Effect Of Friction Stir Processing On Microstructure And Mechanical Properties Of As-Cast Al-Si Alloy

Al-Si alloy is widely used as a casting alloy in engine cylinder head,piston and other components because of its good liquidity,high strength,small shrinkage and good casting properties.Due to defects such as pores and dendrites,the mechanical properties of the cast Al-Si alloy can?t meet the requirements of industrial production widely.It is found that the surface modification of the alloy by friction stir processing can effectively solve the problems of porosity and coarse dendrite in the casting alloy,and achieve the purpose of eliminating porosity and densification and homogenization of the alloy,so as to improve the mechanical properties of the casting alloy.The effects of friction stir processing on the microstructure and mechanical properties of two Al-12.7Si and Al-12.7Si-0.7Mg alloys were investigated by measurement and tensile test at room temperature and by means of microstructural analysis,such as optical microscopy and scanning electron microscopy.The effects of advance speed,rotation speed and processing pass on the microstructure evolution and mechanical properties of the alloy were analyzed experimentally.The results are as follows.The friction stir processing of the as-cast Al-12.7Si alloy,in the range of experimental parameters,the increase of the rotation speed can better refine the silicon grains in the weld zone.The greater the advancement speed,the more uneven the distribution of silicon particles in the weld zone.Increasing the number of passes can effectively improve the size and distribution of the silicon particles;the size and distribution of the silicon particles have a great influence on the change in the hardness value of the weld zone.When the particle size and distribution are not uniform,the hardness value of the weld zone is more fluctuating;the tensile strength decreased slightly,but it can reach more than 90% of the base metal strength.There is significant variation in the extension rate,the maximum is 4.1 double parent material elongation.In this experiment,when the speed and speed are matched only,the best effect can be achieved by the microstructure and mechanical properties of the alloy.When the as-cast Al-12.7Si-0.7Mg alloy was subjected to friction stir processing,the effect of parameters on the microstructure of the weld zone is similar to that of the Al-12.7Si alloy;In addition to the influence of the size and distribution of silicon particles on the hardness of the alloy,the dissolution and precipitation of the precipitated phases are also important factors leading to hardness changes;After friction stir processing,the strength of the alloy base material are improved compared with the elongation of three;The 3-pass on the tensile strength of alloy without significant improvement effect,but significantly increased the elongation reached 2.8 times that of the base metal.