Microstructure Evolution Of C_p/AZ91D Composite Material During Partial Remelting

In this paper,C_p/AZ91D magnesium matrix composite were prepared by composite casting and then the structural evolution during the partial remelting process was studied.The optimum ball milling process was obtained by changing the parameters of ball milling.C_p/AZ91D composite prefabricated bar was prepared by cold pressing and sintering of the prepared composite powder.The effects of different casting processes on the microstructure and mechanical properties of C_p/AZ91D composites were studied Explore the C_p distribution and solidification mechanism in composites.The semi-solid temperature and semi-solid holding time were studied on the process of microstructure evolution and phase change of C_p/AZ91D composites.(1)By studying the influence of C_p content,ball grinding speed,ball grinding time,ball material ratio and other parameters on C_p/AZ91D composite powder,the optimal ball grinding parameters were obtained:C_p addition amount 5wt.%,Ball milling speed It is250r/min,the ball milling time is 8h,and the ball to material ratio is 20:1.The relationship between working pressure and holding time on the density of cold pressing block was studied,and the best preparation technology of C_p/AZ91D composite cold pressing block was obtained:the working pressure was 50MPa,and the holding time was 5min.(2)In this paper,C_p/AZ91D magnesium matrix composites were prepared successfully by composite casting method,and the effects of different process parameters on the structure and properties of C_p/AZ91D composites were studied.The experimental results show that the optimal casting structure of C_p/AZ91D composites can be obtained by adding 1.5wt.%C_p and holding it for 15min.According to the performance test,its mechanical properties are the best.According to the interface thermal conductivity solidification theory and the self-stabilizing effect of C_p in the melt,a small amount of C_p tends to be evenly distributed in the melt,and tends to be phagocytic C_p distributed in the grain during solidification.Adding a large number of C_p is easy to aggregate and tends to repel C_p distribution at grain boundaries during solidification.(3)After partial remelting of C_p/AZ91D composites,semisolid particles with spherification can be obtained.The effects of different holding time and heating temperature on the semi-solid structure evolution of C_p/AZ91D composites during partial remelting were studied.The microstructure evolution of C_p/AZ91D composites mainly includes the following four stages:rapid coarsening stage,tissue separation stage,spheroidization stage with coarsening and rapid coarsening stage.According to the result of experiment shows that appropriate increase of semi-solid during partial remelting heating temperature is helpful to obtain semi-solid microstructure with small globular primary particles.however,if the temperature is too high,the particles will be coarse,and too much liquid is not conducive to production.Too low temperature will result in too little liquid phasel.At the same time,it is not good to get fine globular semisolid particles because of the consolidation among grains.