which has a high degree of radiant energy absorption in the predetermined wavelength range could be applied to the substrate surface. The coating might be sacrificed during the heat treatment or it might be selected such that it could survive the heat treatment.

[0105] Figures 33 - 35 show a first embodiment of the invention. The structure of device 700 permits accurate temperature control of the local substrate area immediately under the device.

Device 700 also has an attachment means which permits the device to be secured to substrates with a somewhat irregular surface morphology. It is noted that device 700 is adapted to work on horizontal surfaces, sloped surfaces, vertical surfaces, and even on surfaces that are slightly beyond vertical. It is to be understood that the means used to attach the device of Figures 33 - 35 to a substrate are show as suction cups. However, if the substrate of interest is ferrous, magnetic means could be used in place of suction cups. It is also possible to use a releasable adhesive means to mount the device of Figures 33 - 35 to a substrate of interest.

[0106] Figure 33 shows a side view of device 700 while Figure 34 shows a bottom view of the device viewed from the direction of arrows A - A in Figure 33. Figure 35 shows a top or plan view of device 700. These figures will be described together as they are different views of the same device with some common components hidden in one view but visible in the other.

[0107] Device 700 comprises a base 726 which is shown with the shape of an irregular hexagon. Obviously, other shapes than an irregular hexagon could be used, as desired and/or necessary. Base cover 732 is mounted to the upper portion of base 726. Also mounted to base 726 are leg base mounts 712, 712' and 712". These leg base mounts provide the mounting means for the suction cup assemblies 701, 701' and 701". Heater mount 750 is mounted to the lower portion of base 726 by multiple dowels which are fixed to base 726 and slidably secured in heater mount 750. Three of these dowels 752, 754 and 756 are shown in Figure 33. This permits the heater mount 750 to slide towards and away from base 726 in a controlled manner while keeping heater mount 750 generally parallel to base 726. The motion of heater mount 750 is controlled by screws 722 and 722' which are rotatably fixed in heater mount 750 and threaded in base 726 such that rotation of screws 722 and 722' moves heater mount 750 away from or towards the lower portion of base 726. Heating unit 600 is affixed to the lower portion of heater mount 750. Thus, movement of heater mount 750 towards or away from base 726 causes heating unit 600 to move towards or away from base 726.

[0108] Each suction cup assembly comprises a large bellows-type pneumatic suction cup 703, 703' and 703" with a coaxial venturi 702, 702' and 702" mounted to the upper portion thereof. Venturi mount assemblies 708 [not shown in the drawings], 708' and 708" attach coaxial Venturis 702, 702' and 702" to adjustment screws 704 [not shown in the drawings], 704' and 704". Elongated, threaded adjustment screws 704, 704' and 704" are loosely carried in a through-bore [not shown in the drawings] which runs vertically through adjustment screw mounts 710, 710' and 710".

Adjustment screw mounts 710, 710' and 710" — as can be seen from Figure 33— are generally shaped as an inverted "L" with the inverted, vertical leg of the "L" mounted to leg base mounts 712, 712' and 712"', respectively. Each adjustment screw mount has a transverse slot 760 [not shown in the drawings], 760' and 760" in the horizontal portion of the "L". Adjustment nuts 706, 706' and 706" which are threaded onto elongated, threaded adjustment screws 704, 704' and 704", respectively are captured within transverse slots 760 [not shown in the drawings], 760' and 760" to permit fine height adjustment of adjustment screws 704, 704' and 704" with respect to the adjustment screw mounts 710, 710' and 710". This happens because adjustment nuts 706, 706' and 706" are threaded onto adjustment screws 704, 704' and 704", respectively, and thus have only limited horizontal movement in the plane of transverse slots 760 [not shown in the drawings], 760' and 760". The top and bottom of transverse slots 760 [not shown in the drawings], 760' and 760" restrain adjustment nuts 706, 706' and 706" in the vertical direction such that rotation of an adjustment nut in one direction will move the adjustment screw it is threaded onto up [or down] with respect to transverse slots 760, 760' and 760" while rotation of the same adjustment nut in the other direction will cause said adjustment screw to move in the opposite direction to the first movement. In this manner the device can be raised away from a substrate of interest or lowered toward a substrate of interest. Because the motion is controlled by the threaded connection between adjustment screws 704, 704' and 704" and adjustment nuts 706, 706' and 706" the device movement is slow and this connection provides a fine height adjustment means. It is noted that each adjustment screw 704, 704' and 704" can be independently adjusted for height.

