Microstructure and Mechanical Properties of Welded AA6082 Aluminium Alloys

Abstract

The present work have investigated variants of an AA6082 aluminium alloy. Five different alloys with various amounts of Mn, Cr and Zr have been subjected to three homogenization procedures. After homogenization, the aluminium billets were extruded into plates that were artificially aged to T6-temper. Further, the profiles were MIG welded to obtain a heat affected zone. The effect of these parameters on microstructure and mechanical properties of the various alloys in welded state have been studied. The microstructure after extrusion and welding were investigated by optical microscope and hardness measurements. In addition, subsequent heat treatments have been performed in an attempt to further increase the density of dispersoids for one specific alloy. Welding of age-hardened aluminium alloys change the microstructural hardening phase that can be a challenge for the mechanical properties in the heat affected zone (HAZ) and lead to a reduction of the yield strength. The strength of the ageing effect is crucial for the load-bearing capacity of welded structure. The degree of work hardening in the HAZ is important to achieve the same yield strength level as the base material. Introduction of dispersoids in the alloys can affect the microstructure and strength of the aluminium alloys, and in the present work, an attempt to increase the strength by the introduction of dispersoids is carried out. Results from this study show that chemical composition, homogenization procedure, artificial ageing and welding influence the grain structure and mechanical properties of these AA6082-alloys. Density of dispersoids increases with increasing amount of Mn, Cr and Zr, low homogenization temperature and short holding time. Dispersoids retard recrystallization effectively after extrusion and welding. A typical welding profile were obtained for all of the tested alloys and the different levels of dispersoids formed during this work have not improved the welding properties significantly.