On the weldability, composition, and hardness of pulsed and continuous Nd:YAG laser welds in aluminum alloys 6061,5456, and 5086

Abstract

The effect of Nd:YAG laser welding aluminum alloys 6061, 5456, and 5086 was studied from a perspective of alloying element vaporization, hot cracking susceptibility, and resultant mechanical properties. Both continuous wave and pulsed Nd.YAG laser welds were investigated. It was found that Mg was vaporized during welding, the extent of which was a function of the weld travel speed. Calculations based upon evaporation theory, and assuming a regular solution model, resulted in an estimation of weld pool surface temperatures from 1080 to 1970 K for the continuous wave welds. Pulsed Nd:YAG laser welds were observed to be extremely susceptible to weld metal hot cracking whereas continuous wave Nd:YAG laser welds were crack-free. The hardness of 6061 welds was affected by the Mg vaporization such that base metal strengths could not be achieved by subsequent re-heat treatment to the T6 condition. This loss in hardness was attributed to a reduced ability of the alloy to precipitation harden due to a lower Mg concentration. In the cases of 5456 and 5086, when samples containing welds were processed to the O condition, the weld metal had reduced hardness relative to the base metal. This loss of hardness was also attributed to the loss of Mg in these welds, resulting in reduced solid solution strengthening.