Effects of I- and W-Phases Under Identical Conditions on Microstructure and Mechanical Properties of As-Cast Mg–Zn–Y Alloys at Room and Elevated Temperatures

Three alloys (Mg–6Zn–1.2Y, Alloy I; Mg–3.65Zn–1.65Y, Alloy II; and Mg–4.3Zn–1.4Y, Alloy III) with same volume fraction and grain size were designed to evaluate the effects of the I-phase (Mg₃Zn₆Y) and W-phase (Mg₃Zn₃Y₂), which are the major phases in Mg–Zn–Y alloys, on the mechanical properties. The tensile strength of Alloy I with the I-phase at room temperature was the highest among the tested alloys because the coherent interface between the I-phase and the α-Mg phase was more resistant to cracking than the incoherent interface between the W-phase and the α-Mg phase. A cross-sectional microstructure analysis of a sample that was tensile-tested at 423 K revealed that the morphology of the I-phase remained relatively stable. In contrast, the W-phase was broken and fragmented during the tensile test at 423 K because it had higher brittleness under the test conditions. Therefore, the tensile and creep properties of Alloy I at 423 K were better than those of Alloys II and III containing the W-phase. According to the results, the I-phase in the Mg-Zn-Y alloy was more beneficial to the mechanical properties at room temperature and 423 K than the W-phase. Graphic Abstract: [Figure not available: see fulltext.].