采用交流钨极氩弧焊在不同焊接热输入下对2 mm厚的热轧态AZ31镁合金薄板进行对接焊试验，采用显微镜、硬度仪及拉伸试验机等对焊接接头的显微组织与力学性能进行了研究。结果表明：焊接接头母材区的组织为单相α-Mg固溶体，热影响区和焊缝区的组织为α-Mg单相固溶体和弥散分布的β-Mg₁₇Al₁₂相；随着焊接热输入增大，焊缝区的晶粒变大，β-Mg₁₇Al₁₂相增多；焊缝区的显微硬度最高，母材区的次之，热影响区的最低；随着焊接热输入增大，焊接接头的抗拉强度先增大后减小，并在90 A时达到最大，为223 MPa，可达到母材的89.2%，此时的伸长率为10.0%；拉伸断裂位置主要出现在热影响区，断裂方式为准解理断裂。

Butt welding test was carried out on hot-rolled AZ31 magnesium alloy sheets with thickness of 2 mm by TIG (tungsten inert gas) welding at different welding heat inputs. Microstructure and mechanical properties of welded joints were analyzed by using microscope, micro-hardness tester, tensile testing machine and so on. The results show that the microstructure of the base metal is single-phase α-Mg solid solution, and the microstructures of heat affected zone and weld zone are all single-phase α-Mg solid solution and dispersively distributed β-Mg₁₇Al₁₂. With the increase of the heat input, the grain size in weld zone grows and the amount of β-Mg₁₇Al₁₂ increases. The micro-hardness from large to small is weld zone, base metal zone and the heat affected zone. The tensile strength of welded joints increases firstly, and then decreases with the increase of the heat input. The welded joints owned the best tensile strength of 223 MPa at welding current of 90 A, the value was about 89.2% of the base metal, meanwhile, the elongation was 10.0%.It is founded that the fracture mainly occurres in HAZ and the fracture mode is quasi-cleavage fracture.