CA1181617A - Wrought aluminum base alloy products having refined intermetallic phases - Google Patents

Abstract

Abstract of the Disclosure A wrought aluminum alloy product is disclosed. The alloy comprises 0.5 to 10 wt.% Mg, 0 to 0.35 wt.% Cr, at least 0.005 wt.% Sr, less than 1 wt.% Fe, 3.5 wt.% max. Zn, 1 wt.%
max. Cu, 0.3 wt.% max. Ti, the remainder aluminum and incidental impurities, and wherein the alloy further comprises either: (a) 0.1 to 1.6 wt.% Mn and 1 wt.% max. Si, and the product has at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined; or (b) 0.3 wt.% max. Mn and 0.3 wt.% max. free Si, and the product has an intermetallic phase of the type containing Al-Fe in a refined condition.

Description

This inven-tlon relates to aluminum alloys and more particularly it relates to ~rouyht aluminum alloy products such as sheet products suitable for forming in-to substrates Eor memory discs, for example.
In the fabrication of aluminum alloy substrates Eor memory discs, normally the substrates are machined usually on both sides prior to applying a coating thereto which functions as memory medium. It will be appreciated that for use as a mernory disc substrate, the surface has to be extremely smooth in order not to interfere with the coatings and for storage of information therein. Normally information is stored in such coating by electrical impulses or magnetized spots where presence or absence of such represent data and accordingly, it will be seen that irregularities in the surface can interfere with the ability of the coating to retain data accurately. The machining step referred to has not been without problems. For example, in some of the alloys used, insoluble constituents have presented problems from a machining standpoint, resulting in a high rejection rate for the substrates. That is, it has been found that in certain aluminum base alloys, insoluble constituents such as Al-Fe-Mn-Si constituents or phases, form in rather large particle sizes, sometimes greater than 1 m, and interfere with with the machining operation, particularly tha-t required in the preparation of substrates for memory discs.
These constituents can in-terfere with the machining operation by catching on the cutting tool and being removed therewith or being pulled across the machined surface leaving scratches. In either case, it adversely affects the smoothness desired.
Further, it is believed that when a machined surface is etched, the large constituents interfere with uniformity of etching.
Even if the surface has been found to machine adequately, there can be ins-tances where the coating or undercoatlng therefor is interfered with to an extent which affects storage of data in the coating. The interference is believed to result from relatively large int-rme-tallic phases or constituents as noted above. Thus, it can be seen that such phases or constituents must be provided in a refined or modified condition which provides freedom from such conditions.
In addition, it has been found that such or similar problems can arise when aluminum-based alloys are anodized for use as bright trim on automobiles. Tha-t is, -these in-termetallic constituents can resist e-tching and anodization treatments resulting in holes or unanodized spots in -the protec-tive anodic coating which, of course, can severely interfere with the useful service life of the trim. Thus, again, it can be seen -that it is very important to provide the intermetallic phases or insoluble constituents in a refined or modified condition which avoids these problems. Similarly, with fine wire forming, such as a screen wire, the large particles interfere with the forming operation. That is, the large par-ticles can cause severe breakage problems in wire drawing. It will be understood that the problems referred to are used more for illustrative purposes and that there are many other applications where relatively large particle constituents interfere with the use of the particular aluminum alloy.
The present invention provides an aluminum base alloy wrought product having a refined or modified intermetallic phase or insoluble constituent which may be machined -to a smoo-thness suitable for use as memory disc substrates, for example. In addition, aluminum base alloy products, e.g. extrusion or sheet-type products, in accordance with the invention have, inter alia, enhanced anodizing characteristics.
According to the invention there is provided a wrought aluminum alloy produc-t, wherein the alloy comprises 0.5 to 10

- 2 -wt.% Mg, 0 to 0.35 wt.% Cr, at least 0.005 wt.% Sr, less than 1 wt.% Fe, 3.5 wt.% ma~, ~n, 1 wt.~ max. Cu, 0 -to 0.3 wt.% Ti, the remainder aluminum and incidental impuri-ties, and wherein the alloy further comprises either: ~a~ 0.1 to 1.8 wt.% Mn and 1 wt.% max. Si, and the product has at least one intermetal-lic phase of the type containing Al-Fe Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined; or (b) 0.3 wt.% max. Mn and 0.3 wt.% max. :Eree Si, and the product has an intermetallic phase of the type containing Al-Fe in a refined condition.
Also provided according to the invention is a method of producing a wrought aluminum alloy product, comprising the steps of (1) providing a body of aluminum base alloy as defined above in accordance with part (a); (2) heating the body to a temperature of not greater than 1100F (595C); and

