Study On Microstructural Characteristics And Dimensional Stability Mechanism Of Submicron SiCp/2024Al Composite

Al based composites reinforced with150nm and5.5μm SiC particle with volumefraction of30%were fabricated by pressure infiltration technique. By comparing themicrostructure, aging behavior, mechanical properties and dimensional stability of thetwo composites, analysis the different of composite reinforcement and dimensionalstability mechanism between sub-micron particle reinforced composite materials andmicron-sized particles reinforced composite.The result of the aging behavior of the two composites shows that the twocomposites have the highest peak aging hardness when aging at160℃.150nmSiC_p/2024Al has a higher hardness than5.5μmmSiC_p/2024Al. Micron particlesaccelerated aging precipitation and sub-micron particle has little effect on the agingprecipitation.The result of the microstructure of the two composites shows that there is a bigdifference between150nmSiC_p/2024Al and5.5μmmSiC_p/2024Al. It is difficult to findthe dislocation in150nmSiC_p/2024Al while it can be seen the large amount ofdislocation around particle in the5.5μmmSiC_p/2024Al. This is because the small size ofparticles have large active surface, the material in the casting process of hardeningparticles absorb large amounts of space, so that the original is difficult to form adislocation loop. On the other hand, as the reduction of the size of particle, the thermalmismatch stress of composite decreases, when the size of particle decreases to a certainrange, the thermal mismatch stress sufficient plastic deformation of the matrix occurs, itis difficult to form a dislocation. It makes many enhanced mechanism associated withdislocations of micron particle reinforced composites can not be explained in150nmSiC_p/2024Al composites. Precipitated phase with small punctate is only a fewnanometers in size. HREM micrographs of the interface of composites show that theinterface combine well and don’t find interfacial reaction product, and growingdirection of the molten aluminum is along the strong plane. While the interface betweenthe SiC particles and the aluminum is semi-coherent.Flexural strength of the two composites have little difference, but150nmSiC_p/2024Al have a higher micro-yield strength. Dimensional stability of the two composite are very close. Dimensional stability of150nmSiC_p/2024Al has little changewith the reduce of minimum temperature of thermal cycles. But the dimensionalstability of5.5μmmSiC_p/2024Al become better with the reduce of minimumtemperature of thermal cycles.