采用单面两道焊方式对8 mm厚G20Mn5铸钢板进行熔化极活性气体保护电弧（MAG）对接焊，研究了接头的显微组织、硬度、拉伸性能、疲劳性能。结果表明：接头表面成形良好，无明显的焊接缺陷；接头由母材、热影响区、焊缝组成，其中热影响区可分为不完全正火区、正火区和过热区；由母材到焊缝中心，接头硬度整体呈先升高后降低的趋势，熔合处的硬度最高，达到70 HRB左右，焊缝的硬度为55~60 HRB，略高于母材的；接头的抗拉强度明显高于母材的，而断后伸长率低于母材的；接头的高周疲劳强度与母材的相当，且断裂位置均位于热影响区。该接头的性能满足设计要求。

G20Mn5 cast steel plates with thickness of 8 mm were connected by metal active gas (MAG) arc butt welding with one-side two-pass welding method. The microstructure, hardness, tensile property and fatigue property of the joint were studied. The results show that the joint had the good surface and no obvious welding defects were found. The joint consisted of base metal, heat affected zone and weld zone, and the heat affected zone was subdivided into incomplete normalized zone, normalized zone and overheated zone. From the base metal to the weld center, the hardness of the joint increased first and then decreased. The fusion zone had the highest hardness of about 70 HRB, and the hardness of the weld was 55-60 HRB, which was a little higher than that of the base metal. The tensile strength of the joint was obviously higher than that of the base metal, while the percentage elongation after fracture was lower than that of the base metal. The high cycle fatigue strength of the joint was equivalent to that of the base metal, and both fractured at heat affected zone. The properties of the joint met the design requirements.