Effects of pulse level of Nd-YAG laser on tensile properties and formability of laser weldments in automotive aluminum alloys

Tensile properties and formability are important parameters in many applications. Being a lightweight material, aluminum is increasingly employed in the fabrication of automotive body panels. This study performs butt welding without filler metal on two frequently used automotive body panel aluminum alloys, 5754-O and 6022-T4E29. Welding is conducted using a Nd-YAG laser with a rectangular wave form having various pulse levels (ΔP) but a constant mean power of 1.5 kW. For both alloys, the results indicate that the travel speed required to achieve a successful butt joint increases as ΔP decreases. For a constant pulse level, the travel speed required for the higher Mg content 5754-O alloy (2.9 wt.% Mg) is approximately 2.5 times that of the lower Mg content 6022-T4E29 alloy (0.61 wt.% Mg). Additionally, it is shown that the tensile strength, percentage elongation and formability of both alloy weldments increase with decreasing ΔP level. In the 5754-O alloy, these trends are attributed primarily to the occurrence of magnesium evaporation during the welding process, microstructure refining, and porosity reduction in the resultant welds. However, for 6022-T4E29, the evaporation of Mg is not significant, and consequently, the variation in porosity is not great. These results are caused by a lower Mg content in the base metal. Therefore, the enhancement of the mechanical properties observed in the weldments is a result of a refinement of the weld microstructure.