AZ61B镁合金搅拌摩擦搭接焊接头断裂特征分析

Fracture Characteristics Analysis for FSW Overlap Joint of AZ61B Alloy

采用搅拌摩擦焊对2 mm厚的AZ61B镁合金进行了搭接试验,通过剪切拉伸实验对断口处的显微组织进行观察,研究了焊接接头的断裂部位特征及断裂机理。结果表明,搭接接头的断裂部位在热机影响区,断裂起源于钩状缺陷。当搭接形式为上板置于前进侧时,接头断裂形式为45°剪切断裂,表现为韧脆混合断裂,其接头强度较高;当搭接形式为上板置于后退侧时,接头断裂形式为V型断裂,表现为韧性断裂,其接头强度相对较低。接头钩状缺陷、接头厚度方向受热梯度及热机影响区的晶粒定向拉长是影响接头断裂特征及力学性能的主要因素。

The friction stir welding for lap joints of AZ61B alloy with 2 mm thickness was investigated. The microstructure of fracture was observed after lap shear test, and the fracture characteristics and fracture mechanism of the welded joints were studied. The results show that： the fracture location occurs at the heat affected zone, and the fracture with preferential crack initiates from the source of hook defect. The overlap joints that the top sheet is arranged on the advancing side which exhibited a 45° fracture, performed for the mixed ductile brittle fracture, and the strength of the welded joints is higher. While, the overlap joints that top sheet is arranged on retreating side which exhibite V fracture, performed for ductile fracture. The strength of the joints is relatively lower. The main factors for hooking defect, joint thickness gradient and the grain orientation elongated in thermomechanically affected zone can influence the characteristics of fracture and the mechanical properties of overlap joint.