| The influence of different aluminium content (6-8%) upon the alloy microstructure, the mechanical properties and creep properties of the Mg-Al-Zn alloys was studied in this paper. The zinc content's influence upon the Mg-Zn-Al alloys' was studied as well. And the effect of microalloying and solid solution with aging treatment on the mechanical properties and creep properties of the above-mentioned two series alloys was also studied. Optical microscope, SEM, XRD were adopted to analyse microstructure of the alloys, the electro universal testing machine was used to test the tensile properties at room temperature and high temperature, and creep testing machine creep properties were tested by creep testing machine. The main results are presented as follows.The main phase of the Mg-Al-Zn casting magnesium alloys are theα-Mg and theβphase (Al12 Mg17). With the addition of Si, Sb and RE to the alloys, Mg2Si phase is found. With the increase of aluminium content, theβphase in the alloys increases individually, the size becomes big, the appearance changes into a continuous net from the skeleton form.With the increase of Al content (6-8%) in the casting Mg-Al-Zn alloys, the mechanical properties increase not only at the heat work condition (150℃), but also at the room temperature. When the Al content reaches 8%, the room temperature tensile strength arrives at 200 Mpa, the yield strength reaches 115 MPa, but the increase extent shows lower obviously.The bulkyβphase that exists in the grain boundary of Mg-Al-Zn casting alloy can be removed after solid solution with aging treatment, and strengthen the alloy . The study shows that when the aluminium content is 7%, the strengthening effect shows better. The room temperature tensile strength attains 226 MPa, the yield strength attains 139 MPa, the specific elongation is 8%, the heat tensile strength attains 211 MPa, the yield strength attains 98 MPa, and the specific elongation is 9.56%.With the increase of the testing temperature and the testing load in the creep experiment, the creep speed of all the alloys increases. Adding Si, Sb, RE to the alloys, the creep resistance of the Mg-Al-Zn alloys increase effectively, making the creep speed lower obviously. At 150℃, 50 MPa condition, the creep speed is 1.32×s 10-9(S-1), while without Si, Sb, RE addition, the creep speed of the alloy is 3.1×s 10-9(S-1), and the creep speed increases to 10-7(S-1) quantity classes when the load increases to 100 MPa.The Al content has no obvious influence on the creep of the alloys, each reaches 10-9(S-1) quantity classes. The heat treatment can increase creep-resistant of magnesium alloys.When the zinc content is 8%-12% in the casting Mg-Zn-Al alloys, the main strengthening phases are (p-Al2Mg5Zn2 phase and (?)-Mg32 (Al, Zn) 49 phase, which distribute along the grain boundary. The heat treatment can remove the net texture, and make the phases present granular distributing in the matrix.With the zinc content increase from 8% to 10% of the casting Mg-Zn-Al alloys, the yield strength and tensile strength change weak, but the plasticity lowered with the increase of the Zn content. The strength and plasticity show the same tend after heat treatment. The study shows RE can raise the creep resistanceof the alloys, and improve the creep property.
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