Corrosion Resistance Of Aluminum Alloys Research Articles

Investigation of Zirconium Effect on the Corrosion Resistance of Aluminum Alloy Using Electrochemical Methods and Numerical Simulation in an Acidified Synthetic Sea Salt Solution.

Corrosion resistance of Zr that has been added to an Al alloy (U1070) is higher than that of a commercial Al alloy (A1070). A decreasing number and size of Al3Fe intermetallic particles (IMPs) were observed by electron microprobe analysis and transmission electron microscopy. Based on the numerical corrosion simulation, it was confirmed that decreasing the number and size of IMPs was favorable for improving the corrosion resistance of the Al alloy due to the reduction of the galvanic effect. In addition, Al3Zr was found to be insignificant in promoting galvanic corrosion within the Al matrix. Thus, Zr is an advantageous alloying element for improving the corrosion resistance of the Al alloy.

Study of anti-corrosion and anti-wear properties on superhydrophobic aluminium alloy surfaces

ABSTRACTTo improve the wear and corrosion resistance of aluminium alloys in salt environments, we produced superhydrophobic surfaces via high-speed electrical discharge machining. The specimens were characterised using a scanning electron microscope and a laser scanning confocal microscope and through contact angle (CA) measurement, measurement of electrochemical corrosion at an electrochemical workstation and wear testing. Results showed that the superhydrophobic specimens had a water CA of 151.5°. The corrosion of the as-obtained superhydrophobic specimens was significantly reduced by more than 50%, indicating their excellent anti-corrosion properties. The wear of as-obtained superhydrophobic specimens were reduced by approximately 10–35% in dry conditions and by approximately 45–85% in 3.5% NaCl solution, revealing their excellent anti-wear properties in both dry and salt environments.

Nanoceria induced grain refinement in electroless Ni-B-CeO2 composite coating for enhanced wear and corrosion resistance of Aluminium alloy

Nickel-based coatings on aluminium with specific surface properties are of great interest for anti-corrosive, anti-wearing, and self-lubricating applications. In the present study electroless Ni-B alloy and Ni-B-CeO2 nanocomposite coatings were formed on 356 aluminium alloy surfaces. Ceria incorporation to Ni-B coating reduces the average nodular grain size from 1150 nm to 650 nm and Ni crystallite size from 15 nm to 9.97 nm. Ni-B-CeO2 nanocomposite shows remarkable improvement in microhardness of 684 VHN compared to pure Ni-B coating with 424 VHN. Enhanced wear resistance and reduction in friction coefficient are observed for the nanocomposite coatings compared to 356 Al alloy and Ni-B alloy coating. Potentiodynamic polarization measurements show a remarkable reduction in the corrosion current density for ceria added nanocomposite coating (2.48 × 10−6 A cm−2) than that of the particle-free counterpart (11.18 × 10−6 A cm−2). Uniform Ni-B-CeO2 composite coating was obtained on centrifugally cast A356 aluminium alloy cylinder liners which have potential applications in automotive systems.

Improvement in Corrosion Resistance of Aluminium Alloy by Permanganate-based Conversion Coating

This investigation on permanganate-based conversion coating describes a chromate-free coating and efforts at reducing the environmental foot prints of metal finishing industries. A golden coloured coating on aluminium specimen was obtained from the permanganate coating (PMC) bath with nominal pH of 7.9. Results from scanning electron microscopy (SEM) examination showed that the conversion coatings are continuous, and the surfaces of the specimens treated in the coating bath are composed of irregularly shaped and mud-cracked coating materials. The coatings, as revealed from energy dispersive spectroscopy (EDX) analyses in the SEM are composed essentially of aluminium, oxygen and manganese compounds which are likely to be hydrated. Accelerated corrosion tests in near neutral 3.5% sodium chloride solution and natural exposure tests revealed that the replacement of chromate with permanganate improved paint adhesion and corrosion resistance on aluminium substrates. Furthermore, the results indicated that the corrosion resistance of the permanganate-based conversion coating matched those from the traditional chromate coating bath, but for the corrosion resistance, after application of a top coat of lacquer, the former was adjudged better than the later. Keywords: Aluminium, permanganate, corrosion resistance, conversion coating, corrosion

Effect of NaAlO2 sealing on corrosion resistance of 2024 aluminum alloy anodized film

