| This article takes 7A85 aluminum alloy extruded high-strength plate with ribbed for aviation as the experimental object.Through the microstructure observation such as metallographic microscope(OM),transmission electron microscope(TEM),scanning electron microscope(SEM)and electron backscatter diffraction microscope(EBSD),explored the rule of precipitates in 7A85 aluminum alloy ribbed plate during two-stage aging,and used the tensile test of mechanical properties at room temperature,conductivity test,electric polarization test,intergranular corrosion test and exfoliation corrosion test to exploring the performance of 7A85 aluminum alloy ribbed plate under different two-stage aging systems,or different directions(LT,L and T)under the same two-stage aging system.The main results are as follows:(1)Under the condition of single-stage solid solution,the appropriate solid solution temperature and holding time of 7A85 aluminum alloy ribbed plate are 470 ℃/ 70 min.At this time,the second phases in the aluminum alloy disappears,and the plate had a good solution effect.After peak aging(120 ℃ / 24 h),the precipitates in7A85 aluminum alloy are fineer and dispersed,the precipitates at grain boundaries are continuously,and the precipitate free zone is narrow and dark;The tensile strength(626.5 MPa)and elongation(17.7%)of 7A85 aluminum alloy ribbed plate is higher as well,but the conductivity(32.6% IACS)value is lower.(2)After two-stage aging treatment,the GP zones and η’ phase grows,and there are some η phase at the grain boundary position,which is disconnected,and the precipitation free zone becomes wider;By controlling the change of the time and the temperature in the final aging stage,the tensile strength of 7A85 aluminum alloy ribbed plate decreases with the increase of time and temperature,and the conductivity of it increases with the increase of time and temperature.(3)Through the range of orthogonal experiment,the influence order of each factor of two-stage aging on the tensile strength of 7A85 aluminum alloy ribbed plate is: final aging temperature > final aging time > initial aging time > initial aging temperature;The influence order on conductivity is: final aging time > final aging temperature >initial aging temperature > initial aging time.The optimum two-stage aging system is110 ℃ / 6 h + 155 ℃ / 8 h.,in this condition,the tensile strength(617.0 MPa)and elongation(12.3%)of the 7A85 aluminum alloy decreased slightly compared with the peak aging,but the conductivity(37.2% IACS)increased significantly and the corrosion resistance of the alloy increased.(4)Under the two-stage aging system of 110 ℃ / 6 h + 155 ℃ / 8 h,the grain deformation degree of 7A85 aluminum alloy ribbed plate is larger in the “LT” and“L ”positions.The proportion of small-angle grain and small-size grain is higher than that of the “T” position,and there is a strong “Cube” texture in the “LT” and“L ”positions.The tensile strengths of 7A85 aluminum alloy ribbed plate in “LT”、 “L ”and “L ”positions are 604.0 MPa,608.7 MPa and 595.5 MPa respectively,and the elongations are 12.4%,12.7% and 11.7% respectively.The anisotropy of mechanical results is smaller.(5)Under the two-stage aging system of 110 ℃ / 6 h + 155 ℃ / 8 h,the numbers of self-corrosion potential of 7A85 aluminum alloy ribbed plate in “LT”、 “L ” and“L ”positions are-0.735 V,-0.708 V and-0.687 V respectively.The order of corrosion resistance is: “T > L > LT”.The immersion corrosion test results show that the 7A85 aluminum alloy ribbed plate has a same intergranular corrosion grade in the “LT”、 “L ”and “L ”positions,which is grade 3,and the maximum corrosion depth appears in the“L ” position,is 67.20 μm;The exfoliation corrosion results show that there is skin explosion on the surface of “LT”、 “L ” and “L ”positions,and the corrosion leves are the same(PA).The anisotropy of corrosion results is smaller,which is fit the engineering design requirements... |
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