半固态挤压铸造A356合金在热处理过程中的组织和性能演化

Microstructure Evolution and Properties Improvement of Semi-solid Squeezed A356 Alloy During Heat Treatment

半固态挤压铸造的A356合金首先在540℃下进行固溶处理,随着固溶温度升高,Mg和Si原子逐渐溶解于基体中,并产生了固溶强化作用。抗拉强度、延伸率和硬度在固溶6 h达到峰值,之后合金力学性能随固溶时间延长而下降。在固溶处理之后合金在180℃下进行了不同时间的时效处理。随着时效时间延长,Mg_(2)Si相逐渐在基体中析出,析出相显著球化细化,尺寸约为2μm。经过对合金组织和力学性能的分析,半固态挤压铸造A356合金的最佳热处理制度为:540℃固溶6h,180℃时效4h。经过固溶和时效处理后的合金抗拉强度达到336 MPa,延伸率达到6.9%,硬度达到1240 MPa,相较于热处理前的性能提升了106.7%。

A356 alloy was processed by semi-solid squeeze casting followed by solution treatment at 540 oC.With increasing the solution time,Mg and Si elements dissolved into the matrix and led to solid solution strengthening.Results show that the tensile strength,elongation and hardness peak at 6 h and then decrease during solution treatment.Aging treatment at 180 oC for different time was carried out after solution treatment.With increasing the aging time,the fine spherical Mg_(2) Si phases are precipitated in the A356 alloy matrix,which are~2μm in size.The optimum heat treatment process is solid solution at 540 oC for 6 h followed by aging at 180 oC for 4 h.After solution and aging treatment,the tensile strength and elongation reach 336 MPa and 6.9%,respectively.Hardness reaches 1240 MPa after heat treatment,which is 106.7%higher than that of the cast alloy.