AZ91D镁合金的均一化前处理与化学镀Ni-P

采用新型环保的均一化前处理工艺在AZ91D镁合金表面制备了化学镀Ni-P镀层。研究了前处理过程中AZ91D基体微观形貌、镀层沉积过程、成分和相结构。研究结果表明：基体表面的β相在前处理过程中被选择性去除,表面组织得到均一化,从而获得均匀致密的浸Zn层。Ni-P颗粒均匀形核生长,并最终形成致密的镀层。镀层具有优良的耐腐蚀性能。     

AZ91D镁合金表面化学镀镍工艺的研究

研究了以NiSO4·6H2O为主盐在AZ91D镁合金表面进行化学镀镍及其电化学原理,比较了浸锌和不浸锌施镀对镀镍层的影响.结果表明AZ91D经过浸锌处理后施镀Ni-P层更容易沉积,通过二次浸锌后获得的化学镀镍层致密、平整,对镁合金基体有较好的保护作用.     

Organic-magnesium complex conversion coating on AZ91D magnesium alloy

An organic-magnesium complex conversion (OMCC) coating on AZ91D magnesium alloy was obtained by treating in a solution containing organic compounds. SEM, FESEM and XPS were used to examine the surface morphology, thickness and structure of the conversion coatings. The results show that the continuous and uniform conversion coating is deposited on AZ91D alloy and the main component of the coatings is organic compound containing benzene ring, which forms a chemical bond with magnesium. The polarization measurement and salt spray test show that the corrosion resistance of the conversion coating is much higher than that of traditional chromate conversion coating.     

镁合金在镀液中的腐蚀行为

摘要：通过腐蚀实验和阳极极化曲线研究了硫酸镍主盐配制的化学镀镍液成分和温度对AZ91D镁合金的腐蚀行为的影响，比较了碱式碳酸镍主盐和硫酸镍主盐两种镀镍液的腐蚀性以及施镀后的镀层质量。结果表明：硫酸镍镀液的腐蚀性比碱式碳酸镍镀液大，在低温下，镁合金在硫酸镍镀液中表面的氟化镁膜不致密，镀液对基材的腐蚀性高；而在高温下，Mg^2 与F^-的反应性增强，氟化反应完全，形成的氟化镁钝化膜致密性高，可保护镁合金基体免遭镀液的腐蚀。在施镀温度下，镀液中F^-的缓蚀作用，可使SO4^2-离子对镁合金的腐蚀速率大大降低。     

Barium phosphate conversion coating on die-cast AZ91D magnesium alloy

Poor corrosion resistance limits the application of magnesium alloys.Conversion coating is widely used to protect magnesium alloys because of easy operation and low cost.A novel conversion coating on die-cast AZ91D magnesium alloy containing barium salts was studied.The optimum concentrations of Ba(NO_3)_2,Mn(NO_3)_2 and NH_4H_2PO_4 are 25 g/L,15 mL/L and 20 g/L,respectively,based on orthogonal test results.The treating time,solution temperature and pH value are settled to be 5-30 min, 50-70℃and 2.35-3.0...     

A novel dual nickel coating on AZ91D magnesium alloy

Magnesium alloys covered with metal coating display excellent corrosion resistance,wear resistance,conductivity and electromagnetic shielding properties.The electroless plating Ni-P as bottom layer following the electroplating nickel as surface layer on AZ91D magnesium alloy was investigated.The coating surface morphology was observed with SEM and the structure was analyzed with XRD.Electrochemical tests and salt spray tests were carried out to study the corrosion resistance.The experimental results indi...     

AZ91D镁合金化学复合镀Ni-P-ZrO2的工艺与性能

对镁合金传统化学镀工艺进行了改进,避免了使用氢氟酸和六价铬等有毒物质。采用化学镀与化学复合镀相结合方法,在AZ91D镁合金上获得了Ni-P-ZrO2纳米化学复合镀层,并研究了新工艺化学镀前处理和镍沉积机理及复合镀层的结构和性能。结果表明:新工艺方法获得的Ni-P镀层更均匀、致密,耐蚀性优于传统工艺化学镀层;Ni-P-ZrO2复合镀层与AZ91D合金基体在3.5%NaCl溶液中的动电位极化曲线对比表明,该复合镀层对镁合金可以起到明显的保护作用;从磨损实验结果可见,Ni-P镀层的磨损质量损失率几乎为Ni-P-ZrO2镀层的3倍,说明ZrO2纳米粉的加入能改善镀层的耐磨性。     

