IE41714B1 - Aluminium alloys - Google Patents

Abstract

A drinking mug (1) includes a removable lid (4) which is dish-shaped. The lid (4) has a flat upper surface (6) so that when it is removed from the body of the mug and placed upside down on a table it acts as a container for a teabag. A handle (5) is in the form of a tab which does not extend above the level of the upper surface (6) so that the lid (4) is stable when placed on a table. The lid provides for keeping beverages warm and also for the holding of a teabag when in use.

Description

The present invention is concerned with evaporation-condensation alloys, that is alloys produced by evaporation-condensation processes.

In accordance with the present invention an evaporation-condensation aluminium alloy consists of 2 to 12% by weight of chromium, 0.2 to 3.0% by weight of iron, the balance being aluminium apart from minor proportions Of impurities and incidental elements wherein most of the chromium is present as a mestastable Solution in the aluminium lattice whioh contains a precipitate phase of iron rich sones the major proportion of which have dimensions of 2θθ2 or less, and preferably 50& or less, the presence of large intermetallic particles, particularly at grain boundaries, being at a minimum.

Impurities and incidental elements whioh may be present in alloys of the present invention may include a total of up to about 0.5% by weight of any one or more of the following: nickel, cobalt, silicon, copper, zino, gold, silver, oxygen, magnesium, cadmium, tin, manganese, titanium, molybdenum, carbon and beryllium.

Advantageously aluminium alloys of the present invention consist of 4 to 10% by weight of chromium, 0.3 to 2.0% by weight of iron, the balance being aluminium apart from minor proportions of impurities and incidental elements, and preferably consist of 5 to 9% by weight of chromium and 0.6 to 1.5% by weight of iron. In a particularly preferred embodiment of the present invention an aluminium alloy consists of 5 to 8% by weight of chromium, 0.8 to 1.3% by weight of iron, the balance being aluminium apart from minor proportions of impurities and incidental elements; a major part of the chromium content being present as a metastable solid solution in the aluminium lattice and having a precipitate phase of iron rich zones a major proportion of whioh have dimensions of 5θ2 or less, Preferably substantially all of the iron rich zones have dimensions of 50S.

The miorostruotures whioh are characteristic of the alloys of the present invention, whioh may require appropriate working treatment to aohieve(are not obtainable by conventional melting casting forging or solution heat treatment and precipitation techniques.

The techniques of producing alloys by deposition from the vapour phase is described in British Patent Specification No. 1,206,586 A process of producing an evaporation-condensation alloy of the present invention inoludes the steps of evaporating the oonsti- .

V tuents of the alloy from a heated source means within a vacuum or low pressure system, depositing the constituents of the alloy upon a temperature controlled collector until a required thickness is deposited and opening the vacuum or low pressure system and removing the deposit from the collector in a oondition capable of undergoing metallurgical working.

Alloys in acoordaaee with the present invention may have very useful mechanical properties after suitable working in order to consolidate them. Xn particular they may be strong and ductile at room temperature and have impact strength, Young's modulus, fatigue properties, elevated temperature tensile strength, creep resistance and corrosion behaviour muoh better than^hcse of other aluminium alloys commonly used heretofor.

It has been found that the microstructure of alloys obtained by evaporation-condensation varies considerably with the temperature at whioh the collector is controlled. For example the miorostruoture characteristic of alloys of the present invention is obtained when the collector temperature is controlled, at about 260°C. When the collector temperature is maintained at about 37O°C an easily worked, high strength alloy may be produced in whioh the iron and chromium are substantially entirely in the form of a precipated phase or phases of fine particles, a major proportion of which have dimensions of about 2000 & or less. Such an alloy may have low porosity but may have a tendency to poor corrosion properties. At collector temperatures between about 260°C and 37O°G alloys with microstructures intermediate these two types are formed. At collector temperatures below about 260°C, for example about 170°C, a more porous deposit without the precipitate phase of iron rich zones is obtained but working, ie pressing and or rolling, may remove the porosity and heat treatment causes precipitation of the iron rich zones.

It has been discovered that the metastable solution of chromium in the aluminium lattice when originally deposited is in the form of narrow elongated grains having a diameter of 5/an or less. After working, for example hot pressing or hot rolling these grains can be converted to flat extended plate like grains having a thickness of 5i® or less. Preferably these dimensions of the grains are 1 After suitable working alloys Of the present invention may he obtained, with a tensile strength of at least'45 tonf/in^.

