Abstract: 2024 aluminium alloy was welded by electron beam welding (EBW).The microstructure and mechanical properties of welded joints were investigated.The results show that the microstructure of the weld zone was fine equiaxed grains,which mainly consisted of α-Al matrix phase and a few θ(CuAl2)and S(Al2CuMg)strengthening phases,while the heat-affected zone (HAZ)was composed of coarse dendrite.The tensile strength of the welded joint was about 80% of that of the base metal,and the HAZ was the weakest area of the joint.Microhardness of the weld metal was lower than that of both the base metal and HAZ,and a softening area existed in the HAZ.The joint tensile fracture present typical dimple fracture,while the dimples were fine and distributed uniformly.