Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/053—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with zinc as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/057—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with copper as the next major constituent

Definitions

• ALUMINUM-LITHIUM ALLOYS AND PROCESS THEREFOR This invention relates to aluminum base alloy products, and more particularly;, it relates to improved lithium containing aluminum base alloy pro- ducts and a method of producing the same.
• the lithium containing alloy have both improved fracture toughness and strength properties.
• the present invention solves problems which limited the use of these alloys and provides an improved lithium containing aluminum base alloy product which can be processed to provide improved strength characteristics while retaining high toughness properties.
• the pro ⁇ duct comprises 0.5 to 4.0 wt. % Li, 0 to 5.0 -wt. % Mg, up to 5.0 wt. % Cu, 0.03 to 0.25 wt. % Zr, 0 to 2.0 wt. % Mn, 0 to 7.0 wt. % Zn, 0.5 wt. % max. Fe, 0.5 wt. % max. Si, the balance aluminum and incidental impurities.
• the method of making the product com ⁇ prising the steps of providing a body of a lithium containing aluminum base alloy and heating the body for hot working operations, e.g., hot rolling to a first intermediate sheet product. After cold rolling to a second intermediate gauge, the sheet product is reheated and hot rolled to a final sheet product while avoiding substantial recrystallization thereof, the hot rolling adapted to relieve stored energy capable of initiating recrystallization during a subsequent heat treating step.
• the final sheet product is solution heat treated, quenched and aged to provide a substantially un ⁇ recrystallized product having improved levels of strength and fracture toughness.
• Figure 1 shows that the relationship between toughness and yield strength for a worked alloy product is increased by stretching.
• UTE SHEET Figure 2 shows that the relationship between toughness and yield strength is increased for a second worked alloy upon stretching.
• Figure 3 shows the relationship between toughness and yield strength of a third alloy product after stretching.
• Figure 4 shows that the relationship between toughness and yield strength is increase for another alloy product after stretching.
• Figure 5 shows that the relationship between toughness (notch-tensile strength divided by yield strength) and yield strength decreases with increase amounts of stretching for AA7050.
• Figure 6 shows that stretching AA2024 beyond 2% does not significantly increase the toughness-strength relationship for this alloy.
• Figure 7 illustrates different toughness yield strength relations-hips where shifts in the upward direction and to the right represent improved com- binations of these properties.
• Figure 8 shows a plot of elongation versus tensile yield stress of aluminum-lithium alloy processed in accordance with the invention and processed con ⁇ ventionally.
• Figure 9 shows tear test results of an aluminum-lithium alloy processed in accordance with the invention and processed conventionally.
• Figure 10 shows a metallurgical structure of an aluminum-lithium alloy processed in accordance with conventional practices.
• Figure 11 shows an unrecrystallized metallurgical structure of an aluminum-lithium alloy processed in accordance with the invention.
• Figure 12 shows a metallurgical structure of an aluminum-lithium alloy processed in accordance with conventional practices.
• Figure 13 shows an unrecrystallized metallurgical structure of an aluminum-lithium alloy processed in accordance with the invention.
• the alloy of the present invention can contain 0.5 to 4.0 wt. % Li, 0 to 5.0 wt. % Mg, up to 5.0 wt. % Cu, 0 to 1.0 wt.% Zr, 0 to 2.0 wt.% Mn, 0 to 7.0 wt.% Zn, 0.5 wt.% max. Fe, 0.5 wt.% max. Si, the balance aluminum and incidental impurities.
• the impurities are pre ⁇ ferably limited to about 0.05 wt.% each, and the com ⁇ bination of impurities preferably should not exceed 0.15 wt.%. Within these limits, it is preferred that the sum total of all impurities does not exceed 0.35 wt. %.
• a preferred alloy in accordance with the present invention can contain 1.0 to 4.0 wt.% Li, 0.1 to 5.0 wt.% Cu, 0 to 5.0 wt.% Mg, 0 to 1.0 wt.%
• a typical alloy composition would contain 2.0 to 3.0 wt.% Li, 0.5 to 4.0 wt.% Cu, 0.to 3.0 wt.% -Mg, 0 to 0.2 wt.% Zr, 0 to 1.0 wt.% Mn and max. 0.1 wt.% of each of Fe and Si.
