Recycling of foundry aluminum scrap


There are about two hundred cast aluminum alloys - in addition to two hundred wrought alloys.

Classification of cast aluminum alloys

The casting alloys alloying elements, usually, much bigger, than wrought alloys. This makes them more difficult to process aluminum scrap in anything other than such as casting alloys.

The thing is, that the removal of the majority of alloying elements, Besides, may be, magnesium, aluminum melt is completely impractical.

As in the case of wrought alloys, литейные алюминиевые сплавы подразделяют на серии (или классы, группы) по применяемым в них легирующих элементам. This classification, as well as the classification of wrought alloys has been developed in the US in the 1950s and is now accepted all over the world. Digital signage series casting alloys roughly corresponding to the designated series of wrought alloys, Only the last digit is separated from the rest of a decimal point.

casting alloys designation system

  1. Первая цифра: Главный легирующий элемент (или два)
  2. Вторая и третья цифры: Уникальное обозначение сплава внутри серии (группы)
  3. Четвертая цифра (после десятичной точки):
  • 0 – cast
  • 1 – standard ingots
  • 2 – ingot with a narrower chemical composition.

The letters A, B и C (например, А356.0) указывают на небольшую модификацию состава сплава (356.0).

Casting alloys 1hh.h

Casting alloys contain 1hh.h 99 % and a similarly deformable aluminum alloys 1xxx. They are rarely used in products, and used in the form of ingots for remelting and podshihtovki the production of other alloys. Their use in the form of products is limited to applications, which require high electrical conductivity, as, for example, injection molded bus bars of complex shape.

Casting alloys 2hh.h

These alloys contain 3,5-10,7 % copper. copper here, in deformed alloys 2xxx, It is the main alloying element. 2hh.h foundry alloys can also have a significant iron content, magnesium, nickel and silicon. These alloys are the most heat-resistant and all of the solid cast aluminum alloys. They require heat treatment to prevent corrosion cracking. Similarly wrought alloy series 2xxx these casting alloys require staining and protective coatings due to their low corrosion resistance.

Casting alloys 3hh.h

3hh.h alloys series are the most popular among the cast aluminum alloys. They have a silicon content ranging from 4,5 to 20 %, and copper - from 0,5 to 5,0 %. Некоторые сплавы 3хх.х включают также магний (0,2-1,5 %), а некоторые еще и никель (0,5-3,0 %). The high silicon content of these alloys provide high fluidity, It reduces the hot cracking and minimizes shrinkage porosity. Copper and magnesium give hardening due to formation of the solid solution. Nickel reduces the coefficient of thermal expansion, which is useful for the pistons and cylinders of internal combustion engines.

Casting alloys 4hh.h

These alloys contain 3,3 to 13 % silicon, but very little of other alloying elements. Sometimes add small amounts of copper, iron or nickel. 4hh.h casting alloys have high ductility and toughness, which makes them useful in the manufacture of food processing equipment, as well as parts for the marine atmosphere.

Casting alloys 5hh.h

As in the case of wrought alloys, these alloys contain 5xxx 3,5-10,5 % magnesium. Often contain small amounts of iron, silicon and zinc. As well as casting alloys 2hh.h, 7xx.x and 8hh.h 5hh.h series alloys do not differ such as a high fluidity with high silicon content alloys therefore require special attention in the design of the molds.

Casting alloys 7hh.h

Specifications for these alloys require content 2,7-8,0 % zinc - like wrought alloys 7xxx. Во многих этих сплавах присутствует магний (0,5-2,0 %), иногда добавляют также и никель (0,2-0,6 %). These alloys have a higher corrosion resistance as compared to other casting aluminum alloys. They get their strength through natural aging, that enables eliminating heat treatment.

Casting alloys 8hh.h

Alloys of the last series of casting alloys - 8hh.h - contain 5,5-7,0 tin and 0,7-4,0 % copper, that gives them, one side, strength, and on the other - gives lubricity. These alloys are used for bearings. The spread of these alloys is very limited.

Processing difficulties casting alloys

In the production of aluminum alloy casting alloys by refining the same problem as with the deformable alloys - high level of undesirable impurities. Most alloys - except alloys 7hh.h - have a hard upper limit on the allowable zinc content, and some alloys 3hh.h series require a low iron content.

Universal cast alloy 380.0

Convenient for the processing of an alloy 380.0, which has a fairly high levels of all the major alloying elements. Он имеет следующий химический состав:

  • 7,5-9,5 % silicon;
  • 1,5 % gland;
  • 3,0-4,0 % copper;
  • 0,5 % марганца;
  • 0,5 % никеля;
  • 0,1 % magnesium,
  • 0,15 % tin.

Thanks to this "omnivorous" alloy 380.0, He is the main product of many recyclers of aluminum scrap. The alloy can then be thinned from the scrap and alloys 1xxx series 1hh.h or primary aluminum to obtain a more suitable alloy.

for instance, there is 100 kg remelted alloy 380.0 со следующим химическим составом:

  • 8,5 % silicon;
  • 2,0 % gland;
  • 3,5 % copper;
  • 0,5 % марганца;
  • 0,5 % никеля;
  • 0,1 % олова;
  • 3,0 % zinc.

To dilute the alloy add 200 кг первичного алюминия:

  • 0,05 % silicon;
  • 0,06 % gland.

Received 300 кг следующего сплава:

  • 2,87 % silicon;
  • 0,71 % gland;
  • 3,0 % copper;
  • 0,5 % марганца;
  • 1,0 % magnesium;
  • 0,5 % никеля;
  • 1,0 % zinc;
  • 0,25 % titanium.

The result was a popular cast alloy 332.0 castings for the automotive industry.

A prerequisite of such tactics production of secondary aluminum alloys is the presence of the desired amount of primary aluminum and aluminum alloys 1xxx and 1hh.h. However, this method makes it possible to recycle aluminum scrap casting without time-consuming sorting of alloys.

A source: Mark E. Schlesinger, Aluminum Recycling, 2017