EP0035055B1 - Use of a mixture of capital scrap, originating from aluminium cast alloys and aluminium wrought alloys in the manufacture of semi-finished rolled products and semi-finished rolled products produced from scrap - Google Patents

Abstract

1. The use of mixed aluminum scrap for aluminum casting alloys selected from the group consisting of AlSi, AlSiCu and/or AlSiMg and for wrought aluminum alloys selected from the group consisting of AlMn, AlMg, AlMgMn, AlZnMg, AlZnMgCu, AlMgSi and/or AlCuMg, said casting alloys having a weight ratio to said wrought alloys of from 1:1 to 2:1, and without addition of primary aluminum for the making of rolled aluminum intermediate products, comprising from 1 to 6% Si, 1 to 3% Mg, 0.5 to 3% Zn, 0.5 to 3% Fe, 0.3 to 2% Cu as well as up to 1% Mn, up to 0.2% Ti, up to 0.5% Cr and up to 0.5% Pb, Bi, Sn, the remainder aluminum.

Description

The invention relates to the use of mixed old scrap for the production of aluminum rolled products by continuous or strip casting of rolled ingots or plates and by subsequent hot and cold rolling.

Aluminum scrap comes from used consumer goods or machines that either consist entirely of aluminum alloys or contain significant components from aluminum and its alloys. These consumer goods or machines made of aluminum or their aluminum parts can be produced from aluminum wrought materials by cold or hot molding or from aluminum casting materials by molding. Because of the requirements of the various manufacturing processes, the compositions of wrought aluminum alloys and aluminum casting materials differ fundamentally. Aluminum wrought materials have high alloy contents of Mg, Mn and Zn, while cast aluminum materials are characterized by high Si and often higher Fe and Cu contents.

When such used aluminum materials are reused, the scrap parts are therefore kept separate after their division into kneading and casting materials in order to avoid malfunctions in the forming or casting processes in the new production processes after melting. Sorting the old scrap by type of material must be done before melting.

However, since aluminum castings in particular are frequently cast or adhered foreign metals such. B. contain iron, zinc and copper, there is often accumulation of disruptive metals for the further production process, even with scrap melt batches from sorted old scrap, which can only be compensated for by blending with pure primary aluminum. Another source of interference are castings made of zinc or magnesium alloys, which are difficult to separate during sorting processes and lead to inadmissibly high Mg or Zn contents in the scrap melt batches for further use as an aluminum remelting casting alloy. In addition to blending with primary aluminum, the environmentally unfriendly chlorination treatment or an energy-intensive vacuum treatment at elevated temperature serves to lower such excessive Mg or Zn contents.

Another source of increasing Mg and Zn contents in scrap melt batches is the frequent assembly of consumer goods and machines made from wrought aluminum and cast aluminum materials.

For example, engine blocks and cylinder heads as well as gearbox housings are often made of an AISiCu cast aluminum alloy, attached auxiliary unit housings are made of die-cast zinc, but chassis parts and planking in the body area consist of wrought aluminum alloys of the types AIMgSi or AIMg5. The same applies to large household appliances in which cast aluminum parts and cladding, facings and decorations made from wrought aluminum alloys are processed together.

In order to achieve economical scrap size reduction and to remove built-in iron parts from aluminum castings, aluminum scrap can be subjected to a shredding process with subsequent magnetic separation for iron part removal. The product of such shredding processes is small-scale shredder scrap, in which the original aluminum kneading and aluminum casting materials are mixed and no longer distinguishable. After melting such scrap, the above-mentioned methods of blending with valuable primary aluminum or chlorination must be used in order to produce reusable casting alloys.

The object of the present invention was to find a way of using mixed old scrap from used casting and kneading materials while avoiding the disadvantages mentioned above.

As can be seen from DIN 1725 Part 1, aluminum wrought semi-finished products and thus also semi-finished rolled products are made from special alloys with a very narrow and defined composition, their properties depending on the type and amount of the alloy components contained therein. Surprisingly, it has now been shown that sheets made from a completely unconventional alloy melted from uncut scrap metal have excellent properties with regard to strength and, above all, formability during roll forming or deep drawing.

This enables a sensible and economical use of such old scrap mixed from cast and kneaded materials for the production of sheets and strips.

The sheets, plates or strips are produced by melting together old scrap from cast aluminum alloys and wrought aluminum alloys without adding primary aluminum to an alloy with contents of 1 to 6% Si, 1 to 3% Mg, 0.5 to 3% Zn, 0 , 5 to 3% Fe, 0.3 to 2% Cu and up to 1% Mn, up to 0.2% ì ↑ up to 0.5% Cr and up to 0.5% Pb, Bi, Sn, whereby the cast alloy scraps of type AISi, AISiCu, AISiMg with wrought alloy scraps of type AIMn, AIMg, AIMgMn, AtZnMg, AIZnMgCu, AIMgSi and / or AICuMg are melted together in a mass ratio of 1: 1 to 2: 1.

According to the invention, the alloy melt is kept at at least 730 ° C. for 1 to 2 hours and then poured off at an inlet temperature of at least 710 ° C. The rolled bars are annealed at 490 ° C for 12 to 24 hours and then hot and cold rolled to the desired final thickness in the usual manner.

