Effect Of Rare Earth Metals On Microstructure And Properties Of 7085 Aluminum Alloy

7085 aluminum alloy is developed by American Alcoa as the new generation aluminum alloy. With high quench sensitivity, high strength and high damage tolerance, it is applied to the areas of large aircraft. However, one of the main drawbacks for its wider application is the corrosion resistance.One of the most important properties for Al alloys in aircraft is its corrosion resistance, since they often suffer various conditions such as temperature, loading stress, creep, fatigue and so on. Recently,7085 aluminum alloy forgings are mainly used in and Airbus 380 commercial aircraft as spar, ribs and the landing gear, and other important bearing structures, which requires high strength. Therefore, it is a significant research work to solve the contradiction between strength and corrosion resistance through micro-alloying, deformation behaviors and proper heat treatment process. The 7085 alloy was taken as the research object in this paper, the micro-alloying effect of rare earth metals and the heat treatment process were investigated. The research contents can be concluded as follows:(1) Four kinds of Al-7.5Zn-1.5Mg-1.4Cu-0.15Zr alloys contacting different rare earth metal were prepared using water chilling copper mould ingot metallurgy process. Then the homogenization processing, plastic deformation, solid-solution treatment and aging treatment were conducted. This paper studied the effect of different rare earth metal on microstructure and properties of 7085 aluminum alloy, found that the degree of improvement of rare earth metals on mechanical and corrosion properties of 7085 aluminum alloy was:Sc>Er> Y.(2) Studied effect of content of Sc (0.1wt%,0.15wt%,0.2wt%) on microstructure and properties of 7085 aluminum alloy, the best content was 0.15wt%. Then the mechanical properties and corression properties of 7085 aluminum alloy containing 0.15wt% Sc were the best, and the exfoliation corrosion of alloy containing 0.15wt%Sc was improved from EB to PB.(3) Studied the comprehensive properties of 7085-0.15Sc undergoing conventional solid-solution, dual solid-solution, enhanced solid-solution, respectively. It’s found that enhanced solid-solution(450℃/1h+460℃/2h+475℃/2h) could observably decrease the coarse second phases and the source of pitting corrosion. As a result of it, inter-granular corrosion and exfoliation corrosion were significantly improved.(4) Based on the conclusion above, T6 aging treatment, T76 aging treatment, RRA aging treatment were studied. Meanwhile, analyzed the evolution rule of polarization curves and the relationship between precipitated phase and corrosion resistance after different heat treatment. It’s shown that the the degree of improvement of heat treatment on mechanical and corrosion properties of 7085 aluminum alloy from high to low was: T76>RRA>T6.By analyzing and discussing the existence form and mechanism of Sc on 7085 alloy, and investigating the the development of corrosion process and corrosion mechanism of alloy after different solid-solution and aging treatments, the paper found that the most appropriate heat treatment process of Al-7.5Zn-1.5Mg-1.4Cu-0.15Zr-0.15Sc was enhanced solid-solution (450℃/lh+460℃/2h+475℃/2h) and T76 aging treatment(120 ℃/5h+160℃/7h). The alloy possessed better comprehensive performance after those, which provided scientific guidance to the actual production.