NO814390L - PRODUCTS OF ALUMINUM ALLOY, AND PROCEDURES FOR PREPARING SUCH - Google Patents

Description

This invention relates to aluminum alloys and more

specifically, it concerns aluminum alloy products such as sheet

, products suitable for forming into substrates for storage unit wafers, for example.

In the manufacture of aluminum alloy substrates for bearing unit washers, the substrates are normally machined, usually on

both sides before applying a coating that functions as a storage device medium. It will be understood that for use as a storage unit disk substrate the surface must be extremely smooth so as not to adversely affect the coatings, and the storage of information therein. Normally, the information is stored in such a coating by electrical impulses or magnetized places where the presence or absence of such represent data, and it will consequently be seen that irregularities in the surface can have a damaging effect.

depends on the coating's ability to retain data accurately. The above machining steps have not been without problems; In some of the alloys used, for example, insoluble constituents have

parts entailed machining problems, which has resulted in a high percentage of scrap for the substrates. Thus, with certain aluminium-based alloys, it has been found that insoluble constituents, such as Al-Fe-Mn-Si constituents or phases, are formed with relatively large particle sizes, sometimes greater than 1 µm, and make the machining operation difficult, especially that which is required in the manufacture of substrates for bearing unit wafers. These components can be harmful during machining by adhering to the cutting tool and being removed with it, or by being pulled over the machined surface.

flat and leaves, scratches. In both cases, achieving the desired smoothness or evenness is made difficult. Furthermore, it is believed that when a machined surface is etched, large constituents will make it difficult to achieve uniform etching.

Although the surface has been found to be machineable satisfactorily, there may be cases where the coating or undercoat for this is damaged to an extent that affects the storage of data in the coating. The harmful effect is believed to

be the result of relatively large intermetallic phases or constituents, as mentioned above. It will thus be seen that such phases or components must be provided in a refined or modified state which eliminates the aforementioned conditions.

Furthermore, it has been found that such or similar problems

can occur when aluminum-based alloys are anodized for use as bright parts on automobiles. Thus, these intermetallic components can resist etching and anodizing treatments, resulting in holes or unanodized spots in the protective anodic coating, which of course can reduce the lifetime of the shiny parts. It will thus again be seen that it is very important to provide the intermetallic phases or insoluble constituents in a refined or modified state which eliminates these problems. In the production of thin metal threads, such as thread for the production of cloth, the large particles are harmful during the production operation. Thus, the large particles can cause major problems with breakage when pulling metal wire. It will be understood that the aforementioned problems are stated more for illustration purposes and that there are many other applications where components with relatively large particle sizes are harmful when using the particular aluminum alloy.

The present invention provides an aluminum-based alloy knurled product with a refined or modified intermetallic phase or insoluble component, which can be machined to a smoothness suitable for use as bearing unit disk substrates, for example. In addition, the products according to the invention, for example extrusion products or products of the plate or sheet type, have, among other things, improved anodizing properties.

According to the invention, a product of aluminum alloy is provided, where the alloy comprises 0.5-10 wt% Mg, 0-0.35 wt% Cr, at least 0.005 wt% Sr, less than 1 wt% Fe, max. 3.5 wt% Zn, max. 1 wt% Cu, max. 0.3 wt% Ti, the rest aluminum and random impurities, and where the alloy also comprises either: (a) 0.1-1.6 wt% Mn and max. 1% by weight 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, where at least one of these phases is refined; or (b) max.' 0.3 wt% Mn and max. 0.3% by weight of free Si, and the product has an intermetallic phase of the type containing Al-Fe in a refined state.