(3) working said body to produce a wrought aluminum alloy product having at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.
In the accompanying drawings:
Figure 1 is a photomicrograph (500X) of an aluminum base alloy sheet product showing constituent particles of Al-Fe-Mn-Si which interfere with machinability of the sheet.
Figure 2 is a photomicrograph (500X) of an aluminum base alloy sheet product of Figure 1 having refined or modified constituent particles, the sheet product having improved ' - 3 -machining characteris-tics and beiny particularly suitable for memory disc substrates.
Figure 3 is a photomicrograph (500X) of the aluminum base alloy of Figure 2, except the sheet product is provided in a thinner gauge.
Figure 4 is a phase diagram showing the relationship of intermetallic phases and composi-tions of an aluminum base alloy containing 0.2 wt.% Fe after a soak period at 950F
(510C).
In certain aluminum base alloys, because of advances in the technology in which the alloy is used, it has become necessary to refine the constituent particle size in order to permit use of the new technology. For example, in disc-storage technology, efforts have been made to increase the amount of data which can be stored on a single disc and to switch the medium traditionally used for storage purposes in order to circumvent problems. Efforts have been made to switch from iron oxide-type memory medium in order to increase the medium's resistance to erasure. Thin surface layers of cobalt, for example, have been investigated quite successfully to determine its suitability for such applications. ~pplications of a layer of memory medium such as iron oxide to an aluminum substrate involve different technology and thicker layers than that used for applying the thin layer of cobalt, for example. For instance, the iron oxide medium is applied to the substrate as a slurry or dispersed in a plastic binder, whereas plating or other forms of deposition, e.g. vapor or vacuum deposition, can be used for applying thin, meta:Llic layers such as the thin cobalt layers. In addition, the thin metal films are very sensitive to defects on the surface of the aluminum substrate to which it is applied. For example, large constituen-t particles can interfere with the plating or deposition of the thin metallic layer. Also, as noted earlier, the larye par-ticles can interfere with -the smoothness of the finish at-tainable on the aluminum substrate by machining, which in turn, is reflected in roughness of the thin metallic film deposited on the substrate.
It must be remembexed that particles, e.g. dust particles of about 0.3 ~ m, can in-terfere wi-th the effectiveness of the head used for storing or reading data from the medium layer, particularly where the medium layer is comprised of a thin metallic layer. Accordingly, it can be seen why it is so important to minimize roughness on the surface of the aluminum substrate on which the layer is deposited.
Similarly, such problems with large constituen-t particles can be encountered in anodization of aluminum alloys used for auto trim, for example. That is, the constituent particle on or near the surface can react or oxidize quite differently from surrounding material resulting in defects in the anodic coating. Such defects can adversely affect the corrosion resistance o:E the anodic coating on the trim. Thus, in the two examples given, it can be seen that such particles are best avoided.

Figure 1 is a photomicrograph of an aluminum base alloy which had been used for memory disc substrates where the memory layer consisted particularly of iron oxide applied by the slurry. In the micrographs, the distance between the vertical lines corresponds to or represents 1 ~ m in the alloy microstructure The alloy contains 0.20 wt.% Fe, 0.11 wt.% Si, 0.37 wt.% Mn, 4.06 wt.% Mg, 0.02 wt.% Cu, 0.08 wt.% Cr, 0.02 wt.% Zn and 0.01 wt.% Ti, the remainder aluminum and impurities.
However, as can be seen from the micrograph, rather large Al-Fe-Mn-Si consti-tuent particles occur throughout the metal.
Some of the particles are on the order of about 1 ~ m which, as '7 noted earlier, can in-terfere with machininy and conse~uently with the memory medium.
Figure 2 shows a photomicrograph of a wrought aluminum sheet product, particularly suitable for memory disc substrates, in accordance with the invention. The alloy of Figure 2 contains 0.22 wt.% Fe, 0.18 wt.% Si, 0.40 w-t.% Mn, 3.85 wt.% Mg, 0.08 wt.% Cr, 0.033 wt.% Sr, 0.02 wt.% Zn, 0.03 wt.% Cu and 0.01 wt.% Ti, the remainder aluminum and incidental impurities.
Inspection of the micrograph reveals the absence of constituent particles havi.ng a size compared to that shown in Figure 1. It is the freedom from relatively large particles which interfere with machining that provides the wrought sheet product shown in Figure 2 with superior characteristics. Also, it is -the absence of large particles which makes the product highly suitable for substrates such as those used in memory discs, particularly where the memory medium is a thin layer or film of metallic material which ls plated or deposited on the substrate.
Further, in compositions or alloys in accordance with the invention, the absence of such large particles makes the extrusion product, e.g. auto trim, as well as sheet product particularly suitable for anodizing. The sheet products of Figures 1 and 2 were rolled to 0.162 inch (4.11 mm) gauge.
However, even when the sheet product of Figure 2 is rolled to a sheet thickness of 0.082 inch (2.08 mm) gauye, it still retains its refined or modified structure, as can be seen by examination of the photomicrograph of Figure 3.
When a wrought product in accordance with an embodiment of the invention is desired, the alloy can consist essentially of 0.5 to 9 wt.% Mg, 0.1 to 1.4 wt.% Mn, 0 to 0.35 wt.% Cr/ 0.005 to 2.5 wt.% Sr, less than 1 wt.% Fe, 1 wt.% max.
Si, 3.5 wt.% max. ~n, 1 wt.% max. Cu, the remainder aluminum and incidental impurities.

Maynesium is added or provided in -this class of aluminum alloys rnainly for purposes of strength and is preferably maintained in the range of 0.5 to 5~6 wt.%.
~agnesium is also useful since it promotes fine aluminum grain size in the alloy which, of course, aids formability. It should be noted, though, that higher levels of magnesium can lead to fabrication problems. Thus, it becomes important to balance the strengths desired against problems in fabrication. With respect to machining, the higher levels of magnesium in solid solution favor machinability. Aluminum alloys having the poorest machining characteristics have a low alloy content and are usually in the annealed or softest condition. Conversely, increasing alloy concentration, cold work, solution and aging treatments, result in an improved surface finish by hardening the alloy, by reducing adherence of metal to the tools and by reducing the number of burrs. That is, these additions or treatments improve machinability. Thus, for purposes of machining aluminum alloy substrates for memory discs, i-t is desirable to maintain the magnesium in the range of about 3.5 to 5.5 wt.~. Where the application is aluminum screen wire, which is drawn to a very fine diameter, maynesium should be in the range of 4.5 to 5.6 wt.%, and where the application is aluminum easy-open-ends for beverage containers and the like, magnesium should be in the range of 4 to 5 wt.%. While higher levels of magnesium have been referred to for purposes of exemplification, lower levels of magnesium are also important in certain applications such as alloys used for rigid containers, auto trim, architectural products, trucks and railroad vehicles and are contemplated to be within the purview of the invention.

