Numerical Simulation In The Temperature Field And Thermal Stress Field Of Large Specification 7050 Aluminum Alloy Billets During Solidification Process

7050 aluminum alloy having the important usages in aviation material, is one of high-strength alloy series of Al-Zn-Mg-Cu, which still have the characteristics of high-ductility and high-tensile stress property. The crystallizing temperature range of 7050 aluminum alloy is wide because of its complex composition. The specification and width/thickness ratio of 7050 aluminum alloy billets are both bigger, so they have much bigger trend to crack while casting. How to control the casting cracks of 7050 aluminum alloy cast ingot is worth studying. The casting cracks are the quality defects of cast ingot which happen during the process of casting based on the temperature changing. It's very necessary to master the dynamic regulations of the temperature field and stress field during the process of casting in order to analyze the mechanism of crack forming.In the dynamic process of casting, cooling and solidification can be effectively analyzed, and the changes of temperature and the formation and development of thermal stress of the casting system can be truly reflected by using the tool of numerical simulation for temperature field and thermal stress field during casting, which could be the base for improving and optimizing the casting technology and enhancing the performances of the cast ingot.In this paper, the temperature field and thermal stress field in casting process of two kinds of 7050 aluminum alloy billets (1120×400 billets and 1320×620 billets) were simulated by using the FEM software named ANSYS. The data show the temperature distribution inside billets was changing according to the different time and different position, temperature of upper angle part in the transversal surface of billet was low, whereas that of the core area was high. The area with bigger thermal stress was the surface layer of billet, especially the wide surface and angle parts. In the late period of cooling, the bigger thermal stress was collecting in the core area of the billet. Based on the results of comparison for two numerical simulations, crack exponent of core area of wide surface of the billets was maximum, the bigger the ratio of width/thickness, the bigger trend of crack forming is. And crack exponent is more suitable to be used to judge the possibility of crack forming than the stress is. Sampling some billets produced in plant, it was discovered the cracks during the process of casting are the intercrystalline cracks by metal structure analyzing. The affect factors of the crack forming were analyzed and the technique measures for reducing crack were discussed here. Finally, the achievements of this project are as follows:The suitable temperature for casting 7050 aluminum alloy billets is 700℃, the suitable speeds for casting 7050 aluminum alloy billets of specifications of 1120×400 and 1320×620 are respectively 30mm/min-50mm/min and 10mm/min.The results above and the technique measures proposed have the value for the production of 7050 aluminum alloy billets, and have already been proved in practical casting.