Microstructure And Properties Of Quasicrystal Strengthened Mg-Zn-Y Alloys Produced By Equal Channel Angular Pressing

Magnesium and magnesium alloy are becoming more and more attractive for many engineering structural applications owing to their low density and high specific strength, especially the significant advantage of easy-recycling. However, the application of most magnesium alloys has been greatly restricted due to their poor strength, oxidation and creep resistance. In order to extend the application of magnesium alloys, many methods have been reported to improve mechanical properties.Icosahedral quasicrystalline phase (I-phase) that has attractive mechanical and physical properties attributed to their unique atomic structure, such as high strength, high hardness at elevated temperature and low friction coefficient has been reported in many alloy systems. Recently, it has been reported that the Mg-Zn-Y alloys containing I-phase as a secondary solidification phase exhibit good mechanical properties at room temperature and elevated temperature, which provide a good method for the development and application of new magnesium alloys.In this paper, several as-cast Mg-Zn-Y bulk alloys, which consist of a coarse eutectic I-phase in the a-Mg matrix, were fabricated by using the conventional casting method of the design of composition. The effect of the alloy content and Zn/Y ratio on the microstructure of Mg-Zn-Y alloys was studied, and the precipitate behavior of the alloy and thermal stability of I-phase was also investigated. Based on the aging-treated sample, the effect of two deformation processing—hot extrusion and equal channel angular pressing(ECAP), on the microstructure and mechanical properties of Mg-Zn-Y alloys were studied. Moreover, the refinement mechanism, fracture behavior and strengthening mechanism were investigated.The results showed that, when the content of Y was from 0.3at.% to 2.0at.% and the content of Zn was from 1.7at.% to 6.0at.%, the as-cast microstructure and the phase constitution of Mg-Zn-Y alloys were determined by the atom ratio of Zn/Y and the content of Zn element. When the atom ration of Zn/Y is 6, the as-cast Mg-Zn-Y alloys were composed of two different types of phases: the primary a-Mg phase and I-phase. The formation capability and the volume fraction of I-phase in Mg-Zn-Y alloys were determined by the solidification rate of alloys. Because the growth of I-phase was restricted by the high solidification rate, the volume fraction of I-phase in...