This study aimed to conduct a comparative study on the microstructure and mechanical performance of 5083, 6005A and 7N01 Al joints used in China Railway High-speed (CRH) trains. We connected 10 mm-thick plates by three-layer and three-pass gas metal arc welding (GMAW). The results indicated that 6005A and 7N01 Al joints were more sensitive to grain boundary liquation in the partially melted zone (PMZ) than 5083 Al joins. Besides, recrystallization was obtained in heat-affected zones (HAZ). The 5083 Al joints experienced the most severe recrystallization and the grain size changed from 6.32 (BM) to 32.44 (HAZ) μm duo to intracrystalline strain induced by cold-rolled processes. The 7N01 Al alloys experienced the lowest extent of recrystallization and the grain size increased from 5.32 (BM) to 22.31 (HAZ) μm. Furthermore, significant precipitate evolution in the HAZ was observed. Original thin β” precipitates dissolved in HAZ of 6005A Al joints and transformed to the softer β phase. However, less precipitation transition was examined in 5083 and 7N01 Al joints. The precipitates’ evolution produced a softening region in HAZ of 6005A joints where the hardness was only 55 HV. The microhardness profile of the other two Al joints was less affected. The tensile strength of 5083, 6005A, and 7N01 Al alloy joints reached 323, 206 and 361 MPa, respectively. The 5083 Al and 6005A Al joints failed at HAZ near the fusion line while 7N01 Al joints failed at the fusion zone owing to the high strength of the base metal. The liquation, coarse grains by recrystallization, and precipitate evolution all decreased local strength, resulting in the fracture at HAZ.

Pore defects are one of the most common defects in the aluminum alloy electron beam welding process. In this paper, research on the pore defects and related mechanisms of the electron beam welding of dissimilar aluminum alloys was carried out with 1060 and 2A12 aluminum alloys. Under the test conditions, the pore defects of the aluminum alloy joint were related to the penetration status, the porosity of the critically penetrated joint was low, and the porosity of the beam joint increased when it was slightly penetrated. When the welding speed changed from 300 mm/min to 1200 mm/min, the porosity in the critically penetrated joint first increased and then decreased. When the welding speed was set to 300 mm/min and the beam current was set to 26 mA, the porosity of the joints reached its minimum value at 0.23%. Based on the actual process of electron beam welding, a flow simulation model was established to study the aluminum alloy welding process. The stability of the keyhole was related to the electron beam energy density reaching the inner keyhole, so increasing the electron beam for the fully penetrated joints was advantageous for reducing the pore defects.