With respect to manganese, it can range up to 1.4, 1.
or 1.8 wt.% but preferably it is maintained to less than 1 wt.%, and typically it is maintained in the range of 0.1 or 0.2 to 0.8 wt.~. Manganese ls a dispersoid forming element. That is, manganese is an element whlch is precipitated in small particle form by thermal treatments and has, as one of its benefits, a strengthening effect. Manganese can form dispersoid consisting of Al-Mn, Al-Fe-Mn and Al-Fe-Mn-Si. Thus, in some magnesium-containing alloys where it is desired to increase corrosion resistance, magnesium can be lowered and manganese added at no loss in strength, but with increased resistance to corrosion. Likewise, chromium can have the advantage of increasing corrosion resistance, particularly stress corrosion.
Also, chromium can combine with manganese to provide more dispersoid which, as noted earlier, can increase strength.
Chrornium can also have an effect by influencing preferred orientation with respect to earing, in cups for example. It will be understood that earing is detrimental because it results in wastage of metal. Preferably, chromium should not exceed 0.25 wt.% for most of the applications for which alloys of the invention may be used.
Solid solubility of iron in aluminum is very low and is on the order of about 0.04 to 0.05 wt.~ in ingot. Thus, normally a large part of the iron present is usually found in aluminum alloys as insoluble constituent in combination with other elements such as manganese and silicon, for example.
Typical of such combinations are Al-Fe-Mn, Al-Fe-Si and Al-Fe-Mn-Si. It will be appreciated that -the elements in these combinations can be present in various stoichiometric amounts.
For example, Al-Fe-Si can be present as A112Fe3Si and AlgFe2Si2 which are considered to be the most commonly occurring phases.
Also, Al-Fe-Mn can be present as A16(FexMnl x~' where x is a number greater than 0 and less than 1. With respect to Al-Fe-Mn-Si, this combination can be present as A112(FexMnl x)3Si, where x is a number greater than 0 and less -than 1. It shoulcl be noted that these constl-tuen-ts are considered to be the most common intermetallic phases found in these types of alloys. However, it should be understood -that other elements such as Cu, Ti and Cr and the like can appear in or enter into the intermetallic phases referred to in minor amounts by substituting usually for part of the Fe or Mn. Such intermetallic phases are also contemplated within -the purview of the invention. These insoluble constituents tend to agglomerate and form relatively large particles such as Al-Fe-Mn-Si constituents, as may be seen in Figure 1, some of which are approximately 1 ~ m in length. As noted earlier, it is these larger, insoluble constituents that are so undesirable from the standpoint of machinability and formability. However, it must be remembered that iron has a beneficial effect as a grain refiner which, of course, aids machinability and formability.
Further, it must be understood that iron is normally present in most aluminum alloys, mainly from an economic standpoint. That is, processing aluminum to remove iron for most applications is normally not economically feasible. Thus, many attempts have been made to work with iron in the alloying by taking advantage of its benefits and neutralizing its disadvantages often with only limited success. Thus, preferably, for purposes of the present invention, iron is maintained at 0.8 wt.% or lower, and typically less than 0.5 wt.%, with amounts of 0.4 wt.% or less being quite suitable.
Titanium also aids in grain refining and should be maintained to not more -than 0.2 wt.%.
For purposes of the present invention, it is believed that the amount of silicon also should be minimized since, at relatively low levels it can combine with magnesium, resulting in significant strength reductions. Thus, preferably, silicon _ g _ should be maintained at less than 0.5 wt.% and typically less than 0~35 wt.%.
Strontium, which should be considered to be a character-forming element, is also an important component in the alloys of the presen-t inven-tion. S-trontium must not be less than 0.005 wt.% and preferably is maintained in the range of 0.005 wt.~ to 0.5 wt.% with additional amounts not presently believed to affect the performance of the produc-ts adversely, except that increased amounts may not be desirable from an economic standpoint. For most applications for which alloys of the present invention may be used, strontium is pre:Eerably present in the range of 0.01 wt.% to 0.25 wt.%, with typical amounts being in the range of 0.01 wt.% to 0.1 wt.%.
The addition of strontium to the composition has the effect of refining or modifying intermetallic phases or insoluble constituents of the type containing Al-Fe-Si, Al-Fe Mn and Al-Fe-Mn-Si, as noted earlier. Because of the complex nature of these phases, it is not clearly known how this effect comes about. That is, because of the multiplicity of alloying elements and the interaction with each other, it is indeed ~uite surprising that significant refinement of insoluble constituent is obtained.
However, the benefit of adding strontium can be clearly seen by comparing the micrographs of wrought sheet products shown in Figures 1, 2 or 3. The compositions for these sheet products were provided hereinabove. The ingot from which these sheet products were rolled was cast by the direct chill method. An ingot having this composition was first scalped, homogenized for 2 hours at 1050F (565C), and then, starting at about a temperature of 950F (510C), hot rolled to a thickness of about 0.182 inch (4.62 mm). From an examination of Figure 1, it will be seen that some of the Al-Fe-Mn-Si particles or insoluble constituen-ts are relatively large and have lengths of about 1 ~ m~ Figure 2 is a micrograph (500X) of an alloy haviny the same composition as that shown in Figure 1 except 0.02 wt.%
strontlum was added. The alloy was rolled in the same way as for the alloy of Figure 1. It will be seen that -the A1-Fe-Mn-Si particles are greatly reduced in size when compared to Figure 1.
Also, the insoluble constituents including the dispersoid phase have a substantially uniform distribution throughout the matrix.
Thus, it will be observed tha-t the s-tron-tium has the effect of refining the intermetallic phases.
Even if the sheet product of Figure 2 is further cold rolled to 0.082 inch (2.08 mm) gauge after annealing, the small insoluble constituent or intermetallic phases are maintained.
For example, Figure 3 is a micrograph (500X) of an aluminum base alloy having the same composition and fabricated in -the same way as Figure 2, except that it was rolled to 0.082 inch (2.08 mm) gauge. As will be observed from Figure 3, -the fine particle constituent was maintained. Thus, from these micrographs it will be seen that strontium has the effect of refining these intermetallic phases in the alloy and maintaining the refined condition after the alloy has been fabricated into a wrought sheet product, for example.
An x-ray diffraction analysis using a Guinier-type camera of the sheet samples referred to in Figures 1, 2 and 3 shows the relative amounts of the intermetallic phases present.
The results of the analysis are tabulated in the following Table.

