7A04铝合金在海洋大气环境中初期腐蚀的电化学特性

通过盐雾腐蚀试验模拟研究7A04铝合金在海洋大气环境中的腐蚀初期规律,采用电化学交流阻抗测试和扫描Kelvin探针技术,研究7A04铝合金在初期腐蚀过程中的电化学行为.结果表明:Cl-对铝合金腐蚀有显著的加速作用,盐雾试验初期表面出现点蚀坑;随盐雾时间增长,点蚀相互连接并扩展,电化学反应阻抗下降.扫描开尔文探针测试结果表明:随腐蚀的不断进行,金属表面阴极区和阳极区不断发生变化,呈现局部腐蚀的特征,表面电位也随时间逐渐升高,阴极区和阳极区逐渐变得明显,腐蚀反应处于不断加速过程.     

化学沉积Ni-P合金层在7A04铝合金表面的应用研究

确定了在7A04铝合金表面化学沉积Ni-P合金镀层的镀液组成和操作工艺参数,并对镀层的表面和截面形貌进行了观察,对镀层的结合强度、显微硬度以及耐腐蚀性等进行了测试。结果表明,该Ni-P镀层沉积速度快,镀层结晶致密均匀,镀层与基体间结合力强,镀层使基体的显微硬度提高8.6倍,且镀层在w(NaCl)=3.5%的NaCl水溶液中表现出良好的耐蚀性。     

7A04铝合金压缩力学性能的各向异性

采用Gleeble-3800型热模拟试验机进行压缩试验,变形温度为320～480℃、应变速率为0.1～1 s-1.压缩方向与7A04铝合金棒材轴向分别成0°、45°、90°.结果表明:7A04铝合金高温变形的流变应力随温度的升高和应变速率的降低而减小;在低温(T=320℃)和小应变速率(ε=0.1 s-1)的条件下7A04铝合金的各向异性最明显;在高温(T=480℃)和小应变速率(ε=0.1 s-1)的条件下,7A04铝合金的各向异性最不明显.     

稀土Ce对7A04铝合金耐腐蚀性能的影响

目的提高7A04铝合金的耐腐蚀性能。方法采用周期浸润腐蚀试验模拟海洋大气环境,研究了不同稀土Ce含量的7A04铝合金的腐蚀行为及规律。通过金相显微镜和扫描电子显微镜,观察了不同试样的组织和夹杂物形貌。采用失重法和电化学阻抗技术,分析了试样的腐蚀动力学规律及电化学行为特性。结果在Ce质量分数分别为0%、0.39%和0.81%的7A04铝合金中,稀土Ce的加入量为0.39%时,其晶粒最细小,第二相与夹杂最少且分布最均匀,合金的基体组织得到了改善。稀土7A04铝合金的腐蚀失重明显低于不含稀土Ce的7A04铝合金,且锈层电阻升高,其中含0.39%稀土Ce的7A04铝合金的锈层电阻最高。结论三种7A04铝合金均发生了明显的局部腐蚀,主要为点蚀。稀土Ce的加入,改变了非稀土铝合金中的T相和S相,生成了新的细小的块状金属间化合物,改善了组织的均匀性,提高了其腐蚀锈层电阻,增加了锈层对基体的保护能力,使铝合金耐海洋大气腐蚀性能提高。在三种稀土Ce含量的铝合金中,含0.39%稀土Ce的7A04铝合金的耐蚀性最佳。     

7A04铝合金壳体失效分析

7A04铝合金壳体在使用过程中发生开裂失效,通过对失效件的外观、断口宏微观形貌观察,以及对失效件和库存件材质、显微组织、力学性能和表面应力等方面的测试,对壳体的开裂原因进行了分析。结果表明,失效壳体为沿纵向脆性断裂,壳体横向力学性能较低,使用过程中承受较大的工作应力是导致开裂的主要原因。     

7A04和2A12铝合金在吐鲁番干热大气环境中的腐蚀行为

采用现场暴晒试验,研究了7A04和2A12两种铝合金在吐鲁番干热大气环境中的腐蚀行为和机理。1a暴露后的失重分析发现7A04的腐蚀速率大于2A12;采用SEM和EDS观察分析了两种合金表面的腐蚀产物,结果表明,均主要由铝的氧化物和氢氧化物组成。去除腐蚀产物后,7A04表面呈现大量密集腐蚀坑,而2A12表面腐蚀坑则较少。EIS结果表明,两种合金的腐蚀产物层电阻电容差别较大,带腐蚀产物2A12的耐蚀性优于7A04。     

7A04铝合金工件阳极氧化后表面出现"黑斑"的原因

对出现“黑斑”和未出现“黑斑”的7A04铝合金工件进行宏观组织和微观组织的对比和分析，并配合相应的热处理试验。可知：有“黑斑”的工件再结晶程度小，基体内亚晶数量较多，且聚集成堆，成片分布，对有“黑斑”的工件重新热处理后阳极化处理，其“黑斑”便消失。这说明工件出现的“黑斑”是因为工件的热处理程度不够，即淬火保温时间不足。     

