| The effect of heat-treatment on mechanical properties, electrical conductivity andinterlgranular corrosion of7A85aluminum alloy had been investigated by tension,Vickers hardness and electrical conductivity measurement combined with DSCanalysis, OM, SEM and TEM. The major conclusions are drawn as follow:(1) The effect of single-solution treatment on microstructure and properties on7A85aluminum alloy was studied. The rational single solution temperature was470℃.The rational solution time was2hours. Most of the second phase had been into thematrix, and the tendency of grain growth was not obvious after single solution at470℃/2h.(2) During single aging,7A85alloy shows remarkable aging hardeningcharacteristic and high resistance to over-aging. Aged at120℃for24h, the hardnessand strength of the alloy reach peak value, and maintain the peak value with theprolonging of aging time. The favorable single aging treatment of7A85alloy was120℃/24h. At this condition, hardness, tensile strength, yield strength, elongation andelectrical conductivity of the alloy were220.5HV,760.8MPa,713.4MPa,8.9%and29.7%IACS, respectively.(3) The favorable two-step aging treatment of7A85alloy was120℃/8h+165℃/12h. At this condition, hardness, tensile strength, yield strength, elongation andelectrical conductivity of the alloy were597.7MPa,565.8MPa,9.4%and38.1%IACS,respectively. Compared with T6temper, electrical conductivity of the alloy increase by28%aged at120℃/8h+165℃/12h, Which could improve SCC resistance of the alloyeffectively.(4) After pre-aging at120℃/24h, retrogression at220℃/6min, and then re-agingat120℃/24h, the tensile strength, yield strength, elongation and electricalconductivity of the alloy were731.7MPa,694.6MPa,8.4%and36.5%IACSrespectively. RRA treatment not only improved electrical conductivity and SCCresistance but also obtained a tensile strength as high as T6temper.(5) The large quantities of GP zones and some η’ phase precipitated dispersedly ingrain, with few second phases precipitated in grain boundary, and the precipitation freezone was not obviously near grain boundary in the T6temper.7A85alloy obtained thefavorable corrosion properties, with the phases in grain boundary discontinuous and PFZ widening in the T73temper.7A85-RRA showed good comprehensive performance,with the combinations of high tensile strength and conductivity, as well as betterintergranular corrosion sensibility. Compared with T6temper, the alloy obtained lowerintergranular corrosion sensibility in T73temper and RRA. The intergranular corrosionsensibility of7A85alloy decreased with equilibrium phases in grain boundarydiscontinuous and PFZ widening. |
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