| As the lightest structural metallic materials applied currently, magnesium alloys show excellent room temperature performance. However, when the temperature exceeds120℃, the creep resistance significantly decreases and its application is extremely limited. Enhancing the high temperature properties of magnesium alloys, especially high-temperature creep resistance, is an important direction for the research and development of magnesium alloys. The industrialized heat-resistant magnesium alloys are mainly rare earth heat-resistant magnesium alloys and magnesium matrix composites which are difficult to meet the need of the civilian industry due to the expensive price. The research emphasis of heat-resistant magnesium alloys is focus on the development of new low-cost heat-resistant magnesium alloys recently. The magnesium alloy structural components which are mainly made of cast magnesium alloy show lower strength and poor plasticity. Deformation magnesium alloys with high strength and high elongation, etc. can meet higher design requirements. Thus, using equal channel angular processing (ECAP) technology in the R&D of heat-resistant magnesium alloy and systematically investigating the effect law of ECAP technology on the microstructure and properties of heat-resistant magnesium alloy can establish the basis for the development of new heat-resistance magnesium alloys with low-cost and excellent combination properties.In this study, typical AZ61magnesium among Mg-Al system and ZK60alloy among Mg-Zn system was selected as matrix materials. Higher amounts of element Si was added to form high temperature phase Mg2Si for improving its heat resistance. The AZ61-4Si and ZK60-4Si heat-resistance magnesium alloys were made. ECAP technique was used to refine the alloys microstructure and to improve its mechanical properties. Optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to analyze the alloys microstructure. Electronic universal tensile testing machine was used to test the alloys room temperature mechanical properties and high temperature creep resistance. The magnesium alloys refinement mechanism by ECAP, magnesium alloy tensile deformation and fracture mechanisms and the effect mechanism of Mg2Si phase morphology on the room temperature mechanical properties and high temperature creep resistance of the magnesium alloys were studied. The research results are shown as follows:(1) The microstructure of magnesium alloys can be significantly refined by ECAP. After4-pass ECAP, the matrix grains of AZ61-4Si alloy are changed from300μm of the as cast alloy to10μm. Chinese script type Mg2Si particles are changed from the maximal70μm of the as cast alloy to7μm. After8-pass ECAP, the matrix grains are further refined to6μm and the Mg2Si particles to5μm. The matrix grains of ZK60-4Si alloy are changed from400μm for as cast alloy to55μm. Chinese script type Mg2Si particles are changed from the maximal76μm of the as-cast alloy to18μm after4-pass ECAP. The matrix grains are further refined to25μm and the Mg2Si particles are very small particles after8-pass ECAP. The refinement mechanism of magnesium alloy by ECAP is continuous dynamic recrystallization caused by large plastic deformation.(2) The mechanical properties of the experimental alloy improve due to the microstructure refinement effect by ECAP. The yield strength, tensile strength and elongation of AZ61-4Si alloy after4-pass ECAP increase by128%,89%and340%, respectively. The yield strength of the8-pass ECAP AZ61-4Si alloy further improves while the tensile strength and elongation slightly reduce. The yield strength, tensile strength and elongation of ZK60-4Si alloy after4-pass ECAP are improve by90%,63%and203%, respectively. The yield strength of the8-pass ECAP ZK60-4Si alloy slightly decreases while the tensile strength increases significantly. The hardness of the experimental alloy increases with the pressing times increasing.(3) Mg2Si phase is shown with Chinese script type in the as-cast microstructure of the experimental alloy. The micro-cracks in the a-Mg/Mg2Si phase interface become the main crack source. The crack propagation easily along the a-Mg/Mg2Si phase interface can result in the brittle fracture of the materials. However, the Mg2Si was broken into grainy by ECAP. The fracture of the alloy shows a ductile fracture mechanism with nucleation model.(4) Both the high temperature creep resistances of the AZ61-4Si alloy and ZK60-4Si alloy improve remarkably by ECAP. The mechanism is that a large number of high-temperature stable phase of Mg2Si particles are distributed in the grain interior and grain boundaries, which not only hinder the intragranular dislocation movement, but also prevent grain boundary sliding.
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