Influence of pulse energy density in micro laser weld of crack sensitive Al alloy sheets

The demand for micro-joining of aluminium (Al) alloy thin sheets has increased for electronics and energy industry. Micro laser welding is preferred over other conventional joining techniques, such as resistance spot welding and soldering due to the advantages of high precision, design flexibility and throughput. Nonetheless, this process could be associated with lack of fusion, formation of weld defects, serious weld distortion and poor weld strength. Laser welding of Al alloy has been known to form solidification cracks. This study aims to investigate the role of process parameters on the crack formation of Al alloy. A pulse wave Nd:YAG laser source was used for laser spot welding of 250 mu m thick Al alloy sheets. Process parameters namely pulse duration and peak power were varied and the weld quality obtained was investigated. Weld quality in terms of weld geometry, weld microstructure, formation of weld defect, shear strength of welds, fracture mechanism of welds and micro-segregation in welds were systematically investigated. Results obtained were indicative that formation of crack is strongly determined by the level of pulse energy applied in welding and the degree of micro-segregation developing within welds. Fracture analysis of the welds reveals that the penetration depth of welds as well as the direction of pull force applied during the shear strength tests affects the fracture mechanism. In summary, defect free welds were achieved by micro laser welding process in this study.