Finite Element Simulation Of The Reaction Synthesis Of Ag / Sno <sub> 2 </ Sub> Composite Extrusion Process

It is well known that Ag/SnO2 electric contact composites would substitute Ag/CdO composites for they are nontoxic,and they will be put to use widely in the future.At present,as the preparation process being concerned,the Ag/SnO2 contact composites have high intensity,high hardness and high rate of hardening etc,which can bring about some difficulties for the following process. So,to develop advanced electric contact composites,it is very important to understand the flow behavior of Ag/SnO2 composites.In this dissertation,the stress,strain,temperature and the development of grain size of Ag/SnO2 composites prepared by reactive synthesis in the hot extution were studied.The flow behavior and the other concerned datas of Ag/SnO2 composites prepared by reactive synthesis was investigated by use of isothermal constant speed compression test. Then,the constitutive equation of Ag/SnO2 composite prepared by reactive synthesis was derived through the algebraic transformation.The recrystallization kinetics was derived through the algebraic transformation also.the metal flowlines,stress,strain,temperature and the development of grain size of Ag/SnO2 composites prepared by reactive synthesis in the hot extution were simulated by using the FEM software named MSC.Superform.a. Metal flowing in the extrusion is non-uniform.The flow velocity of internal metal is higher than the external metal.b. In the initial stage of extrusion,the external metal,which was contact with the inner wall of container,suffered a larger equivalent stress. The all metal was suffered a larger equivalent stress when metal was into deformation zone. And in the all extrusion,metal in the transition zone of deformation zone and calibrating straight suffered the largest equivalent stress.c. In the initial stage of extrusion, the temperature of external metal, which was contact with the inner wall of container, rapidly decrease due to heat transfer with container. But the temperature of internal metal keeps invariant. The temperature gradually rose due to the deformation heat producted by severe deformation of metal when workpiece was into deformation zone. There was a negative temperature gradient from the inner to the outer side in workpiece due to the heat transfer from external metal to container. In the last stage of extrusion, temperature of the metal in the calibrating straight was highest due to deformation heat and frictional heat.d. In the initial stage of extrusion,grain size had little change. When metal was into deformation zone,grain was severe crushed due to the great stress action. When metal was into calibrating straight,grain growing rapidly due to a large number of deformation heat and frictional heat. In the last stage of extrusion,the average grain diameter was about 785nm,and was umiform distributed.