Interfacial Bonding and Fracture Behaviors of AZ63 Magnesium Alloy Sheet Processed by Accumulative Roll Bonding

In order to understand the strengthening and the failure mechanism of accumulative roll bonding (ARB)-processed AZ63 Mg alloy, the interfacial bonding and fracture behavior of an ARB-processed AZ63 sheet were studied through electron microscopic analysis. The correlation between the mechanical properties, the microstructure, and the ARB processing parameters of an AZ63 sheet were presented. The experimental results have demonstrated that the average grain size of AZ63 Mg alloy processed by ARB was remarkably refined from 12.8 μm to 5.7 μm when the ARB processing temperature was set to 623 K, indicating the occurrence and development of dynamic recrystallization (DRX) nucleation. With the increase in ARB passes, the microstructure obviously became uniform. However, after five passes of the ARB process at 623 K, grains with different crystallographic orientations at the interface can be rearranged to generate the coherent eutectic plane, which inhibits the further refinement of grain size. During the ARB process of the AZ63 Mg alloy, the grain refinement was controlled by twin-induced recrystallization and dynamic recrystallization. Microcracks at the bonded interface of the ARB(1) sample were eliminated during the following 3~5 rolling passes at 623 K. After three passes of the ARB process at 623 K, the strength and elongation of the AZ63 Mg alloy increased from 232 MPa and 18.5% to 282 MPa and 26.3%, respectively. The tensile fracture morphology of the sample processed by three passes of ARB exhibited numerous dimples, and the slip lines caused by the cooperative deformation of refined grains can produce a network-like dimple structure, indicating that excellent ductile fracture characteristics could be obtained.