Apparatus suitable for the production of alloys in accordance with the present invention is illustrated in the accompanying drawings in whioh:Figure 1 is a schematic cross-sectional representation, Figure 2 is a perspective view of a oontrollably heated source means, , Figure J is a shaped ingot of feed metal and Figuiv A is a perspective view of a temperature controllable I collector. I Referring non to Figure 1 which is a schematic representation, a vacuum or low pressure vessel 10 is evacuated by a conventional vacuum pump 11 and a pressure gauge 12 is provided to monitor the pressure. A heated source means 1} is provided with metal by a metal supply 14 and a temperature controllable collector 15 is provided upon whioh metal evaporated from the heated source means 1} may be deposited.

A removable shutter 16 is provided operated by a handle 17 outside the vaouum vessel 10. The metal supply means 14 is preferably provided with a vacuum look so that it can be oharged without breaking the vaouum in the vaouum vessel 10, and in duplioate so that one may be charged while the other is in operation and continuous operation thus achieved.

Any suitable heated source means may be used but preferably the oontrollably heated source means disolosed in British Patent Soecification No. 1,440,-921 is used. Figure 2 is a perspective view of one embodiment of a oontrollably heated source means and is shown empty so that the internal structure is visible. A melting compartment 20 heated by an electron gun 21 connects with a mixing compartment 22 through a ohannel 23 whioh contains a partition 24 vzith a slit 25 therein. The mixing compartment 22 connects with a channel 26 with an evaporation compartment 27 heated by an electron gun 28. The compartments are enclosed in a copper cooling jacket 29 provided with copper pipes 30 for the circulation of cold water, the entrance and exit of which is not shown. The material of the compartments is heat and corrosion-resistant ceramics.

Metal may be supplied to the heated source means 13 in the form of discs obtained by casting a cylindrical ingot, turning it on a lathe and cutting it into evenly sized discs. One suitable feed mechanism is described in British Patent Specification No. 1,434,016. However preferably metal is supplied in the form of ah ingot as illustrated in Figure 3.

Suoh an ingot is oast in suoh a manner that the necks 80 solidify first and early in the solidification so that each of the pieoes 81 has substantially the nominal composition of the original material. This can be lovzered into a melting vessel in such a manner that it meltB one piece at.a time and is degassed.

Suitable specific temperature controllable collectors 15 are described in British Patent Specifications Nos. 1,279,975 and 1 ,433.,753.

However a preferred form of collector is disclosed in British Patent Specification No. 1,443,144 and one embodiment is shown in perspective view in Figure 4. The collector 15 comprises a thick metal plate 110 having a surface 111 for the deposition of the alloy and on the reverse surface 112 two longitudinal ridges 113. A metal is selected which has a similar coefficient of thermal expansion as the alloy to be deposited. Copper bars 114 are bolted in pairs to the ridges by means of a single bolt. 115 per pair.

A copper block 116 is held between eaoh pair of plates 114 by end plates 117 positioned outside the copper bars 114 and having bolts 118 passing through the copper block 116. Individual copper blocks 116 are hollow having inlet and outlet pipe 119 and. 120.

The shank of the bolt 115 has a lower coefficient of thermal expansion than the material of the ridge 113 so that when the assemblyheats up the bars 114 are pulled, more tightly on the ridges 113 ensuring efficient thermal contact. Similarly the bolts 118 have a lower coefficient of thermal expansion than copper so that effioent thermal contaot is ensured between the bars 114 and copper block 116. The collector plate 110 is also provided with a thermocouple 121 by whioh the temperature of the surface 111 can be monitored. Heatere 122 to pre-heat the plate 110 are also provided. Leads to thermocouple 121 and heaters 122 are not shown. A safety device is provided at the top of eaoh bar 114 to prevent the collector falling into the source 13 should the bolts 118 loosen for any reason. The safety device oonsists of a washer 124 extending beyond the edges of the bar 114 and held in plaoe by a bolt 123.

In use the thickness of the bars 114 are preselected according to the reguired operating temperature of the collector. For example, increasing the thioknees of the bars 114 increases the heat flux, whioh they carry and. thus for a given thermal input lowers the temperature of the oollector plate. 110. Similarly the copper blooks 116 can be positioned close to the plate 110 to remove heat more quickly again resulting in a relatively . lower plate temperature. During operation of the apparatus minor adjustments can be made by varying the rate of flow and/or temperature of the cooling fluid, whioh is preferably water.

In a typical deposition the collector is of aluminium alloy, suoh as duralumin, and is polished and cleaned before deposition begins.