[0109] Adjustment screw mounts 710, 710' and 710" are attached to base 726 by leg base mounts 712, 712' and 712". The means attaching the adjustment screw mounts to the leg base mounts permits a coarse height adjustment of adjustment screw mounts 710, 710' and 710" with respect to the leg base mounts 712, 712' and 712" as will be further described below. Electrical connections 734 and 736 are provided to furnish power to device 700 to power the heating unit 600 as described below.

[0110] The device of the invention has a means to control the temperature of the substrate of interest in the area in the area immediately underneath the device. It is noted that the embodiments disclosed herein all use heating means to control the temperature of the local substrate area immediately beneath the device; however, it is recognized that some situations might call for a cooling means to control these temperatures.

[0111] The temperature control features of the instant invention involve the use of heating elements in thermal contact with the substrate of interest in the area directly underneath the device. The temperature control feature will be further discussed below. In addition, this embodiment requires compressed air to power the coaxial venturi assemblies 702, 702' and 702" in order to provide a vacuum in suction cup assemblies 701, 701', 701"'.

[0112] The temperature control means for the substrate of interest is heating unit 600. This is shown in some detail in Figures 34 and 36. Heating unit 600 comprises a hollow shell 601 with spaced walls 602 and 604 which hollow shell is shaped like an inverted box an open bottom. As shown in Figures 34 and 36 [plan views], shell 601 has the shape of a rectangle with rounded corners. It is obvious that other geometric shapes could be used for the shape of hollow shell 601, for example, it could be square or trapezoidal [with or without rounded corners], round, oval or any other suitable shape, as desired. Filling the space between spaced walls 602 and 604 is a continuous insulation piece 612. Inside the inner wall 604 are spaced heating coils 620,620', 620", 620"', 620"" and 620""'. Hex adjustment screws 722 and 722' [shown in Figures 32 and 34] permit the heating unit 600 to be moved towards or away from base 726. Mounting posts 621 and 621' serve to mount heating coil 620 to inner wall 604. They also provide power to heating coil 620. In like manner heating coils 620', 620", 620"', 620"" and 620""' are mounted and powered by mounting posts 622, 622'; 623, 623'; 624, 624'; 625, 625' and 626, 626' respectively. Flexible heat shields 650, 651, 652 and 653 are generally rectangular pads of heat-resistant and insulative material which are designed to localize and limit the spread of heat applied by the heating coils.

[0113] A cross-section of heating unit 600 and hollow shell 601 is shown in Figure 37. Shell 601 further comprises spaced outer wall 602 and inner wall 604 curve over at the top and are also insulated in the top area by continuous insulation piece 612. Spacers 606, 607, 607' and 607" are fastened to and run between outer wall 602 and inner wall 604. These spacers and others not shown in the drawings serve to maintain the distance between inner wall 602 and outer wall 604. They pass through the insulation material 612. It is obvious from the above description that thermal energy from heating coils 620, 620', 620", 620"', 620"" and 620""' can escape out of the open bottom of hollow shell 601 to impinge upon the surface of a substrate of interest.

[0114] Figure 38 shows the means which attaches adjustment screw mount 710 to leg base mount 712 and provides a coarse height adjustment as discussed above. Obviously, similar means are provided to attach adjustment screw mounts 710' and 710" to leg base mounts 712' and 712". In Figure 38 adjustment screw mount 710 is shown with a proximal face 762 and a distal face 764. Five linearly spaced holes 740,740', 740", 740"' and 740"" of a first diameter are bored into proximal face 762 of adjustment screw mount 710 at a first pre- determined spacing. Each hole 740,740', 740", 740"' and 740"" has a smaller perpendicular hole 741,741', 741", 741"' and 741"" bored there through to permit a push pin [not shown] to be inserted into the holes.

