Experimental Researches On Friction Stir Processing And Welding Of Aluminum Silicon Alloy

Aluminum-silicon alloys have been widely used in the automotive,aerospace,electronic packaging etc.because of their excellent performances of light weight,low thermal expansion coefficient,good abrasion resistance and corrosion resistance etc.Al-20 Si is mainly applied in the production of automotive pistons.However,the large primary silicon particles and needle-shape eutectic silicon particles are harmful to mechanical properties and limited their further development and application.Friction stir processing and welding(FSP/W)technology was used in manufacturing and joining of Al-20 Si alloy in the present study.This paper investigated the effect of tool shape,FSP/W parameters and the number of stir passes on the microstructure and mechanical properties of Al-20 Si alloy.The results showed that,the flowability of material and the effect of grinding material were better during friction stir processing with cylinder threaded pin.So the processing effect of cylinder threaded pin was better than that of conic threaded pin and square-shaped pin.Materials softened seriously when the heat input(rotation rate/traverse speed)was too high,and the effect of material grind weakened,so that it is hard to refine the silicon particles adequately.While the heat input was too low,the flow of material was insufficient,the silicon particles were difficult to uniformly distribute.The desirable microstructures and mechanical properties were obtained at 950 rpm and 47.5 mm/min.With the number of FSP passes increase,silicon particles refined obviously and distributed uniformly.The optimal microstructure and mechanical properties of as-cast Al-20 Si could be obtained after three-pass FSP.As the number of pass further increase,the silicon particles were hardly been further refined,and the distribution also had no obvious change.Thus,the mechanical properties of Al-20 Si couldn't be improved continuously.Friction stir welding could eliminate the defects such as porosity and cracking caused by fusion welding and produce joints with good surfaces and microstructures.Tensile strength and elongation of the weld nugget zone increased by 43.22% and 143.27% respectively than that of the base metal.