Interlayer Integrity and Mechanical Anisotropy of WAAM-Processed Al-Mg Alloys

Abstract

Wire Arc Additive Manufacturing (WAAM) has emerged as a promising technique for fabricating large-scale aluminum alloy components, owing to its high deposition efficiency, low material waste, and accessible equipment requirements. It shows particular potential for structural applications in the aerospace and transportation sectors. However, porosity formed during multi-layer deposition often induces pronounced mechanical anisotropy, undermining structural integrity. This study systematically evaluates the microstructural features, pore formation, and mechanical performance of two representative WAAM-deposited aluminum alloys: Al-5356 and Al-Mg-Sc-Zr. The Al-Mg-Sc-Zr alloy exhibited refined grains (~15 μm) and strengthening from Al₃(Sc,Zr,Ti) precipitates, but also showed severe interlayer porosity (~1%), which caused a marked reduction in vertical strength and ductility (UTS dropped by ~30%, elongation by ~75%). In contrast, the Al-5356 alloy displayed coarse grains (~95 μm), very low porosity (~0.02%), and relatively consistent properties in both orientations. These results demonstrate that, although microalloying enhances intrinsic strength, the dominant factor governing anisotropy in WAAM-fabricated aluminum alloys is the spatial distribution of interlayer porosity. The findings highlight the critical importance of optimizing interlayer fusion and gas management strategies to fully exploit WAAM for high-performance aluminum applications.