Improving the wear resistance of AZ91D magnesium alloys by laser cladding with Al-Si powders

To improve the wear resistance of AZ91D magnesium alloy, laser surface cladding with Al and Si powders was investigated using a Nd:YAG pulsed laser. With appropriate processing parameters and the suitable weight ratio of Al to Si in powders, a modified surface layer free of cracks and pores was formed by reaction synthesis of Mg with Al and Si. X-ray diffractometry (XRD) confirmed the main phases in the layer to be Mg₂Si and Mg₁₇Al₁₂. The surface hardness increased from 35 HV for as-received magnesium alloy to more than 170 HV for laser treated sample. Accompanying the increase in hardness, the wear resistance of the clad layer increased more than 4 times that of the substrate.     

Effect of neodymium on microstructure and corrosion resistance of AZ91 magnesium alloy

The corrosion behavior of a new Mg–9Al–1Zn (AZ91) magnesium alloy containing neodymium (Nd) is investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), immersion tests and electrochemical experiments. The results indicate that Nd decreases the size and volume fraction of the β (Mg₁₇Al₁₂) phase and forms Al₂Nd in the alloy. In addition, during corrosion, Nd is incorporated into corrosion film in the form of Nd₂O₃. AZ91 alloy containing 1.0 wt.% Nd possesses an outstanding passivation property and excellent corrosion resistance. The corrosion resistance enhancement is attributed to the reduction in the size and volume fraction of the β phase and the incorporation of Nd₂O₃ in the corrosion film.     

AZ91D镁合金表面电沉积n-ZrO2/Ni复合镀层及耐蚀性研究

在AZ91D镁合金表面化学镀Ni-P的基础上电沉积n-ZrO2/Ni复合镀层和纯Ni电镀层,并对其表面形貌、截面形貌和耐蚀性进行了对比分析。结果表明AZ91D镁合金表面电沉积纳米复合镀层比纯镍镀层组织更细小,镀层更致密、平整。n-ZrO2/Ni复合镀层具有明显的钝化区,具有良好耐蚀性。     

Corrosion and wear resistance of AZ91D magnesium alloy with and without microarc oxidation coating in Hank’s solution

Immersion test, electrochemistry test and block-on-cylinder type wear test have been applied to study the corrosion and wear resistance of AZ91D Mg alloy with and without microarc oxidation (MAO) treatment in Hank’s solution. Through MAO, a ceramic coating is directly formed on the surface of AZ91D Mg alloy, by which its corrosion and wear resistances are greatly improved. The immersion test results show the mass loss of untreated AZ91D Mg is 15 times of that of MAO ones after 21 days immersion test. The electrochemical corrosion experiments show that the corrosion potential of Mg alloy is improved from −1.5786 V to −0.43019 V through MAO surface treatment, the corrosion current is reduced from 0.028703 A/cm² to 2.0456 × 10⁻⁷ A/cm², and the polarization resistance is improved from 1.2753 × 10⁻⁵ Ω/cm² to 0.90886 Ω/cm². The lubricate sliding wear test results show the mass loss of untreated AZ91D Mg is 1.5 times of that of MAO ones.     

AZ31镁合金表面激光熔覆Al-TiC复合涂层微观组织与腐蚀性能

为有效改善AZ31镁合金表面的腐蚀性能,本文采用激光熔覆技术在AZ31镁合金表面成功制备了无缺陷的Al-TiC复合涂层。研究了不同成分含量的Al-TiC复合涂层的相组成、微观组织和耐腐蚀性能的影响。结果表明：在Al-TiC复合涂层内形成了大量的Al₁₂Mg₁₇、Mg₂Al₃和TiC相。复合涂层内微观组织呈现出连续网络状分布特征。随着Al-TiC混合粉末中Al含量的减小,复合涂层中Al₁₂Mg₁₇、Mg₂Al₃和TiC相的含量呈递增趋势,网络状分布的微观组织结构变得更加均匀连续。复合涂层与AZ31基体之间形成了良好的冶金结合界面。激光熔覆制备的Al-TiC复合涂层耐腐蚀性能较AZ31基体显著提升。自腐蚀电位由基体的-1.563 V提升至-1.144 V,自腐蚀电流由基体的1.55×10^-4 A减小至2.63×10^-6 A。     

