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。     

热锻态AZ80A镁合金腐蚀行为研究

采用金相显微镜(OM)、扫描电镜(SEM)及X射线衍射(XRD)分析,对热锻态AZ80A镁合金在3.5%NaCl溶液中浸泡前后的显微组织进行了研究,并对其点蚀过程中的失重和析氢行为进行了分析,通过交流阻抗谱获得了合金腐蚀时的等效电路。结果表明:在3.5%NaCl溶液中,热锻态AZ80A镁合金析氢速度随浸泡时间的延长而加快,合金的失重速率为2.0378mg/(cm~2·d)。热锻态AZ80A镁合金在3.5%NaCl溶液中腐蚀时,首先在晶界处发生腐蚀,随着腐蚀进行,锻件腐蚀由晶界逐渐向晶内扩散,导致整个晶粒腐蚀剥落。     

镁合金AZ31表面磷酸盐涂层在人工血浆中的降解行为

采用浸涂法在镁合金AZ31表面上制备了磷酸盐涂层,采用浸泡腐蚀、电化学等方法研究了涂层在人工血浆溶液中的腐蚀速率和降解行为,利用电子探针(EPMA)测定涂层的表面形貌及化学成分。结果表明,磷酸盐涂层使镁合金AZ31在人工血浆中的腐蚀速率明显降低,受腐蚀区域缩小,腐蚀程度降低。     

汽车用AZ91镁合金的耐腐蚀性能

以AZ91镁合金为研究对象,研究了NaCl溶液的浓度、腐蚀时间、温度和搅拌速度对AZ91镁合金耐腐蚀性的影响。利用扫描电镜观察了腐蚀后的表面形貌和横截面形貌,定性分析了AZ91镁合金在NaCl溶液中的腐蚀行为。结果表明,随NaCl溶液浓度、腐蚀时间、温度和搅拌速度增加,AZ91镁合金腐蚀速率主要呈递增趋势,且腐蚀形式为沿晶腐蚀。     

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.     

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。     

压铸AZ91D镁合金在不同pH值的Na2SO4溶液中的腐蚀行为（英文）

研究压铸AZ91D镁合金在不同pH值的0.1mol/LNa2SO4溶液中的腐蚀行为,利用SEM、FTIR及XRD等手段对压铸AZ91D镁合金在Na2SO4溶液中的腐蚀速率、腐蚀产物形貌和腐蚀产物组分进行定量和定性分析。结果表明:压铸AZ91D镁合金在不同pH值Na2SO4溶液中的腐蚀速率顺序从高到低依次为pH2,pH4,pH7,pH9,pH12,酸性溶液的腐蚀速率大于碱性溶液的腐蚀速率;在Na2SO4溶液中,腐蚀产物主要为Mg(OH)2和MgAl2(SO4)4·22H2O,不同的pH值能改变腐蚀速率和腐蚀产物形貌;氯离子和硫酸根离子有不同的点蚀引发时间。     

AZ31镁合金激光焊件的力学性能和应力腐蚀行为

采用Nd-YAG激光对AZ31 HP镁合金进行激光自熔焊接。显微组织分析表明,使用或不使用填料（焊料）AZ61镁合金得到的激光焊接接头的平均晶粒尺寸大约为12μm,显微硬度和拉伸强度与母材相近。然而,慢应变速率拉伸表明,在ASTM D1384溶液中两种焊接接头的抗应力腐蚀性能比母材略差。可观察到应力腐蚀裂纹在焊缝金属萌生并向热影响区（HAZ）扩展。然而,在以AZ61镁合金为填料（焊料）获得的焊接接头中,观察到裂纹起源及扩展出现在热影响区（HAZ）。在慢应变速率拉伸试验中,由于试样表面暴露在腐蚀环境中,在氢氧化镁/氧化镁层形成局部损伤,从而导致应力腐蚀裂纹的生成。     

