EP0211831B2 - Process for the cold extrusion of aluminium or aluminium alloys - Google Patents

Abstract

Process for fabricating high resistance and/or high wear resistant bodies, with a high deformation degree, of aluminum or aluminum alloys, wherein the body is molded by cold extrusion.

Description

The invention relates to a method for cold extrusion of aluminum or aluminum alloys, a slug (also called butze, round blank or blank) being used as the blank.

Known extrusion processes differ in their process management in particular by the starting materials chosen in each case, namely aluminum or naturally hard (solid solution strengthened) alloys and alloys hardenable by precipitation.

Pure aluminum and non-hardenable aluminum alloys are extruded only in the “soft annealed” condition. The state “soft annealed” describes the state of lowest strength.

For the same reason, hardenable alloys are extruded only in the “soft annealed” condition.

The formability of the materials is determined with the help of the reproducing test methods (compression, tensile and torsion tests) and essentially determined by the following parameters. The formability decreases with an increasing proportion of alloying elements and with an increasing proportion of hardening phases. The degree of deformation also drops in cases where the materials are pre-consolidated, e.g. B. by cold rolling, drawing etc. Finally, the degree of deformation also decreases depending on the particular structure. For this reason, casting alloys are not used at all for cold extrusion.

Alloys of the type AIMgSi are an exception. From the aluminum paperback, 14th edition, 1984, page 472, it is known to process AIMgSi alloys in the “freshly quenched” or “cold-hardened” state using cold extrusion. The reason for this is that after solution annealing and quenching, these alloys are not significantly stronger than in the "soft annealed" condition. The deformability does not decrease very much either. AIMgSi alloys show no particularly pronounced cold hardening. The strength of this alloy does not increase significantly due to cold hardening, in contrast to other hardenable alloys, e.g. B. of the type AICuMg or AIZnMgCu.

Naturally hard alloys of the type AIMg, with an alloy content of 2 to 3% by weight of magnesium, are only processed if it is absolutely necessary, since the shape change capacity compared to pure aluminum is significantly reduced (K. Mayerhofer «Cold extrusion of steel and non-ferrous metals» , 1983, pages 29, 30).

As an example of alloys that can only be poured in the “soft annealed” condition, according to “Aluminum-Taschenbuch, 14th edition, 1984, pages 471, 472” and K. Mayerhofer “Cold extrusion of aluminum and non-ferrous metals, 1983, pages 30, 31 »AICuMg1 and AlZnMgCu0.5. Responsible for this is the low formability of the hardenable alloys.

Disadvantages of known extruded parts made from hardenable alloys in the “soft annealed” state are their often insufficient strength and the fact that only thick-walled bodies can be produced. In order to achieve higher strengths, the parts extruded in this way are then subjected to a further heat treatment by solution annealing and quenching and, if appropriate, subsequent cold and / or hot aging. Despite this rather complex post-treatment, the strength values of the bodies are usually still lower than those of extruded or forged semi-finished products. Another disadvantage is that the quenching after solution annealing can lead to a distortion of the components, so that an additional straightening process is necessary, which further increases the cost of the process considerably.

Of the non-hardenable materials, especially pure aluminum is used due to the low strength values and the associated high deformation characteristics. Despite the high forming characteristics, the extruded parts made with pure aluminum are often inadequate in terms of their absolute strength values.

Cold extrusion of aluminum and aluminum alloys is known from the Zeitschrift für Metallkunde, Volume 61, 1970, Issue 10, page 683 ff will. A procedural difference lies in the temperature uptake of the extruded material, which can be up to 360 ° C and where critical overheating can occur, which lead to poor mechanical properties. According to DIN 8582 and 8583, there is a clear separation of the production processes «cold extrusion» and «cold extrusion.

The invention is intended to show a way to improve the strength values of extruded parts made of pure aluminum and aluminum alloys, regardless of their manufacture and their assembly, with good elongation properties, without adversely affecting the economy of cold extrusion. The aim is also to use this process to produce moldings which have hitherto not been able to be produced by cold extrusion

The invention offers three alternative methods depending on the aluminum materials used for the production of bodies by cold extrusion, which are described in detail by the features of claims 1 to 3.

In the prior art, the formability is assessed according to one of the usual replica test methods for solid bodies (tensile, compression and torsion tests). It is assumed that, depending on the deformation parameters determined for a certain material, there is also a maximum of deformability for the corresponding material.

