AZ91D镁合金表面扩渗铝锌膜层改性研究

采用Al、Zn固体混合粉末对AZ91D镁合金表面进行化学热扩散处理,在不同扩散温度下得到不同的热扩渗层,并对得到的渗层进行显微组织形貌、物相组成分析,并在3.5％NaCl溶液中对基体材料、扩渗试样进行了浸泡腐蚀实验.结果表明,在410、430和450℃恒温热扩散8h,扩渗层与基体材料表面之间能够形成组织均匀细密的渗层,但在不同扩渗温度形成的渗层结构不同.在410℃扩渗时,扩渗层由Mg-Al-Zn固溶体组成,随着扩渗温度的提高,扩渗层厚度增加,同时渗层开始有合金化合物生成,当扩渗温度为450℃时,则形成了稳定的表面合金层AlMg2Zn与Mg-Al-Zn固溶体层共同组成的扩渗层.同时浸泡腐蚀实验结果也表明,形成的扩渗层组织大幅度提高了AZ91D镁合金表面的耐腐蚀性.     

镁合金表面锌合金化层组织及性能研究

采用消失模铸造方法在镁合金表面制备了一层锌合金化层,并对合金化层进行了光学显微分析、扫描电镜分析、能谱分析、X射线衍射及腐蚀性能分析.研究结果表明:当充型到合金化涂料层表面的镁合金液体温度较低时,镁合金表面锌合金化层才能形成;合金化层的组成物相为Mg17Al12、Al5Mg11Zn4、Zn、Mg;合金化过程中锌一方面可以参与合金化反应形成蜂窝状物质Al5Mg11Zn4,另一方面可以诱导镁合金表面形成Mg17Al12和α-Mg组成的共晶组织;经合金化后的镁合金自腐蚀电位升高,自腐蚀电流下降,耐蚀性能上升.     

ZM5镁合金表面电火花合金化改性层的获得

利用电火花合金化技术在ZM5镁合金上进行本体修复和提高耐蚀性的目的，研究了在保护气体的条件下，使用ZM5电极在ZM5基材上进行电火花合金化，基材表面形成了厚0．15mm，显微硬度102～114HV(基材82～90HV)，耐蚀性改善的改性层。表面改性层主要由a-Mg、β(Al12Mg17)和Al2Mg组成。合金化层腐蚀性能的提高可归因于快速凝固组织结构的形成和该层中Al，Zn，Mn元素含量的富集。     

镁合金ZM5高频感应表面合金化改性层的腐蚀行为

采用高频感应对ZM5镁合金表面进行合金化改性处理，并对改性层组织和腐蚀行为进行了研究，结果表明，镁合金经高频感应表面合金化改性处理，表层区域具有几乎连续的β－（Mg17Al12)相的细化晶粒区，认为这种均匀连续的β相将外部环境与镁的合金中的α相隔离，从而使镁合金的腐蚀速率降低。     

混合稀土阻燃ZM5合金表面氧化膜再生能力研究

将ZM5-0.1%RE合金加热到800℃,当表面氧化膜形成后,冷却至室温,去除表面氧化膜,制成经过氧化的ZM5-0.1%RE合金,通过分析该合金的TGA曲线、恒温氧化动力学曲线以及表面氧化膜的XRD谱,对其表面氧化行为进行研究。结果表明:该合金具有良好的杭氧化性,氧化质量增加主要发生在400～700℃;该合金在600、700℃的氧化动力学曲线遵循抛物线规律,在合金表面生成了一层由(RE)2O3、MgO、Al2O3、Mg17Al12组成的厚度为4.0～5.5μm致密氧化膜,以抑制基体镁合金的进一步氧化;说明ZM5-0.1%RE合金表面氧化膜具有良好的再生能力。     

混合稀土对ZM5镁合金在介质中耐蚀性的影响

研究了添加0.1%的混合稀土对ZM5镁合金显微组织的影响,分析了ZM5和ZM5-0.1RE镁合金在不同介质中的腐蚀行为。结果表明:加入0.1%的混合稀土后ZM5镁合金组织细化,β相变得均匀、连续,且生成了块状分布的Al3Ce相和Al11La3相,降低了Al元素在晶粒内部的偏析,使得ZM5镁合金在pH=3的HCl溶液和pH=7的3.5%NaCl溶液中的耐蚀性得到提高。在pH=10的NaOH溶液中,ZM5镁合金腐蚀的热力学倾向降低,腐蚀轻微。     

