Development of microarc oxidation process to improve corrosion resistance on AZ91HP magnesium alloy

A new anodizing process, which does not contain chromate but can improve the corrosion resistance of magnesium alloys significantly, was developed using a microarc power supply. Surface morphology was observed and the coating was compact and ceramic-like. In addition, the corrosion resistance of samples before and aider anodization by the new process and a method in US Patent 5470664 was compared by potentiodymaic polarization curves, electrochemical impedance spectroscopy （EIS） and salt spray test. The results show that the anodization can improve the corrosion resistance of magnesium alloy. The samples obtained by the new process and the method mentioned in the US Patent 5470664 achieve 9 and 7 rates aider 336 h salt spray test, respectively.     

Preparation and corrosion resistance of superhydrophobic coatings on AZ31 magnesium alloy

In order to improve the corrosion resistance of the Mg alloys, the superhydrophobic coatings on AZ31 Mg alloy were prepared by a two-step process of micro-arc oxidation treatment and superhydrophobic treatment in stearic acid ethanol solution. The effects of voltages, frequencies and treatment time on the contact angle of the superhydrophobic treated sample were investigated. The results showed that with increasing the voltage, frequency and treatment time, all of the contact angles of the superhydrophobic treated sample increased first, and then decreased, reaching the maximum values at 350 V, 1000 Hz and 5 min, respectively. The optimal superhydrophobic coating was mainly composed of MgO and Mg₂SiO₄ phases, with the pore diameter of ～900 nm, the thickness of ～6.86 μm and the contact angle of 156.96°. The corrosion current density of the superhydrophobic AZ31 sample decreased by three orders of magnitude, and the amount of hydrogen evolution decreased by 94.77% compared with that of the AZ31 substrate sample.     

微弧氧化电解液中加入Al_2O_3胶体对AZ91D复合陶瓷层性能的影响

在硅酸盐体系中加入Al_2O_3胶体对AZ91D镁合金进行微弧氧化,研究了Al_2O_3胶体的加入时间和加入量对陶瓷层组成、结构以及耐蚀性的影响。结果表明,在微弧氧化后期6 min(约为总氧化时间的3/5)时加入Al_2O_3胶体生成的复合陶瓷层耐蚀性最好;随Al_2O_3胶体用量的增加,陶瓷层的腐蚀速度明显减小,但当用量约超过电解液总容量的20%时,对陶瓷层的耐蚀性能提高不明显。     

电解质对AZ91D镁合金微弧氧化的影响

在Na2SiO3和NaAlO2为主成膜剂的硅铝复合电解液中,利用交流脉冲电源对AZ91D镁合金进行微弧氧化处理,研究主成膜剂含量的变化对微弧氧化过程及膜层特性的影响规律。利用扫描电镜(SEM)和膜层测厚仪分别研究了膜层的微观形貌和膜层厚度,通过电化学阻抗谱(EIS)测试膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,随着主成膜剂含量的增加,微弧氧化过程中起弧电压和终止电压均呈下降的变化趋势,而膜层耐蚀性则基本呈先增大后降低的变化趋势,膜厚的变化趋势与其耐蚀性一致;Na2SiO3含量的变化对膜层内部致密层和外部疏松层的耐蚀性均有影响,而NaAlO2含量的变化则主要影响膜层内部致密层的耐蚀性;适量的主成膜剂含量是获得致密耐蚀膜层的关键。     

Influence of intermetallic Al-Mn particles on in-situ steam Mg-Al-LDH coating on AZ31 magnesium alloy

The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide (Mg-Al-CO₃^2--LDH) steam coating on AZ31 Mg alloy was investigated. The alloy was pretreated with H₃PO₄, HCl, HNO₃ or citric acid (CA), followed by hydrothermal treatment, for the fabrication of Mg-Al-LDH coating. The microstructure, composition and corrosion resistance of the coated samples were investigated. The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment, which promotes the growth of the Mg-Al-LDH steam coating. Further, the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings. The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy.     

微弧表面处理对AZ31B镁合金耐腐蚀及耐腐蚀疲劳性能的影响

采用微弧表面处理技术(微弧氧化MAO和微弧复合MCC)在AZ31B镁合金基体上制备出不同断面结构的防护涂层。通过电化学腐蚀及腐蚀疲劳测试方法,研究了MAO、MCC涂层的电化学腐蚀及腐蚀疲劳性能。结果表明,生长10 min的MAO涂层具有较好的耐电化学腐蚀性能。MAO涂层表面存在微孔和微裂纹,在应力条件下微孔和微裂纹作为疲劳断裂的裂纹萌生点,可加速裂纹的萌生与扩展,使其腐蚀疲劳寿命相较AZ31B合金基体降低了55%。而具有MCC涂层的AZ31B合金试样腐蚀疲劳极限为(64.0±5.4) MPa,比AZ31B合金基体提高了59%。在低应力载荷下(＜80 MPa),微弧复合涂层试样的腐蚀疲劳强度得到明显提高。     

