镁及镁合金在NaCl水溶液中的腐蚀行为

研究了纯Mg、AZ31和AZ91D镁合金在pH=12,浓度为5%的NaCl溶液中的腐蚀行为,从腐蚀形貌和腐蚀速率等方面对其进行了定性和定量描述,并对其腐蚀杌理进行了探讨.随着腐蚀时间的延长,纯Mg,AZ31和AZ91D镁合金的腐蚀速率呈现出先急剧减小再缓慢降低,最后达到一个稳定值的趋势.同时,随着合金中Al含量的提高,镁合金腐蚀速率降低,因此AZ91D镁合金表现出比AZ31镁合金更好的耐腐蚀性能.     

β相对Mg-Al系镁合金板材耐腐蚀性能的影响

为了研究β相对Mg-Al系镁合金板材腐蚀性能的影响,通过析氢试验和电化学阻抗谱等测试方法,研究了AZ31B,AZ91D1和AZ91D2三种镁合金轧制态板材的腐蚀性能。结果表明,在w(Na Cl)=3.5%的Na Cl溶液中,三种镁合金的耐腐蚀性能为:AZ91D2镁合金耐腐蚀性能最好,AZ91D1镁合金的其次,AZ31B镁合金耐腐蚀性能较差。通过光学显微镜和扫描电子显微镜等方法测量了试样表面腐蚀产物的形貌,发现AZ31B和AZ91D2镁合金出现点状腐蚀,而AZ91D1镁合金则出现丝状腐蚀。在AZ31B镁合金中,β相含量非常少,并且比较粗大,在腐蚀过程中对合金的耐腐蚀性能起降低作用,而AZ91D1和AZ91D2镁合金中第二相含量较多,降低了合金的自腐蚀性能,AZ91D2镁合金中第二相颗粒比AZ91D1镁合金的更细小,并且含量也较多,因此其耐腐蚀性能最好。     

La对AZ91D镁合金力学性能和腐蚀性能的影响

镁合金AZ91D中加入质量分数为1％的La时,合金在常温下的抗拉强度和延伸率分别增大了21％和101．2％,并且腐蚀速率下降为原AZ91D的47．2％．其中力学性能的提高主要是由于加入La后形成了（Al,Mg）11La3强化相,同时,细化了β相．耐蚀性的提高则是由于La的加入形成了具有类网状结构的β相,这种类网状结构的β相能有效地抑制腐蚀过程的进行,从而提高了镁合金的耐蚀性．当La加入量进一步增大时,合金力学性能缓慢增大,但其耐蚀性却明显降低,特别是当La达到2％时,合金的腐蚀速率甚至高于原合金的腐蚀速率．这主要是由于过多的La导致镁合金基体α相的Al含量大大降低,从而降低了镁合金的耐蚀性．     

ZK60/AZ31异种镁合金搅拌摩擦焊接头的组织与性能研究

研究了ZK60/AZ31异种镁合金搅拌摩擦焊接头的显微组织、微区织构、显微硬度和力学性能。结果表明,ZK60合金侧和AZ31合金侧焊缝区的晶粒尺寸都相对母材更加细小,且ZK60合金侧热影响区、冠状区和搅拌区的平均晶粒尺寸都要小于AZ31合金侧相应区域;ZK60/AZ31镁合金焊接接头的屈服强度在AZ31合金母材和ZK60合金母材之间,而断后伸长率远小于两种合金母材;ZK60合金侧搅拌区边部、搅拌区中心和AZ31合金侧搅拌区边部的孪晶体积分数分别为7.7%、2.8%和32.3%;ZK60/AZ31镁合金焊接接头的断裂位于后退侧AZ31合金侧过渡区与搅拌区界面处。     

Effect of La on the Mechanical Property and Corrosion Resistance of AZ91D

镁合金AZ91D中加入质量分数为1%的La时, 合金在常温下的抗拉强度和延伸率分别增大了21%和101.2%, 并且腐蚀速率下降为原AZ91D的47.2%。其中力学性能的提高主要是由于加入La后形成了(Al, Mg)11La3强化相，同时, 细化了相。耐蚀性的提高则是由于La的加入形成了具有类网状结构的相, 这种类网状结构的相能有效地抑制腐蚀过程的进行, 从而提高了镁合金的耐蚀性。当La加入量进一步增大时, 合金力学性能缓慢增大，但其耐蚀性却明显降低, 特别是当La达到2%时，合金的腐蚀速率甚至高于原合金的腐蚀速率。这主要是由于过多的La导致镁合金基体相的Al含量大大降低, 从而降低了镁合金的耐蚀性。     

