| The 7A85 aluminum alloy is an age-hardenable alloy, and its strengthening effect is determined by the degree of solid solution. Therefore the solution treatment is an important means to improve the microstructure and the comprehensive properties of the alloy. The effects of single-step, multi-step solution treatment on the microstructures, mechanical properties and corrosion resistance of the as-extruded 7A85 aluminum alloy rods were investigated. Hardness testing, ambient temperature tensile testing, polarization curves determination, intergranular corrosion testing, optical microscopy, scanning electron microscopy and transmission electron microscopy were used for characterization of microstructures, mechanical properties and corrosion resistance of the alloy rods. The main results obtained in this paper are as follows:?1? The optimal solution temperature for the single-step solution of 7A85 aluminum alloy is 470?. With solution temperature increasing from 450? to 490?, the volume fraction of the residual phase decreases and the conductivity gradually decreases, and the degree of alloy's saturation increases. The overburn temperature of 7A85 aluminum alloy is 490?. Under the comprehensive influence of aging precipitation and recrystallization, the tensile strength ?Rm? and elongation of the alloy reache the peak value at 470?, increases from the as-extruded of 588MPa and 11.7% to 680MPa and 14.3%, respectively. Meanwhile, the corrosion potential of the alloy is the highest, the corrosion current is the lowest, and the depth of intergranular corrosion is very shallow?138.65?m?, the results indicate that the alloy has a higher corrosion resistance at the solution temperature of 470?.?2? 7A85 aluminum alloy can obtain higher strength, hardness and better corrosion resistance when the solution treatment is performed at 470? for 1h. In the range of 30min-3h, with prolonging solution time, the strength and elongation of the alloy change little; the volume fraction of the residual phase, conductivity and recrystallization change obviously in 1h, but remain unchanged when solution time is more than 1h. The effect of solution time on the mechanical properties of the alloy is smaller than that of solution temperature.?3? Compared with the single-step solution treatment,7A85 aluminum alloy has a higher solid solubility and lower volume fraction of recrystallization grains through the double-step solution and step-solution. The strength of the alloy increases by about 20 Mpa through double-step solution, while high temperature pre-precipitation treatment leads to a 6.7% decrease in strength. The alloy reaches the highest strength after step-solution treatment, its yield strength and tensile strength is 641MPa and 698MPa respectively.?4? The optimal corrosion resistance of 7A85 aluminum alloy is obtained through the step-solution treatment. After different solution treatments, the corrosion resistance of the alloy decreases as the following order:step-solution treatment ?SST?> double-step solution treatment ?DST?> high temperature pre-precipitation treatment ?HTPT?> single-step solution treatment. After step-solution treatment, the intergranular corrosion depth is 43.05?m, the electrochemical corrosion potential and the corrosion current is -0.258V and 1.24×10-9 J/(A·cm-2), respectively.?5? The optimal solution treatment of the as-extruded 7A85 aluminum alloy rods is 200?×1h+300?×1h+400?×1h+470?×0.5h?heating rate is 60?/h?, through which high strength and excellent corrosion resistance performance is obtained. |
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