Furthermore, according to the invention, a method is provided

for the manufacture of a product of aluminum alloy, comprehensive

the following steps:

(1) a body of aluminum-based alloy is provided;

ing where the alloy comprises 0.5-10 wt% Mg, 0-0.35 wt% Cr,

at least 0.005 wt% Sr, less than 1 wt% Fe, max. 3.5% by weight

Zn, max. 1 wt% Cu, max. 0.3 wt% Ti, the rest aluminum and random impurities, and where the alloy further comprises 0.1-1.6 wt% Mn and max. 1. wt% 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, where at least one of these phases is refined;

(2) the body is heated to a temperature of no more than 595°C, and

(3) the body is crushed to produce a product of aluminum alloy with at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, where at least one of these phases is refined. Reference is made to the drawing: • Fig. 1 is an image taken through a microscope (500X) of a sheet product of an aluminium-based alloy, which shows particles of Al-Fe-Mn-Si which reduce the machinability of the sheet product. Fig. 2 is an image taken through a microscope (500X) of a sheet product of an aluminum-based alloy as shown in fig. 1, with refined or modified constituent particles, which sheet product has improved machinability and is particularly well suited for bearing unit disk substrates. Fig. 3 is a picture taken through a microscope (500X) of the aluminum-based alloy in fig. 2, with the exception that the sheet product has a smaller thickness. Fig. 4 is a phase diagram showing the relationship between intermetallic phases and compositions of an aluminum-based alloy

ing containing 0.2 wt% Fe after a period of temperature equalization at 510°C.

Due to advances in the technology in which the alloy is used, it has become necessary for certain aluminium-based alloys to refine the size of the constituent particles in order for the new technology to be used. For example, when it comes to disk storage technology, attempts have been made to increase the amount of data that can be stored on a single disk,

and to change the medium traditionally used for storage purposes, with the aim of circumventing the problems. Effort has become

done on changing from iron oxide-type storage unit medium with the aim of increasing the medium's resistance to smearing. For example, thin surface layers of cobalt have been investigated with fairly good results to determine their suitability for such purposes. Applications of a layer of storage device medium, such as iron oxide, on an aluminum substrate involve a different technology and thicker layer than that used for applying, for example, the thin layer of cobalt. For example, the iron oxide medium is applied to the substrate as a slurry or dispersed in a plastic binder, while plating or other forms of deposition, for example vapor phase or vacuum deposition, can be used to apply thin metallic 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 on which they are applied. For example, large component particles can have a detrimental effect on the plating or the deposition of the thin metallic layers. As mentioned, the large particles can also have a detrimental effect on the smoothness of the finish that can be achieved on the aluminum substrate by machining, which in turn is reflected in the roughness of the thin metal film that is deposited on the substrate. It must be remembered that particles, for example dust particles of approx. 0.3 yum, can be detrimental to the efficiency of the head used for storing or reading data from the medium layer, especially when the medium layer consists of a thin metallic layer. Accordingly, it will be seen why it is so important to minimize surface roughness of the aluminum substrate on which the layer is deposited.

In a similar way, such problems with large constituent particles can become apparent when anodizing aluminum alloys that are used for, for example, glossy automobile parts. Thus, the constituent particle on or near the surface may react or oxidize quite differently from surrounding material, resulting in defects in the anodic coating. Such defects can adversely affect the corrosion resistance of the anodic coating on the shiny parts. In the two examples given, it will thus be seen that such particles are best avoided.

Fig. 1 is an image taken through a microscope of an aluminum-based alloy which has been used for storage unit disk substrates, where the storage unit layer specifically consisted of iron oxide applied by means of the slurry. In the microscope images, the distance between the vertical lines corresponds to or represents 1 µm in the microstructure of the alloy. The alloy in-

holds 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 rest aluminum and impurities. However, it will be seen from the microscope image that relatively large Al-Fe-Mn-Si constituent particles are found throughout the metal. Some of the particles are of the order of approx. 1^um, and as mentioned earlier, such particles can be harmful during machining and consequently to the bearing unit medium.

