Casting alloys 

Casting alloys of aluminum-silicon-copper

Unlike deformable aluminum alloys, casting alloys have a much higher content of alloying elements.

Copper and silicon in aluminum

Of all casting aluminum alloys alloys of the aluminium-copper-silicon system have the widest application. These alloys have good castability properties. The combination of silicon and copper allows to apply heat treatment to improve the mechanical properties.

The amount of these alloys like copper, and silicon varies very widely. Therefore, in some alloys, aluminum-copper-silicon, copper predominates, while in others - silicon.

In these alloys:

  • Copper provides strength, a
  • Silicon improves the casting properties and reduces the hot cracking.

Alloys of aluminum-silicon-copper with a copper content of more than 3-4 % are thermally hardening. However, the heat treatment is usually used only, if these alloys also contain magnesium, which increases their susceptibility to heat treatment.

Alloys with a high silicon content (more 10 %) have low thermal expansion, which is an advantage for products, operating at elevated temperatures. When the silicon content exceeds 12-13 %, up to 22 %, present in the alloy of silicon primary crystals. When these crystals are properly distributed, they provide high wear resistance alloy. From these hypereutectic alloys is manufactured, for example, Automobile engine block.

Effect of magnesium

Many alloys of the Al-Si-Cu system also contain magnesium: AL3, AL4M, AK5M2, AL5, AL5-1, AL6, AK7M2, Ak4M4, AL32. This gives them a high thermal stability with operating temperatures 250-275 oC. These alloys are inferior to the alloys Al-Si and Al-Si-Mg casting properties of, corrosion resistance and tightness. Does not require modification and pressurized crystallization.

A casting aluminum alloy 380.0

Alloy formula: 8.5Si-3.5Cu

Chemical composition:

  • copper: 3,0-4,0 %;
  • magnesium: 0,10 % Max.;
  • manganese: 0,50 % Max.;
  • silicon: 7,5-9,5 %;
  • iron: 2,0 % max. $
  • nickel: 0,50 % Max;
  • zinc: 3,0 % Max.;
  • lead: 3,5 % Max.;
  • others: 0,50 % Max.;
  • aluminum: rest.

Effect of impurities

High iron content reduces the plasticity. The impurity content can reach relatively high values ​​before it starts to manifest their serious impact.

Typical mechanical properties:

  • tensile strength: 330 MPa;
  • yield point: 165 MPa;
  • relative extension: 3 %;
  • Poisson's ratio: 0,33;
  • elastic modulus: 71,0 GPa.

Physical properties:

  • density: 2,71 g / cm3;
  • liquidus temperature: 595 ºS;
  • solidus temperature: 540 oC.

Technological properties:

  • the melting temperature: from 650 to 760 ºS;
  • temperature spills: from 635 to 705 ºS;
  • annealing temperature to increase ductility: 260-370 oC,
    excerpt - 8 hours, cooling with an oven or in calm air;
  • tempering temperature for stress relief: 175-260 oC,
    excerpt - 4-6 hours, in still air cooling.

aluminum-silicon phase diagram, and aluminum-copper

fazovaya-diagramma-alyuminiy-kremniyThe phase diagram of aluminum-silicon

fazovaya-diagramma-alyuminiy-med
The phase diagram of aluminum-copper

Sources:

Aluminum and Aluminum Alloys, ASM International, 1996

Aluminum Alloy Castings: Properties, Processes And Applications – J. Gilbert Kaufman, Elwin L. Rooy