Corrosion Behavior of SiCp／2024 Al Matrix Composites in 3.5 wt pct Sodium Chloride

The influences of volume fraction and particle size of SiC particulate reinforcements on the corrosion characteristics of SiCp/2024Al metal matrix composites in aerated 3.5wt pct NaCl aquecus solution were investigated.The electro-chemical behavior was investigated by prtentiodynamic polarization and electrochemical impedance spectroscopy, the general corrosion behavior of the composites was studied further by immersion tests.The results showed that pitting susceptibility was about the same for the composites and the alloy.The corrosion potentials were also independent of SiC phase.The corrosion resistance for the composites decreased as the volume fraction increased or particle size decreased.     

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1μm diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.     

Study on the Rare Earth Sealing Procedure of the Porous film of Anodized 2024 Aluminum Alloy

The rare earth sealing procedure of the porous film of anodized aluminum alloy 2024 was studied with the field emission scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS),The results show that RE solution can form cerium oxide/hydroxides precipitation in the pores of the anodized coating at the beginning of sealing ,At the same time,the spherical deposits formed on the surface of the anodized coating created a barrier to the precipitation of RE solution in the pores,When the pore-sturctured anodizting film is covered all with the spherical deposits,RE conversion cfoating will form on the surface of the anodized coating,The reaction of the coating formation was investigated by employing cyclic voltammetry ,The results indicate that accelerator H2O2 acts as the source of O2 by carrying chemical reaction in course of coating formation ,In the mean time,it maybe carries electrochemical reaction to generate alkaline condition to accelerate the coating formation,The porous structure of the film is beneficial to the precipitation of the cerium hydroxdies film.     

Corrosion Behavior of the Rare Earth Sealing Anodized Coating on Aluminum Alloy LY12

Technological process of rare earch sealing anodized LY12 (2024) alloy is introduced.Corrosion behavior of the film was studied by polarization curves and electrochemical impedance spectroscopy (EIS).The results showed that the coating remained passivity at the potential range from the open circuit potential (-780mV) to -250mV in NaCl solution.When the potential exceeded -200mV,corrosion reaction happoened on the coating.the results of EIS analysis was consistent with the results of polarization curves.     

XPS Analysis of the Cerium Conversion Coatingon the Anodized A16061／SiCp

A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced.The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites Al6061/SiCp was then studied according to this method.The results revealed that the Ce conversion coating on the anodized Al6061/SiCp consisted of Al oxide,Ce oxide and Ce hydroxide.The state of Ce element exhibited the mixture of Ce^3 and Ce^4 .Some of Cell was oxidized to be CelV in the outer layer coating.     

Evolution of Thermoplastic Shear Localization and Related Microstructures in Al／SiCp Composites Under Dynamic Compression

The localized shear deformation in the 2024 and 2124 Al matrix composites reinforced with SiC particles was investigated with a split Hopkinson pressure bar (SHPB) at a strain rate of about 2.0×103 s-1. The results showed that the occurrence of localized shear deformation is sensitive to the size of SiC particles. It was found that the critical strain, at which the shear localization occurs, strongly depends on the size and volume fraction of SiC particles. The smaller the particle size, the lower the critical strain required for the shear localization. TEM examinations revealed that Al/SiCp interfaces are the main sources of dislocations. The dislocation density near the interface was found to be high and it decreases with the distance from the particles. The Al matrix in shear bands was highly deformed and severely elongated at low angle boundaries. The AI/SiCp interfaces, particularly the sharp corners of SiC particles, provide the sites for microcrack initiation. Eventual fracture is caused by the g     

Effect of Ni Content on Mechanical Properties and Corrosion Behavior of Al/Sn－9Zn－xNi/Cu Joints

The effects of Ni content on the microstructure and the wetting behavior of Sn-9Zn-xNi solders on Al and Cu substrates, as well as the mechanical properties and electrochemical corrosion behavior of Al/Sn-9Zn-xNi/Cu solder joints, were investigated. The microstructure of Sn-9Zn-xNi revealed that tiny Zn and coarsened Ni 5 Zn 21 phases dispersed in the β-Sn matrix. The wettability of Sn-9Zn-xNi solders on Al substrate was much better than that on Cu substrate. With increasing Ni content, the wettability on Cu substrate was slightly improved but became worse on Al substrate. In the Al/Sn-9Zn-xNi/Cu joints, an Al4.2Cu3.2Zn0.7 intermetallic compound (IMC) layer formed at the Sn-9Zn-xNi/Cu interfaces, while an Al-Zn-Sn solid solution layer formed at the Sn-9Zn-xNi/Al interface. The mixed compounds of Ni3Sn4 and Al3Ni dispersed in the solder matrix and coarsened with increasing Ni content, thus leading to a reduction in shear strength of the Al/Sn-9Zn-xNi/Cu joints. Al particles were segregated at both interfaces in the solder joints. The corrosion potentials of Sn-9Zn-xNi solders continuously increased with increasing Ni content. The Al/Sn-9Zn-0.25Ni/Cu joint was found to have the best electrochemical corrosion resistance in 5% NaCl solution.     

