Influence of Higher Zn/Y Ratio on the Microstructure and Mechanical Properties of Mg-Zn-Y-Zr Alloys
- PDF / 1,318,448 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 68 Downloads / 219 Views
INTRODUCTION
BECAUSE a new stable icosahedral phase (I-phase) was discovered in Mg-Zn-RE (RE = rare earth metal) system alloys,[1–5] the strengthening effect of the I-phase on the mechanical properties of Mg alloys at both room and elevated temperatures has been deeply researched.[6–8] Generally, quasicrystal I-phase can offer some outstanding properties, such as high hardness, high corrosion resistance, low surface energy, high thermal stability, and low friction coefficient.[9,10] It has been indicated that, depending on the volume fraction of the I-phase, Mg-Zn-Y-Zr alloys could have a yield stress ranging from 150 to 450 MPa at room temperature.[11] In addition, Xu et al. reported that, through introducing I-phase into Mg-Li alloys, the yield strength and ultimate tensile strength (UTS) could be improved to 166 and 247 MPa, respectively.[12] Therefore, I-phasestrengthened Mg materials can be considered potential candidates for many applications in the automobile and aerospace fields. At present, the strengthening effect of D.K. XU, was Ph.D. Student with Institute of Metal Research, Chinese Academy of Sciences, is currently Research Fellow with the Department of Materials Engineering, Monash University, Clayton, VIC 3800, Australia. EN-HOU HAN, Professor, is with the State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, 62 Wencui Road, Shenyang 110016, P.R. China. Contact e-mail: [email protected] L. LIU, Associate Professor, and Y.B. XU, Professor, are with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China. Manuscript submitted November 13, 2007. Article published online April 28, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
the I-phase on the mechanical properties of Mg-Zn-Y and Mg-Zn-Y-Zr system alloys has become the focus currently under study.[13–16] Based on many reports about Mg-Zn-Y and Mg-ZnY-Zr system alloys,[6,7,13,15–20] it is thought that the secondary phases mainly included icosahedral quasicrystal I-phase (Mg3Zn6Y) and cubic W-phase (Mg3Zn3Y2). In addition, the addition of Zr had no effect on the phase composition of Mg-Zn-Y-Zr alloys.[21] According to the chemical formulas of the I-phase and W-phase, the Zn/Y (in weight percent) ratios for these two phases are 4.38 and 1.10, respectively. The research done on Mg-Zn-Y-Zr system alloys indicated that, when the Zn/Y ratio was larger than 4.38 (considering that parts of the Zn dissolved in the Mg matrix), the Mg-Zn-Y phase primarily formed was the I-phase.[16] When the Zn/Y ratio was between 1.10 and 4.38, the Mg-Zn-Y phases formed included the I-phase and the W-phase.[16] When the Zn/Y ratio was lower than 1.10, the primary secondary phase of the alloys was the W-phase.[22] In addition, Lee et al. has also systematically investigated the influence of the Zn/Y ratio on the microstructure of Mg-Zn-Y alloys.[17] These studies indicated that the phases identified in the as-cast Mg-Zn-Y alloys were a-Mg + Mg7Zn3, w
Data Loading...
