Experimental study on hardness property improved by PWHT of AA-7075-T6 welded by FSW process

Abstract

Heat treatment can sensibly change the properties and microstructure of the material. Nevertheless, few studies have addressed the effect of postweld heat treatment (PWHT) on the mechanical properties and microstructure change of the friction stir welded joints of AA7075-T6. The purpose of this study is to investigate the effect of several post-weld heat treatments. Using different solution heat treatment, followed by quenching in ambient water and different ageing treatment for a different ageing time to improve the mechanical properties of 3 mm aluminium alloy 7075-T6 plate welded by FSW processes. Hardness profile is obtained across the weld using destructive test 'Vickers's hardness test' for both as-welded and post-weld heat treatment. Microstructure is characterised by the optical microscope to compare both treated and non-treated welded plate. The experimental results prove that friction stir welding process resulted in a loss of hardness and change in microstructure on the joined zone, dependent mostly on welding parameters including: tool shape, rotation speed, velocity or travel speed and tool tilt. The post-weld heat treatments lead to a significant change of microstructure in the joint area and provide a remedy for the loss of hardness of the welded bead.