In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. Sealing after anodization is an important step to improve the corrosion resistance of aluminum alloys. In this paper, sealing effect of NaAlO2 solution on the oxalic acid anodized aluminum alloy was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), and X‐ray photoelectron spectroscopy (XPS). Experimental results show that unsealed anodized aluminum alloys display a porous structure and have poor corrosion resistance but the pores are filled and the corrosion resistance of the sample is significantly improved when anodized aluminum alloy was immersed in 0.2 m/L NaAlO2 solution with pH of 7 for 5 min at 85 °C. Moreover, the anodized aluminum alloy with NaAlO2 sealing exhibited better corrosion resistance compared to the hydrothermally sealed sample, because of the formation of more AlOOH in NaAlO2 sealing treatment.

Effect of Fe3+ Ion on Corrosion Behavior of 5083 Aluminum Alloy in Neutral Environment

5000 series aluminum alloys are wildly used as high corrosion resistance aluminum alloys for Marine structures. As atmospheric corrosion test, iron powder and artificial sea water were spread on 5083 Aluminum alloy plate. A plate with only artificial sea water was also prepared. And the plates were kept in a humid environment for one week. After testing, pitting corrosion was only observed in plate with iron powder and artificial sea water. However, Fe3+ that is stable Fe ion was reported not to effect on corrosion of aluminum alloys.Cations derived from salts such as Na and Mg are investigated in detail as their effect on the corrosion resistance of aluminum alloys. On the other hand, the effect of Fe ions derived from steel materials, which are often used together in structural materials, on aluminum alloys is not clear. So, this study focused on effect of Fe ion on corrosion behavior of 5000 series aluminum alloy. Then, the effect of Fe ion on the corrosion resistance of aluminum alloys was investigated through electrochemical method in beaker test. Open circuit potential in Fe3+ and Cl- solution was measured. FeCl3 aq which contained 0.53% Fe3+ and 1.0%Cl- was prepared. Its pH was adjusted to 7.0 with NaOH. NaCl aq (1%Cl-) was also prepared. OCP of 5083 Aluminum alloy in NaCl aq was -0.8 V vs SCE. However, OCP of FeCl3 aq was gradually lowered and -1.2V at last. Comparing the surfaces after 500hrs in FeCl3 aq and NaCl aq, Surface of 5083 Aluminum alloy in FeCl3 aq showed general corrosion. Surfaces at 0.5 hrs, 30 hrs, and 160 hrs in FeCl3 aq were also observed. The matrix arounds precipitations were dissolved at 0.5hrs. Dissolved area expanded after 30hrs. At last, Discoloration appeared at free surface after 160hrs. Al and O were detected at discoloration area by EDS. It implied that aluminum oxide likely was produced as corrosion product. Anodic polarization curve in Fe3+ and Cl- solution was measured. The anodic polarization curve in FeCl 3 aq after 0.5hrs was the same as in the NaCl aq.However, OCP lowered after 24hrs. Anode current increment is necessary to lower the OCP. Then, activation of precedence dissolution caused OCP lowering as anodic reaction.Anodic polarization curve in 160 hrs had slightly higher activation potential and lower passivity current than that of 24hrs. So, Al oxide on the surface might possibly protect matrix from corrosion. However OCP kept lower and it did not return to the potential after 0.5hrs.So, the anode reaction was probably kept active even after the oxide was formed on the surface. Therefore Fe3+ ion accelerated anode reaction that caused OCP lowering and corrosion acceleration of 5083 Aluminum alloy.

Research on Corrosion Control Factors of 2A02 Aluminum Alloy of Different States before and after Laser-Shock-Processing

The variation of corrosion behaviors and microstructure of 2A02Aluminum alloy before and after Laser Shock Processing (LSP) were analyzed, and the effects of LSP on corrosion resistance of the alloy were explored. The results show that the corrosion resistance of aluminum alloys with different aging conditions is quite different before and after laser shock. The corrosion potentials of the aluminum alloys with different aging conditions vary with the initial state, the natural aging state, the two aging stages (150°C/6h, 190°C/6h, 8h+160°C/6h), indicating that the grain size and morphology and distribution of precipitated phase under different aging conditions before impact are the main controlling factors in the process of corrosion. The micro-analysis revealed that LSP can form a compact strengthened layer at the surface of the material and can refine grains, at this point the strengthening effect caused by LSP was the main controlling factor in the corrosion process.