[0115] In Figure 38 leg base mount 712 is shown with a proximal face 766 and a distal face 768. Distal face 768 has a set of linearly spaced holes [not shown] bored therein at the same spacing as the first pre- determined spacing with the holes being the same diameter as said first diameter. Pins 742, 742' are removably secured in two of the holes in distal face 768 of leg base mount 712 by pins [not shown in the drawings], threads [also not shown in the drawings] or by any other suitable means. Pins 742 and 742' have transverse bores 744 and 744' there-through. In operation, leg base mount 712 would be assembled to adjustment screw mount 710 with pins 742, 742' being inserted into corresponding holes 740 and 740" in adjustment screw mount 710. When assembled, the perpendicular holes 741 and 741" in adjustment screw mount 710 align with the transverse bores 744,744' of pins 742, 742'. Push pins [not shown] are inserted through the aligned perpendicular holes and transverse bores 744, 744' to secure the assembly. In order to adjust the relative vertical position of adjustment screw mount 710 and leg base mount 712, the push pins would be removed, adjustment screw mount 710 and leg base mount 712 would be separated, and pins 742 and 742' could then be inserted into different holes, for example 740' and 740"'. This would give a different relative position between adjustment screw mount 710 and leg base mount 712. In addition, pins 742, 742' could be removed from their holes in leg base mount 712 and placed in other holes to achieve different relative positioning of adjustment screw mount 710 and leg base mount 712.

[0116] Figure 39 illustrates how another embodiment 800 of the device can be used to apply heat to a non-planar surface 810. Base cover 832 is mounted to the upper portion of base 826. Also mounted to base 826 are leg base mounts 812, 812' and 812". These leg base mounts provide the mounting means for the suction cup assemblies. The suction cup assembly and its associated mounting means with leg base mount 812" is not shown in the drawings but is substantially similar to those of suction cup assemblies for leg base mounts 812 and 812'. Heater mount 850 is secured to the lower portion of base 826 by multiple dowels 852, 854 and 856 which are fixed to base 826 and slidably secured in heater mount 850. This permits heater mount 850 to move towards and away from the lower portion of base 826 is a controlled manner while maintaining heater mount 850 generally parallel to base 826. The motion of heater mount 850 is controlled by hex adjustment screws 822 and 822' which are rotatably fixed in heater mount 850 and threaded into base 826 such that rotation of screws 822 and 822' moves heater mount 850 away from or towards the lower portion of base 826. Heating unit 900 is attached to heater mount 850 and moves with it. Thus, movement of heater mount 850 towards or away from the lower portion of base 826 causes heating unit 900 to move towards or away from the lower portion of base 826. When the device 800 is secured to a substrate, this arrangement permits the heating unit to be moved towards and away from the substrate of interest as will be explained below.

[0117] Generally horizontal rods 801, 801' are movably mounted to leg base mounts 812, 812'. As shown by the arrows in Figure 39, these rods can move up or down on leg base mounts 812, 812'. Generally perpendicular upper legs 802, 802' are attached to horizontal rods 801, 801' as shown. Lower legs 803, 803' are attached to upper legs 802,802' by universal joints 804,804'. Thus, lower legs 803, 803' have a large range of motion with respect to upper legs 802, 802'.

This arrangement permits suction cup assemblies 805, 805' a considerable amount of movement such that they can be aligned with uneven surfaces as shown.

[0118] Although not shown in Figure 39 a horizontal rod 801" is movably mounted on leg base mount 812". A generally perpendicular upper leg 802" [not shown in Figure 39] is mounted to horizontal rod 801". A lower leg 803" [not shown in Figure 39] is mounted to upper leg 802" by a universal joint 804" [not shown in Figure 39]. This arrangement permits suction cup assembly 805" [not shown in Figure 39] a considerable amount of movement such that it can be aligned with uneven surfaces. It is noted that the suction cup assemblies 703', 703" shown for device 700 in Figure 33 are rather large bellows-type suction cup assemblies. The construction of the bellows- type suction cup itself permits attachment of the suction cup to rather uneven surfaces because of the flexibility of the bellows-type suction cup. Thus, if suction cup assemblies 805, 805' and 805" are bellows-type suction cups, the very construction of the suction cup coupled with the flexible mounting means shown in Figure 39 will permit attachment of device 800 to a wide range of non- planar surfaces.

