Impact behavior of dissimilar AA2024-T351/AA7075-T651 butt joints produced by Friction Stir Welding: effects of microstructure and Al2O3-SiC particles addition

Friction Stir Welding (FSW) is an innovative solid-state process well-known for the excellent microstructural and mechanical properties of the resulting permanent joints. Nowdays, dissimilar joints in aluminium alloys are widely employed for structural applications. Moreover, the addition of reinforcement particles in the joint line during the FSW process is even more a topical issue to enhance resistance and hardness. FSWed joints between AA2024-T351 and AA7075-T651 aluminium plates were performed, and process parameters were selected through a full factorial 2k design of experiments method: both the rotational and translational speed of the tool, as well as the addition of Al2O3-SiC microparticles were considered as input parameters. The AA2024-T351 and AA7075-T651 plates were positioned on the advancing side (AS) and on the retraning side (RS), respectively, without considering different offset parameters. In the present investigation the impact properties of the joints were studied by means of 10 x 5 x 55 mm un-notched samples drawn from the FSWed joints and tested through an instrumented 50 J Charpy pendulum. The total impact energy, the two complementary initiation and propagation energies as well as the peak force were calculated for each sample and correlated to the process parameters. Microstructural analyses were also performed on the samples by means of optical microscopy (OM) and scanning electron microscopy (SEM/EDS) in order to study how the typical microstructural features of the produced FSWed joints affected their impact properties. The presence of wormhole defects as well as the lack of penetration played an important role in the impact behaviour of the samples and guided the path of the propagation crack.