Cu添加对Mg-Bi合金铸态组织和沉淀硬化的影响

Effects of Cu addition on as-cast microstructure and precipitation hardening of Mg-Bi alloy

制备Mg-5Bi-xCu(x=0,0.2,0.5,1.0,质量分数,%)合金铸锭,研究其铸态组织和沉淀硬化行为。结果表明:铸态Mg-Bi-Cu合金主要由α-Mg枝晶、Mg3Bi_(2)相、MgCu_(2)相和Mg_(2)Cu相组成,Mg_(3)Bi_(2)相和α-Mg基体的取向关系为(■)Mg_(3)Bi_(2)//(■)Mg、[■]Mg_(3)Bi_(2)//[■]Mg,Mg_(2)Cu相和Mg_(3)Bi_(2)相之间的取向关系为(■)Mg_(2)Cu//(■)Mg_(3)Bi_(2)、[■]Mg2Cu//[0001]Mg_(3)Bi_(2)。铸态合金硬度随Cu添加量提高先增大后减小,添加0.5%Cu时硬度最高,为(50.9±1.2)HV。固溶态Mg-5Bi-0.5Cu合金硬度为(49.8±0.9)HV。在175℃时效64 h后,硬度达到峰值(56.1±0.7)HV。时效硬度的提高主要是由于高密度Mg3Bi2相的沉淀强化作用,且由于Cu元素的添加,长杆状Mg3Bi2沉淀相转变为颗粒状和短棒状Mg_(3)Bi_(2)沉淀相。

The Mg-5Bi-xCu(x=0,0.2,0.5,1.0,mass fraction,%)alloy ingots were prepared by conventional casting.The microstructures of as-cast alloys and precipitate hardening behavior were investigated.The results show that the as-cast Mg-Bi-Cu alloy is mainly composed ofα-Mg,Mg_(3)Bi_(2),MgCu_(2) and Mg_(2)Cu phases.The orientation relationships betweenα-Mg matrix and Mg_(3)Bi_(2) phase are(■)Mg_(3)Bi_(2)∥(■)Mg and[■]Mg_(3)Bi_(2)∥[■]Mg.The orientation relationships between Mg_(2)Cu phase and Mg_(3)Bi_(2) phase are(■)Mg_(2)Cu∥(■)Mg_(3)Bi_(2) and[■]Mg_(2)Cu∥[■]Mg_(3)Bi_(2).The hardness of the alloy increases firstly and then decreases with the increase of Cu addition amount,and the highest hardness of(50.9±1.2)HV is achieved in the alloy with 0.5%Cu.The hardness of Mg-5Bi-0.5Cu alloy after solid-solution treatment is(49.8±0.9)HV.After aging at 175℃for 64 h,the peak hardness of the alloy is(56.1±0.7)HV.The increase of aging hardness is attributed to the precipitation strengthening effect of high density Mg_(3)Bi_(2).Moreover,due to the addition of Cu element,the long rod-shaped Mg_(3)Bi_(2) precipitates transform to the granular and short rod-shaped precipitates.