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r~
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r-i ~ :~

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r~
--I r-l ri ~ rl ~1) t~
U~
r-1 rl r~i ~I r-l U~ ~I r-i r-l V~

4~ ~1 4~
O O O
-1 t`l ~ ~ :~
O O ' O -r-i ~) ~ ~ r~
r-i rl ~1 rl r-i -r~l As well as providiny the wrought pro~uc-t in compositions haviny controlled amounts of alloyiny elements as described above, it is preferred that comp~si-tions be prepared and fabricated into products according to speciEic method steps in order to provide the most desirable characteris-tics. Thus, the alloys described herein can be provided as an ingot or billet or can be strip cast for fabrication into a suitable wrought product by techniques curren-tly employed in the art.
The cast material, such as the ingot, may be preliminarily worked or shaped to provide suitable stock for subsequent working operations. In certain instances, prior to the principal working operation, the alloy stock may be subjected to homogenization treatment and preferably at metal temperatures in the range of 800F to 1100F (425C to 595C) for a time period of at least 1 hour to dissolve magnesium or o-ther soluble elements and to homogenize the internal structure of the metal and in some cases to precipitate dispersoids. A preferred time period is 2 hours or more at the homogenization temperature.
Normally, for ingot the heatup and homogenizing treatment do not have to extend for more than 24 hours; however, longer times are not normally detrimental. A soak time of 1 to 12 hours a-t the homogenizatio~ temperature has been found quite suitable.
After the homogenizing treatment, the metal can be rolled or extruded or otherwise subjected to working operations to produce sto~k such as plate, sheet, extrusion or wire or other stock suitable for shaping into the end product. To produce a sheet-type product, a body of the alloy is preferably hot rolled to a thickness in the range of about 0.125 to 0.25 inch (3.17 to 6.35 mm). For hot rolling purposes, the temperature should be in the range of 600F to about 1050F
(315C to about 565C) and preferably the temperature initially is in the range of 850F to 950F (455C to 510C)~ The temperature at comple-tion is preferably 400F -to 600F (205C -to 315C) When the in~ended use of a selected composition is a typical wrought sheet product such as is suitable for memory disc substrates, for example, final reduction as by cold rolling can be provided. Such reduction can be -to sheet thicknesses in the range of 0.058 to 0.162 inch (1.47 to 4.11 mm). The disc substrates may then be stamped from the sheet and thermally flattened at a temperature in the range of 350F to 750F (175C
10 to 400C) for a period of time of 1 to 5 hours with a typical flattening treatment being 3 to 4 hours at 425F to 650F (220C
to 345C) under pressure. The substrates are usually rough cut and then precision machined to remove about 0.006 inch (0.15 mm) in order to obtain the proper degree of flatness and smoothness before applying the memory medium. After machining, it may be desirable to thermally flatten the substrates again. In additlon, after machining, normally the substrates should be degreased and given a light etching treatment. Prior to applying the memory medium, the substrates may be given a 20 chemical conversion treatment, particularly if the iron oxide-type memory medium is used.
In certain applications, depending on the properties required, it may be desirable to subject the product after working to a thermal treatment. This treatment may be provided as an intermediate anneal or after the product has been worked to final dimensions. For a partial anneal, the temperature is usually in the range of 200F to 500F (95C to 260C) with a typical range being about 300F to 500F (150C to 260C) for time periods in the range of about 1 to 4 hours. For full 30 anneal, generally the temperature is in the range of 600F to 775F (315C to 415C) for most applications with typical annealing practices normally being in the range of 650F to 750F (345C to 400C~. For full anneal, time at annealing temperature is in the range of 1 -to 2 hours for batch ma-terial.
When the intended use of the wrought product in accordance with the invention is screen wire, for example, preferably the alloy consists essentially of 4 to 5~6 w-t.% Mg 0.05 to 0~2 wt.% Mn, 0.05 to 0.2 wt.% Cr, not less than 0.005 wt.% Sr, 0.4 wt.% max. Si, 0~4 wt.% max. Fe, 0.1 wt.% max. Cr, 0.25 wt.% max. Zn, the remainder aluminum and incidental impurities. Additional impurities should not constitute more 10 than 0.15 wt.% total. When the intended use of the wrought sheet product is truck body panels and the like, for example, the alloy can consist essentially of 2.2 -to 2.8 wt.% Mg, 0.1 wt.% max. ~n, 0.15 to 0.35 w-t.% Cr, 0.005 to 0.25 wt.% Sr, 0.25 wt.% max. Si, 0.4 wt.% max. Fe, 0.1 wt.% max. of both Cu and Zn, the balance aluminum and impurities, the total of impurities not exceeding 0.15 wt.%. In instances where higher strengths may be required, such as in tank cars and the like, while maintaining weldability and formability, manganese may be increased in the latter alloy to be in the range of 0.5 to 1 wt.%. Likewise, 20 where high degrees of strength are required, such as in armor plate or in liquefied natural gas containers, magnesium can be increased to be in the range of 4 to 4.9 wt.%.
In another aspect of the invention, it may be desirable to control the amount of manganese in the alloy composition in accordance with the invention to not greater -than 0.3 wt.% and preferably not greater than 0.2 wt.%. This may be desirable where the sheet product is to be used for easy-open-ends, for example. The phase diagram of Figure 4 shows the relationship of compositions and phases when manganese is in the range of 0 to 0.3 wt.% and free silicon is less than 0.3 wt.% in aluminum base alloy compositions having 0.2 wt.% Fe.

