CA1176084A

CA1176084A - Process for using scrap aluminum materials

Info

Publication number: CA1176084A
Application number: CA000372238A
Authority: CA
Inventors: Wolfgang Gruhl; Edgar Lossack
Original assignee: Vereinigte Aluminium Werke AG
Current assignee: Vereinigte Aluminium Werke AG
Priority date: 1980-03-05
Filing date: 1981-03-03
Publication date: 1984-10-16
Also published as: JPS56139667A; EP0035055A1; DE3008358B1; DE3008358C2; JPS6014828B2; NO155399B; NO803675L; EP0035055B1; NO155399C; ATE4128T1

Abstract

ABSTRACT
The present invention relates to aluminum alloy products and their production from a mixed melt of scrap aluminum casting alloys and wrought aluminum alloys. The product is a mixed aluminum alloy consisting essentially of a melt of at least one aluminum casting alloy selected from the group consisting of AlSi, AlSiCu and AlSiMg and at least one wrought aluminum alloy selected from the group consisting of AlMn, AlMg, AlMgZn, AlZnMg, AlZnMgCu, AlMgSi and AlCuMg, said casting alloys having a weight ratio to said wrought alloys of from about 1:1 to about 2:1, said melt consisting essentially of from about 1 to about 6 weight percent silicon, from about 1 to about 3 weight percent magnesium, from about 0.5 to about 3 weight percent zinc, from about 0.5 to about 3 weight percent iron, from about 0.3 to about 2 weight percent copper, up to about 1 weight percent manganese, up to about 0.2 weight percent titanium, up to about 0.5 weight percent chromium, up to about 0.5 weight percent lead, up to about 0.5 weight percent bismuth, up to about 0.5 weight percent tin, the remainder aluminum and associated impurities.

Description

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PROCESS FOR USING SCRAP
1 _ ALUM NUM_MATERIALS___ sack~round of the Invention _ _ _ _ _ _ _ _ _ _ _ The present invention is related to alumin~m alloy products and more particularly to the use of mixed ~elts of scrap aluminum casting alloys and wrought aluminum alloys, for making rolled aluminum intermediate products by continuous or casting of strip~Ycasting of ingots or plates and subsequent hot and cold rolling.
Aluminum scrap generally comes from discarded consumer goods and worn out industrial or consumer machinery which was constructed, either in whole or substantial part, from aluminum alloys or aluminum and its alloys. These consumer goods, as well as machines and components which include aluminum alloy or aluminum metal and alloy components are generally fabricated from wrought aluminum alloy by cold or hot forming processes or from aluminum casting alloy by mold casting processes. The compos~tion of wrought aluminum~forging alloys differs from that of aluminum casting alloys for reasons related to the particular requirements of the manufacturing processes. The wrought aluminum alloys can have high alloy contents of magnesium, manganese and zinc, while the aluminum casting alloys generally have a high silicon content and often higher iron and copper content.
~hen these aluminum casting and wrought products have been discarded or worn out and collected for purposes of recy-cling, it has been necessary in the past to separate the products, prior to smelting, according to their original process source;
for example, the scrap wrought alloy is separated from the scrap casting alloy in order to avoid possible material failure during the reshaping or recasting of a mixed melt.

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1 Aluminum castings frequently contain metal impurities, such as iron, zinc and carbon, cast therein or adhering thereto.
Therefore, the smelting charges from sorted scrap aluminum castings will frequently have enrichments of these impurities.
Such enrichments are detrimental to reprocessing. To compensate for their presence, it has been necessary to blend pure primary aluminum into the smelting charge.
A further source of failure are castings from zinc or magnesium alloys. These alloys are difficult to separate during sorting operations. Their presence can lead to scrap melting charges which have amounts of magnesium or zinc too high for reuse as re-smelted aluminum casting alloy. In order to reduce the unfavorably high magnesium or zinc content, besides blending primary aluminum into the smelt, one can use an environmentally harmful chlorination process or an energy-intensive vacuum treatment at elevated temperatures.
A further source of increased content of magnesium and zinc in scrap smelting charges is the frequent use of both wrought aluminum alloy and aluminum casting alloy in consumer goods and machinery. For example, engine blocks, cylinder heads and gear housings are frequently produced from an aluminum casting alloy of the AlSiCu type. Attached auxiliary units are frequently produced from die cast zinc. Moving gear parts and sheetings for automobile body applications consists of wrought aluminum alloys such as AlMgSi or AlMg5. The same holds true for large household appliances where aluminum castings are used side-by-side with sheetings, facings and decorations of wrouyht aluminum alloys~
To economically comminute the scrap and remove the built-in iron particles from aluminum castings, the aluminum scrap can be subjected first to shredding and then magnetic separation to remove the iron particles. The comminution 1 17~08~

