Semi-solid Al-23Si-4.5Fe-3Cu-1Mg Alloy Slurry Fabricated By Rotating Induced Nucleation And Rheo-diecasting

In hypereutectic Al-Si alloys with high Fe content, the morphology and distribution of the primary Si particles (PSPs) and Fe-rich phase play an important role in the performance of the alloy. In Al-Si alloys, the PSPs and Fe-rich phase can improve the wear-resisting property as hard phase. But at conventional casting condition, the thick PSPs and noodle-like Fe-rich phase can fragmented the Al-matrix, reduce the mechanical properties of alloy. Researches show that. at semi-solid processing, the primary phase refinement and its morphology would be improved, improve the mechanical properties. In this paper, semi-solid slurry of Al-23Si-4.5Fe-3Cu-1Mg alloy fabricated by Rotating-Rod Induced Nucleation (RRIN). The influence of different parameters on the alloy microstructure was studied, and the effect of semi-solid die casting on the alloy microstructure has investigated.The experiment results show that, the microstructure of alloy can be effectively improved by RRIN, not only the PSPs were refined, the Fe-rich phase has obvious refinement also, the eutectic phase and other phase has the corresponding influence. With different RRIN process parameters, there will be different microstructures. The movment of the alloy melt changed with the speed of rotating-rod changed. The speed at a higher or lower level, the contact-area of the rotating rod and the melt would be reduced, the heat transfer would be slowly. When the rotating speed is lower, the gravity of the melt plays a main role. The relative velocity of inside and outside melt at rotating direction will be small, the contact area of the melt and the rotating-rod smaller, the thickness of melt bigger. When the rotating speed is higher, the centrifugal force will plays a main role, the melt will break away from the rotating surface before the melt spread, the contact area will be small.At the same time, the copper-rod with high thermal conductivity can take away more heat in melt, the effectiveness of nucleation is superior to the steel-rod. More high pouring temperature, more residual heat in slurry, it can promote the grain growth. When pouring temperature is higher, the grain have formed in melt will be re-melted, the number of free nucleus in the melt reduced, and the gain grew up into a large grain size, eventually. The result shows that, with (?)75mm copper-rod, rotating speed is 600r/min. and the pouring temperature is 830℃, the refinement effect is best.The microstructures of liquid die-casting and semi-solid die-casting were investigated, the result shows that, not only can primary phase were refined, such as the PSPs and the Fe-rich phase, the rich Cu phase and eutectic phase has obvious optimization improved also. With semi-solid rheo-die-casting process, the microstructure can further refined. The equivalent diameter of the primary Si and Fe-rich phase reduced to 15μm and 20μm, respectively. In semi-solid slurry, the volume fraction of solid phase is higher, with the increase of injection process, the volume fraction of secondary primary phase increased significantly.