Organic coatings silane-based for AZ91D magnesium alloy

Organic coatings silane-based containing electron withdrawing group or electron donating group have been synthesized and evaluated as prospective surface treatments for AZ91D magnesium alloy by hydrolysis and condensation reaction of the different silanes. Electrochemical tests were employed to confirm the corrosion resistance ability of the two kinds of organic coatings. The results showed that the coating with electron donating group had better corrosion protection performance. On the basis of the spatial configuration and the density of charge of those silanes molecules which was obtained through Gaussian 03 procedure based on B3LYP and density functional theory, combining experiment results, the rational explanation was provided.     

Calorimetric analysis of AZ91D magnesium alloy

In order to study the activation energies and microstructure evolution of β-Mg₁₇Al₁₂ and eutectic structure in AZ91D magnesium alloy, calorimetric analyses were carried out using non-isothermal measurements by DSC and scanning electron microscopy (SEM) with EDX. During DSC tests, two peak temperatures of β-Mg₁₇Al₁₂ dissolution/precipitation and eutectic transformation were delayed in the heating/cooling process with the increase of scanning rates due to the occurrence of superheating/supercooling. Activation energies of β-Mg₁₇Al₁₂ dissolution and eutectic transformation were derived using multiple heating rates. Furthermore, the results of SEM and EDX revealed that the size and morphology of eutectic structures in the alloy had a close relationship with the time of β-Mg₁₇Al₁₂ phase dissolution during the heating process. More eutectic structures formed at low scanning rate due to sufficient time for the diffusion of Al in α-Mg regions.     

植酸浓度对AZ91D镁合金表面植酸转化膜的影响

选择AZ91D镁合金为实验材料,在通过正交实验优化镁合金表面植酸转化膜成膜工艺的基础上,利用扫描电镜、能谱分析、点蚀实验和电化学测量等分析手段研究了植酸浓度对植酸转化膜表面形貌、表面成分及其耐蚀性的影响.结果表明植酸转化膜主要由Mg、A1、O、P和C元素组成,其中Mg元素含量随着植酸浓度的增大而减小,而P元素含量随着植...     

Microarc oxidation coating formed on SiCw/AZ91 magnesium matrix composite and its corrosion resistance

A ceramic coating was synthesized on the surface of SiCw/AZ91 magnesium matrix composite by means of microarc oxidation (MAO) technique. Scanning electron microscope (SEM) was employed to characterize the surface morphology and cross-section microstructure of the coating. The phase structure and the chemical composition of the ceramic coating were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coating was evaluated by immersion test and electrochemical method. The results showed that the corrosion rate of the coated SiCw/AZ91 composite was decreased greatly compared with that of the bare composite because of the protective microarc oxidation coating.     

Surface coatings for improving the corrosion resistance and cell adhesion of AZ91D magnesium alloy through environmentally clean methods

Two different coatings, Mg-Al hydrotalcite and aragonite (CaCO₃), were produced on die-cast AZ91D Mg alloy (Mg-9wt.%Al-1wt.%Zn) through environmentally clean methods. The corrosion resistance and human mesenchymal stem cell adhesion properties of the coatings on AZ91D were investigated. Results showed that through environmentally clean methods, both Mg-Al hydrotalcite and aragonite CaCO₃ surface coatings could be produced on AZ91D surfaces. These coatings increased the corrosion potential and polarization resistance and decreased the corrosion rate of AZ91D in simulated body fluid. Both surface coatings also improved stem cell spreading and interaction in culture. Further long-term animal testing is suggested before these surface coatings can be recommended for use in clinical applications.     