Fig. 2 shows a microscope image of a sheet product of kna-aluminium, which is particularly well suited for bearing unit disc substrates, according to the invention. The alloy on

fig. 2 contains 0>22 wt% Fe, 0.18 wt% Si, 0.40 wt% 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 rest aluminum and random impurities. Inspection of the microscope image reveals the absence of constituent particles of a size comparable to that shown in FIG. 1. It is the absence of relatively large particles which are harmful during machining, which results in the sheet product shown in fig. 2, with superior characteristics. Furthermore, it is the absence of large particles that makes the product suitable for substrates such as those used in storage unit wafers, especially when the storage unit medium is a thin layer or film of metallic material deposited on sub-

strated by the plating. With compositions or alloys 1 according to the present invention, the absence of such large particles in the extruded product makes further. For example, glossy car parts, as well as the sheet product particularly well suited for anodizing. The sheet or plate products of fig. 1

and 2 was rolled to 4.11 mm thickness. Even when the product in fig. 2 is rolled to a thickness of 2.08 mm, however, it still retains its refined or modified structure, which will be seen by examining the microscope image in fig. 3.

When a knuckle product according to an embodiment of the invention is desired, the alloy can mainly consist of 0.5-9 wt% Mg, 0.1-1.4 wt% Mn, 0-0.35 wt% Cr, 0.005-2.5 wt% % Sr, less than 1 wt% Fe, max. 1 wt% Si, max. 3.5 wt% Zn, max. 1% by weight Cu, the rest aluminum and random impurities.

Magnesium is added or provided in this class

of magnesium alloys mainly for strength or firmness purposes and is preferably kept in the range 0.5-5.6% by weight. Magnesium is also beneficial because it promotes the formation of fine aluminum grain sizes in the alloy, which of course increases formability. However, it should be noted that higher levels of magnesium can lead to fabrication problems. Thus, it becomes important to balance the desired firmness properties against problems during production. With regard to machining, machinability is improved with a higher content of magnesium in solid solution. Aluminum alloys at their worst machinability have a low alloy content and are usually in the annealed or softest state. Conversely, increasing alloy concentration, cold-working, dissolution and aging treatments will result in an improved surface finish by hardening the alloy, by reducing metal-to-tool adhesion and by reducing the number of burrs. These additions or treatments thus improve machinability. When machining aluminium-alloy substrates for bearing unit discs, it is therefore desirable to keep the magnesium content in the range approx. 3.5-5.5% by weight. When the application is aluminum wire for wire cloth, where the wire is drawn to a very fine diameter, the magnesium content should be in the range of 4.5-5.6% by weight, and when the application is easily removable aluminum lids for mineral water containers and the like, the magnesium content should be in the range of 4-5% by weight. While higher magnesium content has been indicated for exemplification purposes, lower magnesium content is also important in certain applications, such as alloys used for rigid containers, blank automobile parts, building products, trucks) and the like and railway carriages and shall be considered to fall within the scope of the invention frame.

As far as manganese is concerned, the content thereof can be up to 1.4, 1.6 or 1.8% by weight, but it is preferably kept below 1% by weight, and as a rule it is kept within the range between 0.1 or 0.2 to 0.8% by weight. Manganese is a dispersoid-forming element. This means that manganese is an element that is precipitated in small-particle form during heat treatments and has, as one of its beneficial effects,

a reinforcing effect. Manganese can form dispersoids consisting of _ Al-Mn, Al-Fe-Mn and Al-Fe-Mn-Si. In the case of some magnesium-containing alloys where you want to increase the corrosion resistance,

the magnesium content can thus be reduced and can be added without any loss in strength, but with increased resistance to corrosion.

In a similar way, chromium can have the advantage of increasing corrosion resistance, especially in the case of stress corrosion cracking. Furthermore, chromium can combine with manganese and provide more dispersoid, which as mentioned earlier can increase the strength, chromium can also have an effect by affecting the preferred orientation with

view to wrinkle formation, for example in the case of cups. It will be understood that wrinkling is undesirable because it results in loss of metal. The chromium content should preferably not exceed 0.25% by weight for most applications for which the alloy according to the invention can be used.