Sol-Gel Coating with 3-Mercaptopropyltrimethoxysilane as Precursor for Corrosion Protection of Aluminium Metal

Sol—gel coatings offer a number of advantages over other methods of protection for metallic materials.In the present work,3-mercaptopropyltrimethoxysilane（MPTS） was used as the precursor for sol—gel coating on aluminium metal.The gelation of MPTS sol—gel was characterized by Fourier transform infrared spectroscopy（FT-IR） studies.The formed film was found to be stable up to 350 ℃ as evident from thermogravimetric analysis.X-ray diffraction study and scanning electron microscopy supported the formation of MPTS coating on aluminium surface while the characterization of the coating was done by FT-IR studies.The corrosion inhibition potential of the sol—gel coatings on metal in 3.5%（w/v） of NaCI solution was assessed as a function of different concentrations of MPTS using electrochemical polarization and impedance measurements.The corrosion inhibition efficiency was found to increase with increasing MPTS concentration.The results of the study unravel the use of MPTS as a precursor in the formation of sol—gel coating over aluminium surface so as to protect the metallic surface from corrosion in neutral environment.     

Improvement on the Corrosion Resistance of AZ91D Magnesium Alloy by Aluminum Diffusion Coating

By combination of magnetron sputtering deposition and vacuum annealing, an aluminum diffusion coating was prepared on the substrate of AZ91D alloy to improve its corrosion resistance. The microstructure and composition of the diffusion coating was investigated by scanning electron microscopy and X-ray diffraction. The diffusion coating was mainly comprised of β phase-Al12Mg17. The continuous immersion test in 3.5 wt pct neutral NaCl solution indicated that the specimen with diffusion coating had better corrosion resistance compared with the bare AZ91D alloy specimen. The potentiodynamic polarization measurement indicated that the diffusion coating could function as an effectively protective layer to reduce the corrosion rate of AZ91D alloy when exposed to 3.5 wt pct NaCl solution.     

Preparation and Corrosion Resistance of Magnesium Coatings by Magnetron Sputtering Deposition

Magnesium coatings were fabricated on stainless steel substrates (1Cr11Ni2W2MoV) by a plane magnetron sputtering technique. The argon pressure and the substrate condition (including temperature and the substrate was rotated or fixed) were varied in order to evaluate the influence of the parameters on the crystal orientation and morphology of the coating. The corrosion behavior of the coatings in 1 wt pct NaCl solution was studied by electrochemical methods.The results showed that all coatings exhibited preferred orientation (002) as the argon pressure increased from 0.2 to 0.4 Pa. The morphologies of the coatings varied with the argon pressure and with whether the substrate was rotated or fixed. The open circuit potential of the coatings was more positive than that of cast AZ91D magnesium alloy.However, the immersion test in 1 wt pct NaCI solution showed that the corrosion rates of the coatings were higher than that of cast AZ91D magnesium alloy.     

Corrosion protection and formation mechanism of anodic coating on SiCp/Al metal matrix composite

The corrosion protection from sulfuric acid anodized coatings on 2024 aluminum and SiC particle reinforced 2024 aluminum metal matrix composite (SiC_p/2024Al MMC) in 3.5 wt.% NaCl aqueous solution was investigated using electrochemical methods. The results show that the anodized coating on 2024Al provides good corrosion protection to 3.5 wt.% NaCl, and the anodized coating on the SiC_p/2024Al MMC provides some corrosion protection, but it is not as effective as for 2024Al because non-uniformity in thickness and cavities present are associated with the SiC particulates. Cavities above SiC particles are the reason that the anodized coating on the MMC cannot be completely sealed by hot water as with anodic Al alloy. SiC particle anodizes at a significantly reduced rate compared with the adjacent Al matrix. This gives rise to alumina film encroachment beneath the particle and occlusion of the partly anodized particle in the coating. It was found that the barrier layer of anodized Al MMC is not continuous, and it is composed primarily of the barrier layer of anodized Al matrix and a barrier-type SiO₂ film on occluded SiC particles in the coating. A new formation mechanism of coating growth during anodizing of a SiC_p/2024Al MMC was proposed.     

2024铝合金阳极氧化膜的结构和耐蚀性能

为促进2024铝合金的进一步应用,用动电位阳极极化和电化学阻抗方法研究了2024 Al合金阳极氧化膜的结构及其在3.5% NaCl水溶液中的耐蚀性.结果表明,经硫酸阳极氧化的2024 Al合金较未处理基体的腐蚀速度降低了2个数量级以上,表现出相当好的保护性能;用光学显微镜、扫描电镜和透射电镜对阳极氧化膜的形貌观察发现,氧化膜表面平整,孔隙分布均匀,每个孔隙周围多含6个孔隙,也有5和7个孔隙结构,其孔隙尺寸细小,大小在10～30 nm之间.     