Cleaning may be carried out by washing with detergent, rinsing, drying and heating to about 25O°C, or any suitable alternative process.

One suitable process is by glow disoharge cleaning, as disclosed in British Patent Specification No. 1,447,754. The metal charge is also washed with detergent, rinsed and dried. The desired.quantities of metal-charge are then loaded into the container or containers of the heated souroe means, and the feed magazine. The relative concentrations of aluminium:chromium: iron in the starting material in the oompartment 27 are not of aourse the same as the nominal concentrations required in the condensed alloy, due to the widely differing fugacities of the metals. However the initial concentrations required to produce an alloy of the present invention may easily be ascertained by those experienced in the art.

The apparatus is then assembled and the system evacuated, generally -5 to about 1 to 2 x 10 torr. The collector 15 is then preheated to the required operating temperature, for example by heaters 122, and is then maintained as near to this temperature as possible throughout the entire deposition experiment. The temperature of the heated souroe means 13 is then raised until the charge is evaporating fast, for example by means of electron guns 21 and 28, however the shutter 16 is kept in place until splashing of the charge has essentially stopped. The shutter 16 is then removed so that deposition on to the collector 15 may take place, extra charge from the metal supply 14 being admitted at suitable regular intervals. Deposition is terminated when a desired thickness has been deposited on the collector by switching off the 8.. electron gun^ allowing the collector to oool and opening the vacuum chamber. The deposit may then be removed from the collector by any suitable means. For thick deposits a band-saw may be used whilst for thin deposits the applioation of a parting agent to the surface of the collector prior to deposition may allow easy peeling of the deposit from the collector.

Alloys of the present invention require meohanioal working by any suitable working technique in order to consolidate them prior to use. Advantageously the working temperature should not exceed the temperature at whioh the collector was maintained during deposition. Suitable working teohniquee to consolidate and thus remove porosity may include pressing and rolling or extrusion and be followed by shaping. Other techniques may include annealing anc/or stretching to remove internal stress.

The following Examples describe specific alloys within the present invention and processes by whioh they may be produced and are given by way of example only, except Example 2 whioh is of the production of an alloy not having the desired structure.

EXAMPLE 1 A crucible of the type illustrated in Figure 2 was used. The following materials were loaded in the melting compartment 20, the mixing compartment 22 and the evaporation chamber 27 respectively:- 945 grams Al IKS Cr ingot 945 grams 99.8J4 Al plate 25 22 706 grams Al 10$ Cr ingot 63 grams Swedish iron 27 1650 grama 99.5^ Al plate 480 grams Cr aro-melted buttons 533 grams Swedish iron A feed magazine, (the metal supply means 14) was loaded with 148 discs of 64 mm diameter, consisting alternatively of discs of 9-1-9-5% Or in Al weighing 74g each, and 99-8/5 Al discs weighing 53g each. All the charge was first washed with detergent, rinsed and dried. A duralumin hlook collector of the type shown in Figure 4 was placed with its lower surface 36Ο mm above the evaporation chamber 27 of the crucible, the removable shutter 16 being positioned between. The collector had previously been, polished washed and dried.

The vacuum -chamber containing crucible, collector and feed magazine -5 was pumped out to about 2 x 10 torr. The collector was then heated to 32O°C and when the shutter was opened the current in the collector heaters was reduced and the collector temperature maintained as near to 32O°C as possible, ie from 308°C to 323°C, during the rest of the experiment.

The electron gun 21 was switched on and the beam was focussed on the metal in the melting compartment 20; the accelerating voltage was 18 Kv and. the emission current about 300 mA. The seoond electron gun 28 was switched on, and the beam was focussed on to the metal in the evaporating compartment 27 of the orucible; accelerating voltage 15-5 Kv, emission current about 250 mA. The voltages on both guns were kept constant and the emission currents were gradually increased to melt the crucible oharge without too muoh splashing. After about 70 minutes the emission current of electron gun 21 had reaohed 1 amp, and splashing had essentially stopped. Three minutes later the-shutter was moved away to allow deposition of evaporated metal on the collector lower surfaoe. Two minutes after this the mechanical feeding of discs from the feed magazine into crucible chamber 20 was started, one disc being introduced about every 100 seconds, until after a further period of 3 hours 50 minutes a total of 139 disos had been introduced. The deposition was then terminated, by switching off the electron guns, the collector was allowed to cool, and the vacuum chamber was opened. During the feeding of the discs the emission current of gun 21 was about 1.06 amps and that of gun 28 was 520-620 mA.