The solid solubility of iron in aluminum is very low and

is of the order of magnitude approx. 0.04-0.05% by weight in the ingot. A large part of the iron present is thus present in aluminum alloys, usually as an insoluble component in combination with other elements such as, for example, manganese and silicon. Typical for such combinations are Al-Fe-Si and Al-Fe-Mn-Si. It will be understood that the elements in these combinations can be present in varying stoichiometric amounts. For example, Al-Fe-Si can exist as Al^F^Si and AlgFe2Si2f, which are considered to be the most commonly occurring phases. Furthermore, Al-Fe-Mn can exist as Al,(Fe Mn,_ ), where x is a number greater than 0 and less than 1.

With regard to Al-Fe-Mn-Si, this combination can exist

as Al.. „ (Fe Mn, )-,Si, where x is a number greater than 0 and less than 1. It should be noted that these constituents are considered to be the most common intermetallic phases found in these alloy types. However, it must be clear that other elements, such as Cu, Ti and Cr and the like, can appear in or enter them

said intermetallic phases in smaller quantities in that they usually replace a part of Fe or Mn. Such intermetallic phases shall also be considered to fall within the scope of the invention.

These insoluble components tend to agglomerate

and form relatively large particles such as Al-Fe-Mn-Si constituents, as can be seen from fig. 1, some of which have a length of approx.

<1>^um.. As already mentioned, it is these•larger, insoluble constituents which are so undesirable for reasons of machinability and formability. However, it must be remembered that iron has a beneficial effect as a grain-refining agent, which of course contributes to machinability and formability. Furthermore, it will be noted that iron is normally present in most aluminum alloys, mainly for economic reasons. Processing of aluminum to remove iron is thus normally not economically feasible for most applications. Thus, many attempts have been made to work with iron in the alloy

by taking advantage of iron's good effects and neutralizing its disadvantages, often with only limited success. For the purposes of the invention, the iron content is therefore preferably kept at 0.8% by weight or lower and typically below 0.5% by weight, quantities of 0.4% by weight or less being quite appropriate.

Titanium also contributes to grain refinement and should be kept at no more than 0.2% by weight.

For the purposes of the invention, it is believed that the amount of silicon should also be minimized, as at relatively low levels it can combine with magnesium, which results in significant strength reductions. - The silicon content should therefore preferably be kept below 0.5% by weight, typically below 0, 35% by weight.

Strontium, which should be considered a character-forming element, is also an important component in the alloys according to the invention. The strontium content should not be less than 0.005% by weight and is preferably kept in the range 0.005-0.5% by weight; amounts beyond this are currently not believed to adversely affect the product's properties, except that increased amounts are not normally desirable for economic reasons. For most applications for which the alloys of the present invention can be used, the strontium content is preferably in the range of 0.01-0.25% by weight, with typical amounts in the range of 0.01-0.1% by weight.

Addition of strontium to the alloy has the effect that the intermetallic phases or insoluble constituents of

the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si is refined or modified, as pointed out above. Because of the complex nature of these phases, it is not entirely clear how

this effect can be achieved Due to the many alloying elements and their mutual influence, it is thus very surprising that a significant refinement of insoluble components is achieved.

The good effects of adding strontium will, however, be clearly seen when comparing the microscope images of the kna products shown in fig. 1, 2 or 3. The composition for these sheet products was given above. The ingot from which these products were produced by rolling was cast by the water-casting method. One. The ingot with this composition was first rough-processed, homogenized for 2 hours at 565°C and then, starting at a temperature of approx. 510°C, hot rolled to a thickness of approx. 4.62 mm. From fig. 1, it will be seen that some of the Al-Fe-Mn-Si particles or the insoluble components are relatively large and have lengths of approx. 1^um. Fig. 2 is a microscope image (500X) of an alloy with the same composition as that shown in fig. 1 with the exception that 0.02% by weight of strontium was added. The alloy was rolled in the same way as the alloy in fig. 1. It will be seen that the Al-Fe-Mn-Si particles are greatly reduced in size compared to fig. 1. Furthermore, the insoluble components including the dipsersoid phase have a substantially uniform distribution throughout the matrix. It will thus be observed that strontium had the effect of refining the intermetallic phases.

