微弧氧化处理对AZ91D镁合金腐蚀行为的影响

采用碱性硅酸盐溶液,在AZ91D镁合金试样表面制得微弧氧化膜,并利用电化学阻抗方法对镁合金及微弧氧化处理试样在3.5%NaCl溶液中的腐蚀行为进行比较研究.结果表明,镁合金经微弧氧化处理后,腐蚀电位和膜层阻抗均有一定程度的提高.但在浸泡过程中,微弧氧化处理试样的电化学参数呈现出不同的变化规律,初期波动较大,后期则逐渐降低,趋向稳定.     

镁合金黑色微弧氧化膜在NaCl溶液中腐蚀电化学演变

目的 评价镁合金黑色微弧氧化热控膜层在氯离子作用下的腐蚀演变行为.方法 在电解液中添加不同浓度的添加剂制备微弧氧化膜层,分析不同微弧氧化膜试样在0.1 mol/L NaCl溶液中的电化学演变过程.采用电化学极化、电化学交流阻抗表征和拟合,结合扫描电镜等方法,对膜层演变规律及机理进行了探讨.结果 未经微弧氧化的镁合金自腐蚀电流密度为17.7 μA/cm2,自腐蚀电位为-1.464 V;经微弧氧化后,试样自腐蚀电流密度减小至0.09 μA/cm2,自腐蚀电位下降至-1.628 V.添加剂加入后制备的微弧氧化膜相比于镁合金基体,其耐蚀性能提高,且随着添加剂浓度的增加,耐蚀效果呈现先增加、后减弱的趋势,添加剂质量浓度在10 g/L时制备的膜层具有最好的防腐效果.镁合金微弧氧化热控膜层在NaCl溶液中腐蚀过程分为三个阶段:一是腐蚀性离子进入多孔膜层,引起界面熔融层变化;二是MgO与水分子反应造成内层膜更加致密,阻抗有所增加;三是腐蚀溶液接触到部分镁合金基底,发生电化学腐蚀,形成楔形效应,引发裂纹,最终导致局部腐蚀失效.结论 微弧氧化提高了膜层的耐蚀性能,其在0.1 mol/L NaCl溶液中的腐蚀过程可分为介质进入孔内、水合反应和局部腐蚀三个阶段.     

AM60压铸镁合金表面ZrO_2微弧氧化陶瓷层的制备方法研究

为了改善镁合金的微弧氧化膜层的性能,利用两步法在AM60压铸镁合金表面制备了ZrO_2微弧氧化膜层.研究了膜层在恒电压控制方式下的生长规律,测量了膜层在w(NaCl)=3.5%溶液中的极化曲线,分析了膜层的物相组成.结果表明:在400 V恒压微弧氧化处理时,微弧氧化膜层的平均生长速度最高可达3.5 μm/min:试样在w(NaCl)=3.5%溶液中的极化曲线显示,镁合金经过两步法在锆盐溶液中微弧氧化后,其腐蚀电位正移,腐蚀电流降低,腐蚀速度大幅降低,其耐蚀性得到了大幅度提高.两步法制备微弧氧化膜层主要由ZrO_2、ZrP_2、Mg_3(PO_4)_2、MgF_2相组成,在溶液中添加的Zr元素可以通过微弧氧化处理时的复杂反应进入膜层中,膜层表现出的优异耐蚀性主要源于膜层中存在ZrO_2陶瓷.     

拉应力条件下微弧氧化膜对铝合金腐蚀及电化学行为的影响

为研究在拉应力条件下微弧氧化膜对铝合金腐蚀及电化学行为的影响,采用恒载荷应力环在3.5% NaCl溶液中研究了经微弧氧化（MAO）处理后的7050铝合金（AA7050）应力腐蚀行为。用原位电化学阻抗谱（EIS）的方法评价在拉应力条件下,膜层的腐蚀破坏随浸泡时间的变化,并建立了相应的等效电路模型。结果表明,在3.5% NaCl溶液中,微弧氧化膜在有无拉应力的条件下都可以提高AA7050的耐蚀性和减少AA7050的塑性损失。在400 MPa拉应力条件下,微弧氧化膜的阻抗在应力腐蚀的过程中呈现出先减小后增大,再减小最后趋于稳定的规律;另外,AA7050在有拉应力的条件下,拉应力会促进基体的点蚀形核,提高腐蚀速率,微弧氧化膜的疏松层在拉应力的作用下会失去对基体的保护作用。     

AZ91D镁合金的微弧氧化陶瓷层电化学腐蚀行为研究

利用微弧氧化技术对AZ91D镁合金在铝酸盐和锫盐溶液中进行表面陶瓷化处理.采用IM6e型电化学工作站,对微弧氧化镁合金进行电化学稳态电流/电位极化曲线测量以及塔费尔斜率测量.通过电化学测量对微弧氧化镁合金的腐蚀行为进行分析.结果表明:镁合金经微弧氧化处理后,点蚀的发生受到限制,镁合金微弧氧化试样的腐蚀电流较原始试样降低4～6个数量级.镁合金微弧氧化试样的耐蚀等级均达到耐蚀以上的等级.     

