Improvements of elevated temperature tensile strengths of Mg-Gd-Y-Zr alloy through squeeze cast

Abstract

The present paper has reported a comparative study on the influence of environmental temperature on the microstructural evolution and tensile mechanical behaviors between squeeze cast (SC) and gravity cast (GC) Mg-10Gd-3Y-0.5Zr (GW103K) alloys. The results revealed that for both alloys, the operative deformation mechanisms at testing temperatures (25–300 °C) were identified to be 〈10−12〉 extension twinning, 〈10−11〉 compressive twinning and 〈10−13〉 compressive twinning in addition to basal or non-basal slips. The elongation increased monotonically with increasing temperature within the range of 25 °C to 300 °C. However, the ultimate tensile strength (UTS) abnormally increased (for GC alloys) or keep constant (for SC alloys) with increasing the temperature from 25 °C to 250 °C, and decreased with further increasing the testing temperature to 300 °C. Moreover, at all testing temperature, both the UTS and elongation of the squeeze cast material were improved relative to those of the gravity cast alloy. The underlying mechanism for the abnormal increase of strength within certain elevated temperature range was attributed to the insufficient strain hardening at lower temperatures that restrict further plastic deformation and lead to pre-mature fracture, and sufficient plastic deformation and softening at higher temperatures promote plastic deformation. The strengths improvements in squeeze cast GW103K alloy can be mainly ascribed to the preventing or limiting of crack nucleation sites and hindering of crack propagations through the reduction of micropores and increasing the amount of grain boundaries.