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

摘要:

半固态挤压铸造的A356合金首先在540℃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小时达到峰值,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℃进行了不同时间的时效处理。随着时效时间延长,Mg2Si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6小时,180℃时效4小时。经过固溶和时效处理后的合金抗拉强度达到336MPa,延伸率达到6.9%,硬度达到HV124,相对于热处理前提升了106.7%。

Abstract:

A356 alloy was processed by semi - solid squeeze casting followed by solution treatment at 540℃. With increasing solution time, Mg and Si elements dissolved into the matrix and led to solid solution strengthening. Tensile strength, elongation and hardness peaked at 6 h and then decreased during solution treatment. Aging treatment at 180℃ for different time was carried out after solution treatment. With increasing aging time, the fine spherical Mg2Si phases precipitated in the A356 alloy matrix, which were ca. 2 μm in size. The optimum heat treatment process was solid solution at 540℃ for 6 h followed by aging at 180℃ for 4 h. After solution and aging treatment, tensile strength and elongation reached 336 MPa and 6.9%, respectively. Hardness value reached 124 HV after heat treatment, which was 106.7% higher than the cast alloy.