| Low-cost Si element added to the magnesium alloys are considered as one of the main choice to get heat-resistance magnesium alloys. In this paper, make use of the crystallization characteristics of Mg-Si alloy and Mg-Zn alloy, it successfully prepared Mg-6Zn-2Si magnesium alloy. Then it is significative to improve the mechanical properties of alloy at room and high temperature through equal channel angular pressing (ECAP) which can refine the organization and bulk Chinese character Mg2Si phase that formed in as-cast alloy. The effects and mechanism with ECAP on the microstructures of the alloy have been inspected using test facilities such as scanning electron microscopy (SEM) and transmission electron microscope (TEM) with energy dispersive spectrometer (EDS), optical microscopy (OM), X-ray diffraction (XRD). The high temperature creep behavior are researched in the different passes of EC AP on Mg-6Zn-2Si alloy and presents a more reasonable mechanism of creep deformation behavior and fracture behavior of8passes ECAPed alloy. It provides some theoretical and practical basis to explore low-cost, high-performance heat-resistant magnesium alloy application.The results show that ECAP can significantly modifies coarse Chinese character Mg2Si phase, at the same time it still has significant grain refinement on Mg-6Zn-2Si alloy. After the as extruded Mg-6Zn-2Si alloy was subjected to4passes and8passes ECAP, the grain size was refined to about13μm and11.5μm, respectively; for Mg2Si, it was refined to about7μm and dispersed granular or blocky. The main mechanism of magnesium alloy refinement is dynamic recrystallization and intragranular refinement.It is believed that with increasing the creep temperature, apparent stress exponent (n) decrease and with the increase of stress, creep activation (Q) decrease through analysis of n and Q. This suggest that creep of stress sensitivity is abate, creep resistance variation. Tiny Mg2Si particle dispersion strengthening effects improve the creep threshold stress of the8passes ECAPed alloy, resulting in higher activation energy and the creep mechanism of the alloy is dislocation climb and enhanced control of the second phase.With the increase of ECAP passes, creep rupture mechanism changed from brittle fracture to ductile fracture. Creep ruputure mechanism determined on creep conditions and the structural constituents of the Mg-6Zn-2Si alloy together. The rough Chinese character Mg2Si particles that distributed in the intracrystaline are easy to cause stress concentration and grain boundary strength is weak, so the fracture mechanism of the as-cast alloy is brittle intergranular fracture. Whereas Mg2Si is refined to tiny particles after4passes and8passes ECAP, distributing in the intracrystalline and grain boundary, which can form dimples in creep fracture processing. So the fracture mechanism of4passes and8passes ECAPed alloy is ductile fracture. By EDS analyzing the cleavage fracture dimple of8passes ECAPed alloy, it can be show that the composition of the dimple are the same as the fracture surface of the remaining cracked Mg2Si particle. This explained that the mechanism of Mg2Si particle in high temperature is brittle fracture. |
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