1 product is small size, shredded scrap in which the original wrought al~minum and cast aluminum alloys are completely mixed togethe{ and no longer distinguishable from one another.
After smelting such scrap, it must be blended with primary aluminum or chlorinated, as discussed above, to produce re-usable casting alloys.
It is an object of the present invention to provide a method for using mixed casting and wrought aluminum alloy scrap while avoiding the drawbacks mentioned above.
According to DIN 1725, Part 1, wrought aluminum inter-mediate products and rolled intermediate products are made from special alloys having very narrow and defined compositional ranges. The properties of these products are related to the type and amount of alloying components contained therein. It has now been unexpectedly discovered that sheets produced from unblended scrap of an unconventional composition have excellent strength characteristics and particularly good forming proper-ties when being rolled or deep drawn.
The aluminum alloy scrap used in the invention is of standardized composition, as set forth in DIN 1725 for wrought and cast aluminum alloys. The inventors also use an alloy designated A199.8Znl.5. This alloy is not described in DIN 1725. It consists of an aluminum alloy on the basis of 99.8 weight percent aluminum having a zinc content of between about 1.2 and 1.6 weight percent, the remainder aluminum.
This invention therefore provides a process for the economical and effective use of mixed casting and wrought scrap materials containing aluminum in the production of aluminum sheets and strips.
Description of the Preferred ~mbodiment According to the invention, sheets, plates or strips are produced by smelting scrap aluminum casting alloys and 1 t~608~

1 wrought aluminum alloys together (and without the addition of primary aluminum), an aluminum containing alloy including from about 1 to about 6% by weight silicon, from about 1 to about 3% by weight magnesiurn, from about 0.5 to about 3~ by weight zinc, from about 0.5 to about 3~ by weight iron, and from about 0.3 to about 2% by weight copper. The alloy may contain up to about 1% by weight manganese, up to about 0.2%
by weight titanium, up to about 0.5% by weight chromium and up to about 0.5% by weight of lead, bismuth and tin.
In a preferred embodiment of the invention, the scrap material is first subjected to comminuting or shredding, followed by magnetic separation. This removes most of the iron contaminants. The comminuting step is optional and can be eliminated. The shredded materials have a particle size of between about 50 and 100 mm. The shredded materials are then melted in a furnace.
The melt is maintained prior to casting at a tempera-ture of at least about 730C for a period of between about 1 to about 2 hours and is then cast into ingots with an entering temperature of at least about 710C. Preferably the ingots are annealed for about 12 to 24 hours at about 490C and are then rolled in the usual hot and cold manner to the desired final thickness. The melt can also be maintained for about one hour at about 750 or about 770C. The temperature of the cast molten alloy smelt can be increased up to about 720C and the ingots can be annealed at a temperature of from about 450 to 520C for a period of from about 12 to 18 hours.
It is preferred that casting alloy scrap such as AlSi, AlSiCu and AlSiMg be used together with wrought alloy scrap such as AlMn, AlMg, AlMgMn, AlZnMg, AlZnMgCu, AlMgSi and/or AlCuMg. The weight ratio of the casting and wrought scraps in the mixture can vary from between about 1:1 to about 2:1.