Although the plate product in fig. 2 cold rolled on to

2.08 mm thickness after annealing, the phases of small insoluble constituents or intermetallic phases are retained. For example, fig. 3 a microscope image (500X) of an aluminum-based alloy with the same composition and produced in the same way as that in fig. 2, except that it was rolled to 2.08 mm thickness. As will be seen from fig. 3, the fine-particle component was retained. From these microscope images it will be seen that strontium has the effect of refining these intermetallic phases in the alloy and of maintaining the refined state after the alloy has been processed into a kna-plate product, for example.

An X-ray diffraction analysis using a Guinier-type camera shows the relative amounts of the intermetallic phases present; The results of the analysis are set out in the following table.

Besides providing the kna product with compositions comprising regulated amounts of alloying elements as described above, it is preferred that alloys are prepared and processed into products according to special process steps aimed at achieving the most desirable properties. The alloys described herein can thus be provided as a block (ingot) or a fine item (billet), or they can be band-cast for the production of a suitable kna product using known techniques in the area. The cast material, for example the block, can be preliminarily kneaded or shaped into a suitable starting material for subsequent processing operations. In certain cases, this starting material of the alloy may, before the main machining operation, be subjected to a homogenization treatment, preferably at metal temperatures in the range of 425-595°C for a period of at least 1 hour, with the aim of dissolving magnesium or other soluble elements<p>g to homogenize it internal structure in the metal and in some cases to precipitate dispersoids. A preferred time space is 2 hours or more at the homogenization temperature. For blocks, the heating and homogenization treatment does not normally need to last longer than 24 hours; a longer period of time is normally not harmful. A temperature equalization time of 1-12 hours at the homogenization temperature has been found to be appropriate.

After the homogenization treatment, the metal can be rolled or extruded or otherwise subjected to kneading for the production of starting materials/semi-finished products such as plates, sheets, extrusion products or wire or other semi-finished products suitable for being shaped into the final product. For the production of a plate-type product, a body of the alloy is preferably hot-rolled to a thickness in the range of 3.17^-6.35 mm. For hot-rolling purposes, the temperature should be in the range of 315-approx. 565°C, and preferably the temperature is initially in the range of 455-510°C. At completion, the temperature is preferably 205-315°C.

When the intended application of a selected alloy is a typical kna plate product of the kind suitable for, for example, bearing unit disk substrates, a final reduction, as in cold rolling, can be used. Such a reduction can be made to plate thicknesses in the range 1.47-4.11 mm. The wafer substrates can then be punched out of the plate material and thermally flattened at a temperature in the range of 175-400°C for a period of 1-5 hours; a typical flat straightening treatment takes 3-4 hours at 220-345°C under pressure. The substrates are usually rough-cut and then precision machined to remove approx. 0.15 mm with the aim of achieving the correct degree of flatness and smoothness prior to application of the bearing unit medium. After machining, it may be desirable to thermally straighten the substrates again. After machining, the substrates should also normally be degreased and given a light etching treatment. Prior to the application of the storage device medium, the substrates may be given a chemical conversion treatment, especially if

a storage unit medium of the iron oxide type is used.

