Numerical Simulation On Extrusion Deformation Of Spray-deposited 7075/SiC_p Aluminum Matrix Composite

As an advanced material preparation technology,Spray Deposition has been widely used to produce alloys and metal matrix composites. However, the spray deposited preforms usually contain more than 10vol.% porosity that is a great disadvantage for the mechanical properties. In order to prepare fully dense products of high mechanical properties, the porous preforms must be further densified and deformed plastically. The densification and plastic deformation behaviors and fracture behaviors of spray deposited porous preforms were investigated in this dissertation. The involved deformation processes are compression and extrusion.The main conclusion are as follows:(1) The extrusion deformation of spray-deposited 7075Al/SiCp composite has been simulated by using rigid-plastic finite element method (FEM) on DEFORM-2D software, the extrusion ratio varies from 4 to100, temperature varies from 300℃to 450℃and ram velocity varies from 2 mm/s to 20 mm/s. The simulation results indicate that:the max stress and temperature occur in the die entry section. The optimally processing parameters for the extrusion of 7075Al/SiCp composite are obtained to be ingot preheating temperature of 350～400℃, extrusion ratio of 16～50 and extrusion ram speed of 5～15 mm/s.These can provid theoretical reference to process design of the extrusion deformation of 7075Al/SiCp composite.(2) The plane strain extrusion and axisymmetric extrusion deformation of spray-deposited 7075Al/SiCp composite have been simulated by using rigid-plastic finite element method (FEM) on DEFORM-2D software.The simulation results indicate that:Compared with plane strain extrusion,there are uniformer metal flowing,less dead space,more densification velocity in axisymmetric extrusion deformation ,but higher unit-area extrusion pressure.The relative density decreases due to positive mean stress,while increases due to negative mean stress,The more the hydrostaty,the more increasement of densification speed.The initial density has effect not only on extrusion pressure,but also on equivalent strain.when the die degree increases,the time of becoming steadily deformation reduces. With the decreasing of die degree,the metal flow becomes uniform,the dead space becomes small,the extrusion pressure diminutes.With the decreasing of ingot preheating temperature,the densification velocity increases.(3) Both the experimental and numerical approaches are applied to investigate the compressive deformation behavior of the 7075Al/SiCp composites from the point of view of macro-and meso-m echanics. The correctness of simulating analysis is verified through the process experiment The investigations on the particlate reinforcements behavior during the deformation showed that:the extrusion ratio and deformation temperature affect the particlate reinforcements rotation and breakage significant,With the increase of the extrusion ratio, the particlate reinforcements breakage degree and rotation degree are enhanced obviously.Moreover, with increasing the deformation temperature the particlate reinforcements breakage degree decreases,whereas the particlate reinforcements rotation degree increases.