AZ91D镁合金表面改性层组织分析及其对耐蚀性影响的研究

以AZ91D镁合金为基体,Al为合金粉末,采用激光表面改性技术对AZ91D镁合金进行表面改性,详细分析了镁合金改性后的表面组织,并通过盐雾实验对比了改性前后镁合金的耐蚀性,探讨了AZ91D镁合金基体及表面Mg-Al改性层的腐蚀机理,确定最佳激光功率参数为1.5 kW。     

稀土Y+AZ91D镁合金的微观组织及耐蚀性研究

通过盐雾腐蚀试验,研究了稀土Y对AZ91D镁合金耐腐蚀性能的影响。用光学显微镜(OM)观察组织结构,应用XRD对其进行物相分析,采用静态失重法计算其腐蚀速率,比较含Y和不含Y的AZ91D镁合金的组织和耐腐蚀性能。结果表明,Y+AZ91D镁合金在NaCl溶液中具有优异的耐蚀性,并且随Y含量的增加,Mg17Al12相增多,针状组织Al4MgY也增多,细化了合金的微观组织,耐腐蚀性能也进一步得到提高。     

稀土镁合金、AZ31及AZ91负极材料耐腐蚀性能及放电行为的比较

通过对动电位极化曲线、电化学阻抗谱图、SEM形貌的分析,研究了AZ31、AZ91和稀土镁合金在8.0%(质量分数)Na Cl溶液中的腐蚀行为。并将上述三种镁合金组装成电池,在8.0%Na Cl溶液中进行恒流放电测试。结果表明:三种负电极的耐蚀性是稀土合金AZ31AZ91;浸泡48 h后稀土镁合金的表面裂纹最少,腐蚀程度最轻,而AZ91负极的腐蚀程度最严重,表面裂纹较深;稀土合金的放电时间最长,达到800 min,AZ31为710 min,AZ91为660 min。     

稀土镧对AZ91D镁合金组织及耐蚀性的影响

采用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)及动电位极化测试等手段研究了稀土镧添加量对AZ91D镁合金组织和耐蚀性的影响。结果表明:镧的添加使AZ91D镁合金组织细化,β-Mg_(17)Al_(12)相的体积分数减小,并且由连续网状分布变为断续、弥散分布,同时生成新的稀土相Al_(11)La_3,其腐蚀速率明显降低,自腐蚀电位和耐蚀性得到提高。当镧的质量分数为1.0%时,镁合金的腐蚀速率为0.157mg·cm~(-2)·h~(-1),约为AZ91D镁合金的58%;腐蚀电流密度为8.8×10~(-4) A·cm~(-2),相对于AZ91D镁合金的显著降低;自腐蚀电位为-1 429mV(SCE),相比于AZ91D镁合金的自腐蚀电位提高了95.4mV。     

钇对AZ91D镁合金盐雾腐蚀行为的影响

利用盐雾法、扫描电镜(SEM)、能谱(EDS)仪和X射线衍射仪等,分析研究钇对AZ91D镁合金在不同浓度的NaCl溶液中的腐蚀规律和腐蚀形貌的影响.结果表明,AZ91D合金的腐蚀速率随着腐蚀时间和NaCl浓度的增加而增大;钇的加入可明显降低合金腐蚀速率,加入1.28%钇的合金的腐蚀随腐蚀时间的延长和介质浓度的增加而呈现先增后减的趋势,合金的耐蚀性达到试验范围的最佳值.合金的腐蚀形貌均表现为不均匀腐蚀,腐蚀产物主要由Mg(OH)2和MgO组成.     

