Aluminum in the car: casting alloys
Casting aluminum alloys
Aluminum casting alloy allow to provide a wide range of mechanical properties of the products by selecting the chemical composition, and, if necessary, heat treatment and strict process control.
Figure 1 – Typical hypoeutectic AlSi7Mg (AA A356) Microstructure:
Al dendrites surrounded by Al+Si eutectic [1]
Casting aluminum alloys combined four major families of alloys, which are based on the following alloying systems:
- Al-Si (-Cu);
- Al-Cu;
- Al-Mg (-Si);
- Al-Zn (-Si).
Most of the cast aluminum parts and products made of aluminum-silicon alloys, due to their exceptionally good casting properties (figure 2).
Some alloys of Al-Cu series, Al-Mg and Al-Zn have higher mechanical properties, than the alloys Al-Si, but their casting characteristics are usually quite low and it is very difficult to pour. In particular, they are very prone to hot cracking.
Aluminum-magnesium casting alloys
1) These alloys are highly corrosion resistant. They can be polished to a mirror finish, and anodizing.
2) They provide high mechanical properties without the need for heat treatment.
3) These alloys are commonly used in high pressure casting..
Aluminum casting alloys Al-Zn-Mg
These alloys are used, when it is necessary to avoid warping during quenching, since they are subjected to thermal hardening by aging at room temperature without preliminary hardening.
Casting alloys Al-Mg-Si and Al-Zn-Si-Mg
Additives silicon in these alloys in an amount sufficient provide them with good castability.
Aluminum casting alloys Al-Cu
1) These are the toughest casting aluminum alloys. Mainly used in the aerospace industry.
2) Of these alloys are also made critical parts of the car suspension.
3) These alloys are very susceptible to hot cracking and are very difficult to cast into complex shapes.
4) Used in limited quantities for sports car parts and other exotic vehicles.
Casting alloys Al-Si
1) The most popular casting alloys around the world (see. Figure 2).
2) Show excellent casting properties: high fluidity – good stuff molds, resistant to hot cracking and generally are the most technologically advanced casting alloys.
3) The addition of magnesium ensures good mechanical properties after heat treatment, and Copper improves machinability and increases strength at elevated temperatures.
4) Al-Si-Mg alloys are used for the manufacture of rims, cast structural parts and elements of the suspension, which require high strength and good viscosity.
5) Al-Si-Cu (-Mg) alloys dominate the power plant parts and assembly market, such as aluminum engine blocks, cylinder head, Sleeve engine cylinders and other cast parts, for which high strength at elevated temperatures and resistance to abrasion important, than the viscosity.
Fig. 2 – Schematic Al-Si phase diagram showing the composition ranges
for the most common foundry alloys [1]
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