In the phase diagram, the area referred to as 1 denotes that the 'Jl~.'7 only intermetallic phase obtained is the Al-Fe t~pe phase such as FeA13 or the metastable phase Fe~16. Similarly, in -the area denoted as 2, the interme-tallic phases of the Al-Fe and Al-Fe-Mn [e.g. (FeMn)A16)] are obtained. The following tabulation identifies the interme-tallic compounds found in the different areas of the phase diagram:
Area Intermetallic Compounds l FeAl3 2 FeA13 + (FeMn)A16 3 3 ( ) 6 12( )3 4 (FeMn)A16 (FeMn)A16 + A112(FeMn)3Si 6 FeAl3 + A~12(FeMn)3 7 All2(FeMn)3Si 8 All2(FeMn)3Si + A1l2(MnFe)3Si 9 All2(FeMn)3Si + A1l2(MnFe)3Si ~ (FeMn)A16 The addition of strontium in the composition can have the effect of refining or modifying the Al-Fe phase when the composition with respect to Mn and free Si is maintained within these limits. By free Si is meant that in Mg-containing aluminum alloys, the silicon is not combined or tied up wi-th Mg.
However, such Si may be combined with Mn, Fe, or both. With respect to the phase diagram, it will be noted that no Mg is present since its effect would be to lower the free silicon content.
The phase diagram was developed as follows. A series of alloys was prepared containing refined aluminum with 0.2% Fe.
Mn was added to provide 0.1, 0.2, 0.3 and 0.5 wt.% and Si was added to provide from 0 to 1 wt~%. Master alloys with 0% Si and 1% Si were made as 2500 gram charges cast as notch bar.
Intermediate Si contents were made by combining the mas-ter alloys. 200 gram charges were melted and cast as 1/4 x 2 x 4 inch (6035 x 50.8 x 101 mm) ingots in molds preheated at 600E' (315C). The ingots were cut into 1 inch (25.4 mm) squares for preheat experiments~ They were programmed 50F/hr (28C/hr) to 850F (455C), 950F (510C), 1050F (565C) or 1125F (605C), held 16 hours at temperature and quenched -to retain phases present at the preheat temperature. Phases were identified in the specimens by x-ray diffraction and the results were used to construct the phase diagram.
The phase diagram shows tha-t ~l-Fe--type interme-tallic 10 is the primary intermetallic phase present in the area denoted as 1 and that this phase is also present in the areas denoted as 2, 3 and 6.
Various modifications may be made in the invention without departing from the spirit thereof, or the scope of the claims, and therefore, the exact form shown is to be taken as illustrative only and not in a limiting sense, and it is desired that only such limitations shall be placed thereon as are imposed by the prior art, or are specifically set forth in the appended claims.

Claims (106)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A wrought aluminum alloy product, wherein the alloy comprises 0.5 to 10 wt.% Mg, 0 to 0.35 wt.% Cr, at least 0.005 wt.% Sr, less than 1 wt.% Fe, 3.5 wt.% max. Zn, 1 wt.% max.
Cu, 0 to 0.3 wt.% Ti, the remainder aluminum and incidental impurities, and wherein the alloy further comprises either: (a) 0.1 to 1.8 wk.% Mn and 1 Wt.% max. Si, and the product has at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and A1-Fe-Mn-Si, wherein at least one of such phases is refined; or (b) 0.3 wt.% max. Mn and 0.3 wt.% max. free Si, and the product has an intermetallic phase of the type contain-ing Al-Fe in a refined condition.

2. A product according to claim 1, wherein Mg is maintained in a range of 0.5 to 5.6 wt.%.

3. A product according to claim 2, wherein Mg is maintained in the range of 3.5 to 4.5 wt.%.

4. A product according to claim 1, wherein the Mn of part (a) is less than 1 wt.%.

5. A product according to claim 4, wherein the Mn of part (a) is maintained in the range of 0.2 to 0.8 wt.%.

6. A product according to claim 1, wherein Sr is maintained in the range of 0.01 to 0.25 wt.%.

7. A product according to claim 1, wherein the alloy defined by part (a) comprises 0.5 to 5.6 wt.% Mg, 0.25 wt.% max.
Cr, 0.005 to 0.5 wt.% Sr, less than 0.5 wt.% Fe and 0.5 wt.%
max. Si.

8. A product according to claim 1 wherein the alloy of part (a) is in the form of a flat rolled or sheet product suit-able for machining and use as a substrate.

9. A product according to claim 8, in the form of a memory disc substrate.

10. A product according to claim 9, having a layer of memory medium provided on said substrate.

11. A product according to claim 1, wherein the Mn of part (b) is 0.2 wt.% max.

12. A product according to claim 2, wherein the alloy defined by part (b) comprises 0.25 wt.% max. Cr. 0.005 to 0.5 wt.% Sr, less than 0.5 wt.% Fe, and 0.2 wt.% max. free Si.

13. A method of producing a wrought aluminum alloy product, comprising the steps of: (1) providing a body of aluminum base alloy as defined in claim 1, the alloy composition being in accordance with part (a); (2) heating the body to a temperature of not greater than 1100°F (595°C); and (3) working said body to produce a wrought aluminum alloy product having at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.

14. A method according to claim 13, wherein in step (3) the body is hot rolled to produce a flat rolled or sheet product.

15. A method according to claim 14, wherein a sheet product is produced which is suitable for machining and use as a substrate such as a memory disc substrate.

16. A method according to claim 15, wherein for producing a memory disc, in step (3) said rolling is completed at a temperature of from 400°F to 600°F (205°C to 315°C), and there are performed the further steps of: (4) cold rolling the sheet product to a final gauge, the sheet having at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined;
(5) stamping a memory disc substrate from said cold rolled sheet; (6) machining said substrate to provide a smooth surface thereon; and (7) depositing a layer of memory medium on said substrate to provide the memory disc.

