The Study Of Al-Zn-Mg Alloys With Electron Theory

Al-Zn-Mg Alloys played an important role in the avigation and spaceflight due to their low density,high strength and preferable age hardness. -One drawback of these alloys was their susceptibility to stress corrosion cracking(SCC). Although overaging processes could improve the performance of resistance to stress corrosion cracking ,it could reduce the alloys' strength simultaneously. The study of the microcosmic mechanism between structure and performances was of great importance in order to keep the alloys' progressive stress corrosion cracking together with their high-strength after appropriate heat treatment. Unfortunately just very limited work has been done on studying the microcosmic mechanism between the structure and performances.The valence electron structures and interphase performances of each solid solution and part of the precipitations in Al-Zn and Al-Zn-Mg alloys were analyzed systematically according to the Empirical Electronic Theory in solid and molecules (EET) and improved TFD method by Cheng Kaijia.The research work made it possible for further study as theoretical basis.The main contents of this paper were as follows:Firstly,the models of valence electron structures of phases in Al-Zn based alloys were established. There were four kinds of cells in Al-Zn based alloys: a-Al cell; Al-Zn cell riching Al; Al-Zn cell riching Zn and Zn cell. The valence electron structures of above cells were calculated based on the average atom model.Then the Spinodal decompound phenomenon and the stability of morphology in Al-Zn alloy were discussed in the valence electron structure level. . -Secondly, the valence electron structures of G.P. zone, interphase and precipitatition in supersaturated solid solution duing aging were calculated in Al-Zn based alloys.The effect of these precipitates on alloys' properties was discussed.Thirdly,the valence electron structures of both Al-Zn, Al-Mg, Mg-Zn segregated cells and Al-Zn-Mg segregated cell were computered. The structural models of precipitates were analyzed.Finally,the interphase energy between G.P. zone and matrix in solid solution during aging of Al-Zn based alloys was calculated.The surface charging density of the interphase was calculated too.