[0119] Once the device 800 has been secured to substrate 810, heating means 900 can be adjusted as described above such that it is thermally sealed to substrate 810. This is achieved by moving heater mount 850 by means of hex adjustment screws 822, 822' such that the attached heating means 900 is biased towards surface 810. The heating means 900 is lowered towards substrate 810 until flexible heat shields 951, 952, 953 and 954 [heat shield 954 is not shown in Figure 39] are deformed as shown in Figure 38— thus sealing heating means 900 against surface 810. Heating coils 620, 620', 620" etc. are energized and the portion of substrate 810 immediately under the heating unit 900 can be subjected to a controlled application of heat. The heat shields 951, 952, 953 and 954 permit the heat to be applied to a very controlled area such that portions of substrate 810 not directly underneath heating means 900 do not suffer significantly elevated temperature.

[0120] No timer or control means is shown for device 700 or for device 800 but it is noted that the art is replete with such control means which are small enough to be mounted on either device 700 or device 800. Either an open loop or closed loop type of heater control means could be utilized to control heating means 600 or 900. It is also possible to simply use an external timer in conjunction with a power on/off switch to control the heat application based upon calibration testing for the particular substrate being treated.

[0121] The above-described embodiments are merely illustrative of the principles of the invention. Those skilled in the art may make various modifications and changes, which will embody the principles of the invention and fall within the spirit and scope thereof. [0122] Obviously, this invention is primarily concerned with the treatment of 5XXX aluminum alloy structures. However, the equipment described above could be used to heat most any type of substrate where heat treatment was desired. For example, other metals could be treated; Gold [Au] or Silver [Ag] for example. Other metals and even non-metallic materials can also be treated with the processes and apparatus of the invention.

[0123] The above - described embodiments are merely illustrative of the principles of the invention. Those skilled in the art may make various modifications and changes, which will embody the principles of the invention and fall within the spirit and scope thereof.

Claims

1. A method of in-situ heat treatment for de-sensitizing all or predetermined portions of a sensitized 5XXX aluminum-magnesium alloy structure comprising the steps of:

defining a treatment area within said sensitized structure;

determining a goal temperature for said treatment area;

determining a goal heat maintenance time for said treatment area;

temporarily attaching a portable heat treatment device to said treatment area;

turning said heat treatment device on and applying heat to said treatment area to achieve said goal temperature within said treatment area;

maintaining said goal temperature for said predetermined heat maintenance time;

turning said treatment device off so that it is no longer applying heat to said treatment area; and, allowing said treatment area of said structure to air-cool back to ambient temperature.

2. The method of claim 1 wherein said defined treatment area is only a portion of the total area of said 5XXX aluminum-magnesium alloy structure and wherein boundary areas surround said defined treatment area, and further wherein said boundary areas are cooled during the heat treatment process to regulate the temperature of said boundary areas.

3. The method of claim 1 wherein said goal temperature is between 100 °C and 350 °C.

4. The method of claim 1 wherein said goal heat maintenance time is 4 minutes or less.

5. A method of in-situ heat treatment for de-sensitizing all or predetermined portions of a

sensitized 5XXX aluminum-magnesium alloy structure comprising the steps of:

defining a treatment area within said sensitized structure;

determining a de-sensitization degree of sensitization [DoS] target value for said treatment area; determining a goal temperature for said treatment area;

temporarily attaching a portable heat treatment device to said treatment area, with said heat treatment device comprising a heat source and at least the sensor portion of a degree of sensitization [DoS] sensor being mounted inside the heat treatment device with said temporarily attaching step further comprising placing said DoS sensor in contact with said treatment area; determining the starting DoS of said treatment area;

1 turning said heat treatment device on and applying heat to said treatment area to achieve said goal temperature within said treatment area;

monitoring the DoS of said treatment area on a predetermined schedule during said heat applying step;

turning said heat treatment device off so that it is no longer applying heat to said treatment area when the monitored DoS of said treatment area reaches the predetermined de-sensitization DoS value for said treatment area; and,

allowing said treatment area to air-cool back to ambient temperature.

6. The method of claim 5 wherein said heat treatment device further comprises a feedback control means which means controls said DoS monitoring and which feedback control means further comprises a means to turn said heat treatment device on or off in accord with the value of said DoS monitoring.

7. A device for in-situ heat treatment to de-sensitize a sensitized 5XXX aluminum-magnesium

alloy structure comprising:

a heat source;

a prism-shaped, shroud containing said heat source with said shroud having an open bottom and a closed top;

a thermal dam mounted to and surrounding said open bottom of said shroud.

