中文摘要：

对AZ31B 镁合金焊接接头和热影响区的疲劳裂纹扩展行为进行研究,分析了焊接接头[L-T（W）]和热影响区的紧凑拉伸试验[C（T）],其中热影响区的C（T）试验包括焊缝平行于挤压方向[T-L（H）] 和垂直于挤压方向 [L-T（H）]两种。结果表明：对于L-T（W） 试样,裂纹沿挤压方向扩展,裂纹扩展经历先快后慢的扩展过程;T-L（H） 试样裂纹平行于缺口方向扩展,L-T（H）试样裂纹为平行于缺口方向和与缺口成一定角度两种扩展方向,裂纹扩展经历先慢后快的扩展过程。裂纹尖端扩展为穿晶和沿晶的混合模式,疲劳断口为准解理特征的脆性断口。

英文摘要：

The fatigue crack propagation behavior of as-extruded AZ31B magnesium alloy welded joint and heat affected zone have been studied. Compact tensions [C（T）] of welded joint [L-T（W）] and heat affected zone（welded joint is parallel [T-L（H）] and vertical [L-T（H）] to the extruded direction） were researched. Results indicate that the crack propagation direction is parallel to the extrusion direction for L-T（W）; fatigue crack propagation rate is a rapid-slow process. T-L（H） is parallel to the notch direction and L-T（H） can be divided into two states （i.e., parallel to or angularly deflected towards the notch direction）; crack propagation rate initially goes through a rapid course before it slows down. The fracture modes of crack tip remain a mixed-mode of transgranular and intergranular fractures. The fatigue fracture consists of quasi-cleavage and is a brittle fracture.