Abstract: New Al-Mg-Mn-Er alloy sheets were welded by TIG welding with filler wires. The microstructure and mechanical properties of the joints were studied. The results show that the center of the weld seam is mainly composed of equiaxed crystals. There is no typical epitaxial solidification appeared, but a fine-grained zone with width of 100 μm is formed near the fusion line. The recrystallized structure is appeared in the heat affected zone. The precipitates in the weld zone mainly exist in the form of primary Al₃Er. Compared with the base metal, the size of primary Al₃Er in the weld seam is smaller and its distribution is more uniform. The number of secondary Al₃Er in the weld seam is relatively small and the secondary Al₃Er is from the base metal. The microhardness of the weld zone and the heat affected zone are lower than that of base metal, and the microhardness of the weld zone is the lowest. With the increase of the welding heat input, the tensile strength of the joints increases first and then decreases. When the welding heat input is 218 J/mm, the tensile strength of the joint is the highest which is 71.4% of that of the base metal. The fracture of all tensile samples is located at the weld zone, and the fracture morphology shows the typical ductile fracture characteristics.