Preparation and Rheocasting of Semi-solid Aluminum-alloy Slurry with Indirect Ultrasonic Vibration Process
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Preparation and Rheocasting of Semi-solid Aluminum-alloy Slurry with Indirect Ultrasonic Vibration Process Shusen Wu, Shulin Lü, Ping An and Zeming Zhu State Key Lab of Materials Processing and Die &Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, P.R. China
ABSTRACT Direct ultrasonic vibration (DUV) method by dipping the horn into the melt can be used to make semi-solid metal slurry, but application of this process is embarrassed because of the erosion problem of titanium-alloy horn by aluminum melt. In order to avoid this problem, a slurry-making process with indirect ultrasonic vibration (IUV), in which the horn is vibrated under the outside of the metallic cup containing alloy melt, has been developed in this research. Semisolid slurry of A356 Al alloy was prepared by this process, and the effects of IUV treatment time on the morphology of the primary α-Al phase and mechanical properties of rheo-diecasting samples were studied. The results indicate that excellent semisolid slurry of A356 Al alloy could be obtained within 50s by applying IUV near its liquidus temperature, and the average diameter and shape coefficient of the primary α-Al particles were 75µm and 0.62, respectively. IUV treatment time had a significant effect on the mechanical properties of the rheo-diecasting samples, and samples treated by IUV for 50s had the maximum tensile strength and elongation. The maximum as-cast tensile strength and elongation were 244MPa and 7.5% respectively, which were increased by 10% and 75% respectively compared to conventional molten-melt die-casting samples. In addition, the mechanism of preparing semisolid slurry of A356 Al alloy by IUV is discussed. INTRODUCTION The semi-solid metal (SSM) processing, including thixoforming and rheocasting, offers the opportunity to manufacture net-shaped components with high integrity, complicated shape and good mechanical properties. More and more researches have been focused on rheocasting in recent years because of its low cost and high productivity. The key to rheocasting is how to efficiently process liquid alloy to create high quality semisolid slurry. Ultrasonic vibration has the potential to be a simple and effective process to produce semisolid metal slurry. The research of ultrasonic vibration for metallurgical application has a long history and previous investigations have revealed that when ultrasonic vibration is applied on the solidifying melt, microstructure changes occur involving grain refinement, increased homogeneity, reduced micro-segregation[1-5] as well as degassing[6-7]. However, ultrasonic vibration developed for preparing semisolid slurry is a relatively new method in SSM processing. The ultrasonic vibration process can be divided into direct and indirect methods. Direct
ultrasonic vibration (DUV) method by dipping the horn into the melt can be used to make semi-solid metal slurry with fine and non-dendritic microstructure [8-11], but application of this process is embarrassed because of the erosion problem of titanium-all
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