固溶处理对激光粉末床熔融AZ91D镁合金显微组织和力学性能的影响

Effect of solution treatment on microstructure and mechanical properties of AZ91D alloy fabricated by laser powder bed fusion

采用激光粉末床熔融的增材制造技术成形了AZ91D镁合金,并研究四种固溶处理制度((420℃,4h)、(420℃,6h)、(450℃,4h)、(450℃,6h))对打印态合金的显微组织和力学性能的影响规律。结果表明:激光体能量密度在160~210 J/mm^(3)之间时,成形的试样致密度大于99%,由α-Mg基体和β-Mg17Al12析出相组成;经(420℃,4h)固溶后,晶粒内部的纤维状β相几乎全部固溶到基体中,晶界处块状β相部分溶解;随着固溶温度的升高和时间的延长,晶界处更多的β相溶解,晶粒尺寸也逐渐增大,这为促进位错滑移提供了条件;相对于打印态合金,(450℃,6 h)态合金在不损失抗拉强度的同时,断裂伸长率由3.56%±0.47%提升到9.25%±1.05%,提高约160%,但屈服强度由(191±7)MPa降低到(141±7)MPa,这主要由于β相中Al原子的固溶强化、β脆性相的减少和晶粒尺寸的增大等。

AZ91D alloy samples were fabricated using laser powder bed fusion,and the effect of solution treatments((420℃,4 h),(420℃,6 h),(450℃,4 h),(450℃,6 h))on the microstructure and mechanical properties was investigated.The results show that the densities of sample are the higher than 99%at the laser energy density of 160-210 J/mm^(3).The as-printed samples consisted ofα-Mg matrix andβ-Mg17Al12 precipitated phase after solution treatment at(420℃,4 h),almost all of the fibrousβ-phase near the grain boundaries were solid solved into the matrix,and the massiveβ-phase at the grain boundaries is also partially dissolved.With the increase of solid solution temperature and time,the amounts ofβ-phases dissolve at grain boundaries and the grain size gradually increase,which provides conditions to promote the dislocation slip.Compared to the printed state,the(450℃,6 h)samples achieve an increase in elongation at break from 3.56%±0.47%to 9.25%±1.05%without loss of tensile strength,an increase of about 160%,but a decrease in yield strength from(191±7)MPa to(141±7)MPa,which is mainly derived from the solid solution strengthening of Al atoms in theβphase,the reduction of theβbrittle phase and the increase of grain size.