Liquation Cracking Tendency of Novel Al-Mg-Zn Alloys with a Zn/Mg Ratio below 1.0 during Fusion Welding

The main obstacle for the application of high strength 7××× series aluminum alloys is that these alloys are susceptible to hot cracking during fusion welding. This study presents the liquation cracking susceptibility of the novel T-Mg32(AlZn)49 phase strengthened Al-Mg-Zn alloy with a Zn/Mg ratio below 1.0 by a circular-patch welding test, and compared the liquation cracking tendency with η-MgZn2 phase strengthened 7××× series alloys whose Zn/Mg ratios are above 1.0. It was found that all these novel Al-Mg-Zn alloys still have as low a liquation cracking susceptibility as traditional 5××× series alloys, surpassing that of traditional 7××× series alloys substantially. It was noticed that the increase of the Zn/Mg ratio will result in a larger difference between the fraction solids of the fusion zone and the partially melted zone during the terminal solidification stage, which can lead to a wider crack healing disparity between these two areas and thus result in different liquation cracking susceptibilities in different alloys.

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