8. The device of claim 7 wherein at least one handle is mounted to said thermal dam.

9. The device of claim 7 wherein said thermal dam is water-cooled.

10. The device of claim 9 further comprising water inlet and outlet means on said thermal dam.

11. The device of claim 7 wherein said thermal dam is made of aluminum.

12. The device of claim 7 wherein said thermal dam is provided with at least one vortex tube air cooler with said vortex tube air cooler further comprising a compressed air inlet, a cold air outlet and a hot air exhaust.

13. The device of claim 12 wherein said hot air exhaust of said at least one vortex tube air cooler is channeled inside the shroud to aid in heating said structure.

14. The device of claim 7 wherein said heat source comprises at least one radiant wire heating

coil.

2

15. The device of claim 7 wherein said heat source comprises at least one radiant heater.

16. The device of claim 7 further comprising at least two, independently adjustable mounting

means secured to said thermal dam which means will secure said in-situ heat treatment device to a substrate of indefinite size.

17. The device of claim 16 wherein each of said at least two independently adjustable mounting means further comprises a base mount secured to said thermal dam and an adjustment screw mount removably mounted to said base mount.

18. The device of claim 17 wherein each of said at least two independently adjustable mounting means further comprises a longitudinal, threaded adjustment screw movably mounted in said adjustment screw mount.

19. The device of claim 18 wherein each of said at least two independently adjustable mounting means further comprises an adjustment nut threaded onto said adjustment screw and retained within said adjustment screw mount such that turning said adjustment nut in one direction moves said adjustment screw in one longitudinal direction and turning said adjustment nut in the other direction moves said adjustment screw in the opposite longitudinal direction.

20. The apparatus of claim 18 wherein each said adjustment screw mount has a proximal side and a distal side with each said adjustment screw being loosely received in a through-bore in said distal side of said adjustment screw mount, with said through-bore being interrupted by a transverse slot;

a threaded adjustment nut rotatably mounted in said transverse slot in such a manner that it can be manually rotated by an operator; and, each said adjustment screw being threaded through the adjustment nut mounted in said transverse slot wherein rotation of said adjustment nut in one direction causes each said adjustment screw to move up through said through-bore and wherein rotation of said adjustment screw in the other direction causes each said adjustment screw to move downwardly through said through-bore.

21. The device of claim 16 wherein said at least two, independently adjustable mounting means further comprise at least one leg base mount secured to said thermal dam with each leg base mount having a proximal side and a distal side;

an attachment arm mounted generally perpendicular to the distal side of each leg base mount;

3 means permitting said attachment arm to be moved along said leg base mount in a first direction perpendicular to said attachment arm; said means also permitting said attachment arm to be moved in a second direction perpendicular to said attachment arm and in opposition to said first direction; a leg mounted generally perpendicular to each said attachment arm, with said leg comprising first and second segments; and, joining means joining said first and second leg segments, said joining means further comprising a locking universal joint to permit the angle between said first and said second leg segments to be widely varied, and to lock said segments in position when said angle has been set.

22. The device of claim 21 wherein said second leg segment carries a suction cup means at the end of said leg segment remote from said joining means.

23. The device of claim 22 wherein said suction cup further comprises a bellows-type

pneumatic suction cup.

24. A method of in-situ heat treatment for de-sensitizing a predetermined portion of a 5XXX

aluminum-magnesium alloy structure which predetermined portion is sensitized and which predetermined portion has at least one non-sensitized boundary area(s) bordering upon said sensitized predetermined portion, without adversely affecting said at least one non-sensitized boundary area(s) surrounding said predetermined portion, and without using any external cooling device to cool said non-sensitized boundary areas, comprising the steps of:

determining a de-sensitization degree of sensitization [DoS] target value for said predetermined portion;

determining a goal temperature for said predetermined portion;

determining a maximum allowable temperature for said at least one non-sensitized boundary area(s);

providing a portable, point source heat treatment device, with said portable, point source heat treatment device comprising a heat source which can be operated intermittently and providing an associated control means to operate said heat source in an intermittent manner;

temporarily attaching said portable, point source heat treatment device to said structure such that said point source heat treatment device is placed over said predetermined portion and can apply