The deposit was removed, from the collector with a band.-saw. The chromium and iron contents near the oentral region of the deposit were: Or 4.8% to 6.$%, Fe 1.0% to 0.6%.

Slabs cut from the deposit were worked to sheet by pressing followed by rolling, using pressing temperatures in the range 20°C to 260°C and. rolling temperature nominally in the range 20°C to 230°C. For «cample one pieoe was pressed at 20°C from an initial thickness of 0.47 inch to a thickness of 0,16 inch and rolled at 20°C down to a thickness of 0.052 inch. It had a room temperature tensile strength in tnis condition of 44 tonf/ins with an elongation of 5%· Another piece was pressed at 25O°C from an initial thickness of 0.75 inch to a thiokness of 0.30 inch and then rolled to a final thickness of 0.057 inch. It had a room temperature tensile strength of 43 tonf/ins and an elongation of 5%· ®he Young's modulus was in both oases about 11.5 x 10^ psi.

A third pieoe was pressed at 200°C from a thickness of 0.55 inch to 0.32 inch and then rolled at 200°C and below to 0.064 inch. It had a tensile strength of 43 tonf/ins at room temperature, elongation ($>, and a Q tensile strength of 28 tonf/ins at 300 C, elongation 10%.

A fourth piece was pressed at 250°C from 0.71 inch to 0.25 inch and rolled at 230°C to 0.058 inch. It had a tensile strength at room temperature of 45 tonf/ins , elongation 4%, and a tensile strength at 200°C of 37 tonf/in, elongation 6%.

Speoiraens pressed, at 200 to 25O°C from 0.55 inch to 0.25 inch and rolled at 230°C to 0.06 inch had the following mechanical properties:(ai Fatigue (tested at fatigue cycle p+0.9p where p = stress) (1) Holed test piece (elastio stress concentration factor K*. s 2.6) At peak stress (1.9p) of 25000 lhf/in :-Sample unbroken after 2.9 x 107 oyoles. 8 At peak stress of 25500 lhf/in: Sample unbroken after 1 x 10 oyoles. (2J Plain test piece 7 At peak stress of 40,000 lbf/in : Sample unbroken after 5.3 x 10' cycles.

Results obtained indicate a fatigue strength about 35/2 greater than standard aluminium aircraft alloys(for example 2024-T3 San Al-Cu-Mg alloy), ( b) Creep Stress for 0.1% total plastic strain in 100 hours at 251 °C = 10 2 tonf/in .

Stress for 0.1% total plastic strain in 100 hours at 223°C = 15 tonf/in^.

Stress for 0.1% total plastic strain in 100 hours at 183°C = 20 tonf/in^.

Stress for 0.1% total plastic strain in 1000 hrs at 195°C = 14 tonf/in^.

Results obtained indicate that this alloy has about a factor of 2 Q advantage in stress, and, for a stress of 20 tonf/in a 70°G advantage in temperature over a standard aluminium aircraft alloy (for example 011001-10^ c Impact Impact properties were measured using miniature Charpy test pieces, 2.8 mm x 2.8 mm x 40 mm unnotched (ON) or notched (N) with 45° notoh, 0.6 mm deep and 0.15 mm root radius.

Results obtained were ON 5.5 to 6.2 ft lb unbroken N 0.9 to 2,5 ft lb unbroken These irapaot strengths are comparable with the titanium alloys IMI 318 (T1-6A1-4V) and IMI 685 (Ti-6Al-5Zr). d Corrosion Weight loss in 5$ aqueous NaCl at 36°C. ο At condensation rate of 1.5 +0.5 mli/hr over a sample area of 80 cm for 6 weeks exposure the weight loss is less than 0.45 mg/em^, whioh is similar to that of pure aluminium.

NOTE: The chemical composition of each test piece is not known precisely but it is in, or near to the range of composition given above. EXAMPLE 2 An experiment was carried out essentially as desoribed in example 1, exoept that the oruoible only had two interconnected chambers - an evaporation oharaber and a feed ohamber. One electron beam played on the metal in the evaporation ohamber, and thermal conduction occurred from this chamber into the feed chamber sufficient to melt the feed.

The collector temperature was held at 356°C to 374°C during deposition.

The deposit composition near the central region was: Or 6.3/° to 8.$; Fe 0.%i to 1.4??.

Several pieoea of the deposit were worked as in example 1. Thus one piece was pressed at 230°C from 0,46 inch to 0.14 inch in thickness and then rolled at 210°C to 0,054 inch. Its room temperature tensile 6 strength was 43 tons/in , elongation 8%, Young's Modulus 11 x 10 psi.

