A356铝合金挤压铸造凝固过程及热处理对其性能的影响

Solidification Process of Squeeze Casting and Effect of Heat Treatment on Properties of A356 Aluminum Alloy

采用数值模拟和金相组织分析研究了A356铝合金挤压铸造成形顺序及凝固过程,发现半固态挤压铸造不仅充形平稳,凝固时间短,且孔隙率低。通过固溶、时效热处理可以改善金属型铸造、液态挤压铸造、半固态挤压铸造试样的组织及性能。结果表明,固溶处理后α-Al基体晶粒形貌与铸态相同,晶粒尺寸稍有长大,共晶Si球化尺寸集中在1.5μm左右。随着固溶温度升高,力学性能与热导率先增加后减小,而半固态挤压铸造后合金力学性能在560℃下固溶时并未降低。进一步时效处理后,过饱和的固溶体中析出弥散分布的Mg_(2)Si强化相,其不仅能够阻碍位错运动,提高A356铝合金的抗拉强度,而且减少了固溶原子与空位对电子的散射作用,提高导热性能。540℃×4 h固溶+180℃×9 h时效处理后,半固态挤压铸造试样性能最佳,其抗拉强度、伸长率、热导率分别为283.65 MPa、13.2%、191.82 W/(m·K)。

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 1.5μm 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 Mg_(2)Si 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.