Enhancing microhardness and tensile strength of in-process cooled Al-7075-T651 FSAM laminates without compromising ductility through PWHT

Abstract

Friction Stir Additive Manufacturing (FSAM) is a promising technique for developing large, irregularly shaped components from non-fusionable aluminum alloys, such as Al-7075, while avoiding solidification defects. Studies on melting-based AM of Al-7075 have shown poor mechanical properties, whereas FSAM has demonstrated comparatively better mechanical properties, though with non-homogeneous properties. Furthermore, conventional post-welding heat treatment (PWHT) has been found to enhance microhardness and strength but significantly reduces ductility. This study addresses these challenges by employing in-process cooling FSAM and cyclic solution PWHT. Seven-layered Al-7075-T651 laminates were manufactured through FSAM, achieving a homogeneous microstructure and mechanical properties using the in-process cooling approach. The cyclic solution treatment resulted in a 38.3 % increase in hardness and a 17.17 % improvement in UTS compared to the as-welded state, without compromising ductility.