The Research On The Influence For Heat Transfer Condition To Solidification Structure Of Aluminum Alloy

Casting technology has a long history. With the development of science and technologyof casting, the performance for castings is required more and more in industry process.Therefore, it has been an important aim for metallurgists to adjust the processing parametersof casting in order to control the macroscopic solidification structure and improve themechanical property.The present paper is focused on the effect of heat transfer parameters on solidificationstructure of aluminum alloy casting. On the basis of experimental devices of solidificationstructure in domestic and foreign countries, a new directional solidification device wasdesigned, which was based on high frequency heater and water cooling. The cooling curves ofspecific position of aluminum alloy samples with different cooling rates, as well as themacroscopic structure have been obtained after a great many experiments.The heat transfer coefficient between the alloy samples and cooling water is an importantparameter, which can describe the condition of heat transfer. In view of the difficulty onmeasuring heat transfer coefficient, an inverse evaluation has been put forward to calculatethe heat transfer coefficient between the alloy samples and cooling water. First, the coolingcurves of the given position in the aluminum alloy samples were obtained from the collectingsystem of computer. Then, the cooling curves of simulation were made coincided withexperimental ones by adjusting the heat transfer parameters. Finally, according to numericalsimulation results of interface heat flux and surface temperature of the samples, the curvesof heat transfer coefficient varied with temperature were obtained. Furthermore, theinfluences of cooling water on heat transfer coefficient of 7050 aluminum alloy samples werealso analyzed in this paper. It can be concluded that as other metals, the maximum of heattransfer coefficient of 7050 aluminum alloy samples is between 200 to 230℃, and the heattransfer coefficient increases with decreasing cooling water temperature, however, the rangeof maximum temperature could not be affected by cooling water temperature.The influences of heat preservation temperature and cooling water temperature onnucleate rate of equiaxed, nucleate rate of columnar and the transfer position from thecolumnar to equiaxed have been analyzed based on orthogonal experiments in this paper. Theresults show that the area of equiaxed increases with decreasing the heat preservationtemperature or increasing the temperature of cooling water. Additionally, nucleate rate of equiaxed and columnar of the samples increases with decreasing the temperature of coolingwater and heat preservation temperature. On basis of orthogonal experiments, the results ofCET position have also been obtained in this paper, and the applicability of CET criteriondeduced in some references has been discussed. A new CET criterion was put forward.