Effect of intermetallic phases on the anodic oxidation and corrosion of 5A06 aluminum alloy

Intermetallic phases were found to influence the anodic oxidation and corrosion behavior of 5A06 aluminum alloy. Scattered intermetallic particles were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) after pretreatment. The anodic film was investigated by transmission electron microscopy (TEM), and its corrosion resistance was analyzed by electrochemical impedance spectroscopy (EIS) and Tafel polarization in NaCl solution. The results show that the size of Al-Fe-Mg-Mn particles gradually decreases with the iron content. During anodizing, these intermetallic particles are gradually dissolved, leading to the complex porosity in the anodic film beneath the particles. After anodizing, the residual particles are mainly silicon-containing phases, which are embedded in the anodic film. Electrochemical measurements indicate that the porous anodic film layer is easily penetrated, and the barrier plays a dominant role in the overall protection. Meanwhile, self-healing behavior is observed during the long immersion time.     

Reduction in secondary dendrite arm spacing in cast eutectic Al-Si piston alloys by cerium addition

The effects of Ce on the secondary dendrite arm spacing (SDAS) and mechanical behavior of Al-Si-Cu-Mg alloys were investigated. The reduction of SDAS at different Ce concentrations was evaluated in a directional solidification experiment via computer-aided cooling curve thermal analysis (CA CCTA). -The results showed that 0.1wt%-1.0wt% Ce addition resulted in a rapid solidification time, △T_S, and low solidification temperature, △T_S, whereas 0.1wt% Ce resulted in a fast solidification time, △ta-Al, of the α-Al phase. Furthermore, Ce addition refined the SDAS, which was reduced to approximately 36%. The mechanical properties of the alloys with and without Ce were investigated using tensile and hardness tests. The quality index (Q) and ultimate tensile strength of (UTS) Al-Si-Cu-Mg alloys significantly improved with the addition of 0.1wt% Ce. Moreover, the base alloy hardness was improved with increasing Ce concentration.     

循环加载下铸造铝合金中硅颗粒的破坏行为

研究了在等效应变幅为0.22%时ZL101 T6铝合金在单轴、比例、非比例圆形路径下的低周疲劳行为,并用金相显微镜观察了在循环加载条件下硅颗粒的破坏行为.结果表明:在循环加载下,硅颗粒表现出断裂和与铝基体界面分离2种破坏行为,但以断裂方式为主;硅颗粒的形貌、大小、分布对硅颗粒的断裂行为有重要影响,形貌率大、颗粒长轴方向平行于拉伸轴或位于试样表面、孔洞边沿突起的硅颗粒优先发生断裂;不同的加载路径可改变硅颗粒的断裂方式,在多轴非比例加载下,同一硅颗粒可能会在多个方向上发生断裂,而在单轴或比例加载下一般只能出现平行断裂或普通断裂;断裂硅颗粒可影响疲劳裂纹的萌生和扩展,在不同路径下硅颗粒的断裂速率由大到小依次是非比例网形路径、比例路径、单轴加载.     

Effect of the microstructure of Al 7050-T7451 on anodic oxide formation in sulfuric acid

The effect of the microstructure of an Al 7050-T7451 substrate on the anodic oxide formation in sulfuric acid was studied in this article. The microstructure of the substrate was assessed by optical microscope (OM) and transmission electron microscope (TEM). The surface and cross-section morphologies of the oxide films were examined by scanning electron microscope (SEM). The chemical composition of intermetallic particles in the alloys and films was investigated using energy dispersive spectroscope (EDS). The roles of intermetallic phases and grain or subgrain boundaries on the oxide film formation were researched using the potentiodynamic and potentiostatic polarization technique in sulfuric acid solution. The results show that the transition of coarse intermetallic particles or grain (subgrain) boundaries at the surface of Al alloys can be characterized by potentiodynamic polarization curves. The surface and cross-section micrographs of the anodic layer seem to preserve the microstructure of the substrate. Large cavities in the anodic films are caused by the preferential dissolution of coarse AItCuMg particles and the entrance of Cu-rich remnants into the electrolyte during anodizing. The Al₇Cu₂Fe particles tend to be occluded in the oxide layer or lose from the oxide surface because of peripheral trenching. Small pores in the films are induced by the dissolution of precipitates in grain or subgrain boundaries. The film surface of recrystallized grain bodies is smooth and homogeneous.     

草酸中多孔阳极氧化铝膜生长动力学和形态结构研究

为分析多孔阳极氧化铝膜形态参数和氧化条件的关系,在恒流条件下对0.3 mol·L-1草酸电解中形成多孔膜的生长动力学进行了研究.采用扫描电子显微镜和氧化膜质量测定方法检验了电流密度、温度和氧化时间对氧化膜生长动力学和氧化膜形态的影响.通过电压-时间曲线研究了氧化膜的电化学特征,并采用一元线性回归模型预测了氧化膜的生长速率.实验结果表明氧化膜的生长速率随电流密度的升高而升高,随温度的升高而下降.氧化膜质量的增长速率也随着电流密度的升高而增大.     

草酸中多孔阳极氧化铝膜生长动力学和形态结构研究

为分析多孔阳极氧化铝膜形态参数和氧化条件的关系,在恒流条件下对0.3 mol.L-1草酸电解中形成多孔膜的生长动力学进行了研究.采用扫描电子显微镜和氧化膜质量测定方法检验了电流密度、温度和氧化时间对氧化膜生长动力学和氧化膜形态的影响.通过电压-时间曲线研究了氧化膜的电化学特征,并采用一元线性回归模型预测了氧化膜的生长速率.实验结果表明氧化膜的生长速率随电流密度的升高而升高,随温度的升高而下降.氧化膜质量的增长速率也随着电流密度的升高而增大.     

间接挤压铸造工艺参数对铝合金中Si偏析的影响

研究间接挤压铸造工艺条件下,浇注温度、挤压压力、挤压速度、冷却速度及参数间的交互作用对6066铝合金中Si元素的偏析影响规律. 以凝固后零件热节位置硅的质量分数与合金初始硅的质量分数的差值定量表征偏析程度,采用考虑一级交互作用的四因素两水平正交设计,研究间接挤压条件下硅的偏析现象. 结果发现:浇注温度、挤压压力、挤压速度和冷却速度对硅偏析都有影响,其中浇注温度是影响最显著的因素. 随着浇注温度的升高,铝合金中Si偏析程度减小. 挤压压力和挤压速度对硅偏析的影响次之,但两者的影响趋势相反;模具冷却能力的影响程度与挤压压力和挤压速度的交互作用的影响程度相似,铜模套(高冷速)比钢模套(低冷速)的硅偏析程度要轻. 间接挤压铸造条件下,工件热节位置可以出现硅的负偏析.