Corrosion behavior of AZ91D magnesium alloy in sodium sulfate solution

The corrosion behavior of as‐cast AZ91D magnesium alloy in 0.1M sodium sulfate solution at the corrosion potential (E_corr) was investigated by using electrochemical impedance spectroscopy (EIS), environmental scanning electron microscopy (ESEM), energy dispersive X‐ray spectroscopy (EDS) and X‐ray diffraction (XRD). The results showed that the corrosion of AZ91D started at both the primary α‐Mg and the eutectic α‐Mg. The surface first was covered by a film (MgO, Mg(OH)₂) which became thicker with time. Due to the dissolution of the eutectic α‐Mg, the concentration of aluminum increased, MgAl₂(SO₄)₄ · 2H₂O precipitated at the primary α‐Mg and progressively spread to the eutectic α‐Mg areas. The surface film changed from two‐layer to three‐layer structure with the increase of immersion time.     

镁合金AZ51直接化学镀镍研究

采用沉积速率计算、镀镍形貌观察和腐蚀性能测试，研究了镀镍时间对镁合金AZ51直接化学镀镍的影响。结果表明，镁合金AZ51表面可通过直接化学镀镍形成镍磷合金镀层。随着镀镍时间的增加，沉积速率先增加后降低并在镀镍时间为0．5h时取得最大值，而腐蚀速率逐渐降低，腐蚀性能逐渐增强。     

Preparation and property evaluation of electroless Ni-P coatings on AZ91D magnesium alloy

Taking a bath with basic nickel carbonate as the source of nickel, sodium hypophosphite as the reducing agent and citric acid as the complexing agent, the N i-P coatings on AZ91D magnesium alloy were prepared. The influence of pH value of the bath on the content of phosphorus, microhardness and corrosion resistance of the deposits was examined. The XRD analysis results show that the Ni-P coatings plated under all conditions have a mixed microstructure of amorphous and nanocrystalline and undergo a phase transformation to crystalline nickel and nickel phosphide upon heat-treatment. The microhardness of the Ni-P coatings increases with the increase ofpH value of the bath and has a maximum at pH=6. The potentiodynamic polarization test in 3.5%（mass fraction） NaCl solution reveals that the Ni-P coatings exhibit a very good corrosion resistance to protecting AZ91D magnesium alloy.     

AZ91D镁合金表面激光重熔Al-Si-Cu涂层的性能

采用等离子喷涂和激光重熔复合工艺在AZ91D镁合金表面制备Al-Si-Cu合金涂层,利用扫描电子显微镜（SEM）、显微硬度计、摩擦磨损试验机等研究了涂层的微观组织、显微硬度与摩擦磨损性能。结果表明,激光重熔后涂层组织致密均匀,涂层与基体呈良好的冶金结合,涂层显微硬度约为基体的2.2倍,由于晶粒细化和硬质相的存在耐磨性较基体明显提高,重熔层的磨损机制主要为磨粒磨损。     

Electrodeposition of zinc on AZ91D magnesium alloy pre‐treated by stannate conversion coatings

A stannate chemical conversion process followed by an activation procedure was employed as the pre‐treatment process for AZ91D magnesium alloy substrate. Zn was electroplated onto the pre‐treated AZ91D magnesium alloy surface from pyrophosphate bath to improve the corrosion resistance and the solderability. The surface morphologies of conversion coating and zinc coating were examined with scanning electron microscope (SEM). The phase composition of conversion coating was investigated by X‐ray diffraction (XRD). The electrochemical corrosion behavior of the coatings in the corrosive solution was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The experimental results showed that the activated stannate chemical conversion coating provided a suitable interface between zinc coating and the AZ91D magnesium alloy substrate. The corrosion resistance of the AZ91D substrate was improved by the zinc coating.     

添加剂对AZ91D镁合金化学镀镍磷耐蚀性的影响研究

采用常温碱性超声波清洗、酸洗和活化的前处理工艺在AZ91D镁合金表面化学镀镍,研究了辅助络合剂氨基乙酸和加速剂巯基乙酸对镀层耐蚀性的影响。结果表明:镀层表面由Ni-P固溶体组成,呈现尖锐的晶态峰,磷原子与镍原子形成置换固溶体,表面平整致密,无明显缺陷。氨基乙酸含量对镀层耐蚀性和腐蚀速率影响不大,随着巯基乙酸含量的增加,镀层腐蚀电位先升高后降低,腐蚀速率整体比镁合金基体慢,镀层总体呈现钝化趋势,在4 g/L时腐蚀电位最高。     

Corrosion and wear properties of electroless Ni-P plating layer on AZ91D magnesium alloy

