Efficient Fabrication Of Aluminum Alloy Semisolid Sluury By Shear/Vibration Coupled Sub-rapid Solidification Technology And Corresponding Equipment

Aimed at the preparation of semisolid slurry needed by rheological forming,a device platform for fabrication of semisolid slurry by shear-vibration coupled sub-rapid solidification has been designed and built based on considering the existing fabrication techniques.Taking Al-8Si Al alloy as the research object,the flow and temperature fields in the melt on the sloping plate were calculated by COMSOL Multiphysics software.Then the effects of technological parameters of the shear-vibration coupled sub-rapid solidification on microstructure of semisolid slurry were experimentally investigated by employing the parameters optimized by the simulation.The achieved results are listed as followings:(1)The designed and built device platform for fabrication of semisolid slurry by shear-vibration coupled sub-rapid solidification realized the automatic control of shear and vibration,and had a higher capability for preparation of high-quality semisolid slurry.(2)The results achieved from the simulation by COMSOL Multiphysics software indicated that the temperature of the melt linearly decreased as it flowed along the sloping plate.The proper technological parameters included the pouring temperature of 893K-933 K,the pouring speed(i.e.,the tilted speed of casting ladle)of 0.843 Kg/s-2.81 Kg/s,the tilt angle of the sloping plate of 25 °-55 ° and the length of the sloping plate of 50 cm-60 cm.(3)The experimental results indicated that:(1)The cooling ability of the cooling plate was improved if cooling water was inputted in the cooling plate.The solidification rate of the melt was accelerated,and the primary particles was thereby significantly refined,i.e.,it was helpful for obtaining semisolid slurry with small and spheroidal primary particles.But the solid fraction was relatively higher.(2)As the pouring temperature rose,the shear action in the melt was intensified due to the accelerated flow speed of the melt.The resulted primary particles were decreased in size and spheroidized in morphology.The solid fraction was decreased because of the shortened cooling time,and the amount of Al alloy left on the sloping plate was also decreased.But as the temperature exceeded 913 K,the action time of the sloping plate on the melt was too short due to too high flow speed of the melt,which leaded to the number of primary particles to decrease and the size to increase,and also leaded them to become more irregular.(3)As the tilt angle of the sloping plate increased,similar to the status of rising pouring temperature,the size of primary particles gradually decreased and their morphology became more spheroidal due to the intensified shear action.Simultaneously,the solid fraction decreased.But when the angle exceeded 45 °,the size of primary particles increased their morphology became irregular again due to the shortened time for the melt flowing the sloping plate.(4)The primary particles increased in size and became irregular in morphology as the vibration frequency increased,as well as the decrease in solid fraction.The reasons that leaded to these results were the decreased cooling time of the melt that attributed to the shortened effect time of the sloping plate on the melt,and thus,the nucleation rate was decreased,resulting in the increase of primary particles and the decease in solid fraction.Furthermore,the amplitude of the sloping plate was decreased,the shear action was thereby decreased,resulting in the large and irregular primary particles.(5)When the pouring speed(i.e.,the tilt speed of casting ladle)increased,the flow speed of melt then increased and the shear action was intensified,resulting in the decrease of primary particle size and more spheroidal morphology,as well as the decrease in solid fraction.But as the tilt speed exceeded 1.405 Kg/s,the size of primary particles increased and their morphology became irregular again due to shortened time for the sloping plate acting on the melt and the increased thickness of melt on the sloping plate.Finally,an optimized fabrication technique of semisolid slurry was achieved,pouring temperature of 913 K,tilt angle of the sloping plate of 45 °,vibration frequency of 60 Hz and pouring speed of 1.405 Kg/s.In this case,the size and shape factor of primary particles in the slurry were 32.45 ?m and 1.48.It was noted that the average pouring speed of 2.81Kg/s.That is,the size of primary particles in the slurry is 38.62?m and the shape factor is 1.66,which means that the primary particles are relatively small and round,and the pulping efficiency is high.