AZ91D镁合金微弧氧化工艺参数的优化

利用自制微弧氧化装置在硅酸盐体系中对AZ91D镁合金进行微弧氧化处理.采用4因素3水平正交试验,从考察膜层厚度、表面粗糙度和耐蚀性出发,确定了AZ91D镁合金在硅酸盐体系中的最佳工艺参数.结果表明：在最佳工艺条件下,微弧氧化膜呈多孔结构、孔径较小,裂纹较少,分布均匀,膜层较为致密;微弧氧化膜由MgO、Mg2SiO4、MgAl2O4和少量的SiO2组成;室温下,在质量分数为3.5%的NaCl中性溶液中浸泡168 h后,膜层表面未出现明显的点蚀现象,耐蚀性较镁合金基体有了很大提高.     

集成压铸缺陷镁合金汽车轮毂耐蚀性工艺研究

对AM60B镁合金汽车轮毂进行了不同工艺的微弧氧化处理,并进行了酸雨(pH=5.3~5.5)全浸腐蚀和含氯离子水(0.5g/L氯化钠)电化学腐蚀测试和分析。结果表明:微弧氧化处理能有效改善AM60B镁合金汽车轮毂在酸雨(pH=5.3~5.5)环境和含氯离子水(0.5 g/L氯化钠)中的抗蚀性,其微弧氧化的优化工艺参数为:氧化电压450 V、电流密度0.08 A/m2、频率800 Hz、占空比25%、氧化时间50 min、溶液温度40℃。     

镁合金阳极氧化膜在NaCl溶液中的腐蚀行为

利用盐水浸泡实验研究了AZ91D镁合金阳极氧化膜层在3．5％NaCl溶液中的腐蚀行为。结果表明：AZ91D镁合金阳极氧化膜层不论封闭与否,在中性NaCl溶液中浸泡出现第一个腐蚀点后,膜层表面均很少再出现新的腐蚀点,而是原有的腐蚀点向纵、横两个方向扩展形成腐蚀坑,表面呈“树枝”状腐蚀形貌;浸泡溶液的pH值对阳极氧化膜层的耐蚀性影响很大,酸性溶液中的腐蚀速率明显大于中、碱性溶液的;随浸泡溶液温度的升高阳极氧化膜层的腐蚀速率加快。据此,提出了AZ91D镁合金阳极氧化膜层在NaCl溶液中腐蚀过程的模型。     

恒载荷下的微弧氧化后7050铝合金在不同pH值NaCl溶液中的腐蚀行为

目的研究pH值对恒载荷下微弧氧化后铝合金腐蚀行为和耐蚀性的影响。方法采用恒载荷应力环,研究微弧氧化后的7050铝合金(AA7050)在不同pH值3.5%NaCl溶液中的腐蚀行为。采用动电位极化曲线和原位电化学阻抗谱(EIS),评价pH值对恒载荷下的微弧氧化后AA7050耐蚀性的影响,以及在不同pH值的3.5%NaCl溶液中膜层的腐蚀过程,并建立相应的等效电路模型。结果恒载荷试验结束后,在pH=7的溶液中,试样表面的微弧氧化膜基本完整,表面覆盖一层腐蚀产物;在pH=3的溶液中,试样表面膜层部分被腐蚀;在pH=13的溶液中,试样表面膜层已经完全脱落。腐蚀初期,在pH为3、7和13的溶液中,试样的低频阻抗模值分别为35 000、90 000、500Ω·cm~2,其腐蚀电位分别为–1.41、–1.43、–1.46 V,腐蚀电流密度分别为2.85×10~(–5)、9.17×10~(–6)、1.75×10~(–4) A/cm~2。恒载荷实验后,在pH为3、7和13的溶液中,试样的伸长率分别为3.41%、3.98%、1.63%。结论溶液的pH值对恒载荷下微弧氧化后AA7050的耐蚀性和塑性产生了显著的影响。在pH=7的溶液中,微弧氧化铝合金的耐蚀性和塑性最好,在pH=3的溶液中次之,在pH=13的溶液中最差。根据试样的EIS,整个腐蚀阶段被分为腐蚀初期、中期、后期三个阶段。腐蚀初期,在不同pH的溶液中,微弧氧化试样的耐腐蚀性先降低后提高。腐蚀中期,耐蚀性先下降后稳定,在pH=13的3.5%NaCl溶液中,试样膜层完全剥落。腐蚀后期,在不同pH的溶液中,微弧氧化试样的耐蚀性再次下降。     

