Effect of welding wires on root bend property of MIG-welded 7N01-T4 aluminium alloy joints

Suitable welding wire is a key factor affecting the quality of 7N01 aluminium alloy welded joints for high-speed trains. The effect of ER5356 and ER5087 welding wires on microstructures and the root bend property of 7N01-T4 aluminium alloy by metal-inert gas (MIG) welding was investigated. Two weld zones were mainly characterized by as-cast structures. There were mainly equiaxed crystals in the microstructure of the bottom layer and cover layer of ER5356 and ER5087 welded joints. While the weld center of the middle layer was mainly columnar crystals. ER5087 welded joint had a smaller grain size than the ER5356 weld joint. The root bend test showed that ER5087 welded joint was cracked at a bend angle of about 120 degrees, and the ER5356 welded joint was cracked at a bend angle of about 150 degrees, indicating that ER5087 welded joint had better-bending performance than ER5356 welded joint. The cracks were generated in the fusion zone (FZ) and weld zone (WZ) of the bottom layer in the ER5356 and ER5087 welded joint, respectively. The weld grains of the bottom layer were elongated, and the grains of the cover layer was extruded. ER5356 welded joint had no fine grain zone between the bottom and middle layers while ER5087 welded joint had a small number of fine grains due to the less recrystallization degree.