17. A method according to claim 16, wherein the memory medium is comprised of a thin metallic layer.

18. A method according to claim 16, wherein the memory medium is comprised of iron oxide suspended in a plastic carrier.

19. A method according to claim 16, wherein the body is rolled at a temperature in the range of 600°F to 1050°F
(315°C to 565°C).

20. A method according to claim 16, wherein the body is rolled at a temperature in the range of 750°F to 950 F (400 C to 510°C)

21. A method according to claim 13, wherein the body is subjected to a homogenization treatment prior to said hot rolling step, said treatment being at a temperature of 900°F
to 1100°F (482°C to 595°C) for a period of at least 1 hour.

22. A method according to claim 16, wherein the body is hot rolled to a gauge in the range of 0.125 to 0.25 inch (3.17 to 6.35 mm).

23. A method according to claim 16, wherein the product is cold rolled to a gauge in the range of 0.058 to 0.162 inch (1.47 to 4.11 mm).

24. A method according to claim 23, wherein after step (5) said sub-strates are thermally flattened at a temperature in the range of 420°F to 750°F (215°C to 400°C) for a period of time in the range of l to 5 hours.

25. A wrought aluminum alloy product, the alloy consisting essentially of about 2.2 to 10 wt.% Mg, 0.3 wt.% max. Mn, 0 to 0.35 wt.% Cr, 0.005 to 2.5 wt.% Sr, 0.04 to 1 wt.% Fe, 0.3 wt.% max. free Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, 0.3 wt.% max. Ti, the remainder aluminum and incidental impurities, *he product being characterized by the presence of an inter-metallic phase of the type containing Al-Fe in a refined condition.

26. The product in accordance with claim 25, wherein Mg is maintained in the range of about 2.2 to 5.6 wt.%.

27. The product in accordance with claim 25, wherein Mg is maintained in the range of 3.5 to 4.5 wt.%.

28. The product in accordance with claim 25, wherein Mn is 0.2 wt.% max.

29. The product in accordance with claim 25, wherein Fe is less than 0.5 wt.%.

30. The product in accordance with claim 25, wherein free Si is less than 0.1 wt.%.

31. The product in accordance with claim 25, wherein Sr is maintained in the range of 0.01 to 0.25 wt.%.

32. A wrought aluminum alloy sheet product, the alloy consisting essentially of about 2.2 to 5.6 wt.% Mg, 0.3 wt.%
max. Mn, 0.25 wt.% max. Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.3 wt.% max. Ti, 0.2 wt.% max. free Si, 3.5 wt.%
max. Zn, 1 wt.% max. Cu, the remainder aluminum and incidental impurities, the product being characterized by the presence of at least one intermetallic phase of the type containing Al-Fe in a refined condition.

33. A wrought aluminum alloy product, the alloy consisting essentially of 0.5 to 10 wt.% Mg, about 0.2 to 1.6 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to wt.% Sr, 0.04 to 1 wt.% Fe, 1 wt.%
max. Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, 0.3 wt.% max. Ti, the remainder aluminum and incidental impurities, the product being characterized by the presence of at least one inter-metallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.

34. The product in accordance with claim 34 wherein Mg is maintained in the range of 0.5 to 5.6 wt.%.

35. The product in accordance with claim 34 wherein Mg is maintained in the range of 3.5 to 4.5 wt.%.

36. The product in accordance with claim 34 wherein Mn is maintained in the range of 0.2 to 0.8 wt.%.

37. The product in accordance with claim 34 wherein Mn is less than 1 wt.%.

38. The product in accordance with claim 34 wherein Cr is less than 0.25 wt.%.

39. The product in accordance with claim 34 wherein Fe is less than 0.8 wt.%.

40. The product in accordance with claim 34 wherein Fe is less than 0.5 wt.%.

41. The product in accordance with claim 34 wherein Ti is less than 0.3 wt.%.

42. The product in accordance with claim 34 wherein Si is less than 0.5 wt.%.

43. The product in accordance with claim 34 wherein Si is less than 0.35 wt.%.

44. The product in accordance with claim 34 wherein Sr is maintained in the range of 0.005 to 0.5 wt.%.

45. The product in accordance with claim 34 wherein Sr is maintained in the range of 0.01 to 0.25 wt.%.

46. A wrought aluminum alloy product, the alloy consisting essentially of 0.5 to 5.6 wt.% Mg, about 0.2 to 1.8 wt.% Mn, 0.25 wt.% max. Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.3 wt.% max. Ti, 0.5 wt.% max. Si, 3.5 wt.% max. Zn, 1 wt.%
max. Cu, the remainder aluminum and incidental impurities, the product being characterized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.

47. An aluminum alloy flat rolled product, the product consisting essentially of 0.5 to 10 wt.% Mg, about 0.2 to 1.6 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 1 wt.%
Fe, 1 wt.% max. Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, the remainder aluminum and incidental impurities, the product being characterized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.

48. The product in accordance with claim 48 consisting essentially of 2.2 to 5.6 wt.% Mg, 0.1 -to 1 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.25 wt.% max. Si, 0.4 wt.% max.
Fe, 0.1 wt.% max. of both Cu and Zn, the balance aluminum and impurities, the total of impurities not exceeding 0.15 wt.%.

49. The product in accordance with claim 48 wherein said product is sheet.

50. A wrought aluminum alloy sheet product suitable for machining and using as substrates, including memory disc substrates, the product consisting of 0.5 to 10 wt.% Mg, about 0.2 to 1.4 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to 0 wt.% Sr, 0.04 to 1 wt.% Fe, 1 wt.% max. Si, 3.5 wt.% max. Zn, 1 wt.% max.
Cu, the remainder aluminum and incidental impurities, the product characterized by the presence of at least one inter-metallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn Si, wherein one of such phases is refined.