This leads to the conclusion that to achieve higher degrees of deformation either materials with originally higher deformation characteristics are selected, or materials with originally lower deformation characteristics are post-treated for the purpose of increasing the deformation capacity, e.g. B. by soft annealing. Pure aluminum may be mentioned as an example of the first-mentioned materials. Pure aluminum, for example, has a tensile strength of approximately 45% in tensile tests, and extruded parts made from pure aluminum have a deformability of over 90% according to the prior art.

Common wrought alloys, e.g. B. AICuMg alloys have a maximum tensile strength in the tensile test in the fully hardened state of 10 to 15%. Without an upstream soft annealing, only extruded parts with a degree of deformation of approximately 30% can be produced therefrom in the direct process according to the prior art.

The invention, on the other hand, offers methods with which much higher degrees of deformation can be achieved, in particular starting from bodies made of aluminum or aluminum alloys with originally lowest deformation characteristics, without, for example, prior to cold extrusion. B. to be soft annealed.

The invention is based on the knowledge that the deformability of all aluminum materials can be significantly increased by a hydrostatic compressive stress state superimposed on the stress. The lower the formability of the starting material, the higher the hydrostatic pressure component used in the method according to the invention.

Exactly in contrast to the teachings given by the prior art, those materials which originally only have very low deformation characteristics, for example, can be used to achieve the highest degrees of deformation with the extrusion process. B. fully hardened AICuMg alloys.

In particular, this also applies to alloys in the as-cast state, in particular also for those with a high silicon content and materials produced by powder metallurgy, which according to the prior art have been completely rejected for extrusion processes because of their brittleness.

By using fully hardened slugs, strength values can be achieved that are considerably higher than those of extruded and then heat-treated parts made from soft-annealed slugs.

On the basis of the teachings given in the prior art, it is already completely unexpected that such brittle aluminum materials can be cold-formed at all, and to the extent that significantly increased strength values can then also be achieved by the process according to the invention, this is completely surprising.

With the method according to the invention, degrees of deformation of well over 90% can be achieved. Insofar as high degrees of deformation are spoken in accordance with the invention, those over 60% are meant.

In addition to the considerable improvement in the mechanical properties of the parts produced by the process according to the invention, there is an additional advantage in the improved economy of the process. This eliminates the need for soft annealing prior to extrusion and the necessary hardening treatment, as well as the straightening of the warped components during hardening.

With the possibility of shaping even high silicon aluminum alloys (cast alloys) by cold extrusion, there are also completely new areas of application, which are due to the special properties of these alloys (very high wear resistance, high heat resistance, low thermal expansion).

According to the method according to the invention, aluminum-lithium alloys can also be used, which are characterized by a particularly high strength and a particularly high modulus of elasticity. Such materials are also characterized by a low specific weight, which results in further areas of application.

Further advantages of the invention result from the processing of powder-metallurgically produced aluminum materials, which are expressed in particular in the high corrosion resistance, very high heat resistance and wear resistance and, depending on the alloy, increased modulus of elasticity. In this respect, additional areas of application are opened up by the invention.

The same advantages arise essentially for the naturally hard alloys.

Insofar as the methods according to the invention relate to blanks obtained directly from the casting and subsequently heat-treated, this is understood to mean soft annealing or heat treatment in the form of homogenization. However, the heat treatment can also consist of solution annealing with subsequent quenching and subsequent cold and / or warm delivery tion exist.

The same also applies to powder metallurgical materials.

For all other aluminum materials, in addition to the aforementioned heat treatments before cold extrusion, alternatively or cumulatively, deformation hardening is also possible. This deformation hardening can be achieved, for example, by extrusion, extrusion, forging and / or rolling.

Such pretreatment methods prior to cold extrusion reduce the deformation characteristics of the aluminum materials, but nevertheless enable higher degrees of deformation when using the methods according to the invention in order to achieve increased strengths.

Further features of the invention are described by the further claims and the other application documents.

The invention is explained in more detail below with the aid of a few exemplary embodiments.

• Aus einem durch Stranggießen hergestellten Rundbarren wird eine Rundstange durch Strangpressen hergestellt, die von der Temperatur beim Strangpressen durch Luft mittels eines Gebläses rasch abgekühlt wird. Anschließend wird die Stange warmausgelagert. Aus der so hergestellten Stange werden die Butzen gesägt, die einen Durchmesser von 26,3 mm und eine Höhe von 14,2 mm aufweisen.

