Effect of subatmospheric pressures on weld formation and mechanical properties during disk laser welding of 5A06 aluminium alloy

Laser welding under subatmospheric pressures exhibits significant potential in the field of large-scale structure connections. In this study, a set of disk laser welding experiments are performed on 35-mm-thick 5A06 aluminium alloy under various ambient pressures. The influence of ambient pressures on weld formation, plasma plume behaviours, microstructures, as well as the mechanical properties is investigated. The experimental results show that the penetration depth increased sharply when welded under the ambient pressure of 10(4) Pa, while the plasma plume and porosity defects were suppressed effectively. With further decrease in ambient pressures, there was little variation in weld characteristics. The microstructure characteristics of joints produced under subatmospheric pressures exhibited more uniformity with a wider heat-affected-zone, and the joints' mechanical properties improved markedly compared with those produced under atmospheric pressure. To obtain a high weld quality, by considering the weld appearance, porosity defects as well as welding stability, the ambient pressures for the laser welding process should be limited to less than 10(2) Pa. Apart from these, with the decrease in ambient pressures, a smaller burning loss of the element Mg as well as greater low-angle grain boundaries and dislocations would be present in the weld seam. This contributes to improvements in the mechanical properties.