Research On The Preparation Of Hypereutectic Aluminum Silicon Alloys By Casting And Friction Stir Processing

Aluminum silicon alloy is an important type of engineering materials,have been widely used in automobiles,defense industry,aerospace,electronic packing and other domains due to the low density,high specific strength,low coefficient of thermal expansion and excellent wear resistance.However,with silicon content increasing,the presence of coarse,irregular morphology,and brittle primary Si particles and acicular eutectic Si particles in high-silicon aluminum alloys produced by conventional methods,cause severe detrimental effects on mechanical properties,which impede their boarder applications.Therefore,it is meaningful and valuable to develop the preparation methods of aluminum silicon alloys with low cost and large production.This paper started from the views of alloying elements addition and severe plastic deformation,so friction stir processing and adding alloying elements were chosen to process aluminum silicon alloys.The results of FSP experiments on Al-Si alloys showed,the coarse microstructure in as-cast alloy were completely eliminated.The average size of silicon particles in 4 different kinds of Al-Si alloys was below 5 μm after FSP 1-pass.Mechanical properties were improved significantly at the same time,the ultimate tensile strength and elongation of Al-20 Si alloy achieved 202.3 MPa and 15.8% after FSP 3-pass at 950 rpm of rotate speed and 47.5 mm/min of traverse speed.Fracture mode of Al-20 Si alloy changed from brittle fracture to ductile fracture as well.The results of alloying elements addition experiments indicated,the size of silicon particles decreased to 25.3 μm after 0.4% P addition,the ultimate tensile strength and elongation increased to 132.1 MPa and 2.8%,respectively.The size of silicon particles decreased in Al-20 Si alloy and the wear resistance increased considerably after Mg addition.Comparing to the unmodified alloy,mass loss of the alloy containing 3% Mg was only 3.6mg,half of the unmodified alloy.It can be seen from the results that,the modification effect of microstructure and mechanical properties in Al-Si alloys by friction stir processing was greater than adding alloying elements method.