7A04铝合金扭转热变形行为研究

利用Gleeble-3500热模拟试验机扭转单元,在温度为360~480℃,应变速率为0.001~1 s~(-1)条件下,研究了具有纤维状晶粒组织7A04铝合金的流变行为。采用ZIESS PL-A662数码光学显微镜分析合金显微组织的演变规律,利用Zener-Hollomon参数法通过数学分析构建了该合金基于扭转的高温塑性变形本构方程。由应力-应变曲线分析可得:流变应力随温度的升高逐渐降低,随应变速率的增大而升高。在扭转中,随着棒材半径的增加,应变增大,晶粒形状也随之变化。组织分析表明:从试样的外表面到轴心的晶粒按形状可大体分为等轴晶粒区、椭圆形晶粒区及纤维状晶粒区。其原因是转动过程中距离试样轴心距离越远,变形量越大,动态再结晶越充分。     

7A04铝合金快速热处理工艺研究

固溶和时效时间是制约高强铝合金力学性能和热处理生产效率的主要因素.本文以7A04铝合金为例通过高温预热装炉、分级固溶和提高时效温度等方法研究了高强度铝合金的快速热处理工艺.并结合金相组织观察、断口分析、X射线分析和力学性能测试,分析了快速热处理对高强铝合金组织和性能的影响.结果表明:①固溶时间相同时,分级固溶的强度高于单级固溶的强度,分级固溶的塑性略低于单级固溶的塑性.②分级固溶时,随着二级固溶时间的增加,材料的强度增加,塑性略有降低.③采用500℃高温预热装炉、470℃5min 485℃9min固溶和140℃6h 150℃1h的快速热处理工艺可以明显缩短热处理时间,提高生产效率50%以上.     

2024-T3铝合金在模拟海洋大气环境中的腐蚀行为

通过循环盐雾腐蚀实验,模拟2024-T3铝合金在海洋大气环境中的腐蚀过程。采用腐蚀质量损失测试、扫描电镜(SEM)、X射线能谱(EDS)和电化学技术分别对腐蚀117、242、362、487和598 h的2024-T3铝合金试样进行测试分析,得到腐蚀动力学、腐蚀产物和点蚀坑的形貌、腐蚀产物的成分以及表面锈层的电化学特性,研究锈层对2024-T3铝合金大气腐蚀的影响。动力学分析表明,腐蚀过程中2024-T3铝合金的表面形成了具有较好保护性的锈层;电化学测试结果表明,锈层的保护性呈现随腐蚀时间的延长先增强后减弱然后再略增强的变化过程。     

Corrosion behavior of aluminum weld overlay alloys with dispersed niobium carbide particles in sodium chloride solution

Aluminum overlay weld alloys with dispersed niobium carbide particles (NbCp/Al) were prepared by a plasma transferred arc welding process. The corrosion behavior of the NbCp/Al alloys was studied in sodium chloride solution by means of electrochemical techniques and scanning electron microscopy. The aluminum alloys under investigation were pure aluminum, aluminum-magnesium, aluminum-magnesium-silicon, and aluminum-copper. The addition of NbC particles shifted the corrosion potentials in the positive direction. However, the pitting potentials were almost similar to that of overlay weld alloy without NbC particles. In the immersion test in quiescent 0.5M NaCl open to the air, preferential localized corrosion of all NbCp/Al alloys was observed at the matrix between NbC particles and crystalline phases.     

Corrosion of LY12 aluminum alloy in sodium chloride solution

1　INTRODUCTIONBecauseofitshighmechanicalperformanceandlowdensity ,LY12alloy(USAA2 0 2 4 )iswidelyusedintheaircraftindustryfornumerousapplicationssuchasfuselage ,doorskin ,dorsalfinandtrailingedgepanels .Nevertheless ,thisalloycaneasilybeaffectedbylocalizedcorrosion ,suchaspittingandexfoliation ,especiallyinchloridecontainingenvironment .Thislocalizedattackcanresultinprematurebreakdownofstructuralparts[1] .Inordertominimizethelocalizedattackonthealuminumalloy ,thecorrosionmecha nismshou…     

坡莫合金在中性氯离子溶液中的腐蚀行为

针对金属薄膜复合板的金属膜选材问题,采用电子探针、金相显微镜研究了坡莫合金膜的成分、显微组织,利用电化学技术,辅以浸泡法研究了坡莫合金在浓度为2.4 mol/L的中性氯化钠溶液中的电化学腐蚀行为,利用SEM和EDS研究了腐蚀产物和腐蚀形貌,结果表明:坡莫合金膜晶粒度8级,组织为奥氏体,腐蚀类型为局部腐蚀,主要表现为晶间...     

