变质及不同时效工艺对A356合金组织和力学性能的影响

Effect of Modification and Different Aging Processes on Microstructure and Mechanical Properties of A356 Alloy

采用金相显微镜、电子万能拉伸机对Na、Sr、Sb变质后以及不同热处理工艺条件下A356合金的组织和力学性能进行研究。结果表明:在相同的生产条件下,Na、Sr、Sb均对A356合金共晶硅具有较好的变质效果,随后熔体保温过程中Na变质40 min后部分失效,Sr和Sb在变质后熔体保温2 h组织没有明显的变化。在Sb变质条件下,(535±5)℃固溶,保温8 h,时效温度为(155±5)℃,不同的时效保温时间下A356合金宏观组织和晶粒度没有明显的变化,随着时效保温时间的增加,合金的抗拉强度、屈服强度、伸长率由266 MPa、205 MPa、8%分别变化为295 MPa、227 MPa、6.5%。可根据工件性能要求选择合适的热处理工艺。

The microstructure and mechanical properties of A356 alloys were investigated by optical microscope and universal testing machine after Na, Sr or Sb modification and different heat treatment processes. The results show that Na, Sr or Sb each has excellent modification effects on the eutectic silicon ofA356 alloy under the same production conditions. After holding for 40 min, the Na modification in the melt was partially invalidated, and the Sr or Sb modification effect has no obvious change even after the melt was held for 2 hours. Under the conditions of Sb modification, solution treatment for 8 h at 535 ℃ ±5 ℃, and aging treatment at 155 ℃ ±5 ℃, the macroscopic structure and grain size ofA356 alloy are not changed obviously with different aging time, but with the increase of aging time, the ultimate tensile strength, yield strength and elongation of the alloy changed from 266 MPa, 205 MPa and 8% to 295 MPa, 227 MPa and 6.5%, respectively. It is possible to choose proper heat treatment process for the alloy according to its different requirements of performance.