Mechanical and stress corrosion cracking properties of AA7019 alloy gas metal arc weldment

To study the weldability of the newly developed AA7019 aluminium alloy, both mechanical and corrosion resistant properties of its Gas Metal Arc(GMA) weldment were evaluated. GMA butt welds with A5356 filler metal were made in the flat and vertical positions of 30mm thick plates. The results of mechanical tests performed on test coupons, which were removed from the welded plates (naturally aged at least 30 days), were correlated directly with softening and subsequent recovery of the strength in the HAZ (Heat Affected Zone) whereas the strength of the weld metal was not significantly affected. The susceptibility to the corrosion and stress-corrosion cracking in an aqueous salt solution (3.5wt.% NaCl) was also evaluated in each weldment. A combination of susceptible microstructure and galvanic coupling was determined as the cause of SCC(Stress Corrosion Cracking) failure, which occurs preferentially in the HAZ adjacent to the weld bead. Results of this study suggest that development of new filler metals higher in strength and avoiding severe corrosion environment be considered for the optimum application of GMAW of AA7019 alloy. (Author)