Characterization of a novel 14H-LPSO structure and related elevated-temperature mechanical behaviors in an extruded Mg–Y–Zn–Cu alloy

Abstract

A Mg-2.1Y-0.5Zn-0.6Cu-0.1Zr (WZC200, in at. %) alloy was developed and conducted to extrusion process to refine the grains as well as LPSO structure, aiming to investigate the mechanical behaviors at ambient and elevated temperatures and their relations with microstructures. A 14H-LPSO structure with stacking sequence of ABCBCACACACBCBA, consisting of twin-related building blocks with a novel CBCA-type, was revealed in the solution-treated WZC200 alloy. Fully recrystallized microstructure with grain size of ⁓14 μm, refined LPSO structure and weaken texture were obtained through extrusion process. The tension results tested at ambient and elevated temperatures revealed ultimate tensile strength (UTS) of 317 MPa along with excellent elongation-to-failure of 26.5% at RT, moderate UTS above 275 MPa with occurrence of serrated flow in the tensile curves in the range 150–200 °C, and obviously declined UTS (⁓150 MPa) along with superplastisity of 155% at 300 °C. The observed serrated flow in the range 150–200 °C was mainly attributed to the dynamic strain ageing. The dramatic drop in UTS at 300 °C was ascribed to fragmenting of LPSO phases and probably significant activation of non-basal slips, these two factors help to coordinate deformation between LPSO and the matrix and restrain the cavity nucleation, resultantly contributing to the observed superplasticity at this temperature.