Solidification Process of Squeeze Casting and Effect of Heat Treatment on Properties of A356 Aluminum Alloy
The numerical simulation and microstructure analysis were applied to understand the forming sequence and solidification process of squeeze casting A356 aluminum alloy.The results indicate that semi-solid squeeze casting exhibits stable filling,short solidification time with low porosity.The microstructure and properties of the alloy by metal mold casting,liquid squeeze casting and semi-solid squeeze casting can be improved after solution and aging heat treatment.The results reveal that the grain morphology of α-Al matrix is the same as that of as-cast ones and the size is slightly larger,and the eutectic silicon is spheroidized and the size is around 1.5 μm after solution treatment.The mechanical properties and thermal conductivity of the alloy are increased at first and then decreased with the increase of solution temperature,while the mechanical properties of semi-solid squeeze casting keeps stable in the solution tem-perature range of 560℃.After further aging treatment,dispersed Mg2Si strengthening phase can be precipitated from the supersaturated solid solution,which can not only improve the tensile strength of A356 aluminum alloy by hindering dislocation movement,but also improve the thermal conductivity by reducing the scattering effect of solid solution atoms and vacancies on electrons.The semi-solid squeeze casting specimen exhibits the satisfied performance after solution treatment at 540℃for 4 h and aged treatment at 180℃for 9 h,where the tensile strength,elongation and thermal conductivity reach 283.65 MPa,13.2%and 191.82 W/(m∙K),respectively.
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