| The use of Al-Mg-Si alloy in vehicles has been an irresistible trend with the rapiddevelopment of automobile industry. On the base of6111aluminum alloy,an Al-Mg-Si-Cualloy with the composition of Al-0.8Mg-1.0Si-0.8Cu-0.3Mn-0.5Fe-0.15Zr (wt%) wasdesigned in order to reduce the cost, improve the mechanical properties of Al-Mg-Si alloy. AnAl-Mg-Si-Cu alloy with high tensile strength and toughness was obtained through themicrostructure and properties of deformation behavior, rolling process and heat treatmentprocess.The grain of Al-Mg-Si-Cu alloy casting ingot fabricated by electromagnetic stirringshows equiaxed crystal, the second phases mainly existing in casting alloy are ?-Al2FeSi,Al9Fe0.84Mn2.16Si, Al4Cu2Mg8Si7(Q phase) and traces of Mg2Si and Si. The tensile strength,yield strength, elongation and hardness of casting alloy are158.6MPa,106.7MPa,5.8%and33.8HB respectively. After homogenization, the second phase particles distribute moreuniformly, Mg2Si and Al4Cu2Mg8Si7phases are not found duing to resolving, Part of Feelement is substituded by Mn element, acicular ?-Al2FeSi phase translates into particle?-(FeMn)1.7Al4Si phase, and the (AlFeMnSi) phase increases.The flow stress of Al-Mg-Si-Cu alloy decreases with the increase of deformationtemperature and the decrease of strain rate during the hot compression deformation. Withincreasing the deformation temperature, decreasing the strain rate and large strain, new nearlyequiaxed grains, coalescence of sub-grain and nucleation mechanism of grain boundary boware the main dynamic recrystallization mechanism of Al-Mg-Si-Cu alloy. With increasing thedeformation rate, decreasing the deformation temperature and small strain, dynamic recoveryis the softening mechanism of the alloy. The hot compression flow stress equation of alloy bycalculating is:?&=1.89×1010[sinh(0.024?)]7.46×exp[166.85×103/(RT)]The microstructure and mechanical properties of alloy on three rolling processes with13%,33%and47%first pressing volumes at the same total deformation are researched. Theresults show that the effect of the first pressing volume on microstructure and mechanicalproperties of Al-Mg-Si-Cu alloy sheet is significant, and the effect is geneticallyinherited.Degree of grain refinement precipitates fragmentation and tissue uniformity in the47%first pressing volume of alloy is obviously superior to that of13%and33%in contrast.The comprehensive mechanical properties of the47%first pressing volume of alloy is the best rolling sheet, the tensile strength is398.4MPa, the yield strength is325.8MPa, the elongationis20%and the hardness is112HB. The precipitations mainly existing in alloy sheet are Mg2Si,Al9Fe0.84Mn2.16Si, Al8Fe2Si and Al3Zr after rolling. After T6heat treatment, the grains are closeto equiaxed fine re-crystallization ones, and the precipitation phase is refined into smallparticle, distributing uniformly in the grain, and Mg2Si, Al9Fe0.84Mn2.16Si, Al8Fe2Si, Al3Zrphases can be observed mainly in the alloy sheet, the little AlCu and (AlCuMgSi) phases ofsheet also exist in alloy.The hardness of alloy after heating up solid solution treatment and high-temperature preprecipitation of solid solution processing increase firstly with higher of solution temperaturethen decrease. The hardness of alloy higher at large than the single solid solution treatment,but with a smaller increase.The alloy on540?×30min+580?×30minheating up solidsolution treatment and570?×30min+540?×30min high-temperature pre precipitation ofsolid solution processing have the best comprehensive mechanical properties.The hardness of alloy after natural aging and artificial aging treatment shows the doublepeaks feature. The alloy sample after180?×0.5h artificial aging treatment appears hardnesspeak after natural aging2d and4d, The alloy sample after180?×5h artificial aging treatmentappears hardness peak after natural aging1d and4d. At the same natural aging, the hardness ofalloy after180?×5h artificial aging treatment is higher than that after180?×0.5h artificialaging treatment.The strength and hardness of welded joints can be improved after proper heat treatment.The strength and hardness of welded joints after solid solution+aging treatment is the best bycomparing several kinds of heat treatment, the joint strength coefficient is83%. The strengthof welded joints with heat treatment before welding is higher than that of without heattreatment before welding, but the joint strength coefficient is not change obviously.For intergranular corrosion, the cross of corrosion specimen show no morphologicalfeatures of intergranular corrosion, but can be observed different size, different amount ofcorrosion pits depth in section of samples. The corrosion resistance of sample is the best after180?×0.5h artificial aging and natural aging48h treatment. The corrosion resistances ofsamples are excellent after artificial aging180?×5h and the15h natural aging treatment. Forthe exfoliation corrosion, the exfoliation corrosion rate of the alloys have certain fluctuations,but small fluctuations under different conditions, and consistent with corrosion morphology. |
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