Numerical Simulation On Indirection Extrusion Of SiCp/7075Al Matrix Composite Prepared By Spray Deposition

Particle reinforced aluminum matrix composites are widely used in structural applications, especially in the aerospace and automobile industries, due to their high specific stiffness and strength, high wear resistance, high dimensional stability, good erosion resistance and low thermal expansion c oefficient. Hot compression tests of the extruded 7075Al/15%Vol Si C particle reinforced composite prepared by spray deposition were performed on Gleeble-1500 system in the temperature range of 300-450 ? and strain rate range of 0.001-1 s-1. The optimum parameters of hot working for the composites can be obtained based on processing maps and optical microstructural observation. Finite element numerical simulation software combined with experiment were used to analyze the infl uences of indirection extrusion temperature, extrusion ratio, extrusion velocity and other parameters on extruded 7075Al/Si C particle reinforced composite, including voids elimination and the rotation, fracture and distribution of Si C particles. The results are shown as follows:(1)The true stress-true strain curve exhibits rapid flow softening absent of obvious work hardening and the stress decreases with increasing temperature and decreasing strain rate. Moreover, the stress levels are higher at temperature below 400 ? but lower at 450 ? compared with the spray deposited 7075 Al alloy. Superplastic deformation mechanism is observed at strain rate of 0.001-0.1 s-1 and deformation temperature of 450 ?.(2) The optimum parameters of hot working for the composites were obtained to be temperature of 430-450 ? and strain rate of 0.001-0.05 s-1 based on processing maps and optical microstructural observation.(3)The 7075Al/Si C particle reinforced composite was densified by indirection extrusion. Increasing initial relative density and extrusion ratio can decrease the low density and inhomogeneous area of the head of the billet. The flow of the matrix alloy is nonuniform, which leads to the rotation of Si C particles. The hard and rigid Si C reinforcements move with nonuniform flow of the matrix alloy, and will fracture when they can not turn in the direction of the resultant force under great stress. The particle fracture failure points of the outboard billet is ob vious higher than that of the inner billet. This failure easily propagate crack in effects of tensile stress during extrusion process. The particle fracture failure points is relatively low at extrusion ratio of 4-25 and extrusion temperature of 400-450? by numerical simulation analyses.(4)The reasonable extrusion velocity at different extrusion temperature are obtained by compared the result of numerical simulation and extruding experiment: T=400?,V<30mm/s;T=425?,V<20mm/s;T=450?, V<5mm/s. It also can be concluded that the composite has a homogeneous distributed Si C particles after indirection extrusion.