超声处理对稀土掺杂AM60B镁合金组织及力学性能的影响

Microstructure and Mechanical Properties of AM60B Magnesium Alloy Co-Doped with Rare Earth under Ultrasonic Treatment

在AM60B镁合金熔炼过程中加入混合稀土Y,Gd并辅以超声熔体处理工艺制备合金,利用光学显微镜(OM)、透射电镜(TEM)和万能试验机,研究了添加复合稀土和超声处理对镁合金微观组织和力学性能的影响,分析了其作用机制。结果表明,添加混合稀土Y,Gd后,未经超声处理的试样,稀土化合物存在于合金组织中,阻碍了位错和晶界滑移,α-Mg基体晶粒明显细化,β相减少,合金抗拉强度σ_b和延伸率δ分别达到257 MPa和9%,强度提高约20%。施加超声处理能进一步细化合金组织,使得α-Mg基体晶粒更加等轴细小,抑制β相在晶界处的连续网状分布。稀土相趋于弥散均匀分布,促进了稀土元素的细晶强化作用,使合金抗拉强度提高到269 MPa,延伸率达到11%。当稀土添加量超过一定范围后,稀土相开始粗化并割裂基体,这时超声处理对合金组织的改善作用有限,合金力学性能呈现下降的趋势。

In order to study the effect of ultrasonic treatment on microstructure and mechanical properties of as-cast AM60 B magnesium alloy with rare earth compound,AM60 B magnesium alloy was fabricated by adding rare earth Y and Gd,and also,with ultrasonic treatment during the process of melting. The mechanism was analyzed through optical microscopy（ OM）,transmission electron microscopy（ TEM） and universal testing machine. The result showed that after adding rare earth Y and Gd,the abundant rare earth compounds without ultrasonic treatment were observed in the alloy microstructure,which suppressed the dislocation movement and grain boundary sliding. By contrast,the AM60 B co-doped with Y and Gd indicated smaller grain size of α-Mg matrix and less β phase than that without Y and Gd. Additionally,the tensile strength σ_bincreased to 257 MPa,the elongation δ also reached 9%,and the intensity improved by 20%. After ultrasonic treatment,a significantly refined grain size of dendritic crystal α-Mg with isometric texture was detected,and the coarsening of β phase distributed in the grain boundary with net morphology was restrained. Also,the homogeneous distribution of rare compounds was accelerated with ultrasonic impact,which improved the tensile strength to 269 MPa and the elongation by 11%. However,this refined crystalline strengthening became invalid when the rare compounds were coarsened by excess Y and Gd,which resulted in a weakening of mechanical properties even with ultrasonic treatment.