51. The product in accordance with claim 51 wherein Mg is in the range of 0.5 to 5.6 wt.%.

52. The product in accordance with claim 51 wherein Mg is in the range of 3.5 to 4.5 wt.%.

53. The product in accordance with claim 51 wherein Mn is in the range of 0.2 to 0.8 wt.%.

54. The product in accordance with claim 51 wherein Mn is less than 1 wt.%.

55. The product in accordance with claim 51 wherein Cr is in the range of 0.05 to 0.25 wt.%.

56. The product in accordance with claim 51 wherein Fe is less than 0.5 wt.%.

57. The product in accordance with claim 51 wherein Zn is less than 0.25 wt.%.

58. The product in accordance with claim 51 wherein Ti is less than 0.15 wt.%.

59. The product in accordance with claim 51 wherein Sr is in the range of 0.005 to 0.5 wt.%.

60. The product in accordance with claim 51 wherein Si is less than 0.35 wt.%.

61. A wrought aluminum alloy sheet product suitable for machining and using as a memory disc substrate, the product consisting essentially of 3.5 to 4.5 wt.% Mg, 0.1 to 1 wt.% Mn, 0.35 wt.% max. Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.35 wt.% max. Si, 0.25 wt.% max. each of Zn, Cu and Ti, the remainder aluminum and impurities, the product characterized by the presence of at least one intermetallic phase of the type consisting of Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein one of such phases is refined.

62. A memory disc substrate consisting essentially of about 3.5 to 4.5 wt.% Mg, 0.1 to 1 wt.% Mn, 0.35 wt.% max.
Cr, 0.05 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.35 wt.% max.
Si, 0.25 wt.% max. each of Zn, Cu and Ti, the remainder aluminum and impurities, the product characterized by the presence of at least one intermetallic phase of the type consisting of Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein one of such phases is refined.

63. A memory disc comprised of an aluminum alloy substrate, (a) the alloy consisting essentially of 0.5 to 5.6 wt.%
Mg, 1 wt.% max. Mn, 0 to 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 1 wt.% Fe and less than 1.0 wt.% Si, 3.5 wt.% max. Zn, the remainder aluminum and impurities, the substrate character ized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined, and (b) a layer of memory medium provided on said substrate.

64. The substrate in accordance with claim 64 wherein the alloy consists essentially of 3.5 to 4.5 wt.% Mg, 0.1 to 1 wt.%
Mn, 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.5 wt.% max. Fe, 0.35 wt.% max. Si, 1 wt.% max. of both Cu and Zn, 0.25 wt.% max. Ti, the remainder aluminum and impurities.

65. The memory medium in accordance with claim 64 wherein the memory medium is comprised of a thin metallic layer.

66. The memory medium in accordance with claim ~ wherein the memory medium is comprised of iron oxide suspended in a plastic carrier.

67. The method of producing a wrought aluminum alloy product, comprising the steps of:
(a) providing a body of aluminum base alloy consisting essentially of 2.2 to 10 wt.% Mg, 0.1 to 1.4 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to 0 wt.% Sr, 0.04 to 1 wt.% Fe, 1 wt.% max. Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, 0.3 wt.% max. Ti, the remainder aluminum and incidental impurities, (b) heating the body to a temperature of not greater than 1100°F., and (c) working said body to produce a wrought aluminum alloy product being characterized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined

68. The method in accordance with claim 68 wherein My is maintained in the range of 2.2 to 5.6 wt.%.

69. The method in accordance with claim 68 wherein Mg is maintained in the range of 3.5 to 4.5 wt.%.

70. The method in accordance with claim 68 wherein Mn is maintained in the range of 0.2 to 0.8 wt.%.

71. The method in accordance with claim 68 wherein Mn is less than 1 wt.%.

72. The method in accordance with claim 68 wherein Cr is less than 0.25 wt.%.

73. The method in accordance with claim 68 wherein Fe is less than 0.8 wt.%.

74. The method in accordance with claim 68 wherein Fe is less than 0.5 wt.%.

75. The method in accordance with claim 68 wherein Ti is less than 0.3 wt.%.

76. The method in accordance with claim 68 wherein Si is less than 0.5 wt.%.

77. The method in accordance with claim 68 wherein Si is less than 0.35 wt.%.

78. The method in accordance with claim 68 wherein Sr is maintained in the range of 0.005 to 0.5 wt.%.

79. The method in accordance with claim 68 wherein Sr is maintained in the range of 0.01 to 0.25 wt.%.

80. A method of producing a wrought aluminum alloy product, comprising the steps of:

(a) providing a body of aluminum base alloy consisting essentially of 0.5 to 5.6 wt.% Mg, about 0.2 to 1.8 wt.% Mn, 0.25 wt.% max. Cr. 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.3 wt.% max. Ti, 0.5 wt.% max. Si, 3.5 wt.% max. Zn, 1 wt.%
max. Cu, the remainder aluminum and incidental impurities, (b) heating the body to a temperature of not greater than 1100°F., and (c) working said body to produce a wrought aluminum alloy product being characterized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.

81. A method of producing an aluminum alloy flat rolled product, the method comprising the steps of:
(a) providing a body of an aluminum base alloy consisting essentially of 0.5 to 10 wt.% Mg, about 0.2 to 1.6 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 1 wt.% Fe, 1 wt.% max. Si, 3.5 wt.% of max. Zn, 1 wt.% max. Cu, the remainder aluminum and incidental impurities, (b) heating the body -to a temperature of not greater than 1100 F., and (c) hot rolling said body to produce a flat rolled product being characterized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is refined.

82. The method in accordance with claim 82 consisting essentially of 2.2 to 5.6 wt.% Mg, 0.1 to 1 wt.% Mn, 0 to 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0025 wt.% max. Si, 0.4 wt.% max.
Fe, 0.1 wt.% max. of both Cu and Zn, the balance aluminum and impurities, the total of impurities not exceeding 0.15 wt.%.

