Study On Rheo-die-casting Process Of Semi-solid Aluminum Alloy Slurry With Indirect Ultrasonic Vibration

Semi-solid metal forming is considered as one of the new and advanced technologies in twenty-first century. Rheoforming has attracted the attention of the academic and manufacturing fields because of its unique advantages such as energy-saving, low costs. In this paper, high-energy ultrasonic field's effects on microstructure and mechanical behaviors of A356 alloy was researched, the mechanism of semi-solid slurry preparation of A356 alloy by indirect ultrasonic vibration(IUV) was studied.The technique of semi-solid aluminium alloy slurry preparation by IUV and the relevant equipment were improved. After functional test and stability test in this research, the technique worked more stably and efficiently.The effects of parameters such as the vibration time and the pouring temperature after IUV on primary Al crystals of A356 alloy were studied. The results show that, with the prolonging of the time during IUV, the average grain diameter of primary Al tended to decrease firstly and then increase, the least diameter appeared after 40-60s vibration, the grain shape coefficient of primary Al tended to increase firstly and then decrease, the maximum value was obtained after 60s vibration. With the pouring temperature dropping, the average grain diameter of primary Al grew up obviously from 55μm to 100μm, the grain shape coefficient of primary Al increased firstly and then decreased, the maximum value was obtained at 611℃. The effective temperature of IUV was between 606-620℃.The influence of parameters such as the vibration time and the pouring temperature after IUV on microstructure and mechanical behaviors of the semi-solid rheo-die-casting A356 alloy was discussed. The result shows that the effect of the vibration time was more remarkable, the highest mechanical properties was obtained after 40-60s vibration, compared with traditional die castings, the tensile strength and elongation of the rheo-die-casting were raised by 10.9% and 93.5% respectively.The mechanism of semi-solid slurry preparation of A356 alloy by indirect ultrasonic vibration was studied. The results show that,in the process of indirect ultrasonic vibration, there have obvious characteristics of ultrasonic vibration such as acoustic streaming, cavitation and thermal effect, and characteristics of high-frequency mechanical vibration such as vigorous surface agitation, the increase of the nucleation which induced by falling off of solid particles formed on the crucible wall. Melt treated with IUV experiences the combined action of ultrasonic and high-frequency mechanical vibration rather than single mechanical vibration effect.