镁合金微弧氧化陶瓷膜的制备及耐蚀性能

利用微弧氧化技术在AZ91D镁合金表面原位生成含有钙、磷元素的陶瓷膜层.用SEM、XRD、EDS等研究陶瓷膜微观形貌、相组成及元素含量,利用Tafel和EIS技术来评价陶瓷膜的腐蚀性能.结果表明,所制备的陶瓷膜层成功地引入了钙和磷元素,陶瓷膜层主要由Mg2SiO4和MgO相组成.增加钙盐浓度,可以使膜层内的钙元素含量增多,微孔增加并且出现了微裂纹.电化学测试表明陶瓷膜使得镁合金在0.9%NaCl生理盐水中的耐蚀性提高了1～2个数量级,当钙盐浓度为0.3 g/L时,陶瓷膜层的耐蚀性最好.     

AZ31镁合金盐浴渗铝改善耐蚀性机制分析

采用真空热扩散渗铝的方法对AZ31镁合金进行表面合金化处理,在不同参数下得到厚度不一的渗铝层,对渗层的显微组织、物相组成进行了分析,并分析了渗铝试样的耐腐蚀性能和显微硬度.绘制了AZ31镁合金基体以及经过400℃扩散渗铝4 h后的试样的极化曲线.结果表明,渗层主要由Mg₁₇Al₁₂,Mg₃Al₂和α-Mg等组成,渗层厚度随扩散温度提高而增加,400℃恒温热扩散4 h时,在基体表面获得了连续且均匀细密的渗铝层,显微硬度值从基体的53 HV提高到80~85 HV,同时,该方法使得镁合金的自腐蚀电位提高了约105 mV,而镁合金的自腐蚀电流密度降低了一个数量级,这表征着镁合金的耐蚀性能得到提高.     

AZ31B镁合金点焊接头的断口特征和耐蚀性分析

利用DN-100型固定式点焊机对AZ31B镁合金进行焊接,采用X射线衍射仪对点焊接头进行物相分析;用光学显微镜对点焊接头进行金相分析;用SEM研究点焊接头断口的微观形貌;并对焊接接头耐蚀性进行实验研究.结果表明,AZ31B镁合金母材为韧性断裂,点焊接头为脆性断裂,点焊接头的断裂倾向比母材大,耐蚀性不及母材.     

钛离子注入对AZ31镁合金表面力学性能及耐蚀性的影响

对AZ31镁合金表面进行了钛离子注入试验,研究了钛离子注入对于镁合金表面改性层的影响。通过XRD、XPS研究了改性层的相结构和元素分布,通过硬度和摩擦磨损试验研究了改性层的力学性能。结果表明,经过钛离子注入之后,改性层中并无新相生成;当注入剂量为2.5×1017ion/cm2时,改性层深度可以达到160 nm,改性层中Ti呈高斯分布,存在形式从外到内为TiO2向Ti过渡。经过钛离子注入之后,镁合金表面硬度大大提高;改性层的摩擦因数并没有降低,但是耐磨性有所提高。随钛离子注入剂量的增加,改性层的耐腐蚀性能呈先上升后下降趋势。     

Al3Ti3B中间合金对AZ91D镁合金组织及力学性能的影响

研究了Al3Ti3B中间合金对AZ91D镁合金显微组织及力学性能的影响.通过光学显微镜和扫描电子显微镜观察发现,Al3Ti3B中间合金能显著减小AZ91D合金的二次枝晶臂间距与晶粒尺寸,在加入0.3%Al3Ti3B时晶粒尺寸就由原来的约260 μm减小至约100μm.伴随着合金晶粒尺寸的减小,合金的抗拉强度、屈服强度和延伸率都明显提高,这主要是由于晶粒细化后能阻碍裂纹扩展的有效晶界增多,晶界强化作用显著;同时,Al3Ti3B中间合金的加入促使溶质均匀分布,使共晶体(α Mg17Al12)形貌发生改变,共晶体尺寸减小,这有利于裂纹切过脆性的共晶体传播,提高合金的变形协调能力.     

CeO2对Al2O3基陶瓷涂层耐蚀性的影响

通过优化Al2O3基陶瓷涂层配方和工艺,并加入适量的稀土氧化物CeO2,对陶瓷涂层的界面形貌、组织结构、结合力和耐蚀性进行了研究。结果表明,添加适量的稀土氧化物CeO2,使Al2O3基陶瓷涂层致密性、结合力和耐蚀性得到提高。     

Effects of Ce addition on microstructure,mechanical properties and corrosion resistance of as-cast AZ80 magnesium alloy

