Experimental study of MIG welding and solid state welding for age hardenable AA 7075 aluminium alloy

ABSTRACT High strength age hardenable 7xxx series aluminium alloy such as AA 7075 is commonly found in several key components of aircraft and automobiles. These alloys are difficult to join by conventional fusion welding techniques. Realizing a weld joint in such alloys without impairing the mechanical properties is difficult task. The 7xxx alloys among the Al-Zn-Mg-Cu versions provide the highest strengths of all aluminium alloys. AA 7075-T6 aluminium alloys with thickness of 3mm were butt welded using friction stir welding and metal inert gas welding (MIG). The joints were compared in terms of electrical conductivity (% IACS), a physical property of aluminium alloy used to define relationship of changes in alloy composition and metallurgy. The same joints were also assessed for hardness and micro structural properties. The results show that the solid state FSW joints have higher electrical conductivity and hardness than MIG joints. The width of heat affected zone of FSW joints is narrower than the MIG fusion welds indicating better mechanical properties. An attempt has been made to correlate the electrical conductivity and the hardness in different weld regions, and found that electrical conductivity and hardness are non linear to each other in FSW joint, but they cannot be co-related to each other in MIG welded joint.