A direct electroless Ni-P plating treatment was applied to AZ91D magnesium alloy for improving its corrosion resistance and wear resistance. Corrosion resistance of the Ni-P coatings was evaluated by potentiodynamic polarization and immersing experiments in 3.5% NaCl solution. The wear resistance of the coatings was investigated by the wear track and the mass change after ball-on-disk experiment. The results show that corrosion resistance and wear resistance of the AZ91D alloy are greatly improved after direct electroless Ni-P plating. No discoloration is noticed until 4 d of immersion in 3.5% NaC1 solution. Potentiodynamic polarization experiments show that the free corrosion potential of magnesium alloy is shifted from -1 500 mV to -250 mV and passivation occurs at 1 350 mV after direct electroless plating. The friction coefficients and wear rates of Ni-P coating and Ni-P coating after tempering are 0.10-0.351, 9.038×10^-3 mm^3/m and 0.13-0.177, 3.056×10^-4 mm^3/m, respectively, at a load of 1.5 N with dry sliding. Although minor hurt on corrosion resistance was caused, significant improvement of wear resistance was obtained after tempering treatment of the coating.     

Effect of alloy microstructure on electroless NiP deposition behavior on Alloy AZ91

Various magnesium alloys, which were assumed as reference to the individual behavior of each microstructural constituents of Alloy AZ91 in the coating bath, were designed to analyze the hypophosphite-reduced electroless nickel coating characteristics on them in both uncoupled and coupled conditions. Galvanic coupling of β phase to the matrix phase in the coating bath was observed to decelerate the deposition rate on the matrix phase. This behavior was attributed to the effective cathodic action of β phase in the coating bath as a result of the catalytic cathodic reactions on it. The variation in the Al content of the matrix phase was also estimated to affect the NiP deposition behavior due to the small scale galvanic interactions. The previously Ni nucleated sites on the alloy surface behaved as the most preferential sites for further Ni nucleation and growth. Low temperature heat treatment (230 °C for 2 h) caused a considerable increase in the surface hardness with negligible decrease in the corrosion resistance. High temperature heat treatment (400 °C for 1 h) improved the surface hardness further with significant deterioration in the corrosion resistance.     

AZ91D镁合金微弧氧化膜在不同浓度NaCl溶液中的腐蚀行为(英文)

采用微弧氧化技术(MAO)在镁合金 AZ91D 表面制备微弧氧化陶瓷膜。利用电化学技术和浸泡实验研究该镁合金试样在不同浓度(0.1%,0.5%,1.0%,3.5%和 5.0%,质量分数) NaCl 溶液中的腐蚀行为。结果表明,试样的腐蚀速率随着氯离子浓度的升高而增大。在较高浓度(1.0%,3.5%和 5.0%)的 NaCl 溶液中的主要腐蚀形式是点蚀,而在较低浓度(0.1%和 0.5%)中是全面腐蚀。腐蚀过程可以分为两个阶段:亚稳态蚀点的出现和蚀点的生长。根据腐蚀过程中阻抗谱的特点,对镁合金微弧氧化膜试样在不同浓度 NaCl 溶液中浸泡 120 h 提出了不同的等效电路来模拟其腐蚀行为。     

AZ91D镁合金化学镀镍前处理工艺及腐蚀行为研究

为了改进传统的镁合金化学镀镍前处理工艺和确定以硫酸镍为主盐的镁合金化学镀镍的最佳工艺.采用碱性焦磷酸盐进行浸蚀代替铬酸浸蚀,去除合金表面的油污和氧化物;然后用氢氟酸溶液进行活化.通过正交试验确定了化学镀镍的最佳工艺.结果表明:采用碱性焦磷酸盐浸蚀的前处理工艺、在最佳施镀条件下镀2h,镀层厚度达到20μm,与基体结合良好;镀层为Ni-P微晶,表面平整、致密,磷的质量分数达11.7%.在质量分数为3.5%的NaCl溶液中的动电位极化测试结果表明,镀层可对AZ91D镁合金起到良好的防护作用.     

Numerical simulation of temperature field of AZ91D magnesium alloy during equal channel angular extrusion

The temperature field of AZ91D magnesium alloy extruded by equal channel angular extrusion (ECAE) has been simulated using finite element method (FEM). A series of tests were designed to obtain the simulation parameters: flow stress of AZ91D, friction factor and heat transfer coefficient. The simulated temperature agrees well with the measured one. The evolution of temperature and influencing factor was discussed in details. Furthermore, the extrusion pressure of ECAE was analyzed.