Microstructural Evolution and Mechanical Property Enhancement in Laser-Arc Hybrid Welded Joints of High-Strength Aluminum Alloy via Zirconium Microalloying

Abstract

In this study, different contents of zirconium were added to the laser-arc hybrid welded joint to improve the mechanical properties of high-strength aluminum alloy welds. The effects of the zirconium element on the microstructure and mechanical properties of the weld joints were analyzed. The results indicated that the grains were refined and the grain morphology was transformed from dendritic to cellular grain structures in the joint with zirconium addition. Additionally, the precipitation phase content decreased, indicating that more strengthening elements were dissolved in the α-Al matrix. The improvement in weld mechanical properties was attributed to three factors: the transformation of grain morphology, grain refinement strengthening, and solid solution strengthening. The maximum tensile strength and elongation of the welded joint with 0.4 wt.% zirconium addition reached 384 MPa and 4.2%, which were improved by 22 and 20% compared to the joint without zirconium addition (313 MPa, 3.5%). Meanwhile, the average microhardness increased from 95 to 115 HV, resulting in a 21% increase. In the fracture surface with zirconium, the cleavage planes disappeared and the depth of the dimples increased, suggesting the ductile fracture mode in the weld joint with zirconium addition. This study demonstrated a method to improve the microstructure homogeneity and mechanical properties for high-strength aluminum alloy joints and offered guidance for microstructure evolution and mechanical performance enhancement.