| Al-Cu-Li alloy of 2A66 is an age-hardenable alloy,which is developed by the domestic institute independently,it has a broad application prospect in field of aerospace,owing to its high specific strength,relatively light weight,good plasticity and processing performance.The effects of single-step,multi-step solution treatment on the hardening behavior,mechanical properties,microstructures and corrosion resistance of the as-extruded 2A66 aluminum alloy roads were investigated.Hardness testing,conductivitu testing,ambient temperature tensile testing,optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),polarization curves determination and intergranular corrosion testing were used for characterization of microstructures,mechanical properties and corrosion resistance of the alloy rods to optimize the heat treatment process and promote the overall mechanical properties.The main conclusion are shown as follows:(1)The optimal solution temperature for the single-step solution of 2A66 aluminum alloy is 520?.With increasing of solution temperature from 480? to 540?for 1.5h,the volume fraction of the residual phase decreases,the degree of alloy's saturation increases,the conductivity gradually decreases,and the hardness of plate increases first,and then decreases.At the temperature of 520?,the strength and elongation of alloy reach the peak value 610MPa and 9.2%.The overburn temperature of 2A66 aluminum is 540?,which generates the volume fraction and the size of the recrystallized grains increasing.(2)The optimal solution time for the single-step solution of 2A66 aluminum alloy is 520?.In the range of 0.5h to 2h at 520?,with prolonging solution time,the strength and elongation of alloy increases first and then decreases,but change little;In the range of 0.5h to 1.5h,the volume fraction of the residual phases gradually decreases and the recrystallized grains gradually increases and the conductivity of alloy gradually decreases,which remain stable after 1.5h.When the solution treatment is performed at 520? for 1.5h,the strength and elongation of alloy reach the peak,the corrosion potential of the alloy is the highest(-0.689V),the corrosion current is the lowest(3.78×10-7A·cm-2),and the depth of intergranular corrosion is very shallow(146.37?m),the results indicate that the alloy under this circumstance has a higher corrosion resistance.(3)Compared with the single-step solution treatment,double-step solution and step-solution can significantly improve the degree of alloy's saturation,the volume fraction of recrystallization is low,the phases(T1 and ?')in the grain dispersion,which increase the alloy's strength.The high temperature pre-precipitation treatment leads to a decrease in strength because of thick precipitate.The alloy can reach the highest strength end elongation after step-solution treatment,tensile strength(Rm)and the yield strength(Rp0.2)reach the peak value 640.7MPa and 605MPa,its elongation is 8.9%.(4)Compared with the single-step solution treatment,multi-solution treatment can increase the alloy's corrosion resistance.According to the different solution treatments,the corrosion resistance of the alloy decreases as the following order:step-solution treatment(SST)>double-step solution treatment(DST3)>high temperature pre-precipitation treatment(HTPT)>single-step solution treatment.After step-solution treatment,the intergranular corrosion depth is 39.15?m,the electrochemical corrosion potential is-0.316V.(5)The optimal solution treatment of the as-extruded 2A66 alumium alloy rods is the step-solution treatment,and the process parameters of this treatme nt is:300?/1h+400?/1h+500?/1h+520?/0.5h(heating rate is 50?/h),which can obtain a good overall performance. |
PDF Full Text Request