Beam scanning effect on properties optimization of thick-plate 2A12 aluminum alloy electron-beam welding joints

Electron-beam welding (EBW) of a 25-mm-thick 2A12 aluminum alloy was performed. Obvious concave defect was detected at the upper surface of welded joint. The grains in weld were coarse, which reduced the strength of the joint via conventional EBW (CEBW). The tensile strength of the joint was 292 MPa, which reached 64% of the tensile strength of the base metal. Therefore, beam scanning was conducted during the EBW. With the addition of beam scanning, the dendrites near the fusion line were broken, the grains were refined, and the strength was enhanced. Additionally, the welding process tended to be stable, and the formation of the weld joint was improved. The eutectic at the grain boundaries reduced the strength of the joint. There was no obvious preferential growth orientation in the fusion zone (FZ) during crystallization, and the distribution of the grain was more uniform. The number of small-angle grain boundaries increased, which was conducive to the precipitation of the secondary phase. Compared with the case of CEBW, the width of the FZ increased from 2 to 4 mm, and the microhardness was basically unchanged. The average tensile strength of the joint increased by 31.2%, to 383 MPa. Moreover, the fatigue strength of the joints satisfied the engineering requirements.