Study On Retrogression And Re-Ageing Treatment Of 7085 Aluminum Alloy Containing Yttrium

Al-Zn-Mg-Cu alloy,as an age-hardening alloy,has been widely used in the aerospace field due to its high strength,high toughness,corrosion resistance,fatigue resistance and high hardenability.In this paper,RE-7085 aluminum alloy is developed by adding 0.3%yttrium(Y).Hardness,electrical conductivity testing and differential thermal analysis(DSC),as well as optical microscopy(OM),scanning electron microscopy(SEM)are used for investigating and analyzing the microstructure,mechanical and corrosion properties of 7085-0.3Y aluminum alloy treated by retrogression and re-ageing treatment(RRA).The main conclusions are as follows:1.The 7085(Al-7.7Zn-l.6Mg-1.8Cu-0.15Zr)alloy which containing 0.3%yttrium is prepared,and the effect of rare earth yttrium on as-cast 7085 alloy is studied.The hardness,tensile strength,elongation,and electrical conductivity of as-cast 7085 alloy are 104.7 HV,238 MPa,6.3%,and 25.47%IACS,respectively,compared to the hardness,tensile strength,and elongation of the 7085 aluminum alloy without yttrium,increased by 40.5%,17.6%,and 16.7%,respectively,the conductivity did not change obviously.The addition of 0.3%yttrium into the 7085 alloy results in the formation of Al3Y eutectic compounds on the grain boundary,which increases the nucleation rate and achieves grain refinement.2.The solid solution aging treatment of 7085-0.3Y alloy is studied.It is found that the appropriate single-stage solid solution aging treatment is 470?/lh,the appropriate peak aging treatment is 120?/24h,and the hardness and electrical conductivity of the peak-aging alloy are 197.4 HV and 29.7%IACS,respectively.3.With the extension of regression time,the hardness of the alloy after RRA treatment increases with the extension of the regression time,reaches a peak and then decreases.The higher the regression temperature,the shorter the time taken to reach the peak.In the RRA treatment,the conductivity of the alloy increases with the increase of the regression temperature and the extension of the regression time,but the increase tends to be gradual.4.Through the orthogonal experiment,the regression and re-aging treatment of 7085-0.3Y alloy is studied.The appropriate regression and re-aging treatment is 120?/12h+160?/60min+120?/30h.Under this condition,the hardness,tensile strength,yield strength,elongation and conductivity of the alloy are 213.9 HV,441 MPa,440 MPa,7.2%,and 35.8%IACS,respectively.The maximum depth of intergranular corrosion is 95?m.And the degree of intergranular corrosion is 3.