Study On Heat Treatment Of The Forging7050 Aluminum Alloy

With the development of aviation industry, higher requirement for aeronautic equipment has been put forward. Forging parts as the main structural components, the service life and flight safety of airplane has close relationship with their properties. Morever, with the accelerating development of lightweight process in aviation, it seems an inexorable trend that light material must be chosen. Aluminum alloy has been widely applied as aircraft forging component, because of the excellent characteristics, such as high specific strength, good machinability, and so on. Solid solution and aging treatment are the final heat treatment process of aluminum alloy forgings, So research on heat treatment after forging has great significance in improving properties of the forgings and meeting requirements of service performance.In this paper, based on 7050 aluminum alloy forging blank, solution and aging treatments have been investigated with aids of metallographic microscope, scanning electron microscope, tensile testing machine and other analysis methods. The relationship of microstructure and property was discussed. Finally the appropriate heat treatment process parameters were given.The results showed that after solution treated at 465℃,η(Mg Zn2) phases dissolved into the matrix. And after solution treated at 471℃,a part of T(Al Zn Mg Cu) phases dissolved into the matrix. but the number of S(Al2Cu Mg) phases didn’t change. After treated at 483℃, only Fe-rich impurity phases were found, no T phases and S phases existed. Thus the reasonable solution process of the alloy is 471℃×240min.Double aging heat-treatment was analyzed though dual factors test. Factors which affect microhardness and conductivity from strong to weak in the following order were found: second-step ageing time, first-step ageing time. In addition, compared with single-stage ageing, double-stage aging treatment can improve stress corrosion resistance with preservation of suitable strength. the precipitation of G.P. zones and η’ phases are major precipitates at this stage. And grain boundary precipitates in double-stage aging treatment are the most discontinuous. The fracture mode of double-stage aging treatment is mainly mixed fracture mechanism of dimple fracture and gliding fracture. Within the experiment analysis, the optimum aging heat treatment process of 7050 aluminum alloy is 121℃,12h+177℃,8h.