• lithium is very important not only because it permits a significant decrease in density but also because it improves tensile and yield strengths markedly as well as im- proving elastic modulus. Additionally, the presence of lithium improves fatigue resistance. Most signifi ⁇ cantly though, the presence of lithium in combination with other controlled amounts of alloying elements permits aluminum alloy products which can be worked to provide unique combinations of .strength and fracture toughness while maintaining meaningful reductions in density. It will be appreciated that less than 0.5 wt.% Li does not provide for significant reductions in the density of the alloy and 4 wt.% Li is close to the solubility limit of lithium, depending to a significant extent on the other alloying elements. It is not presently expected that higher levels of
• copper With respect to copper, particularly in the ranges set forth hereinabove for use in accordance 5. with the present invention, its presence enhances the properties of the alloy product by reducing the loss in fracture toughness at higher strength levels. That is, as compared to lithium, for example, in the present invention copper has the capability of providing 0 higher combinations of toughness and strength. For example, if more additions of lithium .were used to increase strength without copper, the decrease in toughness would be greater than if copper additions were used to increase strength. Thus, in the present 5 invention when selecting an alloy, it is important in making the selection to balance both the toughness and strength desired, since both elements work together to provide toughness and strength uniquely in accordance with the present invention.
• the amount of manganese should also be close- 5 ly controlled.
• Manganese is added to contribute to grain structure control, particularly in the final product.
• Manganese is also a dispersoid-forming element and is precipitated in small particle form by thermal treatments and has as one of its benefits a strengthen ⁇ ing effect.
• Dispersoids such as Al 2 Cu neighborMn- and Al... ⁇ Mg-Mn can be formed by manganese.
• Chromium can also be used for grain structure control but on a less preferred basis. Zirconium is the preferred material for grain structure control.
• the use of zinc results in increased levels of strength, particularly in com ⁇ binatio with magnesium. However, excessive amounts of zinc can impair toughness through the formation of intermetallic phases.
• Toughness or fracture toughness as used herein refers to the resistance of a body, e.g. sheet or plate, to the unstable growth of cracks or other flaws.
• Improved combinations of strength and toughness is a shift in the normal inverse relationship between strength and toughness towards higher toughness ' values at given levels of strength or towards ' higher strength values at given levels of toughness.
• going from point A to point D represents the loss in toughness usually associated with increasing the strength of an alloy.
• going from point A to point B results in an increase in strength at the same toughness level.
• point B is an improved combination of strength and toughness.
• in going from point A to point C results in an..increase in strength while toughness is decreased, but the com ⁇ bination of strength and toughness is improved relative to point A.
• point D at point C, toughness is improved and strength remains about the same, and the combination of. strength and toughness is considered to be improved.
• toughness is improved and strength has decreased yet the combination of strength and toughness are again considered to be improved.
• the alloy be prepared according to specific method steps in order to provide the most desirable characteristics of both strength and fracture toughness.
• the alloy as described herein can be provided as an ingot or billet for fabrication into a suitable wrought product by cast ⁇ ing techniques currently employed in the art for cast products with continuous casting being preferred.
• the alloy may also be provided in billet form consolidated from fine particulate such as powdered aluminum alloy having the compositions in the ranges set forth hereinabove.
• the powder or particulate material can be producted by processes such as atomization, mechanical alloying and melt spinning.
• the ingot or billet may be priliminarily worked or shaped to provide suitable stock for sub ⁇ sequent working operations.
• the alloy stock is preferably sub ⁇ jected to homogenization, and preferably at metal temperatures in the range of 900 to 1050°F. for a period of time of at least one hour to dissolve soluble elements such as- Li and Cu, and to homogenize the internal structure of the metal.
