Research Of External Fields On The Solidification Of Aluminum Alloy

In recent years,with the development of national economy,the needs of high quality metal product and production efficiency increase rapidly.In the industrial production of aluminum alloys,the defects such as gas porosity,fine impurities hinder its improvement a lot. Also,the poor ingot surface,coarse microstructures and segregation can't meet the needs of high quality material in the modern industry.Nowadays,external fields such as electromagnetic field and power ultrasonic field are successfully applied in metallurgy and material processing,which provide an opportunity to produce high quality aluminum alloy.The purpose of the dissertation is to refine solidification microstructure and improve ingots mechanical properties.The main results are as follows:The study of compound field which is a combination of rotating electromagnetic field and power ultrasonic field on the solidification process of Sn-3.5%Pb and A356 are carried out.The results show compound field can increase initial solidification temperature,suppress segregation,refine solidification microstructure,and make the properties of ingots improve largely.On the one hand,power ultrasonic can generate a large number of nuclei above liquidus temperature,and the nuclei are transferred in the whole melt by forced convection which is induced by acoustic stream and the electromagnetic field obtaining the refined microstructure.On the other hand,the temperature fluctuation and concentration fluctuation caused by electromagnetic field and power ultrasonic field are beneficial to the dendritic arms broken or dendritic roots remelting to obtain more fine microstructure.A novel process of compound field which is combination of traveling wave magnetic field and power ultrasonic field) is proposed to improve the quality of horizontal continuously cast Al-1%Si alloy.Experimental apparatus is designed and horizontal continuous casting of Al-1%Si wire rods is conducted to investigate the effects of compound field on the surface quality,solidification structures,segregation and mechanical properties of Al-1%Si alloy.The results show that the uniformity of melt temperature and surface quality of wire rods are enhanced with the application of compound field.Moreover,grains are refined and the tensile properties of the alloy are evidently increased.The effect of compound field is more effective than either external field.