| Magnesium alloy has a series of advantages, such as low density、high specific strength and specific stiffness、good thermal conductivity、good magnetic-shielding ability, good damping ability、easy to recycle and so on, having a wide range of applications in electronic products, automobile、 aerospace and other fields. But their high temperature performance is poor, limiting its application in the industrial sector. Development of heat-resistant magnesium alloys is from rare earth magnesium alloys, adding rare earth elements in magnesium alloys formed a high temperature strengthening phase, in order to improve its heat resistance, and thus developed a series of rare earth heat-resistant magnesium alloy, higher cost of rare earth heat-resistant magnesium alloy limits its widespread application, Therefore, the development of low-cost and good high-temperature creep resistance magnesium alloy is a hot issue in recent years.The Si element has good performance and cheap price. Adding Si element in magnesium alloy can form Mg2Si phase, Mg2Si with high melting point, high hardness and high elastic modulus is a kind of strengthening phase at high temperature. However, the solubility of Si in magnesium is very low, the cast Mg2Si phase is a Chinese character or block shaped, easy to split the matrix, and will reduce the mechanical properties of the alloy. Equal channel angular pressing can effectively refine the matrix grain and broken the second phase.4wt.%Si was added into ZK60magnesium alloy, using equal channel angular pressing to refine matrix grains、Mg2Si phase、Mg-Zn phase and so on, in order to improve the high temperature creep properties of the alloy.Cast and extruded microsturcture are observed by optical microscope, Combined with X-ray diffraction analysis of the alloy constituents. The room temperature mechanical properties and high temperature creep properties of alloy was tested by electronic universal testing machine. The fracture was observed by scanning electron microscopy, at the same time, Equal channel angular pressing on the microstructure and performance was analysed. Results showed that:(1) The cast structure of ZK60-4Si magnesium alloy is composed of a-Mg matrix、Mg2Si phase, Mg51Zn2o phase, MgZn phase and MgZn2phase, the matrix grain is coarse, Mg2Si phase is the Chinese character or block shaped, the Matrix grains was significantly refined after equal channel angular pressing for4passes, Mg2Si and other enhanced phase were also broken into small particles, the grain size is further reduced and the grain is more uniform after ECAP for8passes, Mg2Si phase particles tend to diffuse distribution, Combined with XRD diffraction analysis, the alloy phase did not change before and after extrusion.(2) Mechanical properties of ZK60-4Si-cast magnesium alloy at room temperature is poor, yield strength is only48MPa, the tensile strength is only128Mpa, elongation is7.2%, This is due to the organization shrinkage and coarse grains of cast alloy, and the Chinese character or block shaped Mg2Si phase is angular and sharp, splitting matrix, reduced the mechanical properties of the alloy, the mechanical properties of amorphous alloys has improved significantly after ECAP for4passes, Yield strength and tensile strength increased by62.5%and elongation increased247%. Change in performance of alloy is little after ECAP for8passes.(3) The creep experiment was proceeded at temperature of250℃with the load of70MPa, creep property of cast alloy is poor, after equal channel angular pressing, creep property was greatly improved, creep life of alloy for2、4、6、8passes were8.5、12.8、87.7、124hours respectively. This is due to the grain refinement with the increase of extrusion passes, Mg2Si phase particles also broken into tiny particles and tends to the dispersion of the distribution, hindered the grain boundary and dislocation glide, and thus improved the creep properties of alloy. the creep life of the alloy at temperature of250℃with the load of90MPa is much lower than at temperature of250℃with the load of70MPa. |
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