Effects of Bi on microstructure and properties of Al-Si piston alloy were observed by SEM（scanning electronic microscope）

OM（optical microscope） and tensile testing.The results show that Bi element can form monotectic transition with Al

and it exists as dispersive Bi phase independently in the microstructure of Al-Si piston alloy.The dimensional stability and wear resistance of the Al-Si piston alloy are greatly improved due to the special physical property and self-lubricity of Bi particle.The dimensional change rate of eutectic Al-Si piston alloy is decreased by 26.3% and of hypereutectic Al-Si piston is decreased by 7.7%～9.0%.In addition

the wear resistance of hypereutectic Al-Si piston alloy with Bi is decreased by approximately 50%.