7B04铝合金的时效沉淀析出及强化行为

利用差示量热法(DSC)、透射电镜(TEM)、选区电子衍射(SAED)、常规力学性能测试等手段研究了7B04铝合金时效沉淀析出及强化行为。结果表明:该材料存在显著的自然时效现象,大量的GPⅠ区沉淀析出是自然时效强化的主要原因;合金在120℃进行人工时效的初期析出大量GP区,使材料的强度迅速提高,时效8 h后,其横向极限抗拉强度即可达到570 MPa,时效22 h时可达强度峰值点,此时GP区(包括GPⅠ和GPⅡ区)和η′相是主要强化相;峰值时效后继续延长时效时间,材料的强度无明显降低,极限抗拉强度保持在590 MPa左右。     

Corrosion behavior on aluminum alloy LY12 in simulated atmospheric corrosion process

The corrosion behavior of typical high-strength aluminum alloy LY12 was studied by accelerated corrosion tests of cyclic wet-dry-immersion containing media of NaHSO3 and NaCI to simulate the corrosion process in different atmosphere environment, and the corrosion mechanism was also discussed. The main experimental techniques include mass loss, morphological check, analysis of corrosion products and electrochemical measurement. The result shows that the mass loss of LY12, with or without cladding, has linear relationship with test time in the three kinds of chemical media, 0.02 mol/L NaHSO3, 0.006 mol/L NaCl and 0.02 mol/L NaHSO3＋0.006 mol/L NaCl, respectively. A layer of cladding on high-strength aluminum alloy can raise evidently the resistance of atmospheric corrosion. Cl^- can promote pitting generation on the oxide film of LY12 when HOS3 exists, LY12 can react much intensely with HOS3^- derived from anions.     

Corrosion behavior of LY12CZ aluminum alloy in simulated acid rain solution

The variations of corrosion potential,electrochemical impedance and surface morphology of LY12 aluminum alloy with pH of simulated acidic rain solutions were investigated with EIS and SEM.It is found that corrosion potential shifts to less noble value with increasing pH in the solutions of pH lower than 3.1 and shifts to more noble value in the solutions of pH higher than 3.1.In the solutions of pH lower than 3.1,the electrochemical impedance diagram has a capacitive loop at higher frequency and an inductive loop at lower frequency and the magnitude of high frequency loop decreases with decreasing pH and increasing period of immersion.However,in the solutions of Ph higher than 3.4 two capacitive loops appear and the magnitude of high frequency loops increases with pH ad period of immersion.Observation of SEM shows that the pitting intensity increases with decreasing pH in the range of pH2.0-3.4,no evident pits are observed at pH higher than 3.4.The experiment results were discussed from resistance of oxide film and adsorption processes of anions in simulated acid rain solution.     

Corrosion behavior of various steels in the simulated fluidized bed boiler environment

The corrosion behavior of various austenitic stainless steels and high-alloy steels has been studied in simulated fluidized bed boiler environment to develop a new corrosion resistant austenitic stainless steel for the superheater tube. The superheater is usually not installed within the bed position, which is different from the evaporator installed within the bed position. Therefore, the superheater tubes are exposed to an oxidizing environment; but it is also necessary to estimate the corrosion resistance of the steels in a reducing environment. It is already known that the high temperature corrosion behavior in conditions where CaSO₄ is coated on the steels is more important than the erosion of the superheater tubes. The main results in this present study are as follows: The Nb bearing steels and low C steels showed good resistance to high-temperature corrosion in CaSO₄/CaO, e.g. 347, 304L and HR3C. The corrosion rate of all steels used increased with increase in temperature, particularly at temperatures higher than 650°C. Internal penetration was not detected at temperatures lower than 550°C, but it was detected at temperatures higher than 600°C, in particular, higher than 650°C. The corrosion thickness loss was almost the same as the internal penetration depth at 700 and 750°C in the 300 series steels placed in CaSO₄/CaO, including the fine grained 347 steel, while the internal penetration depth was larger than the corrosion thickness loss in high-alloyed materials such as Alloy 800 and 310 steels. At temperatures higher than 800°C, the same result was also obtained for the fine grained 347 steel. The corrosion during exposure to oxidizing or reducing gases without CaSO₄/CaO or CaS was slight, but when the test specimens were placed in CaSO₄/CaO or CaS, the corrosion rate sharply increased, regardless of the atmospheric gas composition. Cr, Si, Mn (less than 5 %), Mo and Nb are beneficial elements while C, Cu and Al are harmful elements. From the above results, the following steel was developed for high temperature corrosion resistance in CaSO₄/CaO: low C-22/25Cr-17/25Ni-3/5Mn-(2Mo)-Nb-0.08/0.2N-Al-(B).