A preferred application of the process according to the invention is characterized in that the old scrap is processed in a shredder process with downstream magnetic separation.

Through the use according to the invention, such melts from mixed old scrap can advantageously be used without the costly and environmentally unfriendly measures of blending with primary aluminum or chlorination for the production of plates, sheets or strips with good usage properties.

By keeping such melts from mixed old scrap at a temperature of at least 730 ° C for a period of 1-2 hours and by continuous casting into rolled bars or plates with inlet temperatures into the casting device of at least 710 ° C, the continuous casting structure is given a sheet for subsequent rolling particularly suitable structure. The formability necessary for further production steps for the production of sheet metal parts by cold forming z. B. in roll forming or deep drawing is also favorably affected by this treatment of the old scrap alloy melts.

Sheets made from rolled bars produced in this way show an increased sensitivity to corrosion due to the composition, which is unusual for kneading materials. Corrosion protection can be provided in the usual way by painting or coating. It is, however, more advantageous according to the invention if, when rolling out the ingots from such scrap alloy melts, roll cladding of 5-10% on both sides of the rolled semi-finished product is made from an AIZn alloy with 1.5 Zn, made from a semi-finished alloy Al 99.8 or less.

Electrochemical investigations of the corrosion potentials on the alloy sheets according to the invention from mixed old scrap and on cladding materials and on short-circuit elements made of these alloy sheets and various cladding materials have shown that AIZn 1.5 based on AI 99.8 or more optimal corrosion protection both by covering the sheet surface and guaranteed by electrochemical effects due to the potential difference between the core material and the cladding layer.

example 1

Roll ingots were cast from a melt of mixed old scrap in a continuous casting process after the alloy melt had been kept at a temperature of 730 ° C. for two hours. The inlet temperature into the billet ingot molds was set at 710 ° C. during the continuous casting. The rolled bars had the following composition in mass percentages:

The rolling bars were subjected to a 12-hour annealing treatment at 490 ° C. The hot rolling was carried out at an initial temperature of 460 ° C. During hot rolling, a cladding layer made of Al99.8 with 1.5% on both sides of 10% of the sheet thickness was applied. The plated hot strip was then cold rolled to its final thickness. The strength values and some forming parameters in different states are given in Table 1 together with those of Example 2.

Example 2

Roll ingots were cast from a second melt of mixed old scrap in a continuous casting process after the alloy melt had been kept at a temperature of 730 ° C. for two hours. The inlet temperature into the billet ingot molds was set at 710 ° C. during the continuous casting. These rolling bars had the following composition in mass percentages:

The rolling bars were subjected to a 24-hour annealing treatment at 490 ° C. The hot rolling was carried out at an initial temperature of 460 ° C. During hot rolling, a cladding layer of A199.8 with 1.5% Zn was applied to both sides of 10% of the sheet thickness. The plated hot strip was then cold rolled to its final thickness.

The strength values and some forming characteristics in different states are given in Table 1 together with those of Example 1.

The sheets from both examples showed good formability in the soft as well as in the solution-annealed and quenched state, as can be seen from the hardening exponent n and the Erichsen indentation, and achieved high strength values after hot curing.

The corrosion behavior of such plated sheets of scrap alloy melts has proven to be very good. The sheets were well suited for anodic oxidation to create decorative sheet surfaces.

Due to their good properties, the rolled semi-finished products produced in this way can be used for numerous fields of application, for example in construction (facades), vehicle construction (cladding, body parts) or for other purposes.

Claims (4)

1. The use of mixed aluminum scrap for aluminum casting alloys selected from the group consisting of AISi, AISiCu and/or AISiMg and for wrought aluminum alloys selected from the group consisting of AIMn, AIMg, AIMgMn, AIZnMg, AIZnMgCu, AIMgSi and/or AICuMg, said casting alloys having a weight ratio to said wrought alloys of from 1 : 1 to 2 : 1, and without addition of primary aluminum for the making of rolled aluminum intermediate products, comprising from 1 to 6 % Si, 1 to 3 % Mg, 0.5 to 3 % Zn, 0.5 to 3 % Fe, 0.3 to 2 % Cu as well as up to 1 % Mn, up to 0.2 % Ti, up to 0.5 % Cr and up to 0.5 % Pb, Bi, Sn, the remainder aluminum.

2. The use of mixed aluminum scrap for aluminum casting alloys to be used for making rolled aluminum intermediate products as defined in claim 1, wherein the scrap material is first subjected to shredding followed by magnetic separation.

3. The use of mixed aluminum scrap for aluminum casting alloys as defined in claim 1, wherein the alloy melt is maintained at a temperature of at least about 730 °C for a periode of between 1 to 2 hours prior to casting and is then cast into ingots or strips with an entering temperature of at least 710°C, the said ingots or strips preferably being annealed for 12 to 24 hours at 490 °C and being then conventionally hot and cold rolled.

4. Rolled aluminum intermediate products from mixed aluminum scrap as defined in claim 1, the said intermediate products roll-plated on both sides with an AIZn- alloy containing 1.5 % Zn, the said allov being produced from an intermediate alloy containing 99.8 or more percent AI, the thickness of the said platings being 5 to 10 % of the intermediate product.