In this study, Ce was introduced into the AZ80 alloy and the effects of Ce addition on the microstructure, mechanical properties and corrosion resistance of the as-cast AZ80 magnesium alloy were investigated. The results show that the addition of Ce into the AZ80 alloy can not only refine the microstructure, but also result in the formation of the needle-like Al4Ce phase. These tiny Al4Ce phases are homogeneously distributed at grain boundaries and within grains. An appropriate Ce addition can also change the β-Mg17Al12 phase at the grain boundaries from continuous network to small island-like. At the same time, with the increase of Ce content from 0 to 2.0wt.%, the macro-hardness of the as-cast alloy is enhanced linearly, while impact toughness, tensile strength and elongation all firstly increase and then decrease. The AZ80 alloy containing 1.0wt.% Ce exhibits the optimal properties. Its macro-hardness, impact toughness, tensile strength and elongation are 61.90 HB, 15.50 J·cm^-2, 171.80 MPa and 3.35%, increase by 9.95%, 63%, 13.3% and 36.7%, respectively compared with the base alloy. In addition, Ce can enhance the corrosion resistance of the AZ80 magnesium alloy.     

AZ91D镁合金表面激光熔覆Al+WC+La_2O_3复合涂层性能的研究

在Al+WC复合粉末中添加不同量的La_2O_3,利用激光形成熔覆层。采用金相显微镜、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、能谱仪(EDS)分析不同含量的稀土La_2O_3对涂层的显微组织、物相组成及性能影响。研究表明,由于稀土的加入,复合涂层的晶粒进一步细化。当稀土含量为1.2%时涂层的平均显微硬度为280 HV,相比AZ91D镁合金基体的60 HV提高了约4.5倍。     

Effects of organic acid pickling on the corrosion resistance of magnesium alloy AZ31 sheet

Organic acids were used to clean AZ31 magnesium alloy sheet and the effect of the cleaning processes on the surface condition and corrosion performance of the alloy was investigated. Organic acid cleanings reduced the surface impurities and enhanced the corrosion resistance. Removal of at least 4 μm of the contaminated surface was required to reach corrosion rates less than 1 mm/year in salt spray condition. Among the three organic acids examined, acetic acid is the best choice. Oxalic acid can be an alternative while citric acid is not suitable for cleaning AZ31 sheet, because of insufficient removal of iron impurities.     

碱热处理对搅拌摩擦加工AZ31镁合金耐腐蚀性能的影响

对AZ31镁合金进行搅拌摩擦加工(Friction stir processing,FSP),并对母材(Basal material, BM)和FSP试样进行碱热处理(Alkali heat treatment,AHT),研究了AHT对搅拌摩擦加工后AZ31镁合金微观组织和耐腐蚀性能的影响。结果表明,FSP可以显著细化晶粒,平均晶粒尺寸由BM的12.8 μm细化至FSP后的3.1 μm,高角度晶界比例从BM的75.9%降低至FSP后的45.3%,晶界亚结构增多。AHT使材料表面形成致密的MgO和Al₂O₃混合涂层,有效地提高了AZ31镁合金的耐浸泡腐蚀性能。     

AZ31镁合金表面液相渗铝的工艺与性能

采用液相扩渗技术在挤压态AZ31镁合金表面快速渗入铝，在合金表面获得过共晶渗层，并对渗层的成分、相组成、扩渗过程、纳米硬度和腐蚀性能进行分析。结果表明：AZ31镁合金在480℃热扩渗铝过程中发生了“熔化—凝固”变化，渗层为典型的过共晶组织：渗铝层含有Mg17A112相和镁的铝饱和固溶体，这种渗层具有较高的纳米硬度和较好的耐腐蚀性能；通过提高扩渗温度进行液相扩渗可以大大提高扩渗速度，但由于快速凝固收缩会造成表层产生起伏现象，控制冷却速度可以将表层起伏控制在可接受的范围。     

AZ31镁合金在TMPAC-AlCl3离子液体中电镀铝

采用TMPAC-AlCl3离子液体,在浸锌后的镁合金AZ31表面实施恒流电镀铝,采用电化学技术评估镀铝层的耐蚀性,并采用SEM/EDX等技术表征镀层。结果表明：在浸锌后的镁合金表面可获得表面光洁的银白色镀铝层。在不同的电流密度下,呈现出两种形貌不同的镀铝层;在较佳电流密度12.3mA/cm2时,镀铝层表面较致密;电镀时间越长,镀层越厚,镀铝层耐蚀性越好。     

镁合金等离子喷涂Al/Al_2O_3涂层的耐腐蚀性能

采用等离子喷涂技术在AZ31镁合金表面制备Al/Al_2O_3复合涂层,测试了镁合金及表面喷涂有Al/Al_2O_3复合涂层的镁合金试样的极化曲线,研究了没有涂层、经封孔处理和未经封孔处理的喷涂有复合涂层的镁合金三种试样在浸泡腐蚀和5%NaCl盐雾腐蚀情况下的耐腐蚀性能及其腐蚀行为.结果表明,经封孔处理的Al/Al_2O_3复合涂层镁合金试样在上述腐蚀条件下的耐腐蚀性均优于镁合金和涂层未封孔处理的试样,在浸泡试验中未封孔处理的涂层试样比镁合金腐蚀更加严重,在盐雾试验中却优于镁合金.