Effect of Filler Metal and Postwelding Heat Treatment on Mechanical Properties of Al-Zn-Mg Alloy Weldments

This study investigated the effect of three filler metals, namely ER5356, ER5183, and ER5556, and various postwelding heat treatments, including natural aging, artificial aging, T6 and T73, on mechanical properties of AA7005 and AA7003 alloys. Microhardness in the fusion zone, heat-affected zone, and base metal were measured. Both scanning electron microscopy and transmission electron microscopy analyses were also conducted. Results show that AA7005 and AA7003 welded with filler metal ER5356 achieved significant enhancement both in hardness and ultimate tension strength after postwelding heat treatments, indicating that ER5356 is the most suitable filler metal for welding Al-Zn-Mg alloys. While both T6 and T73 heat treatments can enhance precipitation hardening in the fusion zone, T73 yields a wider precipitation free zone on the grain boundary; thus making it a better approach to increasing fusion zone strength in weldments. In sum, appropriate choice of filler metal and heat treatment can enhance overall mechanical strength of welded alloys.