不同热处理态2024铝合金的腐蚀行为

分别在3.5%NaCl溶液、3.5%NaCl＋1.0%H2O2溶液和pH=12的3.5%NaCl溶液中进行动电位极化实验,研究2024 Al-Cu-Mg合金在不同热处理状态下的腐蚀行为。极化曲线表明,随着合金时效时间的延长,合金的腐蚀电位向负方向移动;向NaCl溶液中添加H2O2会使腐蚀电位正移;在pH=12的3.5%NaCl溶液中的极化曲线表现出明显的钝化现象。腐蚀试样表面表现为常见的腐蚀特征,但也有扩大的点蚀、晶间腐蚀现象出现。循环动电位极化曲线显示有宽的循环极化滞后环,不同的腐蚀模式表明合金的点蚀生长对合金的热处理状态敏感。通过显微组织分析,探讨了不同热处理状态下合金在不同NaCl溶液中的腐蚀机理。     

Corrosion resistance of WE43 and AZ91D magnesium alloys with phosphate PEO coatings

The corrosion performance of WE43-T6 and AZ91D magnesium alloys with and without treatment by plasma electrolytic oxidation (PEO) was investigated by electrochemical measurements in 3.5 wt.% NaCl solution. For untreated WE43-T6 alloy, formation of a uniform corrosion layer (Mg(OH)₂) was accompanied by initial pits around magnesium-rare earth intermetallic compounds. The AZ91D alloy disclosed increased corrosion susceptibility, with localized corrosion around the β-phase, though the β-phase network phase acted as a barrier for corrosion progression. PEO treatment in alkaline phosphate electrolyte improved the corrosion resistance of WE43-T6 alloy only at the initial stages of immersion in the test solution. However, PEO-treated AZ91D alloy revealed a relatively high corrosion resistance for much increased immersion times, contrary to the relative corrosion resistances of the untreated alloys. The improved performance of the PEO-treated AZ91D alloy appears to be related to the formation of a more compact coating.     

Corrosion and self‐healing behaviour of AZ91D magnesium alloy in ethylene glycol/water solutions

Corrosion behaviour of magnesium alloy‐based engine parts in cooling system is an urgent fundamental issue in automotive field where magnesium alloys are increasingly used. In the present work, the corrosion behaviour of AZ91D magnesium alloys in various ethylene glycol/water solutions was studied by electrochemical measurements and immersion tests at room temperature. The surfaces of the samples after immersion tests were examined using scanning electron microscope (SEM) and X‐ray diffraction (XRD). The results showed that the corrosion rates of AZ91D magnesium alloys decreased with the increase of ethylene glycol concentration in ethylene glycol/water solutions and the corrosion process was dominated by pitting corrosion. A continuous protective film transferred from corrosion products was formed on the corroded surface after sufficient immersion duration in ethylene glycol/water solutions, which is able to heal the corrosion pits. The self‐healing behaviour inhibited the further corrosion of AZ91D magnesium alloy.     

PREPARATION OF MICROARC OXIDATION COATING ON (Al2O3-SiO2)sf/AZ91D MAGNESIUM MATRIX COMPOSITE AND ITS ELECTROCHEMICAL IMPEDANCE SPECTROSCOPIC ANALYSIS\par

在硅酸盐电解液体系中, 采用交流微弧氧化方法在增强体体积分数为33%的 (Al₂O₃-SiO₂)_sf/AZ91D镁基复合材料表面制备出完整的保护性氧化膜. 利用SEM, EDS和XRD分析了氧化膜的形貌、成分和相组成, 测量了膜层的显微硬度分布. 采用电化学阻抗谱(EIS)评价了微弧氧化表面处理前后复合材料的电化学腐蚀性能, 确立了不同浸泡时间对应的等效电路. 结果表明, 微弧氧化膜主要由MgO和Mg₂SiO₄相组成, 最大硬度达到1017 HV. 氧化膜电化学阻抗模值|Z|与镁合金基体相比大幅度提高, 耐腐蚀性能明显高于基体. 在3.5%NaCl溶液里浸泡96 h后, EIS出现感抗弧, 显示膜内部开始出现点蚀破坏. 氧化膜耐蚀性由膜内致密层特性所决定.     