1 The scrap melt is continuously sampled to determine the weiqht percent of metal components. The smelt composition can be modified in order to provide the desired range of in-gredients by known techniques such as chlorination and degassi-fication. The foregoing procedures can be used to red~ce the level of metal constituents to bring them within the designated ingredient weight percent range. If the melt is deficient in a particular component (as determined by sampling) the requisite quanti.y of that component may be added to bring the composition into the alloy weight range discussed above. If analysis of the smelt discloses a substantial amount of impurity, scrap metal of known composition can be added.
The mixed scrap melt, according to the present invention, can be used for the production of plates, sheets and strips which exhibit good performance properties. As a result of using the novel composition described above, it is not necessary to use the expensive and environmentally harmful steps of blending the scrap melt with primary aluminum or chlor nation.
After maintaining the melts at a temperature of at least about 730C for a period of about 1 to 2 hours and then continuously casting to ingots or plates at a temperature of entry into the casting machine of at least 710C, the ingots or plates obtain a cast structure which is particularly suited for subsequent rolling to shape. The formability required for f~rther processing to make sheet parts by cold forming, e.g.
in rolling or deep drawing is also favorably affected by this treatment of scrap alloy melts.
Because of the unusual composition for wrought materials, it has been found that sheets from rolled ingots made according to the invention show increased corrosion Sensitivity. Corrosion protection can be provided in the l 176084 1 usual manner by either varnishing or coating the sheets. How~
ever, it has been found preferable during the rolling of ingots from scrap alloy melt according to the invention to cover both sides of the rolled sheet with a cladding (having a thickness equal to between about 5 to about 10% of the scrap cor.e sheet) of AlZn 1.5. The AlZnl.5 alloy should be prepared from aluminum having a purity of at least 99.8 weight percent and includes about 1.2 to about 1.6 weight percent zinc, the remainder aluminum.
Electrochemical examinations of the corrosion potential of sheets manufactured from mixed scrap according to the invention and on cladding materials and on short-circuit elements from these sheets have shown that AlZn 1.5 on the basis of Al 99.8 or more assures optimal corrosion protection both by covering of the sheet surface and by electrochemical effects through the difference in potential being created betweeh the core material and the cladding.
Example 1 Ingots were cast in a continuous casting process from a melt of mixed scrap after the alloy melt had been maintained for about 2 hours at a temperature of about 730C.
The temperature of entry into the ingot molds was set at 710C
during the continuous casting. The ingots had the following composition in weight percentages:
Si Fe Cu Mn Mg Cr Zn Ti 4.90 0.94 0.92 0.31 1.0 0.15 0.50 0.035 The ingots were subjected to annealing for a period of about 12 hours at a temperature of about 490C. Hot rolling was effected with a starting temperature of about 460C. During this rolling, a cladding of A199.8Znl.5 was deposited to an extent of about 10% of the sheet thickness and then the clad strip was cold rolled to the final thickness.

l 1~6084 1 Strength values and a few forming characteristics of the product under various conditions are given in Table 1, together with those of Example 2.
Example 2 Ingots were cast from a second melt of mixed. scrap by the continuous casting process after the melt of alloys had been maintained for about 2 hours at a temperature of about 730C.
The entry temperature of the melt into the ingot molds was set Q during the continuous casting at about 710C. The ingots had the following composition in weight percentages:
Si Fe Cu Mn Mg Cr Zn Ti 1.07 1.10 1.08 0.25 2.8 0.16 2.63 0.03 Thereafter the ingots were subject to annealing for a period of about 24 hours at a temperature of about 490C.
Hot rolling was effected at a starting temperature of about 460C. During the rolling a cladding of A199.8Znl.5 was deposi-ted on both sides to an extent of about 10% of the sheet thickness. Following that, the clad strip was cold rolled to final thickness.
The strength values and a few forming characteristics under various conditions are given below in Table 1, together with the characteristics for the product of Example 1.
Table 1: Strength and forming characteristics of sheets of 1.2 mm thickness from scrap alloY melts of Examples 1 and 2.
25 Condition Examples Examples Examples Examples Examples Rpo 2(N/mm ) Rm(N/mm ) A5 (%) n Erichsen (mm) Hard-rolled 260 290 280 310 5 4 H14,semihard 215248 235 268 7 8 - 7 5 Soft 85 80 170 200 27 24 0.18 0.2210 10 Annealed chilled108 102 262 259 22 25 0.28 0.30 8 10 Arti-ficially aged, 24 h 170Ç 345 310 390 400 12 17 0.07 0.13 6 7 P.8a 1 17608~

1 The sheets from Examples 1 and 2 showed good worka-bility in the soft, solution heat-treated and chilled condition, as seen from the strain-hard~ningexponent n and the Erichsen depression; the sheets reached high strength values after artificial aging.
The resistance to corrosion of the clad sheets from scrap alloy melts has been shown to be excellent. In addition, the sheets are well suited for anodic oxidation in order to create decorative sheet surfaces.
As a result of the favorable properties of the products of the mixed alloy melt process, rolled intermediate products produced according to the invention can be used in numerous applications, such as in building construction (facades), vehicle construction (sheeting, body parts) or for other purposes.
While there have been described what are considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without deprting from the invention, and it is, therefore, aimed to cover all such changes and modifications as falls within the true spirit and scope of the invention.

