氩气精炼除气时间对A356合金组织性能的影响

Effects of Argon Refining Degassing Time on Microstructure and Mechanical Properties of A356 Alloy

借助真空负压密度仪、OM、XRD、SEM、EDS与力学性能测试,研究了精炼时间对A356合金微观组织与力学性能的影响。结果表明,随着精炼时间延长,熔体密度当量由11.4%降至1.6%,随后增至3.4%。A356合金铸态组织主要由初生α-Al基体、共晶Si相与少量Mg2Si相组成,共晶Si沿晶界均匀分布,经T5热处理后共晶Si相形貌由不规则板片状转变为球状,断裂机制由沿晶断裂转变为韧窝断裂,Si相长度由184μm降至28μm。随着精炼时间延长与试样厚度降低,内部缺陷由缩孔转变为缩松。相同精炼时间下随着试样厚度增加,力学性能持续下降;同一厚度试样,力学性能随着精炼时间的延长先上升后下降,12mm试样铸态与T5态平均抗拉强度、屈服强度、伸长率与断面收缩率分别为206.3MPa、106.0MPa、6.8%、11.2%与281.3MPa、231.6MPa、10.8%、18.9%,断口晶界处Si相颗粒平均尺寸约为8μm。

The effects of refining time on the microstructure and mechanical properties of A356 alloy were investigated by using the vacuum negative pressure density instrument,OM,XRD,SEM,EDS and mechanical properties test.The results show that the melt density equivalent is decreased from 11.4%to 1.6%firstly and then increased to 3.4%with the increase of refining time.The as-cast microstructure of A356 alloy is mainly composed of primaryα-Al matrix,eutectic Si phase and Mg2Si phase,and the eutectic Si phase is distributed along the grain boundary.The Si phase morphology is changed from irregular plate to spherical,together with the fracture mechanism transformed from intergranular to dimple after T5 heat treatment,meanwhile the Si phase length is reduced from 184μm to 28μm.The internal defect is changed from shrinkage cavity to micro-porosity with the increase of refining time and decrease of thickness.Under the same refining time,the mechanical properties is decreased continuously with the increase of thickness,whereas the mechanical properties are improved firstly and then decreased with the increase of refining time at the same thickness state.The average tensile strength,yield strength,elongation and section shrinkage of the as-cast and T5 states in 12 mm thickness condition are 206.3 MPa,106.0 MPa,6.8%,11.2%and 281.3 MPa,231.6 MPa,10.8%,18.9%,respectively.The Si phase particle nearby the grain boundary is about 8μm.