Research On The High Strength Aluminum Silicon Alloy For Piston

The piston is a key part of automobile engine.The requirements for the properties of pistons are low density,good thermal conductivity,low thermal expansion coefficient,high mechanical strength and fatigue performance,as well as good wear resistance.Casting Al-Si alloy is widely used in production of piston material because of its many excellent properties such as low density,low thermal expansion coefficient,high specific strength and high wear resistance.With continuous improvement of engine performance,the mechanical properties,strength at elevated temperature and fatigue strength of the piston should be improved as well.Many process and metallurgical methods,such as modification treatment,alloying,heat treatment etc.have been created to modify the morphology of eutectic silicon and strength?-Al phase in the microstructure of Al-Si alloy piston for the purpose of improvement of its strength.In alloying treatment,the strength of room temperature and high temperature are improved by means of adding alloy elements to strengthen matrix and to form intermetallic compounds with stability at elevated temperature in the Al-Si alloy.The maximal effects of the alloy elements are obtained by i mprovement of microstructure in combine with multi-alloying and heat treatment.Therefore,in recent years,alloying treatment and improvement of microstructure for the purpose of enhancing the mechanical properties of Al-Si alloy piston have become one of the central issue in the research of piston alloy materials.The hypoeutectic Al-Si alloys with Si content near eutectic composition?Al-?10.5¹1.5?wt.%Si?is investigated in this paper.The purpose of the research is to create a high strength Al-Si alloy piston material by modification treatment and multiple alloying,solid solution and aging heat treatment.?1?The effects of modification and refinement of eutectic silicon in the hypoeutectic Al-Si alloys by adding Sr were studied.The results show that the eutectic silicon in the hypoeutectic Al-Si alloy is transformed from thick needle to small and dispersed fiber shape after adding 0.06%Sr.The average size of eutectic silicon are decreased to 8?m.The optimum modification of the eutectic silicon is obtained by adding 0.06%Sr.?2?The hypoeutectic Al-Si alloys?Al-?10.5¹1.5?wt.%Si?were alloyed by Cu,Ni as well as Mg and Zn alloy elements.The influence of the main alloy elements Cu and Ni on the room temperature and high temperature mechanical properties of the hypoeutectic Al-Si alloys were studied.The results show that the room temperature mechanical properties of the alloys are increased by increasing Cu.While the high temperature mechanical properties of the alloy are increased with increase of Ni content.When 3.5%Cu and 2.0%Ni are added,the tensile strength at room temperature of hypoeutectic Al-Si alloy?Al-11.5wt.%Si?is achieved to 345.2 MPa,and the high temperature tensile strength?300??is reached to 99.53 MPa.This tensile strength at room temperature of the alloy exceeds the highest level of the same alloys investigated in the world.?3?The thermal expansion coefficient of different silicon content?10.5%,11.5%,12%?alloying Al-Si alloy was studied.Within the Si content range,the thermal expansion coefficient of the alloy is not increased significantly with decrease of silicon content.The thermal expansion coefficient of hypoeutectic Al-Si alloy near eutectic composition?300??is between 22.158×10^-6K^-123.381×10^-6K^-1.The thermal expansion coefficient of the alloy can meet the requirement of piston material.