Improvement of Weld Solidification Crack Susceptibility of Al-Zn-Mg Ternary Alloy by Low Frequency Pulsed GMA Welding with Zr Added Al-High Mg Welding Wire

Abstract

Solidification crack susceptibility of GMA weld metal of Al-4.5%Zn-1.2%Mg A7N01 base metal has been successfully improved by combination of low frequency switching pulsed GMAW process and Zr added Al-7%Mg tentative wire. Close relationship between grain size of weld metal and crack susceptibility was observed and remarkable reduction in crack susceptibility was obtained in weld metal with fine equiaxed grains of 20 to 30 μm in diameter. This marked grain refinement can be obtained only by the combination of low frequency switching pulsed GMAW of 2.5 to 50 Hz and Zr added Al-7%Mg tentative wire. No considerable grain refinement was observed with Zr-free wire. Relationship between oscillation behavior of molten pool caused by current pulsation and grain refinement was discussed.