Another piece was rolled, warm, without prior pressing, from a thickness of 0.33 inch to 0.044 inch. Xt had a room temperature tensile strength 6 of 40 tons/in , elongation 8fi>, Young's Modulus 12 x 10 psi.

EXAMPLE 3 A deposit was made by the method desoribed in example 1, except that the collector was heated initially to 2fi0°C and held, during deposition, in the temperature range 252°C to 258°C. The amount of metal evaporated was 9.2 kg in about 3 hours 40 minutes. The composition of the deposit near the central region was: Cr 7.6 to 7.¾ Fe 0.99$ to 1.14$. One piece of the deposit was pressed at 260°C to 230°C from a thickness of 0.47 inch to 0.20 inch, and then rolled at 235°C to 250°C down to a thickness of 0.063 inoh. In this condition the room temperature tensile strength was 47 tonf/in Tilth an elongation of 0$, and the tensile strength at 200 C was 40 tonf/in with an elongation of &/.

EXAMPLE 4 This deposit was formed under the same conditions as those given in example 3, except that the feed was introduced as ingot as illustrated in Fig 3 and whioh was lowered from a vertical stock as contained in an evacuated tower as desoribed in British Patent Specification No. 1,'434,016.

The feed stack contained 7.9 Kg of ingots of composition Al, 7$ Cr, 1·5% Fe. There were four lengths of ingot held one below the other by iron wire.

The oentre of the deposit had the following composition: Cr 7.5$ Fe 1 .6$, The deposit was cut off and small pieces were worked and tested 25 as described in Example 1, and exhibited similar mechanical properties.

EXAMPLE 5 This deposit was made under the same conditions as those used in Example 4, but a crucible charge and ingot feed stack with a lower chromium content were used. The crucible and >> feed charges were as follows:Melting chamber 20 47g Swedish iron 95g arc-melted Cr. buttons 3020g 99.8% Al plate Mixing chamber 22 237g Swedish iron 79g Cr buttons 710g Al plate Evaporation chamber 27 765g Swedish iron 265g Cr buttons 2300g Al plate The feed stack contained 8.5kg of ingot of composition 3% Cr 1.5% Fe balance Al.

The composition of the central region of the deposit was 3.1% to 3.9% Cr. 1.2% to 1.58% Fe balance Al. The deposit was worked and tested as in previous examples after having been cut off the collector.

It should be noted that the materials produced in accordance with the 25 above described Examples suffered from a certain amount of porosity, which resulted in cracks appearing at the edges of the sample as these were worked. Such cracked portions were cut off and discarded before further working or use as test samples.

Claims (10)

1. An evaporation-condensation aluminium alloy which consists of 2 to 12% by weight of chromium, 0.2 to 3.0% by weight of iron, the balance being aluminium apart from minor proportions of impurities and incidental elements wherein most of the chromium is present as a metastable solution in the aluminium lattice which contains a precipitate phase of iron rich zones the major proportion of which have dimensions of 2OoS or less, the presence of large intermetallic particles, particularly at grain boundaries, being at a minimum.

2. An alloy as claimed in claim 1 which consists of 4 io 10% byweight of chromium and 0.3 to 2.0% by weight of iron.

3. An alloy as claimed in claim 1 which consists of 5 to 7/ by weight of chromium and 0.6 to 1.5% by weight of iron.

4. An alloy as claimed in claim 1 whioh consists of 5 to 8% by weight of chromium, 0.8 to 1.3% by weight of iron and in which a major proportion of the iron rich sones have dimensions of 50^ or less.

5. An alloy as claimed in claim 4 wherein substantially all of the iron rich zones have dimensions of 5θ2 or less.

6. An alloy as claimed in any one preceding claim and wherein the metastable solution of chromium in the aluminium lattice is in the form of narrow elongated grains having a diameter of 5pm or less.

7. An alloy as claimed in claim 6 and wherein the metastable solution of chromium in aluminium lattice is in flat extended plate like grains having a thickness of 5pm or less.

8. An alloy as claimed in either claim 5 or claim 6 and wherein the dimension of the grains is 1pm or less.

9. An alloy as claimed in claim 1 and substantially as hereinbefore described and with particular reference to any 5 one of Examples 1, 3, 4 and 5.

10. An alloy as claimed in any one preceding claim and substantially as hereinbefore described and with particular reference to any one of the worked alloy compositions disclosed in any one of the Examples 1, 3, 4 and 5.