AZ31B镁合金表面火焰喷涂Al-Mg_2Si涂层的耐腐蚀性能

为提高AZ31B镁合金表面的耐腐蚀性能,用火焰喷涂方法在镁合金表面制备Al-Mg_2Si复合涂层。采用XRD、SEM和EDS分析涂层的物相组成、微观组织及元素分布;通过电化学试验测试样品在3.5%NaCl溶液中的腐蚀电位、腐蚀电流密度;通过3.5%NaCl溶液浸泡试验测试样品的腐蚀速率;并测试涂层的显微硬度。结果表明:涂层中的主要物相有Mg_2Si、Al,组织比较致密,元素分布均匀。Tafel极化曲线测试表明,Al-Mg_2Si涂层样品与AZ31B镁合金样品相比腐蚀电位从-1.489 V正移到-1.366 V,腐蚀电流密度从2.817×10~(-3) A/cm~2降低到1.198×10~(-3) A/cm~2。浸泡试验结果表明,喷涂Al-Mg_2Si的镁合金的腐蚀速率明显低于没有喷涂的镁合金。显微硬度测试表明,涂层的显微硬度集中分布在259~308 HV0.05之间,镁合金为50~60 HV0.05。因此在AZ31B镁合金表面火焰喷涂Al-Mg_2Si涂层可以提高其耐腐蚀性能,表面硬度显著提高。     

化学镀镍对铸造AZ91镁合金耐腐蚀性能的影响

采用硫酸镍作为化学镀镍镀液的主盐,直接在铸造法制备的镁合金AZ91基体上进行化学镀镍,并对镀层进行腐蚀试验、形貌观察和能谱分析。结果表明,镀镍沉积速率随着施镀时间的增加而增大再减小,镀镍时间为1 h时镀速达到1.42μm/h。在3.5%Na Cl溶液中浸泡4 h后,镀镍镁合金AZ91的腐蚀速率随着施镀时间的增加而减小,镀镍时间为1 h的镁合金腐蚀速率最小,为0.063μm/h,比未镀镍镁合金的腐蚀速率减小96%。腐蚀形貌的观察结果与腐蚀速率的测定结果是一致的。经化学镀镍后可在镁合金AZ91表面得到一耐腐蚀性能良好的镀层,从而改善镁合金AZ91的耐腐蚀性能。     

AZ31镁合金搅拌摩擦焊焊缝电化学性能的分析

试验的样品为3 mm厚挤压态AZ31镁合金,采用搅拌摩擦焊接工艺对焊而成.通过静态失重法、动电位极化曲线以及交流阻抗谱(electrochemical impedance spectroscopy,EIS)测试,研究了室温下浓度5%(质量分数)NaCl溶液中AZ31镁合金搅拌摩擦焊焊缝和母材的电化学行为.结果表明,在室温腐蚀介质中通过静态失重法测得AZ31镁合金母材和焊缝在168 h后的平均腐蚀速率分别为0.154和0.135 g/(m2·h),通过动电位极化曲线及交流阻抗谱(EIS)测得AZ31镁合金母材和焊缝的腐蚀电流分别为0.001 63和0.000 45 A/cm2,极化电阻分别为9.553和12.61Ω/cm2.AZ31镁合金搅拌摩擦焊焊缝的抗腐蚀性能优于其母材的表现.     

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium–AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption, weight reduction and emission reduction. However, joining of aluminium (Al) alloys with magnesium (Mg) alloys by fusion welding process is very complicated. Friction stir welding (FSW) is a feasible method to join these two dissimilar alloys. Mixing these two metals together in stir zone (SZ) leads to poor corrosion resistance. In this investigation, an attempt has been made to understand the corrosion resistance of SZ of FSWed dissimilar joints of AA6061 Al alloy and AZ31B Mg alloy. Potentiodynamic polarization test was conducted by varying chloride ion concentration, pH value of the NaCl solution and exposure time. The corroded surfaces were analyzed using optical microscopy, scanning electron microscopy and XRD techniques. Of these three factors investigated, exposure time is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints of Al/Mg alloys.     

