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

Abstract

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.

Effects of Fe, Si, Cu, and TiB2 Grain Refiner Amounts on the Hot Tearing Susceptibility of 5083, 6061, and 7075 Aluminum Ingots

“…[33,37] and systematic investigations in this study, the mechanisms contributing to hot tearing in Al 3 Mg 2 and T-Mg 32 (Al,Zn) 49 are different. Al 3 Mg 2 can cause stress concentration and continuous cracking along the interdendritic channel, whereas T-Mg 32 (Al,Zn) 49 leads to reduced interdendritic liquid feeding capability [33]. √ " mark means visible, and their contribution to HTS.…”

“…Because the Zn content of the alloy was approximately 0 wt.%, much lower than the 0.68-0.70 wt.% required for T-Mg32(Al,Zn)49 to form both grain boundaries and within grains [28], T-Mg32(Al,Zn)49 predominantly formed at gr boundaries, and such formation impeded liquid flow, which has also been observed ref. [33]. Consequently, the feeding capability of 5C was low, leading to a high HTS val By comparing the microstructural and HTS differences between 5b and 5C, the effects Al3Mg2 and T-Mg32(Al,Zn)49 on hot tearing could be understood.…”

Hot Deformation Behavior and Processing Maps of an As-Cast Al-5Mg-3Zn-1Cu (wt%) Alloy

“…Additionally, research has shown that these alloys have a good adaptability to casting, plastic deformation, and additive manufacturing [8,16,17], and have a satisfactory weldability [18]. These excellent characteristics indicate that Al-Mg-Zn-Cu alloys with low Zn/Mg ratios have promising application prospects in the automotive industry [6,7].…”