Microstructure And Properties Of Heat-resistant Al-Si-Cu-Ni-Ce-Cr Alloy For Piston

The heat-resistant cast aluminum alloy is widely used in pistons,and its price advantages as well as lightweight characteristics are very obvious.As the performance of engine continues to increase,the working load of the piston is significantly increased,so higher requirements are placed on the performance of piston,especially the high temperature properties.The development of high-performance piston alloy contributes to the lightweight in engine,while reducing the workload with the connecting rod and the crankshaft,as well as improving the efficiency of the engine.At present,the method for improving the performance of the piston alloys is mainly alloying.By adding some heat-resistant elements,some heat-resistant second phases are formed in the alloy,and the high-temperature strength of alloy is increased by this heat-resistant phases.The dispersed phase can enhance the performance of the piston by heat treatment.In this paper,taking the Al-Si alloys as the research objects,alloying with Cu,Ni,Ce and Cr elements.Using the orthogonal test to optimize the alloy composition,and improve the properties of alloy by heat treatment.In this way to develop the high performance of Al-Si-Cu-Ni-Ce-Cr alloy for pistons.In order to investigate the influence of different Cu,Ni and Ce contents on the microstructure and properties of cast heat-resistant aluminum alloy,and to optimize the composition of as-cast alloy,Cu content was selected as 4%,5%and 6%,respectively;Ni contents was 1.0%and 1.3%.1.5%;Ce content of0.5%,1.0%,1.5%as the three levels of factors,designed a three-factor three-level orthogonal test,using L₉?3⁴?orthogonal table,according to the orthogonal experimental design There are nine different compositions of Al-Si-Cu-Ni-Ce-Cr alloy.For the optimized alloy,the method of comparative optimization is used to further optimize the solid solution and heat treatment process.By means of XRD,OM,SEM,EDS and mechanical properties test to investgate the microstructure and properties of the alloy.The results show that:In the Al-Si-Cu-Ni-Ce-Cr alloy,its microstructure is mainly composed of?-Al,?-Al₇Cu₄Ni,?-Al₃CuNi,?-Al₂Cu and Si phases.When the Ce content reaches 1.5%,the Ce-rich phase is formed in the microstructure;at the same time,with the increase of Cu and Ni,the number of heat-resistant phase such as reticulated?-Al₃CuNi in the structure increases obviously.Through the range analysis,it is found that the influence of Ce element on the mechanical properties at room temperature and high temperature of 300°C is the most significant.With the increase of Ce content,the tensile strength at room temperature and high temperature at 300°C gradually decreases.Cu has a significant effect on the number of heat-resistant phases in the structure.When the Ce content is 0.5%,with the increase of Cu and Ni content,the heat-resistant phase in the structure increases,and the mechanical properties of the alloy are improved.The single change in the level of Ni element has little effect on the mechanical properties of the alloy.According to the results of orthogonal test analysis,it is determined that the alloy composition corresponding to the highest tensile strength of the alloy at roomtemperatureandhightemperatureof300°Cis Al-12Si-6.0Cu-1.3Ni-0.5Ce-0.5Cr,and its tensile strength at room temperature is193.8 MPa,the tensile strength at high temperature is 128.5 MPa.The heat treatment was optimized for the alloy with the best alloy composition.Temperature and time of solution treatment were optimized,comparing the microstructure and properties after solution treatment.The best solution process of alloy was 490°C×2 h+520°C×2 h.After the solution treatment,the temperature and time of aging treatment were optimized.Comparing the properties under different aging processes,the best aging treatment is 185°C×6 h.Afteroptimizationoftheheattreatment,thestrengthof Al-12Si-6.0Cu-1.3Ni-0.5Ce-0.5Cr in room temperature is 336.1 MPa,and the high temperature?300°C?strength is 156.8 MPa.