AZ91D镁合金锌系磷化膜成膜机理和生长过程的研究

以磷酸盐化学转化膜为研究体系,采用SEM、XRD、OCP等分析方法及检测手段,研究AZ91D镁合金系磷酸盐化学转化膜的成膜机理、膜层结构及生长过程。研究发现AZ91D镁合金在磷化液中成膜过程分5个阶段:初始成核(1～5s)、基体快速溶解(5～60s)、晶体快速生长(1～2min)、膜层稳态生长(2～10min)和膜层沉积溶解平衡阶段(10min以后)。AZ91D镁合金表面的磷酸盐晶核的形成并非在金属进入溶液的最初时刻一次形成,是分批形成。最先形成的晶核逐渐长大,新的晶核不断生成,磷酸盐晶粒对其表面的覆盖度逐渐增大,直至各个晶粒逐渐长大相互接界,将其表面完全覆盖,结晶过程结束。晶核的形成未优先发生在基体金属的晶界上,随着晶核的生长和外延而形成磷化膜。     

乙醇胺添加剂对AZ91D镁合金表面磷化膜微观结构的影响研究

以锌系磷酸盐化学转化膜为研究体系,采用SEM,XRD分析方法及检测手段,研究乙醇胺(MEA)添加剂及其浓度对AZ91D镁合金锌系磷酸盐化学转化膜微观结构的影响.研究发现由于锌系磷化液中乙醇胺的添加:(1)改变了AZ91D镁合金锌系磷化膜晶体层的微观结构,促进了晶核的形成和晶粒细化,晶簇间隙中晶核的形成对晶体膜层完整性和致密度起着关键作用;(2)对(Zn_3(PO_4)_2·_4H_2O)晶体的取向有影响,有控制晶簇尺寸使磷化结晶组织更均匀的作用;(3)MEA在1.2g/L时磷化膜层平整致密、晶簇的尺寸均匀缺陷最少;(4)锌系磷化膜有两层结构:(Zn_3(PO_4)_2·_4H_2O)晶体外层和非晶态内层;(5)MEA的不同添加量对晶体层孔隙的影响有3种类型:表面浅孔(a型),晶簇间缝隙或微裂纹(b型),开放缺陷(c型).     

乙醇胺添加剂对AZ91D镁合金表面磷化膜耐蚀性能的影响研究

以磷酸盐化学转化膜为研究体系,采用动电位极化和交流阻抗分析方法及检测手段,研究乙醇胺添加剂及其浓度对AZ91D镁合金磷化膜耐蚀性能的影响.研究发现,(1)乙醇胺(MEA)作为添加剂可有效改善AZ91D镁合金表面磷化膜的耐蚀性能.在MEA添加量为1.2g/L时,磷化膜的耐蚀性最好.添加乙醇胺1.2g/L时制备的磷化膜,在3.5%(质量分数)NaCl溶液中的耐蚀性能比AZ91D镁合金基体提高了10倍;(2)MEA浓度在0.4～1.2g/L时,磷化膜的R_(ct)随MEA浓度增加成线性增长关系.MEA浓度1.2g/L时达到最大值.磷化膜的R_p在MEA浓度为1.2g/L时达到最高值.当MEA浓度继续增加时,R_p明显下降.MEA浓度控制在0.8＜C_(MEA)＜1.6g/L时获得的磷化膜的耐蚀性能最好.     

