Grain refining and mechanical properties of AZ31 alloy processed by accumulated extrusion bonding

In order to improve the strength and ductility of AZ31 magnesium alloy thin sheet with thickness of 1.5 mm, an accumulated extrusion bonding (AEB) process was conducted for 1 and 2 passes at 473 K. Microstructure evolution and mechanical properties were subsequently investigated. The results showed that the interface bonded successfully with a good bonding quality due to the large strain induced by AEB process. {10-12} tensile twinning dominated the deformation at the initial stage of extrusion. As the strain increasing, dynamic recrystallization (DRX) occurred and dominated the further deformation. A fully DRXed microstructure was observed in the sizing band and the average grain size was significantly reduced to ∼1.4 μm. Grain growth occurred after the extruded sheet exited from extrusion die. AZ31 alloy sheet after by 1 pass AEB process exhibited a double-peak texture with the basal poles inclined from normal direction (ND) towards extrusion direction (ED) and showed a similar texture intensity to as-received sample. Due to the grain refinement strengthening, the AEB processed sample exhibited better comprehensive mechanical properties with a higher yield strength (169 MPa vs. 145 MPa), ultimate tensile strength (336 MPa vs. 385 MPa) and fracture elongation (24.9% vs. 28.0%) at room temperature. However, for the 2 passes extruded sample, the microstructure evolution and mechanical properties showed a similar characteristic to that of first pass sample. This indicated that increase in the number of AEB pass had no more effect on the grain refining and improving the mechanical properties.