Effect of laser welding on the structure and mechanical properties of hot-rolled Al – Zn – Mg – Ca alloy sheets

Abstract

Recent years have seen an ever growing interest in hybrid forming technology, with a special focus on aluminium alloys, which conform with the strategy of reduced weight of parts while maintaining high strength. The problem of combining parts made of such materials into a single assembly unit is of relevance today, alongside the development of new high-tech aluminium alloys. This paper examines the applicability of laser welding for butt joining thin hot-rolled sheets of aluminium alloy Al – 5 Zn – 1.3 Mg – 1 Ca (Fe, Mn, Cu, Si) (wt. %). An unhomogenized ingot of the experimental alloy was hot-rolled at the temperature of 450 oC down to the thickness of 2 mm (reduction degree of 90%). Two sheets were joined together on a robot laser welding machine in an optimum mode, which ensures a visual quality of the seam with minimum porosity of the weld. Laser power — 2,400 W, laser beam speed — 10 m/sec, focal distance — 217 mm, shielding gas consumption rate — 15 L/min. A study of microstructure and physical and mechanical properties helped evaluate the effect of the selected welding parameters on weld seam formation. It was found that the laser processing helps form a high-quality weld joint with no cracks and with low porosity. The strength of such weld is at the following level: σв = 240 MPa, σ0,2 = 170 MPa, with the elongation of δ = 3%. The ultimate strength of the weld joint is 83 % and the yield point is 92.5% of the strength of the base metal. The obtained results suggest that laser welding can potentially be applicable to joining sheets made of experimental Al – 5 Zn – 1.3 Mg – 1 Ca (Fe, Mn, Cu, Si) (wt. %) alloys, which differ from 7ххх series alloys due to the presence of calcium-containing eutectic that ensures high crack resistance and good casting and welding processability. Support for this research was provided under Grant No. 22-19-00121 by the Russian Science Foundation, https://rscf.ru/project/22-19-00121/.