Reduction of transverse hot cracking in laser welds of aluminium sheets by residual compressive stresses induced by forming of near-surface embossings

High-speed laser welding is an efficient method for joining high-strength aluminium components for electromobility applications. However, transverse hot cracks appear in the weld seam and impair the integrity of the components. In this context, the present study proposes a method to reduce transverse hot cracking with residual compressive stress. The residual compressive stress was induced into sheet metal samples by previously forming near-surface embossings next to the weld zone. The release of residual compressive stress and its effect on the formation of transverse hot cracks during welding were investigated. Full penetration welding of 2 mm thick samples of the aluminium alloy 6014-T4 was performed with a welding speed of 18 m/min. The local strain and strain rates transverse to the welding direction were measured by means of digital image correlation, and the influence of the embossings on the geometry of the melt pool was investigated with high-speed video recordings. The results indicated a release of residual compressive stress during welding, which was associated with an increased compressive strain and strain rate. An increased compression of the melt pool favours the melt flow into the intergranular region and thus reduces hot cracking. Additionally, the embossings affected the heat flow due to the reduced cross-sectional area transverse to the welding direction. This resulted in heat accumulation in the weld zone and increased the length of the melt pool. Furthermore, longitudinal sections and X-Ray scans of the weld seams were used to quantify the formation of transverse hot cracks with different embossing configurations. Compared to the reference weld without embossings, welds with embossings exhibited fewer transverse hot cracks in the longitudinal sections, demonstrating that near-surface embossings can be used in aluminium components to reduce transverse hot cracking.