Enhancing the mechanical performance of Al-Zn-Mg alloy builds fabricated via underwater friction stir additive manufacturing and post-processing aging

Our previous studies have demonstrated that underwater friction stir additive manufacturing (FSAM) could effectively suppress the macroscale softening of the fabricated Al-Zn-Mg-Cu alloy build from top to bottom. However, the accompanying local softening problem, i.e., a low-hardness region at the bottom of each stir zone, becomes prominent. In this study, an Al-Zn-Mg alloy with low quench sensitivity was used to fabricate a multilayered build via underwater FSAM. In-process water cooling could effectively solve the macroscale and local softening problems in the FSAM of the Al-Zn-Mg alloy and improve the mechanical performance of the build. The microhardness and ultimate tensile strength (UTS) of the water-cooled build in as-fabricated and aged states were more uniform along the building direction and higher than those of their counterparts. After 90 days of natural aging, the UTS of the water-cooled build in building and traveling directions reached 398 and 400 MPa, respectively, slightly higher than that of the base metal (392 MPa). The enhancement in the mechanical performance of the water-cooled build was attributed to a high degree of supersaturation and age-strengthening ability because of a high cooling rate of the underwater FSAM process and low quench sensitivity of the base metal. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Previous studies have shown that underwater friction stir additive manufacturing (FSAM) can effectively suppress the macro-scale softening of fabricated alloy builds. However, the problem of local softening, specifically the low hardness region at the bottom of each stir zone, remains prominent. This study investigates the use of a low quench sensitivity Al-Zn-Mg alloy and in-process water cooling to address the macro-scale and local softening issues in FSAM, ultimately improving the mechanical performance of the build.