镱对AZ91D镁合金显微组织和力学性能的影响

在Mg-9Al-1Zn合金的基础上添加不同质量分数的Yb,制备了4种合金。通过X射线衍射、金相显微镜、扫描电镜及能谱分析仪等手段分析了Yb的添加对AZ91D显微组织和力学性能的影响。结果表明:Yb的加入,显著改变了AZ91D合金的铸态组织,细化了β-Mg17Al12相,且β-Mg17Al12脆性相由连续网状分布逐渐变为离散状,同时晶界上出现了块状的Al11Yb3和点状Al6Mn4Yb化合物。当Yb含量为1.0%时,该合金具有最佳的综合力学性能,抗拉强度达到194 MPa,比AZ91D提高22%,伸长率和硬度也随着Yb含量的增加而提高。研究表明,重稀土元素Yb在镁合金中显示出与轻稀土更相近的作用效果。

Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro-arc oxidization technique

With increasing applied voltage, three types of anodic coatings, passive film, micro-spark ceramic coating and spark ceramic coating were made by micro-arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali-silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro-spark ceramic coating, prepared in the voltage range of 170similar to220V exhibits compact, homogeneous structure and highest corrosion-resistance.

Microstructures and mechanical properties of as-cast Mg–5Al–0.4Mn–xNd (x=0, 1, 2 and 4) alloys

Mg-5Al-0.4Mn-xNd (x=0, 1, 2 and 4wt.%) alloys were prepared by metal mould casting method. The microstructures and mechanical properties were investigated. The results demonstrated that Al11Nd3 phase was formed and mainly aggregated along the grain boundaries with the addition of Nd. Meanwhile, the grain sizes were greatly reduced with the increasing Nd content.

Electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd in NaCl solution

The electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd (x = 0, 1, 2 and 4 wt.%) alloys in 3.5% NaCl solution was investigated. The corrosion behavior of the alloys was assessed by open circuit potential measure, potentiodynamic polarization, and electrochemical impedance spectroscopy. The electrochemical results show the intermetallic precipitates with Nd behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. During corrosion, Al2O3 and Nd2O3, in proper ratio, is incorporated into the corrosion film, and enhances the corrosion resistance.

Effects of spark discharge on the anodic coatings on magnesium alloy

Spark discharge was the representative phenomenon of Micro-arc oxidation (MAO) method distinguished from other electrochemical oxidation methods. Under the spark discharge treatment, characteristics of the anodic layer were significantly changed. To investigate the influences of the spark discharge, a piece of magnesium alloy AZ91D specimen was partly treated by MAO method in alkaline silicate solution. And the microstructure, element distributions as well as the surface potential distributions of the specimen were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and scanning Kelvin probe (SKP) technique. As a result of intensive spark discharge treatment, porous external layer with dense internal layer were formed on Mg alloy surface. At the same time, the depositions of OH- and SiO32- ions were accelerated, which resulted in the enrichment of element oxygen and silicon at the spark discharge region. Moreover, due to the compact internal layer, the intensive spark discharge region exhibited more positive potentials with respect to other regions, which meant this region could restrain the ejection of electron and provide effective protection to the substrate. In addition, it was found that oxygen played a vital role in determining the intensity and size of sparks, and abundant oxygen resulted in intensive and larger sparks. (c) 2005 Elsevier B.V. All rights reserved.