Study On Mechanical Properties,Quenching Sensitivity And Corrosion Resistance Of 7085 Aluminum Alloy

Al-Zn-Mg-Cu series aluminum alloy boosts high strength,high toughness,low density and good corrosion resistance,so it is widely used in main load-bearing structural parts such as aircraft wings.In order to further improve the safety and fuel efficiency of aircraft,people’s requirements for aluminum alloy structural parts have gradually changed to large-scale and integration.However,the thick plate aluminum alloy has quenching sensitivity,and the alloy properties are not uniformly distributed in the thickness direction.Aiming to further expand the application of 7-series aluminum alloys in the aerospace field,a large number of studies have been conducted on the impact of microalloying and processing on the mechanical properties and quenching sensitivity of the 7xxx aluminum alloys,with an expectation to obtaining high strength and low quenching sensitivity aluminum alloys at the same time.In this paper,based on 7085 aluminum alloy,five kinds of alloy compositions were obtained by increasing the content of Zn,adjusting the content of Cu and adding Sc element.Combined with the thermo-mechanical treatment process,the comprehensive properties of 7085 aluminum alloy were improved.The effects of composition and thermo-mechanical processing on the mechanical properties,quenching sensitivity and corrosion resistance of 7085 aluminum alloy were studied by means of room temperature tensile test and intergranular corrosion test,metallographic microscope,electron microscope,transmission electron microscope observation and other test methods.The main research results are shown as follows:（1）Increasing the Zn content can make the alloy precipitate higher densityη’Phase,thereby effectively improving the strength of the alloy.But the number ofηphases will also increase with the increase of Zn content,significantly improving the quenching sensitivity of the alloy.In addition,increasing the Zn content will also increase the amount of precipitated phases at the grain boundary,reducing the corrosion resistance of the alloy.（2）Increasing Cu content based on high Zn content will raise the total amount of precipitated phases in the alloy,significantly promoting the strength and quenching sensitivity of the alloy,but will reduce the corrosion resistance of the alloy.Cutting down Cu content on the basis of high Zn will reduce the strength and quenching sensitivity of the alloy,and enhance its corrosion resistance.（3）On the basis of 7085 aluminum alloy,adding a small amount of Sc can form fine and dispersed Al₃（Sc,Zr）particles,which can effectively pin the grain boundary,sub-grain boundary and dislocation,refine the grain structure,significantly inhibit the recrystallization of the alloy,and improve the strength and corrosion resistance of the alloy.Under air-cooled condition,Al₃（Sc,Zr）particles can provide additional nucleation sites for theηphase and improve the quenching sensitivity of the alloy.Therefore,adding a small amount of Sc will increase the strength and quenching sensitivity of the alloy,and slightly weaken the corrosion resistance of the alloy.Increasing Zn content on the basis of Sc content will further improve the strength and quenching sensitivity of the alloy,and slightly reduce the corrosion resistance of the alloy.（4）The TMT process combines deformation strengthening with precipitation strengthening,which can effectively improve the strength of each alloy and reduce the quenching sensitivity,but the dislocations introduced during the TMT process can promote the nucleation and growth of the grain boundary precipitation phase and reduce the corrosion resistance.