Comparison of corrosion behaviors of AZ31, AZ91, AM60 and ZK60 magnesium alloys

The corrosion behaviours of four kinds of rolled magnesium alloys of AZ31, AZ91, AM60 and ZK60 were studied in 1 mol/L sodium chloride solution. The results of EIS and potentiodynamic polarization show that the corrosion resistance of the four materials is ranked as ZK60＞AM60＞AZ31＞AZ91. The corrosion processes of the four magnesium alloys were also analyzed by SEM and energy dispersive spectroscopy(EDS). The results show that the corrosion patterns of the four alloys are localized corrosion and the galvanic couples formed by the second phase particles and the matrix are the main source of the localized corrosion of magnesium alloys. The corrosion resistance of the different magnesium alloys has direct relationship with the concentration of alloying elements and microstructure of magnesium alloys. The ratio of the β phase in AZ91 is higher than that in AZ31 and the β phase can form micro-galvanic cell with the alloy matrix, as a result, the corrosion resistance of AZ31 will be higher than AZ91. The manganese element in AM60 magnesium alloy can form the second phase particle of AlMnFe, which can reduce the Fe content in magnesium alloy matrix, purifying the microstructure of alloy, as a result, the corrosion resistance of AM60 is improved. However, due to the more noble galvanic couples of AlMnFe and matrix, the microscopic corrosion morphology of AM60 is more localized. The zirconium element in ZK60 magnesium alloy can refine grain, form stable compounds with Fe and Si, and purify the composition of alloy, which results in the good corrosion resistance of ZK60 magnesium alloy.     

The corrosion performance of anodised magnesium alloys

The corrosion performance of anodised magnesium and its alloys, such as commercial purity magnesium (CP-Mg) and high-purity magnesium (HP-Mg) ingots, magnesium alloy ingots of MEZ, ZE41, AM60 and AZ91D and diecast AM60 (AM60-DC) and AZ91D (AZ91D-DC) plates, was evaluated by salt spray and salt immersion testing. The corrosion resistance was in the sequential order: AZ91D ≈ AM60 ≈ MEZ ? AZ91D-DC ? AM60-DC > HP-Mg > ZE41 > CP-Mg. It was concluded the corrosion resistance of an anodised magnesium alloy was determined by the corrosion performance of the substrate alloy due to the porous coating formed on the substrate alloy acting as a simple corrosion barrier.     

The effect of substrate composition on the electrochemical and mechanical properties of PEO coatings on Mg alloys

Plasma electrolytic oxidation (PEO) is a unique surface treatment technology which is based on anodic oxidation forming ceramic oxide coatings on the surface of light alloys such as Mg, Al and Ti. In the present study, PEO coatings prepared on AZ91D, AZ31B, AM60B and AM50B Mg alloys have been investigated. Surface morphology and elemental composition of coatings were determined using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). SEM results showed that the coating exhibited a porous top surface layer and a subsequent dense layer with micro-pores and shrinkage cracks. Phase analysis of coatings was carried out by X-ray diffraction (XRD). XRD analyses indicated that PEO coatings on AZ alloys had higher amount of Periclase (MgO) followed by the presence of Spinel (MgAl₂O₄) e.g. on the AZ91D alloy compared to that on AM series alloys. In order to examine the effect of substrate composition on adhesion strength of PEO coating scratch tests were carried out. Electrochemical corrosion tests were undertaken by means of potentiodynamic polarization technique in 3.5% NaCl solution at room temperature (20 ± 2 °C). Corrosion test results indicated that the corrosion rates of coated Mg alloys decreased by nearly two orders of magnitude as compared to bare Mg alloys. PEO coatings on AZ series alloys showed better corrosion resistance and higher adhesion properties than AM series alloys. In addition to the PEO processing parameters, such are mainly attributes of the compositional variations of the substrate alloys which are responsible for the formation, phase contents and structural properties of the PEO coatings.     

Analysis on flow stress of magnesium alloys during high temperature deformation

The flow stress of magnesium alloys during hot compression at different temperatures and strain rates was studied by experiments.Materials used were AZ91D alloys in as-cast,homogeneous treatment states,AZ31 and ZK60 alloys in as-cast state. The results show that the thermal simulation curves of different alloys differ from one another at the same deforming condition.The general curves of AZ31 and AZ91D alloys have the character of dynamic recrystallization.There are increase of true stress,drastic fallin...     

Corrosion behaviour of Mg/Al alloys in high humidity atmospheres

The influence of relative humidity (80–90–98% RH) and temperature (25 and 50 °C) on the corrosion behaviour of AZ31, AZ80 and AZ91D magnesium alloys was evaluated using gravimetric measurements. The results were compared with the data obtained for the same alloys immersed in Madrid tap water. The corrosion rates of AZ alloys increased with the RH and temperature and were influenced by the aluminium content and alloy microstructure for RH values above 90%. The initiation of corrosion was localised around the Al–Mn inclusions in the AZ31 alloy and at the centre of the α‐Mg phase in the AZ80 and AZ91D alloys. The β‐Mg₁₇Al₁₂ phase acted as a barrier against corrosion.     