83. The method in accordance with claim 82 wherein said product is sheet.

84. A method of producing a wrought aluminum alloy sheet product suitable for machining and using as substrates, including memory disc substrates, the method comprising the steps of:
(a) providing a body of an aluminum base alloy consisting of 0.5 to 10 wt.% Mg, about 0.2 to 1.4 wt.% Mn, 0 to 0.35 wt.%
Cr, 0.005 to 0 wt.% Sr, 0.04 to 1 wt.% Fe, 1 wt.% max. Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, the remainder aluminum and incidental impurities, (b) heating the body to a temperature of not greater than 1100°F., and (c) hot rolling said body to produce a wrought aluminum alloy sheet product characterized by the presence of at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein one of such phases is refined.

85. The method in accordance with claim 85 wherein Mg is in the range of 0.5 to 5.6 wt.%.

86. The method in accordance with claim 85 wherein Mg is in the range of 3.5 to 4.5 wt.%.

87. The method in accordance with claim 85 wherein Mn is in the range of 0.2 to 0.8 wt.%.

88. The method in accordance with claim 85 wherein Mn is less than 1 wt.%.

89. The method in accordance with claim 85 wherein Cr is in the range of 0.05 to 0.25 wt.%.

90. The method in accordance with claim 85 wherein Fe is less than 0.5 wt.%.

91. The method in accordance with claim 85 wherein Zn is less than 0.25 wt.%.

92. The method in accordance with claim 85 wherein Ti is less than 0.15 wt.%.

93. The method in accordance with claim 85 wherein Sr is in the range of 0.005 to 0.5 wt.%.

94. The method in accordance with claim 85 wherein Si is less than 0.35 wt.%.

95. A method of producing a wrought aluminum alloy sheet product suitable for machining and using as memory disc substrate, the method comprising the steps of:
(a) providing a body of an aluminum base alloy consisting essentially of 3.5 to 4.5 wt.% Mg, 0.1 to 1 wt.% Mn, 0.35 wt.%
max. Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.35 wt.%
max. Si, 0.25 wt.% max. each of Zn, Cu and Ti, the remainder aluminum and impurities, (b) heating the body to a temperature of not greater than 1100°F., and (c) hot rolling said body to produce a sheet product characterized by the presence of at least one intermetallic phase of the type consisting of Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein one of such phases is refined.

96. A method of producing a memory disc comprised of an aluminum alloy substrate and a layer of memory medium, the method comprising the steps of:
(a) providing a body of an aluminum base alloy consisting essentially of 0.5 to 5.6 wt.% Mg, 1 wt.% max. Mn, 0 to 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 1 wt.% Fe and less than 1.0 wt.% Si, 3.5 wt.% max. Zn, the remainder aluminum and impurities, (b) heating the body to a temperature of not greater than 1100°F., (c) rolling said body to a sheet product, with said rolling being completed at a temperature in the range of 400°F.
to 600°F., (d) cold rolling the sheet product to a final gauge, the sheet characterized by the presence of at least one intermetallic phase of the type containing A1-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, wherein at least one of such phases is reinfed, (e) stamping a memory disc substrate from said cold rolled sheet, (f) machining said substrate to provide a smooth surface thereon, said (g) depositing a layer of memory medium on said substrate to provide the memory disc.

97. The substrate in accordance with claim 97 wherein the alloy consists essentially of 3.5 to 4.5 wt.% Mg, 0.1 to 1 wt.%
Mn, 0.35 wt.% Cr, 0.005 to 0.5 wt.% Sr, 0.5 wt.% max. Fe, 0.35 wt.% max. Si, 1 wt.% max. of both Cu and Zn, 0.25 wt.%
max. Ti, the remainder aluminum and impurities.

98. The memory medium in accordance with claim 97 wherein the memory medium is comprised of a thin metallic layer.

99. The memory medium in accordance with claim 97 wherein the memory medium is comprised of iron oxide suspended in a plastic carrier.

100. The method in accordance with claim 97 wherein the body is rolled at a temperature in the range of 600° F. to 1050° F.

101. The method in accordance with claim 97 wherein the body is rolled at a temperature in the range of 750° F. to 950° F. with said hot rolling being completed at a temperature in the range of 400° F. to 600° F.

102. The method in accordance with claim 97 wherein the body is subjected to a homogenization treatment prior to said hot rolling step, said treatment being at a temperature of 900° F. to 1100° F. for a period of at least 1 hour.

103. The method in accordance with claim 97 wherein the body is hot rolled to a gauge in the range of 0.125 to 0.25 inch.

104. The method in accordance with claim 97 wherein the product is cold rolled to a gauge in the range of 0.058 to 0.162 inch.

105. The method in accordance with claim 97 including thermally flattening said substrates at a temperature in the range of 420° F. to 750° F. for a period of time in the range of 1 to 5 hours.

106. A method of producing a memory disc having a substrate of an aluminum base alloy and a layer of memory medium thereon, the method comprising the steps of:
(a) providing a body of an aluminum base alloy consisting essentially of 3.5 to 4.5 wt.% Mg. 0.1 to 1 wt.% Mn, 0.35 wt.%
max. Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.35 wt.%
max. Si, 0.25 wt.% max. each of Zn, Cu and Ti, the remainder aluminum and impurities, (b) subjecting said body to a homogenization treatment at a temperature in the range of 900° F. to 1100° F. for a period of at least 2 hours, (c) thereafter rolling said body at a temperature in the range of 750° F. to 950° F. with said rolling being completed at a temperature in the range of 400° F. to 600° F., said rolling being to a gauge in the range of 0.125 to 0.25 inch, (d) cold rolling the hot rolled product to a sheet product having a gauge in the range of 0.058 to 0.162 inch, (e) stamping memory disc substrates from said sheet product and subjecting the substrate to a thermal flattening treatment at a temperature in the range of 425° F. to 750°F.
for a period of 1 to 5 hours, (f) machining the substrate to a smooth surface, and (g) after cleaning the surface of the substrate, providing a layer of memory medium thereon.