4 heat to the part of said predetermined portion which is immediately under said point source heat treatment device;

providing a degree of sensitization [DoS] sensor comprising a sensor probe and an electronics and control package;

temporarily attaching at least the sensor probe of said DoS sensor to said predetermined portion; using said DoS sensor to determine the starting DoS of said predetermined portion;

turning said point source heat treatment device on and applying heat to said part of said predetermined portion immediately under said point source heat treatment device to achieve and maintain said predetermined goal temperature within said part of said predetermined portion immediately below said point source heat treatment device;

monitoring the DoS of said predetermined portion on a predetermined schedule during said heat applying step;

turning said point source heat treatment device off so that it is no longer applying heat to said predetermined portion when the monitored DoS of said predetermined portion reaches the predetermined de-sensitization DoS value for said predetermined portion; and,

allowing said predetermined portion to air-cool back to ambient temperature.

A method of in-situ heat treatment for de-sensitizing a predetermined portion of a 5XXX aluminum-magnesium alloy structure which predetermined portion is sensitized and which predetermined portion has at least one non-sensitized boundary area(s) bordering upon said sensitized predetermined portion, without adversely affecting said at least one non-sensitized boundary area(s) surrounding said predetermined portion, and without using any external cooling device to cool said non-sensitized boundary areas, comprising the steps of:

determining a goal temperature for said predetermined portion;

determining a goal heat maintenance time for said predetermined area;

providing a portable, point source heat treatment device, with said portable, point source heat treatment device comprising a heat source which can be operated intermittently and providing an associated control means to operate said heat source in an intermittent manner;

temporarily attaching said portable, point source heat treatment device to said structure such that said point source heat treatment device is placed over said predetermined portion and can apply

5 heat to the part of said predetermined portion which is immediately under said point source heat treatment device;

turning said point source heat treatment device on and applying heat to said part of said predetermined portion immediately under said point source heat treatment device to achieve said goal temperature;

maintaining said predetermined goal temperature within said part of said predetermined portion immediately below said point source heat treatment device for the predetermined goal heat maintenance time;

turning said point source heat treatment device off so that it is no longer applying heat to said predetermined portion; and,

allowing said predetermined portion to air-cool back to ambient temperature.

A method of heat treating a substrate comprising;

providing a substrate to be heat treated having a known reflectance - radiation wavelength spectral profile with a pre-determined minimum reflectance wavelength range;

providing a radiant energy emitter which can emit radiant energy over a wide range of wavelengths and, in particular, can provide radiant energy in the pre-determined minimum reflectance wavelength range of the substrate;

directing radiant energy onto a surface of the substrate by causing the radiant energy emitter to emit radiant energy in the pre-determined minimum reflectance wavelength range of the substrate; and,

thus, maximizing the heat transfer between the radiant energy emitter and the substrate.

A method of heat treating a substrate comprising;

providing a substrate to be heat treated;

providing a radiant energy emitter which can emit radiant energy over a pre-determined range of wavelengths;

coating the substrate with a coating which will increase the radiant energy absorption of the substrate in the pre-determined range of wavelengths emitted by the radiant energy emitter, directing radiant energy onto a surface of the substrate by causing the radiant energy emitter to emit radiant energy in the pre-determined range of wavelengths; and,

6 thus, maximizing the heat transfer between the radiant energy emitter and the substrate.

28. A method of heat treating a substrate comprising:

providing a substrate to be heat treated with said substrate having a pre-determined treatment surface;

providing a radiant energy emitter which can emit radiant energy over a pre-determined range of wavelengths;

treating the treatment surface of said substrate in such a way so as to increase the radiant energy absorption of the treatment surface of said substrate in the pre-determined range of wavelengths emitted by the radiant energy emitter;

directing radiant energy onto said treatment surface of said substrate by causing said radiant energy emitter to emit radiant energy in the pre-determined range of wavelengths; and, thus, maximizing the heat transfer between the radiant energy emitter and the substrate.

29. The method of claim 28 wherein said treating step further comprises sanding said pre-determined treatment surface of said substrate.

30. The method of claim 28 wherein said treating step further comprises polishing said predetermined treatment surface of said substrate.

31. The method of claim 28 wherein said treating step further comprises coating said pre-determined treatment surface of said substrate with a coating which coating has a high radiant energy absorption in the pre-determined wavelength range of wavelengths emitted by the radiant energy emitter.