Effect Of Heat Treatment On Microstructure And Corrosion Anisotropy Of Rolled 7150 Alloy

As an ultra-high strength aluminum alloy,Al-Zn-Mg-Cu series alloy can have a tensile strength exceeding 500 Mpa.Due to its excellent mechanical properties,especially high specific strength,specific rigidity and good machinability.It is widely used in aerospace and transportation,But,the corrosion resistance of Al-Zn-Mg-Cu-based alloys is relatively poor.The7150 aluminum alloy thin plate,which came into being in the aerospace field,is an important material for large integral wall panels and wing skins.After rolling,the aluminum alloy plate inevitably produces anisotropy,which brings great difficulties to engineering applications.Understanding and reducing the negative benefits of anisotropy is extremely important.The material of this study is 7150 aluminum alloy that has been subjected to different heat treatments.Vickers hardness test,intergranular/exfoliation/electrochemical corrosion tests,scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS)were employed to study the effects of the 7150 aluminum alloy sheet by different heat treatment Anisotropy of hardness and corrosion.The results show that after the RRA aging treatment of the rolled 7150 aluminum alloy,the second phase at the grain boundary is chain and intermittently distributed,similar to the double aging microstructure;The intragranular tissues is fine and dispersed,similar to the double aging microstructure.This microstructure makes the alloy have higher alloy strength while maintaining good stress corrosion resistance.The better double aging treatment is(120?×8h+165 ?×10h).After the double aging,the average hardness of ND plane of 7150 aluminum alloy plate reaches 143.83 HV,higher than 121.55 HV of ND plane and 129.47 HV of TD plane.Although the hardness is lower than T6 and RRA treatment,it has more comprehensive corrosion resistance.Under this heat treatment state,the intergranular corrosion of 7150 aluminum alloy has experienced a process of fas-low-fas-low-stable,and the corrosion rate of ND plane is slower than that of TD plane and RD plane.The intergranular corrosion depths of ND plane and TD plane were 42.7?m and 70.7?m,and the RD plane had the deepest corrosion depth of 136.4?m.The exfoliation corrosion rating is EC of ND plane,EB-of TD plane and EA-of RD plane.;The self-corrosion current density is 3.846?A of ND plane<6.437?A of TD plane<7.819?A of RD plane.The corrosion anisotropy of 7150 aluminum alloy in different corrosion environments is different.The intergranular corrosion and electrochemical corrosion are similar,and the order of corrosion resistance of different plane was ND > TD > RD.But the exfoliation corrosion resistance happed to be opposite.