The suppression of solidification cracking of Al welds by regulating Zn/Mg ratio

Abstract

7xxx series aluminum alloys are susceptible to solidification cracking during fusion welding. This study systematically investigates the solidification cracking susceptibility of T-Mg32(AlZn)49-strengthened Cu-free Al-Mg-Zn alloy with a Zn/Mg ratio below 1.0. The alloy is different from η-MgZn2-strengthened 7xxx series alloys whose Zn/Mg ratios are above 1.0. The crack length of the studied Al-Mg-Zn series alloys is shorter than traditional Cu-free 7xxx series alloys, which corresponds to lower solidification cracking tendency. Welding cracks tend to grow along the continuous eutectic phases during the end of welding solidification, and thus, cracks occur when liquid can no longer hold the constraining stress. According to the results, Al-Mg-Zn series alloys have the narrower eutectic temperature range and narrower mushy zone than 7xxx series alloys. Thus, the constraining stress during solidification is lower than 7xxx series alloys. The liquid fractions of the Al-Mg-Zn series alloys are relatively high than 7xxx series alloys, making it possible to heal micro-cracks during the end of solidification process.