Pitting behavior of SiCp/2024 Al metal matrix composites

The effects of the volume fraction of SiC particulate reinforcements and the concentration of chloride ions in solution on the localized corrosion characteristics of SiCp/2024 Al metal matrix composites (MMC) were investigated. A scanning micro reference electrode (SMRE) technique was employed to study the dynamic process of pitting initiation and development on the surface of the composites at open-circuit potential. Potentiodynamic polarizations were performed to characterize the electrochemical behavior of the MMCs. The morphology of the localized attack on the MMC sample after corrosion tests were examined by scanning electron microscopy (SEM). The results of electrochemical measurement showed that the composites were less resistant to pit initiation than the corresponding unreinforced metrix alloy. Increase in the volume fraction of SiCp reinforcement in the SiCp/2024 Al composites resulted in a significant decrease of pitting potential. In situ potential mapping of active centers on the surfaces of the composites revealed that local breakdown of passivity and initiation of micro pitting corrosion could take place even at an open-circuit potential which was more negative than the pitting potential, and the number of active centers on the surfaces of the composites increased as the volume fraction of SiC particulates in MMCs increased. Micro-structural analysis indicated that pitting attack on the composites mainly occurred at SiCp-Al interfaces or inclusions-Al interfaces.     

Effect of size of reinforcement on thickness of anodized coatings on SiC/Al matrix composites

The effect of size of reinforcements on morphology and thickness of anodic coatings on 3.5 μm and 10 μm SiC particles reinforced 2024Al metal matrix composites (SiC_p/Al MMCs) formed in sulfuric acid was investigated with optical microscopy and scanning electron microscopy. The thickness of anodized coating on the MMCs is strongly dependent of size of SiC particles, and it is smaller for the MMC with smaller SiC particles because growth of more pores is affected when the concentration of SiC particles is fixed. The oxide/substrate interface became locally scalloped, and the anodized coatings formed on the MMCs were non-uniform in thickness, especially for the MMC reinforced by bigger particles.     

Rare Earth Application in Sealing Anodized Al-Based Metal Matrix Composites

A new method for corrosion protection of Al-based metal matrix composites (MMC) was developed using two-step process, which involves anodizing in H2SO4 solution and sealing in rare earth solution. Corrosion resistance of the treated surface was evaluated with polarization curves. The results showed that the effect of the protection using rare earth sealing is equivalent to that using chromate sealing for Al6061/SiCp. The rare earth metal salt can be an alternative to the toxic chromate for sealing anodized Al MMC.     

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 μm diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024Al composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices.Therefore, the aging peak of the composite appears earlier than that of 2024Al alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.     

Electrochemical study of the corrosion behavior of Ce sealing of anodized 2024 aluminum alloy

The technological process of Ce sealing of anodized LY12 (2024) alloy is introduced in this paper. The corrosion behavior of the film is studied by polarization curves and electrochemical impedance spectroscopy. The results show that the coating remains passive at the potential range from the open circuit potential (−780 mV) to −250 mV. After immersing the sample in NaCl solution for 6 days, the outer layer Ce conversion coating begins to loose its anticorrosive property. The inner Ce sealing anodized film is not corroded until 60 days immersion. Thus, the inner layer Ce sealing anodized film takes the leading role of the corrosion protection for LY12 alloy.     

SiC颗粒尺寸及含量对SiCp／2024Al复合材料性能的影响

本文对粉末冶金法制备的SiCp/2024Al复合材料的性能进行了研究。随SiC颗粒尺寸的增大,复合材料的强度降低,而塑性和磨损抗力则增加。SiC颗粒尺寸对复合材料的物理性能没有什么影响。增加SiC颗粒含量,复合材料的强度、模量均增大,磨损抗力亦明显增加,而塑性和热膨胀系数则降低。     

Intelligent self-healing corrosion resistant vanadia coating for AA2024

This paper is a continuation of our investigation into the designing of chromate-free anti-corrosion coatings for aluminum and magnesium based materials for marine, automotive and aerospace applications. In this paper, a simple vanadia based chemical conversion coating was applied for improving the corrosion resistance of high strength AA2024 alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) on the corrosion behavior was investigated. EIS, linear polarization and cyclic voltammetry techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. Vanadia coatings prepared by dissolving 10 g of vanadate salt per liter showed the best localized corrosion resistance as measured by EIS and polarization techniques. The optimum conditions to obtain corrosion protective coatings for AA2024 were determined. Surface examination of the samples was investigated using AFM, SEM-EDS and macroscopic images.