Characterization of the corrosion performances of as-cast Mg–Al and Mg–Zn magnesium alloys with microarc oxidation coatings

In the present study, corrosion-protective microarc oxidation (MAO) coatings were prepared on AZ31B, AZ80, and ZK60 cast magnesium alloy substrates in an alkaline silicate electrolyte. The corrosion performances of the uncoated and MAO-coated alloys were investigated using electrochemical and salt spray chamber corrosion tests. The microstructure characterization and experimental results show that among the three alloys studied, the ZK60 Mg alloy exhibited the best and AZ31B the least corrosion resistance under the salt spray conditions. The MAO coating provided robust corrosion protection of the Mg substrates and resulted in a significant decrease in the corrosion rate of the alloys by 3–4 orders of magnitude. The MAO coating on ZK60 alloy showed better corrosion protectiveness than that on the AZ series alloys due to the incorporation of different alloying elements in the coating, especially the Zn and Al elements, which are from the Mg substrate. The corrosion performances and mechanisms of the uncoated and MAO-coated Mg alloys are interpreted in terms of the microstructure and phase/chemical compositions of both the substrates and coatings.     

Biodegradation and cytotoxic properties of pulse anodized Mg alloys

Magnesium has the potential to be used as an implant material owing to its non-toxicity. On the other hand, magnesium alloys corrode rapidly in subcutaneous gas bubbles. Consequently, the approach of using magnesium alloys as a biodegradable biomaterial is not well established. Therefore, the aim of this study was to provide corrosion protection by anodizing to surface for a biodegradable material. Micro-arc oxidation by pulsed DC was applied to AZ91D and AZ31B, and the cell bioactivity was defined. The anodic film was characterized by XRD and SEM. The specific mass loss variation from immersion test and potentiodynamic electrochemical test was performed for the quantification of corrosion resistance. Although the AZ91D had better corrosion resistance properties but the result of the in vitro tests showed low cell viability compared with the AZ31B. The results of the cell staining and agar overlay test revealed the AZ31B group had good biocompatibility and a low corrosion rate. In this study, the surfaces of AZ91D and AZ31B showed the formation of a uniform film by pulse power anodization improving corrosion resistance. Also, the cytotoxicity of the materials was examined by the aluminum content change of compound metal.     

镁合金激光焊接气孔问题的实验研究

对变形镁合金AZ31B、AZ80A,砂铸镁合金AM60B、AZ91D及压铸镁合金AM50A激光焊接气孔倾向进行研究.研究表明:变形镁合金激光焊气孔倾向很小,在较宽的焊接工艺参数范围内均能得到无气孔的焊缝. 砂铸镁合金AM60B及AZ91D激光焊时气孔对气体保护条件非常敏感,在侧吹气体保护角度及流量选择不合适时气孔率非常高,在优化的气保护条件下可得到气孔率较低的焊缝.而压铸镁合金AM50激光焊缝中气孔问题非常突出,调整工艺参数无法解决气孔问题,焊接过程中的加热及添加填充材料可以在一定程度上减少气孔.     

Evaluation of corrosion resistance of magnesium alloys in radiator coolants

Abstract

Coolant corrosion is a major drawback for the use of magnesium alloys in engine and cooling system, but the coolant is not normally intended to prevent corrosion of magnesium alloys. This research assessed the corrosion performance of two magnesium alloys, AZ91D and AM50A, in two newly formulated radiator coolants using immersion test, potentiodynamic polarisation test, and corroded surface analysis. Two coolants were named as Irgacool Plus L and Irgacool Plus S. C7, C8-organic acids and polycarboxylic acid were the main inhibitor species in Irgacool Plus L while Irgacool Plus S was formulated with C7, C8-organic acids and sebacic acid inhibitors. Corrosion rates of magnesium alloys decreased twice in Irgacool Plus L compared with Irgacool Plus S. AZ91D alloy had better corrosion resistance than AM50A alloy in both radiator coolants. Both alloys suffered corrosion due to microgalvanic coupling between cathodic β-Mg₁₇Al₁₂ intermetallic and anodic α-Mg matrix, and the presence of Al₈Mn₅ and Al₁₁Mn₄ intermetallics in AM50A led to further microgalvanic corrosion. A continuous network of β-Mg₁₇Al₁₂ phase and higher Al content α-Mg matrix accounted for better corrosion resistance of AZ91D alloy.