• a preferred time is about 20 hours or more in the homogenization tempera ⁇ ture range. Normally, the heat up and homogenizing treatment does not have to extend for more than 40 hours; however, long times are not normally detrimental. A time of 20 to 40 hours at the homogenization tempera ⁇ ture has been found quite suitable. In addition to dissolving consistuent to promote workability, this homogenization treatment is important in that it is believed to precipitate the Mn and Zr-bearing dis- persoids which help to control final grain structure.
• the metal can be rolled or extruded or otherwise subjected to working operations to produce stock such as sheet, plate or extrusions or other stock suitable for shaping into the end product.
• thermomechani ⁇ al steps must be carefully controlled. That is, after the ingot has been homogenized, it may be hot worked or hot rolled. Hot rolling may be performed at a temperature in the range of 800 to 1040°F. with a typical temperature being in the range of 950 to 1000°F. Hot rolling can reduce the thickness of the ingot to one quarter .of its original thickness to provide a first intermediate gauge There ⁇ after, it may be cold rolled to provide a further gauge reduction. Preferably, such cold rolling produces a gauge thickness near final gauge thickness.
• the cold rolled sheet is first subjected to a reheat step and then subjected to a light hot rolling pass where pre- ferably not more than 50% reduction is made. Typically, not more than 30% for example 15 to 20%, reduction is required to condition the sheet so as to obtain an unrecrystallized structure after solution heat treating,
• dynamic recovery is meant a dislocation rearrangement process which results in destroying dislocation substructures or permits the recovery of dislocation structures produced during prior rolling steps. This process of deformation processing acts to substantially avoid recrystallization during solution heat treating.
• the sheet product is given a light rolling pass at a temperature slightly below recrystallization tem ⁇ perature prior to solution heat treating. .Thus, pre- ferably, the hot rolling pass is performed at a temper ⁇ ature of not greater than about 920°F. and preferably not greater than 850°F. with a typical temperature being 800°F.
• the time at these temperature should be minimized so as to avoid recrystallization, e.g. typically not more than 2 hours at the higher temperatures.
• the reheating and light hot rolling can be performed continuously, e.g., with a web of the sheet being continuously passed through a furnace to reach temperature.
• the sheet can be reheated to temperature in coils for light hot rolling.
• the cold rolled pro ⁇ duct (normally rolled to final gauge) is subjected to a controlled reheat treatment. This treatment- is carried out for a time and temperature at which recrystallization does not occur. As noted earlier, the reheat ' treatment is provided to relieve stored energy capable of causing recrystallization during subsequent solution heat treatments.
• a reheat treatment in accordance with the in ⁇ vention which results in an unrecrystallized product after solution heat treating can be achieved when the cold rolled or worked product is subjected to a temper ⁇ ature of 800°F. for 12 hours.
• the time at temperatures for the reheat process is important.
• the initial temperature for the reheat treatment should not be less than 750°F. and the highest temperature should not exceed 920°F.
• the initial temperature is about 800°F. and the temperature increased gradually from 50 to 100°F. until the maximum temperature is reached, sometimes referred to as a ramp anneal.
• the ramped anneal rate can range from.3 to 10°F. per hour from the low to the high temperature with a typical rate being about 6°F. per hour. For example, if
• SUBSTITUTE SHEET reheat is for thin gauge sheet, the temperature should be raised about 50°F. over a period of at least 2 to 8 hours. Thereafter, the sheet should be held at 850°F. for about 1 to 3 hours, typically 2 hours before being cooled to room temperature. If the cooling rate in the furnace is controlled, this can improve the effectiveness of the process. Thus, preferably, the return to room temperature should be over a period of 6 to 10 hours, typically 8 hours, to guard against small amounts of recrystallization, particularly at low lithium levels. If the reheat treatment is applied to extrusions or forgings, then the temperature can be raised from as much as 150°F. from a starting reheat temperature of 750°F. The ramp anneal rate can be as low as 5°F.
• the sheet product is solution heat treated typically at a temperature in the range of 960 to 1040°F. for a period in the range of 980 to 1020 hours.
• the product should be rapidly quenched to prevent or minimize uncontrolled precipitation of strengthening phases referred to herein later.
