Microstructures and mechanical properties of AZ61 magnesium alloy after isothermal multidirectional forging with increasing strain rate

In this work, AZ61 magnesium alloy was processed using a new strategy for multidirectional forging (MDF) with an increased strain rate to obtain homogeneous and fine microstructures. The effect of the MDF process on the microstructure and mechanical properties of the alloy was investigated. It was revealed that the grain size decreases, and the homogeneity of the microstructure simultaneously increases, with the number of MDF passes. After four MDF passes, a homogeneous and fine microstructure with the average grain size of similar to 6.1 mu m was achieved. Additionally, dynamic precipitation of the Mg17Al12 phase occurred during the fifth MDF processing pass. The mechanical properties of the AZ61 alloy increased gradually as the number of passes increased from one to four passes, and the sample undergoing MDF exhibited an excellent combination of mechanical properties after the fourth pass, including the yield strength, ultimate strength and elongation to failure, which reached 241 MPa, 303 MPa and 13%, respectively. These values are 97%, 66% and 189% higher, respectively, than for the sample that did not undergo MDF. After the fifth MDF processing pass, the mechanical properties of the alloy decrease sharply, which may be attributed to the dynamic precipitation of the Mg17Al12 phase during this pass. (C) 2015 Elsevier B.V. All rights reserved.