AZ81镁合金表面固态扩渗Al、Zn渗层形成机理

目的通过表面固态扩渗合金化技术获得金属扩渗涂层,研究扩渗涂层的形成机理。方法在390℃对AZ81镁合金表面固态扩渗Al和Zn,通过X射线衍射仪和光学显微镜,对扩渗合金层的物相结构和形貌进行分析,通过建立扩渗过程模型研究其扩渗形成机理。结果扩渗时间为4~8 h时,合金扩渗层中除了AZ81镁合金的原始相a-Mg+Mg_(17)Al_(12)外,还会发生Mg_(0.97)Zn_(0.03)→Mg_7Zn_3+Mg_2Zn_3+Mg_2Zn_(11)+AlMg_2Zn→Mg_(32)(Al,Zn)_(49)+AlMg_4Zn_(11)+AlMg_2Zn等变化。Al和Zn初始阶段在AZ81镁合金表面的扩渗机理为空位扩散,Al和Zn固溶于镁合金基体表面,Zn原子首先达到最大固溶度,Mg和Zn反应生成化合物。但在390℃下扩渗,Mg和Zn的化合物不稳定,会发生分解,形成更稳定的Mg-Al-Zn化合物。Mg-Zn化合物出现后,渗层的形成机理表现为空位扩散+反应扩散+熔化分解,Mg-Zn化合物的熔化分解加速了扩散和反应扩散的进程。结论 AZ81镁合金表面固态扩渗金属Al和Zn,在同一扩渗温度下,随扩渗时间的延长,渗层的厚度、相组成、大小、形貌逐渐发生变化,扩渗合金层的主要形成机理由物理扩散转变为反应扩散。     

微量Er对ZM5镁合金微观组织及腐蚀性能的影响

利用金相显微镜、扫描电镜、能谱分析、X射线衍射分析、失重法及动电位扫描测试法,研究了微量Er对铸态ZM5镁合金显微组织和腐蚀性能的影响.结果表明微量Er可细化ZM5镁合金的铸态组织,提高耐腐蚀性能;在0～0.6％范围内,随着Er含量的增加,合金中的Mg17Al12相由粗大、连续树枝状分布逐渐转变为细小、弥散的颗粒状均匀分布;当Er含量为0.6％时,组织中有Al3Er相生成.随着Er添加量的逐渐增加,ZM5镁合金的平均腐蚀速率逐渐降低;当Er含量为0.6％时,在3.5％NaCl水溶液中浸泡的腐蚀速率为2.125 6 mg/(cm2·d),仅为常规ZM5镁合金的20％.微量Er使得ZM5镁合金在3.5％ NaCl溶液中的自腐蚀电位升高,自腐蚀电流降低.     

含稀土耐蚀Mg-9Al铸造镁合金腐蚀行为研究

通过盐雾、失重及析氢等腐蚀试验研究了新研制的含稀土的Mg-9Al铸造镁合金AR091在3.5%NaCl溶液中的腐蚀行为,并与目前常用的ZM5和AZ91D镁合金的腐蚀行为进行了对比。结果表明,AR091具有良好的耐腐蚀性能。AR091的微观组织与AZ91有明显差别,其晶粒更为细小,β相明显减少,还存在许多针状含稀土元素(RE)的析出相。合金内各相间的微电偶腐蚀明显减弱,阴极反应过程受到抑制。采用场发射扫描电镜(FESEM)及俄歇电子谱(AES)研究比较了合金的表面腐蚀产物膜,结果表明,在AR091合金表面能形成更为致密、保护性更好的腐蚀产物膜。     

镁合金的微观结构对其上制备植酸转化膜的影响

采用浸没法,以纯Mg及AZ91D,AZ61,ZK60,ZM21镁合金为基体材料,在植酸水溶液中制备植酸转化膜.观察了植酸转化膜的形貌,分析了转化膜的元素组成及浓度分布,进而研究了镁合金的微观结构对制备表面植酸转化膜的影响.结果表明:合金元素对植酸转化膜的形成起着决定性的作用,高价合金元素(Al和Zr)比低价合金元素(Zn和Mn)更有利于植酸转化膜的形成,以固溶体存在的Al比以化合态(Mg17Al12)存在的Al更有利于转化膜的形成.     

