【作者】 李赫亮；

【导师】 袁晓光；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2014， 博士

【摘要】 随着汽车工业的迅速发展，Al-Mg-Si合金在车辆上的应用越来越受到重视。为了降低成本、改善Al-Mg-Si合金力学性能，本文在6111合金成分基础上，确定了一种成分为Al-0.8Mg-1.0Si-0.8Cu-0.3Mn-0.5Fe-0.15Zr (wt%)的铝合金。通过对合金变形行为、轧制工艺、热处理工艺的组织及性能的研究，优化了工艺参数，获得了一种综合性能较好的Al-Mg-Si-Cu合金。合金铸锭采用凝固过程施加电磁搅拌获得，晶粒为等轴晶，第二相主要为β-Al2FeSi、Al9Fe0.84Mn2.16Si及Al4Cu2Mg8Si7(Q相)，并伴有极少量的Si和Mg2Si相，其抗拉强度、屈服强度、伸长率和硬度分别为158.6MPa、106.7MPa、5.8%、33.8HB；经均匀化退火后，第二相质点分布均匀，Mg2Si相、Al4Cu2Mg8Si7相消失；Mn元素替代了部分Fe元素，使针状β-Al2FeSi相转变为颗粒状的α-(FeMn)1.7Al4Si相。在热压缩变形时，Al-Mg-Si-Cu合金的流变应力随变形温度升高和应变速率降低而降低。在变形温度较高、应变速率较低、应变量较大时，在合金的变形区晶界附近生成大量新等轴状晶粒，亚晶合并、晶界弓出形核机制是Al-Mg-Si-Cu合金的主要动态再结晶机制；在应变速率较高、变形温度较低、应变量较小时，合金的动态软化机制是动态回复。通过计算得到合金的热压缩流变应力方程为：ε&=1.89×1010[sinh(0.024σ)]7.46×exp[166.85×103/(RT)]研究了总变形量相同条件下，首道次压下量分别为13%、33%和47%时，三种轧制工艺下合金的组织及性能。结果表明：首道次压下量对Al-Mg-Si-Cu合金的微观组织和力学性能影响显著，并且这种影响具有遗传性。在首道次压下量为47%时，析出相的破碎程度最大、组织最细小、均匀，其综合力学性能最好，抗拉强度、屈服强度、伸长率和硬度分别为398.4MPa、325.8MPa、20%、112HB；轧制终了时第二相主要为Mg2Si、Al9Fe0.84Mn2.16Si、Al8Fe2Si及Al3Zr等。经T6热处理后Mg2Si、Al8Fe2Si、Al9Fe0.84Mn2.16Si、Al3Zr相未发生变化，但出现了AlCu、(AlCuMgSi)相。经升温固溶处理和高温预析出固溶处理的合金布氏硬度均随固溶温度的升高呈先增大后减少的趋势。与单级固溶处理相比，硬度普遍得到提高，但提高的幅度较小。升温固溶处理合金在540℃×30min+580℃×30min时硬度最高；高温预析出固溶处理合金在570℃×30min+540℃×30min时硬度最高。经自然时效+人工时效处理后的合金的硬度呈双峰特征。在人工时效180℃×0.5h，自然时效2d和4d时出现硬度峰值；在人工时效180℃×5h，自然时效1d和4d时出现硬度峰值。在相同自然时效条件下，人工时效180℃×5h的合金硬化效果优于人工时效180℃×0.5h。采用适当的热处理工艺可提高焊接接头的强度和硬度；几种热处理工艺相比，焊后进行固溶+时效处理后焊接接头强度和硬度最高，接头强度系数83%；焊前热处理较未处理的焊件接头强度有所增加，但对焊件接头强度系数影响不大。晶间腐蚀实验表明：合金腐蚀后截面均未出现晶间腐蚀的形貌特征，但时效状态不同，出现不同程度的点蚀现象；在人工时效180℃×0.5h条件下，自然时效48h时合金抗晶间腐蚀性最好；在人工时效180℃×5h条件下，自然时效15h时合金抗晶间腐蚀性最好。剥落腐蚀实验表明：不同条件下剥落腐蚀速度出现一定波动，但总体上波动幅度不大，与腐蚀表观形貌基本吻合。更多还原

【Abstract】 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 β-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 β-Al2FeSi phase translates into particleα-(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:ε&=1.89×1010[sinh(0.024σ)]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.更多还原