In certain applications, depending on the intended properties, it may be desirable to subject the product to a thermal treatment after the kneading treatment. The thermal treatment can be an intermediate annealing treatment or after the product has been kna-treated to final dimensions. In a partial annealing treatment, the temperature is usually in the range 95-260°C, with a typical range between 150 and 260°C, for periods of time in the range from approx. 1 to 4 hours.. For full annealing the temperature is usually in the range of 315-415°C for most applications and in typical annealing practice is normally in the range of 345-400°C. With full annealing treatment, the time at annealing temperature is in the range of 1-2 hours for charge material.

When the intended use of the kna product according to the invention is, for example, wire for wire cloth, the alloy preferably mainly consists of 4-5.6 wt% Mg, 0.05-0.2 wt% Mn, 0.05-0 .2 wt% Cr, not less than 0.005 wt% Sr, max. 0.4 wt% Si, max. 0.4 wt% Fe, max. 0.1 wt% Cr, max. 0.25% by weight Zn, the rest aluminum and random impurities. Additional impurities should not amount to more than 0.15% by weight in total. When the intended use of the kna plate product is, for example, bodies for trucks and the like, the alloy can consist mainly of 2.2-2.8 wt% Mg, max. 0.1 wt% Mn, 0.15-0.35 wt% Cr, 0.005-0.25 wt% Sr, max. 0.25 wt% Si, max. 0.4 wt% Fe, max. 0.1% by weight of both Cu and Zn, the rest aluminum and impurities, the total impurities not exceeding 0.15% by weight. In cases where higher strengths may be required, such as for tankers and the like, the manganese content, while maintaining weldability and formability, can be increased in the latter alloy to the range of 0.5-1% by weight. When high strength is required, such as for armor plates or gas containers for liquefied natural gas, the magnesium content can be increased to the range of 4-4.9% by weight.

In another aspect of the invention, it may be desirable to regulate the amount of manganese in the alloy according to the invention to no more than 0.3% by weight and preferably no more than 0.2% by weight. This may be desirable when the sheet product is to be used for, for example, easily-removable capsules or lids. The phase diagram in Figure 4 shows the relationship between compositions and phases when the manganese content is in the range 0-0.3% by weight and the content of free silicon is less than 0.3% by weight in aluminium-based alloys containing 0.2% by weight Fe. On the phase diagram, the region denoted by 1 means that the only intermetallic phase is the Al-Fe type phase, such as FeAl^, or the metastable phase FeAlg. In the area denoted by 2, the intermetallic phases Al-Fe and Al-Fe-Mn are obtained [e.g. (FeMn) Algae)]. The following table indicates the intermetallic compounds found in different regions of the phase diagram:

The addition of strontium to the alloy can have the effect of

refine or modify the Al-Fe phase when the alloy with respect to Mn and free Si is kept within these limits. By free Si is meant that the silicon in Mg-containing aluminum alloys does not combine with or bind Mg. However, silicon can be combined with Mn, Fe or both. With regard to the phase diagram, it will be seen that no Mg is present, as the effect of this would be to reduce the content of free silicon.

The phase diagram was developed as follows: A series of alloys was prepared containing refined aluminum with 0.2% Fe. Mn was added to a content of 0.1, 0.2, 0.3 and 0.5% by weight, and Si was added to a content of 0-1% by weight. Prealloys with 0% Si and 1% Si were produced as 2500 g chargers cast as notched drills. Intermediate Si contents were achieved by combinations of the pre-alloy. 200 g of charger was melted and cast as blocks with dimensions 6.35 x 50.8 x 101 mm in molds preheated to 315°C. The blocks were split into 25.4 mm square pieces for preheating trials. They were programmed 28°C/hour to 455°C, 510°C, 565°C or 605°C, held for 16 hours at the temperature and quenched to maintain phases occurring at the preheating temperature. The phases were identified in samples by means of X-ray diffraction, and the results were used to produce the phase diagram.

The phase diagram shows that the primary intermetallic phase

is of the Al-Fe type in the area designated by 1, and that this phase is also present in the areas designated by 2, 3 and 6.

