| Al-Si-Cu-Ni-Mg alloy is a heat-treaTable alloy with good casting properties,mechanical properties,heat resistance,low expansion coefficient and other advantages.But as people to pay more and more attention to environmental protection,require more energy efficient light,and piston as the most important part of the car engine,it has a higher demand on the comprehensive performance of piston alloy,which can achieve high performance,light microscopic organization structure is one of the important parameters of mechanical properties,Because there are a lots of in the eutectic Al-Si alloy thick irregular block and stripe primary Si or plate strip eutectic Si,affecting the mechanical properties of alloy,so how to refine the piston alloy organization,increase mechanical properties of the alloy,the development of eutectic Al-Si alloy piston and application has important significance.In this work,by means of metallographic microscopy observation,SEM/EDS,XRD,DSC analysis,electronic universal testing machine,fatigue testing machine and other test methods,the influces of with Ti,Ti-V-Zr on microstructure and mechanical properties on Al-Si-Cu-Ni-Mg-Mn-Fe alloy was investigated.In addition,the relationship between the microstructure and the mechanical properties of alloy microstructure was explored to development of new type of eutectic Al-Si piston alloy.The results are as follows:(1)The study showed that Ti had a good refining effect on both primary Si and eutectic Si in eutectic Al-Si alloy.When Ti content was 0.1%,the size of primary Si in the microstructure was the smallest,decreasing from 29.7?m to 21.15?n.Eutectic Si also changed from long strip to short rod,and the distribution was more uniform.When Ti content is 0.1%,the alloy's tensile strength at 350? is 162.2MPa,which is 36.3%higher than that without Ti element.At this point,the alloy's fracture is mainly brittle fracture,but ductile fracture appears,thus improving its plasticity and strength.When Ti content was 0.15%,the thermal expansion coefficient at 350? was 21.4×10-6?-1.(2)The results show that Ti,V and Zr can further refine the primary Si and eutectic Si.When Zr content is 0.2%,the average size of primary Si is 16.5?m,and eutectic Si is in short bar shape or fine granular shape,which is at level 1 in the metallographic grade.Further increasing the content of Zr will produce acicular rich Zr phase,which will seriously split the matrix.When Zr content is 0.2%,the tensile strength at 350? is 173.2MPa,which is 48.1%higher than that without any trace elements,and the hardness is increased to 128HB.Due to the tight distribution of tissues,larger cohesive force is generated between tissues and larger expansion volume is not easy to occur,which reduces the thermal expansion coefficient.The thermal expansion coefficient at 350? is 21.1×10-6?-1.(3)The high temperature fatigue strength of the alloy material is related to the high temperature tensile strength.The fatigue strength of Ti alloy added alone is 46.43MPa,which is 7.2%higher than that without Ti alloy added.The fatigue strength of the composite added elements Ti,V and Zr is 47.8MPa,which is 10.4%higher than the alloy without added Ti. |
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