| Aimed at the poor high-temperature mechnical properties and creep properties of magnesium alloy, the In situ MgO / Mg2Si reinforced magnesium matrix composite was prepared by adding reactant into the molten magnesium under the protection of Ar gas atmosphere in vacuum induction furnace, With aids of the modern analyses and testing techniques, such as OM, ESEM, EDAX, XRD and mechanical properties, the thermdynamics, kinetics of in-situ reaction of reactant and Mg and feasibility which the reinforcement phase can be formed, were studied. Setting up initiatively the reaction model of the reinforcement phase forming by reaction in-situ. The effect of procesing parameters on the microstucture of pure-Mg base composite was studied. And the reinforcement phase forming by reaction in-situ of the Si and ZM5 alloy was investigated, the effect of Si content on the microstucture and mechnical properties of Mg2Si/ZM5 was study. The effect and mechanism of modification of Sr content on the reinforcement Mg2Si were also studied priliminarily. The main results are as follows:1. the reactants, such as Si, SiO2, AU (SiO4) 3(alumina silicate), A12(SO4)3, B2O3, A12O3, et al. reacting with the Mg melt can form in-situ reinforcement phase Mg2Si and MgO. However the reactant Al2O3 isn't suitable for the reactant to form the in-situ reinforcement phase for its high reaction temperature.2. The reinforcement phase Mg2Si and MgO can improve the mechnical property of the pure Mg matrix. For instance the yield strength at the ambient temperture and at the elevated temperature of Mg-based composite woth 2.5%Si can increase by 85.3%, 74.4% respectively, wiht 5% SiO2 increase by 106.8%, 74.9%. with 5% alumina silicate can increase by 64.6%, 82.6%. However the formation of the reinforcement Mg2Si, MgO can reduce the elongation of the Mg-based composite.3. The processing parameters such as the melting technology, mechanical stirring, the size of the reactant etc. have the great effect on the microstructure of the In situ MgO / Mg2Si reinforced magnesium matrix composite. The mechanical stir can increase greatly the uniformly distribution of the reinforcment phase that reacted in-situ in the composite. The optimum size of the reactant is 50-100um. The pretreatment of the reactant (SiO2) increases further the uniformity of particles formed reaction in-situ, thus improving the uniformity of microsturcture.4. After adding of Si into ZM5 alloy ,the molten magnesium will form in-situ the high hardness, high module, high melting-point, high stable, dispersed Mg2Si reinforcement phase, in addition to Mg17Al12 phase in the as-cast structure of ZM5. The morphology of reinforcement phase Mg2Si is fine short-rod or flake eutectic phase, when the content of Si is less than 0.5%; while the content of Si is higher than 1.0% , the morphology of Mg2Si phase changes into the more coarse bulk or "chinese-script" primary Mg2Si, and becomes more coarse with the increase of Si content. After T6 heat-treatment the alloy of ZM5, the over-saturation 8 (Mg) precipitate directly incoherent equilibrium phase y without any intermediate phase, and it distribute in the grain boundary and transgrain in the form of the discontinuous and continuous phase. The addition of Si can decrease thediscontinuous precipitation in the grain boundary and promote the continuous phase in the transgrain, it also can refine the grain of the 8 (Mg) . The size and morphology of reinforcement phase Mg2Si not affacted in the course of heat-treatment process.5. The strength of the as-cast and heat-treated (T6) Mg2Si/ZM5 composite at the ambient temperature and at the elevated temperature can be improved greatly after addition of Si in the ZM5. The as-cast tensile strength can be increased by 20%, 15%, and the as-cast yield strength increased by 61.5%, 25.7% when Si content is 1.0%-1.5%. But the addition of Si reduce the composite'elongation. After the T6 heat-treatment, comparing to that of as-cast, Mg2Si/ZM5 the strengths at room-temperature and elevated temperature...
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