Microstructure Evolution And Hot Deformation Behavior Of Fine-grained SiC Particle Reinforced Magnesium Matrix Material

To realize the controlling of microstructure and mechanical properties of fine-grained particle reinforced magnesium matrix composites,and widen their application in aerospace industry and automobile ect.,this paper concentrates mainly on the microstructure evolution and hot deformation behavior of fine-grained SiC particle reinforced magnesium(SiCp/Mg)matrix material.The SiCp/Mg matrix material was fabricated by stir casting firstly,and then the grains of which was refined by the combination of forging and extrusion porcesses.After that,the microstructural evolution at elevated temperature was investigated.Then the static recrystallization behavior of fine-grained SiCp/Mg matrix material influenced by SiC particle(SiCp)size and its coupling effect was researched.The deformation mechanism of fine-grained SiCp/Mg matrix material was revealed by analyzing their hot compression flow stress.Based upon the microstructural evolution of fine-grained SiCp/Mg matrix material at elevated temperature,the deformation behavior and dynamic recrystallization(DRX)of the material influenced by SiCp size and its coupling effect had been recognized.Results indicated that the grain size of fine-grained SiCp/Mg matrix material grew up gradually with temperature increasing.Owing to the hindering effect of SiCp on grain boundary movement,the grains of SiCp/Mg matrix material were finer than the matrix alloy.As compared with single-sized SiCp,the combination of micron(M-SiCp)and submicron(S-SiCp)SiCp had much more obvious effect on stabilizing the high temperature microstructure of fine-grained Mg matrix.Particle size had significant effect on the static recrystallization behavior of fine-grained Mg matrix: the M-SiCp was thought propitious to promote the nucleation of static recrystallization based on the formation of deformation zone with high density dislocation(PDZ),which resulted in the finer grains around M-SiCp;the formation of submicron particle dense zones(SPDZs)could stabilize the high temperature microstructure of fine-grained Mg matrix.Owing to the fact that the hindering effect of S-SiCp on dislocation and grain boundary movement was stronger than that of promoting effect of M-SiCp on the recrystallization's nucleation,the static recrystallization process of S-1+M-9 composite was mainly controlled by 1vol.% S-SiCp.During hot deformation process,the compression flow stress of fine-grained SiCp/Mg matrix material decreased with the temperature increasing and strain rate decreasing.The average grain size of fine-grained SiCp/Mg matrix material after hot compression increased with the temperature increasing and the strain rate decreasing,however,it was finer than that of matrix alloy.At the initial stage of compression,the flow stress of S-1+M-9 composite was controlled by S-SiCp.As the increasing of compression strain,the controlling effect of M-SiCp on flow stress became much more obvious.Because of the coupling effect of M-SiCp and S-SiCp,the average grain size of S-1+M-9 composite after hot compression is finer than that of single sized SiCp/Mg matrix material.Addition of SiCp led to the increase of Q and n values of Mg matrix material,and the deformation mechanism of fine-grained SiCp/Mg matrix material was dislocation climbing mechanism controlled by grain boundary diffusion.The DRX behavior of fine-grained Mg matrix influenced by SiCp depended on strain rate: at high strain rate,the existence of SiCp was thought propitious to promote the DRX nucleation of fine-grained Mg matrix;at low strain rate,the SiCp played the hindering effect on DRX nucleation of fine-grained Mg matrix.At the initial stage of compression with low strain rate,the DRX nucleation took place at the original grain boundaries in micron SiCp/Mg matrix material;with the proceeding of compression,the dislocation density around M-SiCp increased gradually,and then the subgrain rotation or migration nucleation occurred at this stage.Owing to the pinning effect of S-SiCp on dislocation and grain boundary,the DRX nucleation was hard to occur in submicron SiCp/M g matrix material composite at the initial stage of compression.With the proceeding of compression,the dislocation multiplication rate increased and the inhibiting effect of S-SiCp on DRX nucleation was weakened simultaneously.As compared with single size SiCp,the bimodal size SiCp had much stronger effect on inhibiting the nucleation of DRX,which led to the increase of critical strain for DRX.With the proceeding of compression,on one hand,the dislocation density around M-SiCp was increased;on the other hand,the dislocation movability was also enhanced,and thus the hindering effect of S-SiCp on grain boundary was weakened,which contributed to the nucleation of DRX.