The Fabrication And Solution Treatment Of Ti@(Al-Si-Ti)_p/A356 Composite Prepared By Powder Thixoforming

In this paper,a novel core-shell structured Ti@(Al-Si-Ti)particle(Ti@(Al-Si-Ti)p)reinforced A356 aluminum matrix composite was prepared by powder thixoforming.The effects of partial reheating temperature on the microstructure and mechanical properties of the composites of the composites were studied.The toughening mechanism of Ti@(Al-Si-Ti)core-shell structured particles was investigated through the in-situ tensile test to observe the crack propagation.A modified strengthening model was also proposed to predict the yield strength of this type of composite.And the effects of solution treatment on the microstructure and mechanical properties of the composite were also discussed.Research indicated that:The reheating temperature had a significant effect on the microstructure and mechanical properties of in-situ core-shell Ti@(Al-Si-Ti)particle reinforced A356 aluminum matrix composites prepared by powder thixoforming(PTF).Increasing with the improvement of the reheating temperatures,the liquid phases and the primary particles grew up,the quantity of the secondary solidification structures gradually increaced,which separated the primary particles,making the grain boundary become clear.At the reheating temperature of 590 °C,the shell of the reinforced particles was thin and consist of ?1 phase.The Ti@(Al-Si-Ti)p/A356 matrix composite obtained at a reheating temperature of 600 °C exhibited a dense dual-phases core-shell structure with the outer shell of a dark gray(Al,51)?Ti phase and inter shell of light gray c1 phase.With the increase of the reheating temperature,the first produced:1 phase with higher Si content was transformed into the(Al,Si)3Ti phase with lower Si content,and then the shell layer was broken and stripped from the Ti core.The mechanical properties of composites first increased and then decreased.When reheating temperature raised to 600 °C,the composite had the best comprehensive tensile properties.The best tensile strength(UTS),yield strength(YS)and elongation were:371 MPa,268 MPa and 8.3%,respectively.The composite of this structure had a high elongation,and the core-shell structured reinforcement can effectively prevent and suppress the crack propagation and improve the plasticity and toughness of the composite.A modified MSL strengthening model was established to predict the yield strength of Ti@(Al-Si-Ti)p particle reinforced aluminum matrix composites.The results kept in good agreement with the experimental values.The results of the solid solution treatment,which use the composite thixoformed at 600 °C for 50 min,showed that the solid solution treatment reduced the segregation of the composite matrix and made the microstructure more uniform,but it also caused the reinforcement particles to continue to react.And the Al-Si-Ti compound shells thicken and even burst.The former has a beneficial effect on the mechanical properties of the composite,but the latter reduces the mechanical properties of the composite.Therefore,the mechanical properties of the core-shell particle reinforced aluminum matrix composites depend on the synthesis of the two functions under the solid solution process parameters.The tensile strength,yield strength and elongation of the composites were all increased with solid solution treatment at 530 °C for 3 h,which increased by 6.6%,13.4%,2.0%respectively.