• the quenching rate be at least 100°F. per second from solution temperature to a temperature of about 200°F. or lower.
• a preferred quenching rate is at least
• the alloy of the invention is slab cast or roll cast, for example, it may be possible to omit some or all of the steps referred to herein ⁇ above, and such is contemplated within the purview of the invention.
• the improved ' sheet, plate or extrusion and other wrought products can have a range of yield strength from about 25 to 50 ksi and a level of fracture toughness in the range of about 50 to 150 ksi in.
• fracture toughness can drop con ⁇ siderably.
• the solution heat treated and quenched alloy product, particularly sheet, plate or extrusion may be stretched, preferably at room temperature, an amount greater than 3% of its original length or otherwise worked or deformed to impart to the product a working effect equivalent to stretching greater than 3% of its original length.
• the working effect referred to is meant to include rolling and forging as well as other working operations. It has been discovered that the strength of sheet or
• SUBSTITUTE SHEET plate, for example, of the subject alloy can be increased substantially by stretching prior to artificial aging, and such stretching causes little or no decrease in fracture toughness. It will be appreciated that in comparable high strength alloys, stretching can pro ⁇ note a significant drop in fracture toughness. Stretch ⁇ ing AA7050 reduces both toughness and strength, as shown in Figure 5, taken from the reference by J. T. Staley, mentioned previously. Similar, toughness strength data for AA2024 are shown in Figure 6. For AA2024, stretching 2% increases the combination of toughness and strength over that obtained without stretching; however, further stretching does not provide any substantial increases in toughness.
• this practive inhibits nucleation of both metastable and equilibrium phases such as Al,Li, AlLi, Al 2 CuLi and Al..CuLi 3 at grain sub-grain boundaries. Also, it is believed that the combination of enhanced uniform precipitation throughout each grain and decreased grain boundary precipitation results in the observed higher combination of strength and fracture toughness in aluminum-lithium alloys worked or deformed as by stretching, for example, prior to final aging.
• the alloy product of the present invention may be artificially aged to provide the combination of fracture toughness and strength which are so highly desired in aircraft members. This can be accomplished by subjecting the sheet or plate or plate or shaped product to a temperature in the range of 150 to 400°F. for a sufficient period of time to further increase the yield strength. Some compositions of the alloy product are capable of being artificially aged to a yield strength as high as 95 ksi. However, the .
• useful strength are in the range of 50 to 85 ksi and corresponding fracture toughnesses are in the range of 25 to 75 ksi in.
• artificial aging is accomplished by sub ⁇ jecting the alloy product to a temperature in the range of 275 to 375°F. for a period of at least 30 minutes.
• a suitable aging practice contemplate a treatment of about 8 to 24 hours at a temperature of about 325°F.
• the alloy product in accordance with the present invention may be subjected to any of the typical underaging treat- ments well known in the art, including natural aging. However, it is presently believed that natural aging provides the least benefit. Also, while reference
• SUBSTITUTE 5! has been made herein to single aging steps, multiple aging steps, such as two or three aging steps, are con ⁇ templated and stretching or its equivalent working may be used prior to or even after part of such multiple aging steps.
• Example I An aluminum alloy consisting of 1.73 wt.% Li, 2.63 wt.% Cu, 0.12 wt.% Zr, the balance essentially aluminum and impurities, was cast into . an ingot suitable for rolling. The ingot was homogenized in a furnace at a temperature of 1000°F. for 24 hours and then hot rolled into a plate product about one inch thick. The plate was then solution heat treated in a heat treating furnace at a temperature of 1025°F. for one hour and then quenched by immersion in 70°F. water, the temperature of the plate immediately before immersion being 1025°F. Thereafter, a sample of the plate was stretched 2% greater than its original length, and a second sample was stretched 6% greater than its original length, both at about room temperature.
• the stretched samples were treated at either 325°F. or 375°F. for times as shown in Table I.
