(华东交通大学 机电工程学院，南昌 330013)
摘 要: 采用HJ-III型超声冲击机对MB8镁合金焊接接头焊趾进行表面处理，就不同冲击工艺参数对焊接接头表层组织及力学性能进行测试。结果表明: 经过超声冲击处理后，接头焊趾及其附近区域表层组织内的原始粗晶转变为晶界清晰、随机取向的纳米晶粒；焊趾处的应力集中系数得到有效降低，表层硬度及其抗拉强度得到提高；超声冲击前后接头拉伸试样均断于焊趾，接头的拉伸断裂机制为准解理断裂。冲击电流为1.2 A、冲击时间为6 min时，与未超声冲击试样相比，MB8镁合金接头的应力集中系数降低12.04%，焊趾表层最大硬度值提高63.2%，抗拉强度提高33.2%，接头表层金属晶粒细化以及焊趾处应力集中程度的降低是提高MB8镁合金焊接接头力学性能的主要原因。
关键字: 超声冲击；焊接接头；表层组织；抗拉强度；晶粒细化
（College of Mechanical and Electrical Engineering, East China Jiaotong University, Nanchang 330013, China）
Abstract:Surface treatment was carried out on the weld toe of MB8 magnesium alloy welded joint with HJ-III type ultrasonic impact treatment equipment. The surface microstructures and mechanical properties of MB8 magnesium alloy welded joints treated by different impact parameters were investigated. The results indicate that, after ultrasonic impact treatment, the primary coarse grains in the surface layer of weld toe and adjacent area turn into randomly oriented nano-crystalline grains with explicit grain boundary. The stress concentration coefficients at weld toe reduce effectively. The surface hardness and tensile strength of joints improve. The joints before and after ultrasonic impact fracture at the weld toe with tensile failure mechanism of quasi-cleavage fracture. In the impact current of 1.2 A and impact time of 6 min, compared with untreated specimens, the stress concentration coefficients reduce by 12.04%, and the surface maximum hardness and tensile strength of treated welded joints increase by 63.2% and 33.2%, respectively. The grain refining of surface layers and the reduced stress concentration at weld toe are main factors which improve the mechanical properties of MB8 magnesium alloy welded joints.
Key words: ultrasonic impact; welded joint; surface microstructure; tensile strength; grain refining
