Effect of cross rolling on the microstructure and mechanical performance of a dual-phase structured Mg-8Li-6Zn-1Y (in wt.%) alloy

Abstract

The microstructure and mechanical performance of the unidirectionally and cross-directionally rolled Mg-8Li-6Zn-1Y (in wt.%) sheets have been investigated and compared. It reveals that after the unidirectional rolling (UR), the broken I-phase particles are aggregated at the α-Mg/β-Li phase interfaces. However, the cross-rolling (CR) process can not only severely break the bulk I-phase, but also cause the obviously uniform distribution of I-phase particles in the matrix phases. Moreover, the average grain size of the CR samples is 3.61 μm and about 50% that of the UR samples. The maximum texture intensities of α-Mg and β-Li phases in the CR samples are slightly stronger than those in the UR samples. Tensile results demonstrate that the CR process can effectively enhance the tensile properties and remarkably reduce the mechanical anisotropy of the alloy. For the UR samples, the yield strength, ultimate tensile strength, and elongation ratio along the rolling direction (RD) are 164 MPa, 198 MPa, and 16.4%, whereas those along the transverse direction (TD) are 157 MPa, 185 MPa, and 22.0%, respectively. For the CR samples, their mechanical properties are basically the same and the mechanical anisotropy is almost eliminated. The yield strength, ultimate tensile strength, and elongation ratio along the cross-rolling direction 1 (CRD1) and 2 (CRD2) are respectively measured to be 181 MPa and 182 MPa, 220 MPa and 218 MPa, 20.6% and 20.7%. Failure analysis indicates that for the UR samples being tensile tested along the RD and TD, micro-cracks are preferentially initiated in the region of aggregated I-phase particles. For the CR samples being tensile tested along both two cross-rolling directions, the initiation of micro-cracks mainly occurs at the I-phase/matrix phase interfaces and in the interior of matrix phases.