The effect of solid diffusion surface alloying on properties of ZM5 magnesium alloy

In this research, solid diffusion process was used to form a diffusion alloying layer on the surface of ZM5 magnesium alloy to improve corrosion and wear resistance. It is shown that the solid diffusion layer was mainly composed of Mg–Al–Zn intermetallic compounds and Mg–Al–Zn solid solution transition zone that had more Zn and Al elements than untreated ZM5 magnesium substrate. The continued immersion test in 3% NaCl solution displayed that the diffusion-treated specimen had better corrosion resistance compared to the untreated ZM5 specimen. The polarization test indicated that the Mg–Al–Zn intermetallic compounds of the diffusion alloying layer were an effective corrosion barrier to decrease the corrosion rate for ZM5 magnesium alloy when exposed to 3% NaCl solutions. In addition, the microhardness values of the Mg–Al–Zn intermetallic compounds were much higher than those of the substrate and this would greatly contribute to the enhancement of wear resistance.     

Laser cladding of Al＋Ir powders on ZM5 magnesium base alloy

Laser cladding of preplaced Al ＋ Ir powders on a ZM5 magnesium alloy was performed to enhance the corrosion resistance of the ZM5 magnesium alloy. A metallurgical bond was obtained at the coating/substrate interface. The corrosion potential （Ecorr） of the laser cladded sample was 169 mV positive to that of the untreated ZM5 substrate,while the corrosion current （Icorr） was some one order of magnitude lower. The laser cladded sample,unlike the untreated ZM5 substrate,showed a passive region in the polarization plot. Immersion tests confirmed that the corrosion resistance of the laser cladded ZM5 sample was significantly enhanced in 3.5 wt.% NaCl solution. The Al-rich phases of AlIr,Mg17Al12,and Al formed in the cladding layer and the rapid solid characteristics were contributed to the improved corrosion behavior of the coating.     

Surface alloying of AZ91E alloy by Al–Zn packed powder diffusion coating

A new surface coating technique, namely packed powder diffusion coating (PPDC), for AZ91E magnesium alloy is reported. This new technique uses a powder mixture of aluminium and zinc as diffusion source and produces uniform and thick coatings at temperatures below 420 °C. Experimental results showed that zinc in the powder mixture significantly promotes the formation of intermetallic layers on the surface of the magnesium alloy at process temperatures between 350 °C and 413 °C, which is more than 50 °C lower than the previously reported processes. Depending on the temperature and the Zn-content in the powder, X-ray diffraction analysis identified three intermetallic phases and Mg(Al, Zn) solid solution that consist of the surface alloyed layer. The intermetallic compounds are τ-Mg₃₂(Al,Zn)₄₉, φ-Al₅Mg₁₁Zn₄ and β-Mg₁₇(Al,Zn)₁₂. The hardness of the over 500 μm thick surface alloyed layers is up to four times higher than the substrate. Both the β-Mg₁₇(Al,Zn)₁₂ phase and the τ-Mg₃₂(Al,Zn)₄₉ phase show one to two order magnitude higher corrosion resistance than the α-phase (solid solution) and the φ-Al₅Mg₁₁Zn₄ phase in 5% NaCl solution. A process parameter window for the layer thickness as well as a schematic model for the formation of the layer is proposed. The PPDC process is a promising technique that provides effective protection of AZ91E alloy from both wear and corrosion.     

扩渗温度和时间对镁合金表面Al-Zn共渗层显微组织的影响

    采用扩渗法在镁合金表面共渗Al-Zn,研究了扩渗时间和温度对表面合金层显微组织的影响.结果表明：当温度为390℃时,随着扩渗时间的增加,生成的表面合金层由不连续金属间化合物层(Al6Mg10Zn、Al5Mg11Zn4)＋过渡层变为连续金属间化合物层+过渡层;此过程应是物理置换扩散机制和反应扩散机制同时存在,生成的金属间化合物相主要为Al6Mg10Zn和Al5Mg11Zn4两种类型金属间化合物,其中Al5Mg11Zn4是较为稳定的相;当温度提高到410℃时,晶界扩散活性提高,晶界扩散通道增强,仅为2小时已出现了严重的沿晶界扩渗,造成合金层中金属间化合物沿晶界呈网状不均匀分布.     

EFFECTS OF TREATMENT TIME ON CORROSION OF DIFFUSION-ALLOYED COATINGS OF PURE MAGNESIUM

The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480℃ for different solid diffusion time (8, 16, and 24h). The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test (in 3.0% NaCl solution, temperature is (28±1)℃, and time is 96h). Optical microscopy (OM) and EDS (energy dispersive spectrum) composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones (especially the samples treated for 24h at 480℃), was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of A_(l5)Mg_(11)Zn_4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous A_(l5)Mg_(11)Zn_4 phase (WP-zone) of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.     