Influence of rare earth element Ce and La addition on corrosion behavior of AZ91 magnesium alloy

Two types of AZ91 magnesium alloys containing rare earth element Ce or La were fabricated. Hydrogen evolution and electrochemical tests were carried out to evaluate the corrosion behavior of new AZRE (RE = Ce or La) and AZ91 alloys in 3.5% NaCl solutions (pH 6.50). Various corrosion rate tests indicated that addition of RE obviously enhanced corrosion resistance of AZ91 magnesium alloy. The optimal content of RE was 0.92% for Ce and 0.66% for La. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and low‐angle X‐ray diffraction (XRD) were used to characterize the effect of RE addition on microstructure and corrosion product film of AZ91 magnesium alloy. The refined β phase and formation of γ phase in AZRE alloy were observed by SEM, which resulted in the improvement of corrosion resistance due to the depression of microgalvanic couples. Moreover, the enhanced protective effectiveness of corrosion products was another reason for the improved corrosion resistance.     

AZ91D镁合金微弧氧化膜的腐蚀行为研究

利用双向全波脉冲电源对AZ91D镁合金在硅酸盐体系中进行了微弧氧化处理,通过电化学阻抗谱(EIS)测试、极化曲线分析并结合XRD和SEM等分析方法对微弧氧化处理的镁合金腐蚀行为进行了研究.结果表明,微弧氧化膜表面分布着几微米的微孔,微弧氧化膜中主要含有MgF2,Mg2SiO4和Al2O3.AZ91D镁合金经过微弧氧化处理之后,耐蚀性能明显提高,自腐蚀电流密度降低3个数量级,自腐蚀电位高出约300 mV,阻抗值高出3个数量级,研制的微弧氧化膜对镁合金具有很好的防腐保护性能.     

Effect of Gd on microstructure and stress corrosion cracking of the AZ91-extruded magnesium alloy

AZ91 and AZ91–xGd (x = 0.5, 1.0, 1.5 wt%) magnesium alloys are extruded into plates. The addition of Gd promotes the formation of Al₂Gd, effectively reducing the volume fraction of the β-Mg₁₇Al₁₂ phase and making the banded structures of the extruded magnesium alloys thinner. The corrosion weight loss tests and electrochemistry analyses demonstrate that Gd significantly improves the pitting resistance of the AZ91 in 3.5-wt% NaCl solution saturated with Mg(OH)₂. Slow strain rate tensile tests show that in a corrosive environment, compared with AZ91, the elongation to failure of the AZ91–1.0Gd alloy is increased by 47%, and the alloy exhibits excellent stress corrosion resistance in this study. The fracture mode of AZ91 is changed from typical intergranular fracture to a mixture of transgranular and intergranular fracture in the corrosion solution by adding Gd. The mechanism of Gd to improve the stress corrosion resistance of the AZ91 magnesium alloy is that Gd increases the corrosion resistance, especially the pitting of AZ91.     

Effect of combinative addition of strontium and rare earth elements on corrosion resistance of AZ91D magnesium alloy

The influencf of strontium（Sr） and rare earth（RE） elements on the corrosion behavior of AZ91D magnesium alloy was investigated by conventional corrosion testing and electrochemical measurements in 3.5% NaCl solution. After comparing the mass loss and hydrogen evolution of the samples, the microstructures of the alloys and the morphologies of their corrosion product films were characterized by electron probe microanalysis-energy dispersive spectrometry（EPMA-EDS） and Auger electron spectroscopy（AES）. Compared with individual addition of Sr or RE to AZ91D, the combinative addition of 0.5% Sr and 1% RE to AZ91D successfully decreases the corrosion rate further, which can be attributed to the depression of micro-galvanic couples, as well as the formation of more protective film due to aluminum enrichment. The combinative addition of strontium and rare earth elements to AZ91D magnesium alloy appears to be a promising approach to increase its corrosion resistance.     

Wear and corrosion properties of laser cladded Cu47Ti34Zr11Ni8/SiC amorphous composite coatings on AZ91D magnesium alloy

To improve the wear and corrosion properties of AZ91D magnesium alloys, Cu-based amorphous composite coatings were fabricated on AZ91D magnesium alloy by laser cladding using mixed powders of Cu47Ti34Zr11Ni8 and SiC. The wear and corrosion behaviours of the coatings were investigated. The wear resistance of the coatings was evaluated under dry sliding wear condition at room temperature. The corrosion resistance of the coatings was tested in 3.5% （mass fraction） NaCl solution. The coatings exhibit excellent wear resistance due to the recombined action of amorphous phase and different intermetallic compounds. The main wear mechanisms of the coatings and the AZ91D sample are different. The former is abrasive wear and the latter is adhesive wear. The coatings compared with AZ91D magnesium alloy also exhibit good corrosion resistance because of the presence of the amorphous phase in the coatings.