AZ91D镁合金超疏水膜层的制备及其表征

采用简单易行的化学刻蚀方法,通过硝酸刻蚀、化学镀银和硬脂酸自组装改性处理,在AZ91D镁合金表面上成功制备出了超疏水膜层,进一步解释了该制备工艺的化学反应机理。利用扫描电子显微镜和视频光学接触角测量仪对AZ91D镁合金表面超疏水膜层的微观形貌和润湿性能进行了表征,利用能谱仪和光谱仪测定了膜层的表面化学组成。结果显示,釆用上述方法处理后的AZ91D镁合金表面呈现出良好的疏水性,水滴在试样表面的表观接触角为153°,滚动角为4°。     

AZ91D镁合金化学镀Ni-P/Ni-W-P双层镀层研究

为了提高镁合金的耐磨耐蚀性,研究了一种镁合金直接化学镀Ni-P/Ni-W-P双层镀层的方法.采用扫描电镜(SEM)和X-射线衍分析射仪(XRD)分析了镀层的微观结构.对镀层进行了极化曲线分析,并进行了盐酸腐蚀试验和结合力试验.结果表明,该复合镀层组织致密无孔,具有较高的显微硬度和高耐蚀性.镀层硬度可达622HKV,试样在10%的HCl溶液中可保持近3h不腐蚀基体,对镁合金起到很好的保护作用.     

半固态AZ91D镁合金的压缩变形和显微组织

利用平行板触变压缩仪研究了电磁搅拌的半固态AZ91D合金试样的压缩变形和组织.结果表明:随着半固态压缩变形温度的升高,AZ91D镁合金试样变形的速度加快,即变形应变速度增大,但压缩应力不断下降;在某一载荷下,AZ91D镁合金试样压缩变形应力和应变呈明显的线性关系,与压缩温度的高低无关.随着半固态压缩载荷的提高,AZ91D镁合金试样变形的速度增加,应变速度增大,应力下降速度加快;在不同的压缩载荷下,AZ91D镁合金试样的压缩变形应力和应变都呈明显的线性关系.在实验中的各种半固态压缩变形条件下,初生α-Mg在压缩后AZ91D镁合金试样组织中的分布很均匀,几乎不存在组织偏析.当初生固相的形态呈球状结构,在相同的变形条件下,不同种类合金的半固态压缩变形规律非常相似.     

Microstructure and mechanical properties of rheo-diecast AZ91D magnesium alloy

A new semisolid metal processing technology, rheo-diecasting (RDC) has been developed for production of Mg-alloy components with high integrity. The RDC process innovatively combines the dispersive mixing power of the twin-screw mechanism for creation of high quality semisolid slurry and the high efficiency, low cost nature of the high pressure die casting (HPDC) process for component shaping. AZ91D Mg-alloy was used to optimise the RDC process and to establish its advantages over both the HPDC process and other existing semisolid processing techniques. In this paper we present the RDC process for processing Mg-alloys and the resulting microstructure and mechanical properties of RDC AZ91D alloy. The solidification behaviour of the Mg-alloys in the RDC process and the co-relationships between microstructure and mechanical properties of the RDC AZ91D alloy are discussed. It was found that the RDC process is capable of producing Mg-alloy samples with close-to-zero porosity and a fine, uniform microstructure throughout the entire sample irrespective of the section thickness. Compared with those obtained by other existing processing techniques, the RDC samples have substantially improved or equivalent mechanical properties, with the tensile elongation showing more than 100% improvement.     

AZ91D镁合金托弹板半固态触变模锻研究

为了掌握半固态触变模锻中工艺参数对成形零件的微观组织和力学性能的影响规律,借助拉伸试验机和金相显微镜对AZ91D镁合金托弹板的半固态触变模锻过程进行了研究.AZ91D镁合金半固态坯料分别采用传统SIMA法和新SIMA法制备.结果表明:压力对托弹板零件的充型过程有很大影响,当压力为500 kN,托弹板零件充型不满;当压力为2000 kN,托弹板零件充型良好.坯料加热温度和保温时间对托弹板零件的力学性能有一定影响.当压力为2000 kN,模具预热温度为450 ℃,坯料在545 ℃保温20 min时,新SIMA法制备的半固态坯半固态触变模锻成形的托弹板零件获得最佳的力学性能.与传统SIMA法相比,新SIMA法制备的半固态坯成形的托弹板零件的室温力学性能和100℃的高温力学性有很大提高.