Property enhancement in 6D10 aluminum alloy welds: A comparative study of CMT+P and oscillating laser welding techniques with novel Al-Si-Cu-Mg-Zn filler wire

Abstract

To solve the issue of weld softening encountered when welding high-strength aluminum alloy with conventional commercial welding wires, this study uses two welding techniques, Cold Metal Transfer Plus Pulse (CMT+P) and Oscillating Laser Welding with Filler Wire (OLWFW), to weld 6D10 aluminum alloy with a novel Al-Si-Cu-Mg-Zn wire. The porosity, microstructure, and mechanical properties of the welded joints are compared. Results show that minimum porosity is 0.42 % in the CMT+P process and 0.11 % in the OLWFW process. Metallurgical pores mainly affect yield strength and ultimate tensile strength, with less impact on elongation. CMT+P produces β'' and θ' strengthening phases (lower number density, larger size) in the weld seam when using Al-Si-Cu-Mg-Zn filler wire, while OLWFW (higher cooling rate) produces finer cellular sub-structures and higher density of smaller β''+ θ'+Q′ strengthening phases. Mechanical properties show that CMT+P joints have 284.5 MPa ultimate tensile strength in the weld seam and 252.5 MPa in the heat-affected zone, which increase to 311.5 MPa and 301.5 MPa respectively with OLWFW. Strengthening mechanisms quantified via dislocation shearing and Orowan mechanisms indicate that OLWFW exhibits greater precipitation strengthening than CMT+P, explaining the strength difference. This study discovered that filling with Al-Si-Cu-Mg-Zn welding wire can precipitate a significant amount of strengthening phase in the weld seam without post-weld heat treatment, especially when using the OLWFW welding technique with a higher cooling rate. This provides a new strategy for welding high-strength aluminum alloys: using novel multi-alloyed filler wires and high-cooling-rate welding techniques can improve both the strength of the weld seam and the welding coefficient, facilitating the broader application of high-strength aluminum alloys in vehicle manufacturing.