• the yield strength values for the samples referred to are based on specimens taken in. the longitudinal direction, the direction parallel to the direction of rolling. Toughness was determined by ASTM Standard Practice E561-81 for R-curve determination. The results of these tests are set forth in Table I. In addition, the results are shown in Figure 1 where toughness is plotted against yield strength. It will be noted from Figure 1 that 6% stretch displaces the strength-toughness relationship upwards and to the right relative to the
• Example I An aluminum alloy consisting of, by weight, 2.78% Li, 0.49% Cu, 0.98% Mg, 0.50 Mn and 0.12% Zr, the balance essentially aluminum., was cast into an ingot suitable for rolling. The ingot was homogenized as in Example I and hot rolled to plate of 0.25 inch thick. Thereafter, the plate was solution heat treated for one hour at 1000°F and quenched in 70° water. Samples of the quenched plate were stretched 0%, 4% and 8% before aging for 24 hours at 325°F. or 375°F. Yield strength was determined as in Example I and toughness was determined by ahn type tear tests.
• Example III An aluminum alloy consisting, of, by weight, 2.72% Li, 2.04% Mg, 0.53% Cu, 0.49 Mn and 0.13% Zr, the balance essentially aluminum and impurities, was cast into an ingot suitable for rolling. Thereafter, it was homogenized as in Example I and then hot rolled into plate 0.25 inch thick. After hot rolling, the plate was solution heat treated for one hour at 1000°F. and quenched in 70° water. Samples were taken at 0%, 4% and 8% stretch and aged as in Example I. Tests were performed as in Example III, and the results are presented in Table IV. Figure 4 shows the relationship of toughness and yield strength for this alloy as a function of the amount of stretching.
• the dashed line is meant to suggest the toughness-strength relationship for this amount of stretch.
• the in ⁇ crease in strength at equivalent toughness is signi- ficiantly greater than the previous alloys and was unexpected in view of the behavior of conventional alloys such as AA7050 and AA2024.
• An aluminum alloy consisting of, by weight, 2.25% Li, 2.98% Cu, .12% Zr, the balance being essentially aluminum and impurities, was cast into an ingot suitable for rolling.
• the ingot was homogenized in a furnace at a temperature of 950°F. for 8 hours followed immediately by a temperature of 1000°F. for 24 hours and air cooled.
• the ingot was then preheated in a furnace for 30 minutes at 975°F. and hot rolled to 1.75 inch thick plate.
• the plate was solution heat treated for 2 hours at 1020°F. followed by a continuous water spray quench with a water temperature of 72°F.
• the plate was stretched at room temperature- ' in the rolling direction with • 4.9% permanent set.
• Example VI An aluminum alloy consisting of, by weight, 2.13% Li, 2.83% Cu, .13% Zr, the balance being essentially aluminum and impurities, was cast into an ingot suitable for rolling.
• the ingot was homogenized in a furnace at a temperature of 950°F. for 8 hours followed immediately by a temperature of 1000°F. for.24 hours and air cooled.
• the ingot was then preheated in a furnace for 30 minutes at 975°F. and hot rolled to 3.5" thick slab.
• the slab was reheated for 4 hours at 1000°F. and hot rolled to 0.144" thick sheet.
• the sheet was " then annealed for 4 hours at 650°F. and cold rolled to 0.080" thick gauge sheet.
• the sheet was. solution heat treated for 1 hour at 1000°F. followed by a cold water quench with a water temperature of 72°F.
• the sheet was stretched 4% at room temperature in the rolling direction. Stretching was followed by an artificial aging of 8 hours at 325°F. for under aged condition and 24 hours at 325°F. for peak aged con ⁇ dition. Examination of microstructure revealed heavily recrystallized microstructure with extremely coarse grain structures, as shown in Figure 10.
• the tensile test result and tear test result are shown in Figures 8 and 9, showing properties at three strength levels, i.e., T3 temper (as stretched), underaged (stretched and aged for 8 hours at 325°F) and peak aged (stretched and aged for 24 hours • at 325°F) .
• T3 temper as stretched
• underaged stretched and aged for 8 hours at 325°F
• peak aged stretched and aged for 24 hours • at 325°F
• An aluminum alloy consisting of, by weight, 2.13% Li, 2.83% Cu, .13% Zr, the balance being essential ⁇ ly aluminum and impurities, was cast into an ingot suitable for rolling.
