| Magnesium alloy matrix composites have great potential for applications in a good many fields due to its low density, high specific strength and good dimension stability, etc. Rapid solidification/Powder metallurgy(RS/PM) is an important method to prepare particle reinforced metal matrix composites (MMCs). Different Si content enhanced AZ91 magnesium alloy powders were prepared through atomization-twin rolls quenching technology in the present dissertation, then the powders were consolidated into composite materials by hot extrusion The effects of different Si addition on the micro structures and age-hardening behavior of the alloy flakes were investigated. And the effects of different Si addition on microstructures, room and elevated temperature tensile properties, elevated creep properties of alloys were investigated. The conclusions are drawn as follows:1. Al(1wt%Si+AZ91),A2(3wt%Si+AZ91),A3(5wt%Si+AZ91) magnesium alloy flakes reinforced by in situ Mg2Si were prepared by atomization- twin rolls quenched technology. The three kinds of alloy flakes all exhibited fine equiaxed grains with the grain size of 1～3μm. And the grain sizes have no remarkably difference with the Si contents increased. After the hot treatment of the flakes, we found that, as aging at 473K and 523K for 60min, the value of microhardness reached maximum. When aging at 573K, the value of microhardness reached maximum in 30min. A3 alloy flakes had the topmost microhardness of 118.02HV after aging for 60min at 473K.2. After the process of extrusion, the microstructure of the alloy has changed significantly. The as-extruded materials exhibited equiaxed grains with the size of 5～15μm. Mg2Si particles generated in situ were grew up gradually as the increasing of Si content. By adding Si to alloy can significantly improve the mechanical properties. The average tensile strength compared to the matrix increased by about 18%. The fracture elongation of alloys decreased with the Si contents increasing. While compared to matrix, the fracture elongation of A1 alloy had a certain increase. At the room temperature, A2 alloy exhibits the best mechanical properties, its 0.2% yield tensile strength,ultimate tensile strength and elongation of rupture were 329MPa, 472MPa and 4.70%. Respectively, the alloy elevated temperature (473K) tensile properties improved as the Si addition increasing, and the tensile strength of A3 alloy reached to 192MPa. While at 523K, all of the alloys tensile strength decreased rapidly, were 90MPa around. The fracture characterization of A1 and A2 alloy exhibited ductile rupture at room temperature. A3 alloy presents the characteristics of compound fracture. The reinforcements Mg2Si were pulled off obviously in the fracture.3. By studying the effects of Si addition on RS/PM(AZ91) alloy elevated temperature creep resistance, found that under the conditions of 150℃/50MPa, the steady-state creep rate of Al alloy was markedly decreased compared to the matrix, is about 1/5 to the matrix. The steady-state creep rate of A2 alloy is of about 1/8 to the matrix. And A3 alloy is 1/18 to the matrix. The creep mechanism of the alloy are controlled by diffusion and dislocation climb mechanism under the experimental conditions of (423K-473K)/(50MPa-90MPa)...
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