镁合金表面新颖多层的耐腐蚀Mg-Al金属间化合物涂层(英文)

通过AlCl3-NaCl熔盐扩散表面改性,在镁合金表面制备多层的Mg-Al金属间化合物层。熔盐扩散的处理温度为400 °C,此温度低于纯铝粉扩散的处理温度。熔盐扩散处理后,在镁合金表面形成 Al12Mg17、Al0.58Mg0.42和Al3Mg2多相层的金属间化合物涂层。通过电化学阻抗实验将表面改性和未经表面改性的镁合金的耐蚀性进行比较,发现镁合金表面经过熔盐扩散处理的极化电阻远大于未经表面改性镁合金的。这是因为在镁合金表面形成均匀的多相金属间化合物层。     

Influence of Zn Interlayer on Interfacial Microstructure and Mechanical Properties of TIG Lap-Welded Mg/Al Joints

This study explored 6061 Al alloy and AZ31B Mg alloy joined by TIG lap welding with Zn foils of varying thicknesses, with the additional Zn element being imported into the fusion zone to alloy the weld seam. The microstructures and chemical composition in the fusion zone near the Mg substrate were examined by SEM and EDS, and tensile shear strength tests were conducted to investigate the mechanical properties of the Al/Mg joints, as well as the fracture surfaces, and phase compositions. The results revealed that the introduction of an appropriate amount of Zn transition layer improves the microstructure of Mg/Al joints and effectively reduces the formation of Mg-Al intermetallic compounds (IMCs). The most common IMCs in the fusion zone near the Mg substrate were Mg-Zn and Mg-Al-Zn IMCs. The type and distribution of IMCs generated in the weld zone differed according to Zn additions; Zn interlayer thickness of 0.4 mm improved the sample’s mechanical properties considerably compared to thicknesses of less than 0.4 mm; however, any further increase in Zn interlayer thickness of above 0.4 mm caused mechanical properties to deteriorate.     

稀土Y和Nd对ZM5合金组织和性能的影响

以ZM5镁合金为基体材料，应用铸造方法制备了4种不同稀土含量和比例的稀土镁合金。考察分析了稀土Y和Nd对ZM5合金组织结构、力学性能和腐蚀性能的影响。结果表明，铸态合金中出现了新相Ti2Mg3Al3，它对于减少晶界处第二相的析出有积极作用。ZM5合金的组织结构、力学性能和腐蚀性能随稀土Y和Nd的比例不同而有比较大的差异，在所有考察的ZM5合金中，添加2％Y和1％Nd稀土的合金综合效果最好。     

表面扩散合金化对ZM5镁合金冲蚀磨损性能的影响(英文)

将ZM5镁合金置入铝、锌混合粉末中,在氩气保护下,于温度(390±5)°C保温8h进行表面固态扩渗合金化处理。研究表面固态扩渗合金化处理前和处理后ZM5镁合金在两种不同冲蚀磨损环境中(油和石英砂,水和石英砂)的冲蚀磨损行为。结果表明:当冲蚀磨损介质为油和石英砂时,冲蚀磨损表面形貌为切削沟痕。油对试样的腐蚀很弱,切削磨损是主要的磨损机制。当冲蚀介质为水和石英砂时,冲蚀磨损试样表面为腐蚀坑和裂纹。水的腐蚀和石英砂的冲刷作用加剧试样的磨损质量损失。在相同的冲蚀介质中,经过表面固态扩渗合金化处理的试样的耐冲蚀磨损性能均比未经过表面固态扩渗合金化处理的试样好。     

Novel multilayer Mg–Al intermetallic coating for corrosion protection of magnesium alloy by molten salts treatment

A novel multilayer Mg–Al intermetallic coating on the magnesium alloy was obtained by AlCl₃–NaCl molten salt bath treatment. The molten salt was treated at 400 °C, which is lower than the treatment temperature of solid diffusion Al powder. The thick Al₁₂Mg₁₇, Al_0.58Mg_0.42 and Al₃Mg₂ multilayer Mg–Al intermetallic coating forms on the magnesium alloy. The corrosion resistance of AZ91D alloy with and without coating by multilayer of Mg-Al intermetallic compound was evaluated by electrochemical impedance spectroscopy measurements in 3.5% (mass fraction) NaCl solution. The polarization resistance value of the multilayer coating on the magnesium alloy by molten salt bath treatment is greater than that of the uncoated one, which is attributed to the homogenously distributed intermetallic phases.