An alloy of the type AIMgSi 0.5 (AA 6060) is used. The Butze is manufactured as follows:

• A round bar is produced by extrusion from a round bar produced by continuous casting and is rapidly cooled by the temperature during the extrusion by air using a blower. The rod is then aged. The slugs, which have a diameter of 26.3 mm and a height of 14.2 mm, are sawn from the rod thus produced.

For the reference examples, the slugs are additionally annealed at 360 ° for four hours, then slowly cooled. The state “hardened in deformation” is applied by extrusion.

The values of the sleeves made from the slugs after extrusion are shown in Table 1. The values given refer to sleeves with a degree of deformation of 92%.

The extruded moldings of the reference example are then solution-annealed (7 minutes at 525 ° C.), then quenched and age-hardened (10 hours at 180 ° C.) in order to achieve an increase in strength.

The maximum strength values that can be achieved in this way according to the prior art are lower than those of the slugs, which are no longer soft-annealed after hot curing, as can also be seen from Table 1.

Despite the extremely high strength of these slugs, they are then cold-extruded with a degree of deformation of 92%. A further substantial increase in strength is brought about. The strengths given in Table 1 are more than 100 N / mm ² higher than the maximum strength values of the bodies manufactured in a conventional manner with a drastic reduction in costs.

Such high strength values can only be achieved using the state-of-the-art method with much higher alloyed materials at much higher production costs (upstream heat treatment and subsequent hardening treatment). Then certain forms can no longer be produced in the prior art.

Corresponding improvements in properties, in particular high strengths, can also be achieved from a blank obtained directly from a casting and optionally subsequently heat-treated, which is cold-extruded at similarly high degrees of deformation.

Finally, the advantages mentioned arise for bodies made of aluminum or aluminum alloys, in which the body is formed from a blank formed from powder metallurgically produced material by subsequent cold extrusion.

Claims (12)

1. A process for manufacturing products showing high strength and/or high resistance to abrasion, with a high degree of deformability, from aluminium or non-hardenable aluminium alloys, in which the product starting :

a) from a blank derived directly from a casting and, if necessary, heat-treated; or

b) from a blank, other than according to a), of a high silicon aluminium alloy, subjected to further treatment if necessary; or

c) from a blank, other than according to a), and if necessary subjected to further treatment excluding a blank post-treated by soft annealing and excluding an alloy of type b),

is formed from slugs by cold impact extrusion. by applying a hydrostatic compression superimposed on the applied stress of the respective material

2. A process for manufacturing products showing high strength and/or high resistance to abrasion, with high degrees of deformability, of hardenable aluminium alloys, in which the product starting :

a) from a blank derived from a casting and, if necessary, then heat-treated : or

b) from a blank, other than according to a) of an alloy of the type AlLi, AISi or AIZn and, if necessary, post treated ; or

c) a blank, other than according to a) and if necessary post treated, of an alloy not of the type b), but not by soft-annealing,

is formed from slugs by cold impact extrusion. by applying a hydrostatic compression superimposed on the applied stress of the respective material

3. A process for manufacturing products showing high strength and/or high resistance to abrasion, with high degrees of deformability, of aluminium or aluminium alloys, in which a blank of a material made by powder metallurgy is cold impact extruded. by applying a hydrostatic compression superimposed on the applied stress of the respective material

4. A process as claimed in Claims 1 to 3 for manufacturing products of high strength and/or high resistance to abrasion with a degree of deformability greater than 90 %.

5. A process as claimed in one of the Claims 1 to 4 for manufacturing thin-walled hollow bodies of high strength and/or high resistance to abrasion.

6. A process as claimed in one of the above claims, characterised in that the blank is solution annealed and quenched before the cold impact extrusion.

7. A process as claimed in one of the above claims, characterised in that the blank is made of an alloy of the type AICuMg, AIZnMg or AIZnMgCu and is cold impact extruded after solution annealing and quenching.

8. A process as claimed in one of the above claims, characterised in that after quenching the blank is stored in the cold before the cold impact extrusion.

9. A process as claimed in one of the above claims, characterised in that after quenching the blank is stored warm before the cold impact extrusion.

10. A process as claimed in one of the above claims, characterised in that after quenching the blank is stored cold and warm before the cold impact extrusion.

11. A process as claimed in one of the above claims, characterised in that the extruded product is cold or hot stored, or both.

12. The use of a blank in the work-hardened state for cold impact extrusion of aluminium and aluminium alloys.