| As a kind of main alloying or micro alloying elements, Sn has a beneficial effect on microstructure and mechanical properties of Mg alloys, which is a potential alternative element for magnesium alloy strengthening instead of RE. At present, almost of the high performance Sn containing magnesium alloys have high Sn content, which results in their high the cost. On the basis of previous work, this paper designs the Mg-6Zn-3Sn-0.5Mn (ZTM630) alloy. In this paper, the influences of heat treatment process and extrusion process on the microstructure and tensile properties of ZTM630 alloy were studied, and the heat treatment process and extrusion process of ZTM630 alloy were optimized.The solidified microstructure and tensile properties of the semi continuous casting ZTM630 were examined. The microstructure of as-cast ZTM630 alloy consists of α-Mg primary, MgZn2 eutectic, divorced eutectic Mg2Sn and the second constituent Mg2Sn. The eutectic Mg2Sn phases distribute mainly along grain boundaries adhering to the eutectic MgZn2 phases. Some of secondary precipitation Mg2Sn appear within grains or along grain boundaries alone and the others appear adhering to eutectic MgZn2 and divorced Mg2Sn.The tensile strength, yield strength and elongation at room temperature of as cast ZTM630 alloy are 212.3Mpa,117.0Mpa and 11.1%.Different process conditions of homogenization treatment were conducted on ZTM630 alloy and process was optimized. After homogenization treatment, all of the MgZn2 phases and the majority of Mg2Sn phases are dissolved into the matrix, only remaining a few Mg2Sn phases in the structure. And the solute distribution within matrix is uniform. The solution treatment obviously enhances the tensile strength and the elongation. After homogenization treatment, the tensile strength and elongation increase by 15.8%,16.2% compared with the as-cast alloy respectively. And the yield strength decrease to 106. 1MPa.The effects of extrusion temperature on Microstructure and tensile properties of ZTM630 magnesium alloy extruded bar are analyzed. The grain size of the alloy is increased with the extrusion temperature increasing which has a significant effect on grain size and the grain sizes are 11.2μm,16.8μm,24.7μm respectively at the extrusion temperature of 300℃,350℃, 400℃. At the same time, the grain size uniformity of the extruded tissue was significantly Improved with the extrusion temperature increasing. The tensile strength and the yield strength of 243.6MPa and 329MPa at 300℃ decreased to 302.5MPa and 243.1MPa at 400℃ because of the increase of grain size leading to the decrease of the tensile strength and yield strength. The coordination of microstructure evolution of the alloy was improved because of the tensile process,which leading to the elongation increasing and the elongation are 14.2%,14.5%, 15.1% respectively at the extrusion temperature of 300℃,350℃,400℃.The aging treatment process was optimized for different extrusion temperatures of Mg alloy bars and The effects of aging treatment on Microstructure and tensile properties of ZTM630 magnesium alloy extruded bar are analyzed. It appears a typical age hardening curve characteristics in the aging process of the alloy that under aging, peak aging and over aging along with the aging increasing and the time of peak aging can be shorten along with the aging temperature raising,whose peak value decreased.The tensile strength, yield strength and elongation rate reache 334.6MPa,287.4MPa and 13.7% respectively after 175℃×16h aging treatment,reaching 367.9MPa,309.2MPa and 10.7% after 175℃×16h aging treatment, reaching 412.4MPa,383.2MPa and 8.4% after 150℃×64h aging treatment. Precipitation of a large number of second phase nanoparticles and secondly phasestrengthening lead to the tensile strength and yield strength improving.The effects of extrusion temperature on Microstructure and tensile properties of the extruded bar and plate of ZTM630 magnesium alloy are studyed. When the Extrusion ratio increased,the grain size decreases and the tensile strength and the yield strength increase. The grain size of extruded bar decrease from 31.7μm at extrusion ratio 12 to 13.5μm at extrusion ratio 108 and the tensile strength and the yield strength iecrease from 299.8MPa,195.2MPa to 322.2MPa,235.9MPa. The grain size of extruded plate decrease from 38.7μm at extrusion ratio 8 to 12.1μm at extrusion ratio 102 and the tensile strength and the yield strength at extrusion ratio 8 inecrease from 260.5MPa,175.6MPa to 315.6MPa,221.3MPa at extrusion ratio 102.The microstructure and tensile properties of different extrusion ratio bars and plates were studyed. A large number of dispersed nano particle phases appear in the alloy,which lead to the tensile strength, yield strength increasing and the elongation rate decreasing. The extruded bar has the comprehensive mechanical properties at extrusion ratio of 61 after aging treatment, whose tensile strength,yield strength and elongation reach 412.4MPa,383.2MPa and 8.5% respectively. Under the premise of ensuring surface quality, the extruded plete has the comprehensive mechanical properties at extrusion ratio of 12 having lower difficulty to ectrude after aging treatment, whose tensile strength, yield strength and elongation reach 373.4MPa,332.9MPa and 4%. |
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