Microstructure evolution and mechanical properties of an AA6061/AZ31B alloy plate fabricated by explosive welding

Abstract

In this paper, both experimental and theoretical studies were conducted to investigate the bonding interface formation, microstructure evolution, and the interface strength of an AA6061/AZ31B alloy cladding plate fabricated by explosive welding. The evolution of microstructures including adiabatic shear bands (ASBs) structure, recrystallized grains, and elongated grains were analyzed using optical microscope (OM), electron back scatter diffraction (EBSD), and transmission electron microscope (TEM). A model was also proposed to study the ASBs formation and recrystallized grains in the ASBs. In the study, during explosive welding, a periodic wavy bonding interface was observed and the formation of such an interface was found due to the periodic jetting caused by the high impact stresses at the impact points during welding. The ASBs were found formed along the directions where the stress waves were concentrated due to high energy accumulation. Near the bonding interface, many crystallized grains were found in the AZ31B alloy plate, while elongated grains were dominant in the AA6061 alloy plate. Difference in the crystal structure of the Al and Mg alloy was believed to be the reason causing such microstructure evolution difference. Nanoindentation tests on the ASBs showed that, due to the existence of fine grains resulted from the recrystallization in the ASBs structure, the hardness of the ASBs structure (1.22 GPa) was higher than that of its surrounding structure. The shear strength of the bonding interface of the explosively-welded AA6061/AZ31B cladding plate can reach up to 201.2 MPa.