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*) E~lanation of the Abbreviations used in Table 1 . _ . ., _ Rpo 2 is yield strength Rm is tensile or ultimate strength A5 is elongation on 2 inches n is strain-hardening exponent according to Kent v. Horn: Aluminium, Am. Soc. of Metals 1967 P. 87 H14 is an American expression for a cold worked temper after 35 % reduction by cold rolliny.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
l. A mixed aluminum alloy consisting essentially of a melt of at least one aluminum casting alloy selected from the group consisting of AlSi, AlSiCu and AlSiMg and at least one wrought aluminum alloy selected from the group consisting of AlMn, AlMg, AlMgZn, AlZnMg, AlZnMgCu, AlMgSi and AlCuMg, said casting alloys having a weight ratio to said wrought alloys of from about 1:1 to about 2:1, said melt consisting essentially of from about 1 to about 6 weight percent silicon, from about 1 to about 3 weight percent magnesium, from about 0.5 to about 3 weight percent zinc, from about 0.5 to about 3 weight percent iron, from about 0.3 to about 2 weight percent copper, up to about 1 weight percent manganese, up to about 0.2 weight percent titanium, up to about 0.5 weight percent chromium, up to about 0.5 weight percent lead, up to about 0.5 weight percent bismuth, up to about 0.5 weight percent tin, the remainder aluminum and associated impurities.
2. A cast aluminum shape comprising an alloy of the composition defined in claim 1.
3. An annealed aluminum alloy comprising the composi-tion set forth in claim 1.
4. A rolled aluminum alloy comprising the composition set forth in claim 1.
5. A clad aluminum alloy comprising a rolled sheet, said sheet having the composition defined in claim 4 and cladding on opposed faces of said sheet.
6. A clad sheet comprising a core consisting of an aluminum alloy as set forth in claim 1, a cladding on said opposed faces of core said cladding comprising an aluminum alloy of AlZn 1.5, the thickness of said cladding being be-tween about 5 to about 10% of the thickness of said sheet.
7. A method of manufacturing aluminum alloy from mixed aluminum casting alloy and wrought aluminum alloy consist-ing essentially of comminuting a mixture of aluminum cast-ing and aluminum forging alloy scrap materials to form a comminuted alloy mixture having a predetermined particle size range, the weight ratio of said casting alloys to said wrought alloys being between about 1:1 to about 2:1, said aluminum casting alloys including at least one member selected from the group consisting of alloys of AlSi, AlSiCu and AlSiMg, and said wrought aluminum alloys includ-ing at least one member selected from the group consisting of the alloys AlMn, AlMg, AlMgZn, AlZnMg, AlZnMgCu, AlMgSi and AlCuMg, separating ferrous scrap material from said comminuted alloy mixture, heating said alloy mixture to form a melt, main-taining said melt at a predetermined temperature for a predetermined time, removing metallic impurities from the melt, and casting said melt to form a predetermined shape at a predetermined temperature.
8. The method of claim 7 wherein said melt comprises by weight, from about 1 to about 6% silicon, from about 1 to about 3% magnesium, from about 0.5 to about 3% zinc, from about 0.5 to about 3% iron, from about 0.3 to about 2% copper, up to about 1% manganese, up to about 0.2% titanium, up to about 0.5% chromium, up to about 0.5% lead, up to about 0.5% bismuth, up to about 0.5% tin, the remainder aluminum and associated impurities.
9. The process of claim 8 further comprising:
annealing said cast melt at a second predetermined temperature for a second predetermined period of time and hot rolling the annealed cast melt, and, cold rolling the hot rolled annealed cast melt to form a sheet product.
10. A process as set forth in claim 9 further compris-ing forming said sheet into a shaped product.
11. A method as set forth in claim 8 wherein said predetermined temperature is of between about 730°C to about 770°C.
12. A method as set forth in claim 10 wherein said predetermined time is between about 1 to about 2 hours.
13. A method as set forth in claim 7 further compris-ing casting said melt into molds, said melt entering said mold being between 710°C to 730°C.
14. A method as set forth in claim 13 further compris-ing forming said melt into the shape of ingots or strips.
15. A method as set forth in claim 14 further compris-ing annealing said ingots or strips at a temperature between about 450°C to 520°C.
16. A method as set forth in claim 14 further compris-ing annealing said strips or ingots at about 490°C for between about 12 to about 24 hours.