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。     

Formation and properties of stannate conversion coatings on AZ61 magnesium alloys

The effects of solution composition and temperature on the microstructure and corrosion resistance of stannate conversion coatings on AZ61 magnesium alloys were investigated. The conversion coating consisted of a porous layer as under layer intimately contacted with the magnesium plate and a hemispherical particle layer as major overlay formed right on top of the porous layer. During the coalescence of the hemispherical particles to form a complete coating on the magnesium alloy, some sites of discontinuity inevitably left and determined the corrosion resistance of the coating evaluated using a salt spray test. Increasing bath stannate ion concentration and lowering bath pH increased the population density of the hemispherical particles whose size was accordingly reduced. The corrosion resistance of the conversion coating was improved with finer particles, which were preferably formed at less alkaline solution with higher stannate ion contents. Furthermore, the conditions favoring the formation of finer particles also reduced the immersion time necessary for producing the conversion coating with optimal corrosion resistance.     

AZ91镁合金表面电化学沉积羟基磷灰石涂层的制备及其耐蚀性

采用电化学沉积方法在AZ91镁合金表面制备了羟基磷灰石(HA)涂层,研究了电沉积工艺参数对羟基磷灰石涂层形貌和相组成的影响,并通过腐蚀浸泡试验、极化曲线测试等方法对该涂层的耐蚀性进行了研究。结果表明:当溶液pH为4.5,温度为60℃时,涂层的致密性最好,呈放射状的结构,主要成分为HA相,涂层的厚度约为60~70μm,与基体结合较好;HA涂层对镁合金基体具有较好的保护作用,显著提高了基体合金在生理溶液中的耐蚀性。     

碳酸钠对搅拌摩擦加工AZ31镁合金缓蚀性能的影响

通过搅拌摩擦加工(FSP)手段,对3 mm厚的AZ31镁合金板材作表面加工处理.然后在质量分数为5%的NaCl腐蚀溶液中添加不同浓度的碳酸钠作为缓蚀剂,通过动电位极化曲线以及交流阻抗(EIS)测试,研究了室温下该缓蚀剂对镁合金母材及搅拌摩擦加工处理镁合金电化学行为的影响.结果表明,添加缓蚀剂后,FSP镁合金及母材的腐蚀电流密度均减小,极化电阻及电荷转移电阻均增大,而且FSP镁合金的缓蚀效率要优于母材的缓蚀效率,且随浓度的增加而增加,碳酸钠是一种有效的无机缓蚀剂,并且其缓蚀作用效果与金属表面状态密切相关.     

AZ31镁合金搅拌摩擦点焊

研究了搅拌头旋转频率以及停留时间对AZ31镁合金搅拌摩擦点焊接头力学性能的影响.随着旋转频率的增大,不同搅拌针条件下,AZ31搅拌摩擦点焊接头的力学性能均呈现先增大后减小的趋势.随着停留时间的延长,AZ31搅拌摩擦点焊接头的力学性能先增大随后在一定范围内波动.结果表明,结合宽度是影响搅拌摩擦点焊接头力学性能的重要因素,...     

Strain localisation and failure of dissimilar magnesium-based alloy friction stir welds

Dissimilar butted combinations of magnesium alloys AZ31, AZ61 and AZ80 were friction stir welded and transverse tensile tested until failure. Strain mapping across the deforming weld nugget and interfaces was carried out to correlate the deformation to the local microstructures. Mechanical performance was found to be highly dependent on the spatial distribution of alloys within the nugget and thus highly sensitive to changes in the tooling geometry. Process control requirements for repeatable, high-quality dissimilar friction stir welds will therefore be far more rigorous and challenging than those of similar welds of these alloys. In addition, proximity to the tool insertion point was found to decrease tensile performance, likely due to changes in tooling temperature.     

Stress corrosion cracking of AZ61 magnesium alloy friction stir weldments in ASTM D1384 solution

Abstract

Stress corrosion cracking (SCC) behaviour of a wrought magnesium alloy (AZ61) friction stir weldment was assessed in ASTM D1384 test solution at two strain rates. The analyses have shown that both the parent and the weldment are susceptible to SCC at a nominal strain rate of 10^–6 s^–1. Fractographic evidence clearly reveals the susceptibility, especially of the fine grained region of the friction stir weld nugget to SCC. The susceptibility to cracking has been observed to increase with decreasing strain rate and under this condition (10^–7 s^–1), the behaviour of the parent and the friction stir weldment were nearly the same.