Claims (15)

1. Kna product of aluminum alloy, characterized in that the alloy comprises 0.5-10 wt% Mg, 0-0.35 wt% Cr, at least 0.005 wt% Sr, less than 1 wt% Fe, max. 3.5 wt% Zn, max. 1 wt% Cu, max. 0.3% by weight Ti, the rest aluminum and random impurities, and in that the alloy further comprises either: (a) 0.1-1.6 wt% Mn and max. 1 wt% 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, where at least one of these phases is refined, or (b) max. 0.3 wt% Mn and max. 0.3% by weight of free Si, and the product has an intermetallic phase of the type containing Al-Fe in a refined state. 2. Product according to claim 1, characterized in that Mg is kept in the range 0.5-5.6% by weight, preferably 3.5-4.5% by weight. 3. Product according to claim 1, characterized in that Mn in part (a) is less than 1% by weight, preferably 0.2-0.8% by weight. 4. Product. according to claim 1, characterized in that Sr is kept in the range 0.01-0.25% by weight. 5. Product according to claim 1, characterized in that the alloy defined by part (a) comprising 0.5-5.6 wt% Mg, max. 0.25 wt% Cr, 0.005-0.5 wt% Sr, less than 0.5 wt% Fe and max. 0.5 wt% Si. 6. Product according to one of the preceding claims, characterized in that the alloy under part (a) is in the form of a flat-rolled sheet product suitable for machining and use as a substrate, in particular a bearing unit disk substrate which preferably has a layer of bearing unit medium applied on the substrate. 7. Product according to one of claims 1, 2, 3 or 6, characterized in that the Mn content in part (b) is max. 0.2% by weight, and that the alloy defined in part'(b) preferably comprises max. 0.25 wt% Cr, 0.005-0.5 wt% Sr, less than 0.5 wt% Fe and max. 0.2 wt% free Si. 8. Method for producing a kna product of aluminum alloy, characterized by the following steps: (1) there is provided an aluminum-based alloy body as set forth in any of claims 1-7, wherein the composition of the alloy is in accordance with part (a), (2) the body is heated to a temperature of no more than 595°C, and (3) the body is processed to produce a kna product of aluminum alloy with at least one intermetallic phase of the type containing Al-Fe-Si, Al'-Fe-Mn and Al-Fe-Mn-Si, where since at least one of these phases is refined. 9. Method according to claim 8, characterized in that the body in step (3) is hot-rolled to produce a flat-rolled product or plate product, and preferably a plate product is produced which is suitable for machining and use as a substrate, such as a storage device wafer substrate. 10. Method according to claim 9, characterized in that, in order to produce a bearing unit disc, the rolling is completed in step (3) at a temperature of 205-315°C, and that the following additional steps are carried out: (4) the plate product is cold-rolled to a final thickness, the plate material having at least one intermetallic phase of the type containing Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si, where since at least one of these phases is refined, (5) punching a bearing unit disk substrate from said cold-rolled flat material, (6) the substrate is machined to give it a smooth surface, and (7) a layer of storage unit medium is deposited on the substrate for the production of a storage unit disc. 11. Method according to claim 10, characterized in that the storage unit medium consists of a thin metallic layer, or it consists of iron oxide suspended in a plastic carrier. 12. Method according to claim 10 or 11, characterized in that the body is rolled at a temperature in the range 315-565°C, ■ preferably 400-510°C. 13. Method according to one of claims 10-12, characterized in that the body is subjected to a homogenization treatment before said hot-rolling step, the treatment being carried out at a temperature of 482-595 <0> Oi for at least 1 hour. 14. Method according to one of the claims 10-13, characterized in that the body is hot-rolled to a thickness in the range 3, 17-6, 3.5 mm, and that it is preferably cold-rolled to a thickness in the range 1,47-4, 11 mm. 15. Method according to claim 14, characterized in that after step (5) the substrates are thermally flattened at a temperature in the range 215-400°C for a period of time in the range 1-5 hours.