Achievement of fine-grained bimodal microstructures and superior mechanical properties in a multi-axially forged GWZ magnesium alloy containing LPSO structures

The effect of multiaxial forging on the microstructure and subsequent mechanical properties of Mg-8.1Gd-4.3Y-1.6Zn-0.4Zr (wt.%) alloy (GWZ) have been carefully examined at the isothermal temperature of 400 degrees C. A fine-grained and bimodal microstructure with an average grain size of 1 mu m developed after only one pass. It is observed that the blocky LPSO phases act as the particle stimulated nucleation mechanism. This leads to the development of a bimodal microstructure. It was also demonstrated that continuous dynamic recrystallization was one of the main grain refinement mechanisms. Furthermore, the transformation of blocky LPSO phases to lamellar ones in the third pass profoundly affected the subsequent mechanical properties. The presence of the lamellar phase not only increased the hardness of the processed microstructure through kinking, but also it was directly responsible for the achievement of the high hardness value around 120-170 HV. The superior mechanical properties of the processed materials, excellent ultimate tensile strength and ductility of 581 MPa and 15.9% respectively, were attributed to the ultra-fine grain microstructure with a high volume fraction of both blocky and lamellar LPSO phases. (C) 2019 Elsevier B.V. All rights reserved.