Mechanisms of transverse hot crack formation during laser welding of high-strength aluminum alloys at high welding speeds

• Fundamental experimental and numerical investigation of transverse hot cracking in laser welding of a 6000-series aluminium alloy as a basis for optimization strategies. • Analysis of the effects of local temperature gradients, solidification rates, and the static pressure distribution in the melt pool on the formation of transverse hot cracks at different welding speeds. • Identification of a significant drop in static pressure at the side of the melt pool at high welding speeds as a key mechanism impairing liquid feeding into the intergranular region and promoting transverse hot cracking. • Metallographic analysis revealed that higher welding speeds promote increased formation of transverse hot cracks in the weld seams. High-strength aluminum alloys provide favorable material properties for components in modern battery systems, such as battery trays used in electromobility applications. However, laser welding of high-strength aluminum alloys at high welding speeds may result in the formation of transverse hot cracks in the weld seam, potentially causing component failure due to leakage. To determine strategies to avoid transverse hot cracks, the influence of the welding speed during full-penetration laser welding is analyzed both experimentally and theoretically using numerical simulations of the temperature field and the fluid flow. A metallographic analysis of the welded samples showed an increase in the number of transverse hot cracks with increasing welding speeds. The results revealed that a major mechanism for the formation of transverse hot cracks at high welding speeds is a significant reduction of the static pressure at the side of the melt pool, which impairs liquid feeding into the intergranular region. These findings provide fundamental knowledge for the development of optimization strategies to reduce the formation of transverse hot cracks at high welding speeds.