Effect of rare Y-microalloyed Al–Mg filler materials on the microstructure and tensile properties of laser welded Al–Mg–Si alloys

Abstract

The Al–Mg filler metals containing various amounts of yttrium (Y) were obtained and used to study the effect of the Y element on the microstructure and tensile properties of laser welded Al–Mg–Si alloys. The results revealed that compared with the unmodified welded joints, 0.1 wt%Y addition cannot effectively refine the grains. However, the 0.1 wt%Y addition effectively decreased the rich-Fe phases size and transformed the bulk β-AlFeMnSi phases into the fine granular AlFeMnSiY phases. Due to the precipitation strengthening, the welded joints with 0.1 wt%Y exhibited excellent mechanical properties, the highest tensile strength and elongation increased by 53.42 MPa and 5.58 %, respectively. As the Y content further increased, a significant grain refinement was observed in the weld zone. However, due to the small growth restriction factor of Y in aluminum alloys, the degree of grain refinement was limited. When 0.3 wt% Y was added, the grain size of the weld was the smallest, which was only reduced by 7.7 μm compared to the unmodified weld and similar to the weld with 0.5 wt%Y addition. Furthermore, the increase in solidification temperature range led to the growth of the second phase, as well as an increase in the number of coarse rich-Fe and Mg2Si phases. These combined reasons prevent further improvement of tensile properties of the welded joints.