Piston manufacturing requires the use of piston materials. Several basic requirements for piston material selection. The alloy has low thermal expansion coefficient and good volume stability when alternating cold and heat; the alloy has low density, thereby reducing the inertial force of the reciprocating motion of the piston; the alloy has sufficient high temperature strength, high temperature thermal fatigue strength and elongation; the piston is under boundary lubrication conditions It has good wear reduction performance, wear resistance and corrosion resistance; the piston must have good technology, can be cast, cut and good heat treatment effect; the price is cheap.

Classification of aluminum piston materials for piston manufacturing: These requirements for piston materials are often contradictory. At present, there is no material that can fully meet the above requirements. The piston material commonly used in automobile engines is aluminum alloy. Its chemical composition and properties are shown in Table 5-16. Among the aluminum-copper alloys, take Y alloy as an example; it is based on Al-Cu-Ni-Mn, and its high temperature fatigue strength, thermal conductivity and ductility are very good, easy to forge and process, but high density, In particular, the thermal expansion coefficient is large and the cost is high.

Piston manufacture Eutectic Al-Si alloy with silicon content of 8.5% to 10.5% is used in low-load gasoline engines. The linear expansion coefficient is slightly larger, but the casting performance is better, which is suitable for mass production. The domestic grade is ZL108. This alloy is rarely used in China, but widely used abroad. The piston is made of eutectic Al-Si alloy with a silicon content of about 12%, which is often called LO-EX alloy abroad and is the most widely used piston material at home and abroad. It is suitable for gasoline engine and diesel engine, and can be cast and forged.

It has low linear expansion coefficient, low density, good wear resistance and corrosion resistance, high hardness, stiffness and fatigue strength, and good casting fluidity. However, the thermal conductivity is reduced, the plasticity is small, and the cutting and forging effect is not good. The silicon content of hypereutectic Al-Si alloys ranges from 18% to 23%. As the silicon content increases, the coefficient of linear expansion decreases, the heat resistance is good, the wear resistance and corrosion resistance are enhanced, and the alloy can withstand higher thermal and mechanical loads. However, the fluidity of the casting is poor, the casting is prone to cold isolation and shrinkage, the processing is difficult, the tool is worn, and the finish is not good. However, due to the continuous emergence of advanced technology, the defects of poor craftsmanship are being overcome.