• the ingot was homogenized in a furnace at a temperature -of 950°F. for 8 hour ' s, followed immediately by a temperature of 1000°F. for 24 hours and air cooled.
• the ingot was then pre- heated in a furnace for 30 minutes at 975°F. and hot rolled to 3.5" thick slab.
• the slab was reheated for 4 hours at 1000°F. and hot rolled to 0.144 B thick sheet.
• the sheet was then annealed for 4 hours at 650°F. and cold rolled to 0.080" thick gauge sheet.
• the cold rolled sheet was annealed for 12 hours at 800°F. to relieve a stored energy capable of com ⁇ mencing recrystallization during the subsequent heat treatment.
• the sheet was solution heat treated for 1 hour at 1010°F. followed by a cold water quench with a water temperature of 72°F.
• the sheet was stretched by 4% at room tempera ⁇ ture in the.rolling direction. Stretching was followed by an artificial aging of 8 hours at 325°F. for under aged condition and 24 hours at 325°F. for peak aged condition. Examination of microstructure revealed an unrecrystallized microstructure, as shown in Figure 11.
• the tensile test result, and tear test result are shown in Figures 8 and 9, showing properties at three strength levels, i.e., T3 temper (as stretched), under ⁇ aged (stretch and aged for 8 hours at 325°F.) and peak aged (stretched and aged for 24 hours at 325°F.
• Example VIII For purposes- of obtaining unrecrystallized thin gauge cold rolled sheet of heat treatable aluminum alloy, a 3.5 inch thick ingot containing 3.0 wt.% Cu, 2.0 wt.% Li and 0.11 wt.% Zr, the balance aluminum, was homogenized for 8 hours at 950"F. followed by 24 hours at 1000°F. and hot rolled to 0.25 inch thick sheet. Thereafter, the sheet was cold rolled to a gauge thickness of 0.1 inch sheet. This sheet was then re ⁇ heated to 800°F. and hot rolled to 0.085 inch gauge to obtain an unrecrystallized product. The 0.85 inch sheet was solution heat treated at a temperature of 1000°F. for 0.5 hour and cold water quenched.
• Figure 11 is an optical micrograph of solution heat treatment material in accordance with the invention.
• Figure 10 shows conventionally treated material. Tliat is.
• Figure 10 shows cold rolled sheet which was solution heat treated. The X-ray analysis shows that the sheet was completely recrystallized.
• Example IX An aluminum alloy consisting of, by weight, 1.97% Li, 2.83% Cu, .12% Zr, the balance being essential' ly aluminum and impurities, was cast into an ingot suitable for rolling.
• the ingot was homogenized in a furnace at a temperature of 950°F. for 8 hours followed immediately by a temperature of 1000°F. for 24 hours and air cooled.
• the ingot was then " preheated in a furnace for 30 minutes at 975°F. and hot rolled to 3.5 inch thick slab.
• the slab was reheated for 4 hours at 1000°F. and hot rolled to 0.144 inch thick sheet.
• the sheet was-, then annealed for 2 hours at 650°F. and cold rolled to 0.063 inch thick gauge sheet.
• the cold rolled sheet (0.063 inch gauge) was solution heat treated for 30 minutes at 1020°F. followed by a cold water quench with a water temperature of 72°F. Examination of microstructure revealed heavily re- crystallized microstructure with extremely coarse grain structures as shown in Figure 10.
• the 0.063 inch thick cold rolled sheet was heated to 800°F. then the temperature was slowly in ⁇ creased at a controlled heat-up rate to reach 850°F. in 8 hours, then soaked for ' 2 hours at 850°F. followed by a furnace cool to 72°F. The annealed sheet samples were then heat treated at 1020°F. for 30 minutes and cold water quenched. Microstructural examination by optical metallography revealed an unrecrystallized structure, shown as S.N. 585703-1 in Figure 13. The ramped anneal practice was found to be a more efficient anneal practice in preventing recrystallization than anneal practices utilizing a constant temperature.

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