Effect of tool pin profile and dimensions on mechanical properties and microstructure of friction stir welded armor alloy

High strength to weight ratio with good corrosion resistance of aluminum alloy (AA) 7039 make it the first choice for armor plate in the defense industry. Friction Stir Welding (FSW) is a solid state welding process and used to join this aluminium alloy. In FSW process the tool design acts an vital role. In the present study, the effect of tool-pin profiles and its diameters has been evaluated on the mechanical properties of Friction Stir Welded (FSWed) joint. Four pin profiles- cylindrical, conical, triangular and square, each with three different diameters (5 mm, 6 mm and 7 mm) are used during experimentation. In microstructure analysis, a high density of fine precipitate of zinc and magnesium is observed in the welds produced with high frictional heat which caused hardening of the processed zone and also a high level of mechanical strength in the joints. Onion ring patterns are found in the joint area due to the movement of material in batches as the edges of the pin forced the material to flow under the tool shoulder at a different pace. The pulsating effect of square tool pin has produced finer and properly distributed grains in the nugget zone. The eccentricity and pulsating effect of the square pin have mixed the softened material more effectively than other pin profiles, therefore, a better quality weld was obtained. The tool pin with diameter 6 mm is found more suitable for producing joints with better properties than pin of diameters 5 mm and 7 mm as it has forced the optimum volume of material to flow in welding. High-level plastic deformation has caused a variation in grain size and dynamic recrystallization across various zones of welded joint, which has resulted in hardness gradient.

Preparation and Corrosion Resistance of Trivalent Chromium-Zirconium Composite Coating

Aluminum alloys are widely used in the various industries because of its superior advantages. However there will be a thin oxide layer on the surface of the pure aluminum to inhibit corrosion, when adding some other elements, the obtained aluminum alloy is easy to be corroded. Surface protection is an important means to improve the corrosion resistance of aluminum alloys. The formal research had already confirmed that the trivalent chromium conversion coating can significantly improve the corrosion resistance, and the usage of the zirconium solution can also protect the aluminum alloy from corrosion. In this study, we constructed the binary conversion coating with the Cr2(SO4)3 and the K2ZrF6. The optimum reaction conditions are as follows: 10g/L H3PO4, 2g/L K2ZrF6, 28g/L Cr2(SO4)3, pH=2.5∼3.5, temperature 40°C, and reaction time 10 min. Copper sulfate titration experiment confirmed that the corrosion resistance was significantly improved.

Effect of ageing time and temperature on corrosion behaviour of aluminum alloy 2014

In this paper, the effect of corrosion behaviour of aluminium alloy 2014 were studied by potentiodynamic polarization in 1 mole of NaCl solution of aged sample. The experimental testing results concluded that, corrosion resistance of Aluminum alloy 2014 degraded with the increasing the temperature (150°C & 200°C) and time of ageing. Corroded surface of the aged specimens was tested under optical microscopes for microstructures for phase analysis. Optical micrographs of corroded surfaces showed general corrosion and pitting corrosion. The corrosion resistance of lower ageing temperature and lower ageing time is higher because of its fine distribution of precipitates in matrix phase.

Life Cycle Prediction Model of Safety Vent Based on Two-Phase Degradation Process

The safety vent, the most important failsafe device of lithium ion batteries, is made of a high-ductility and a corrosion-resistant aluminum alloy. Safety vents are designed to release the gas pressure in the battery shell before a catastrophic explosion happens. This vent is required to keep a balance between the long service life and high operational safety. It is of great significance to understand the failure mechanisms and predict the life of the safety vent. This paper proposes a life cycle prediction method based on a two-phase physical degradation process. First, a piecewise creep equation is established to describe the degradation process of the vent under the slowly increasing inner pressure. Based on this equation, the total life cycle is divided into two parts: one is the time before gas pressure reaches the critical point at which the vent starts to creep and the other is the duration of time from that critical point to the failure threshold, which is calculated through accelerated degradation testing and the creep equation. Finally, life cycle prediction and uncertainty analysis are performed. It is believed that the proposed method can provide a reasonable and effective reference for the life cycle evaluation of the safety vent.

Micro-Electrochemical I n Situ Observation of Pit Initiation at Precipitates in AA5182 Al-Mg Alloy in 0.1 M NaCl

Pit initiation at intermetallic particles in an Al-Mn alloy (AA5182-O) was investigated. Al-Fe-Mn, Al-Fe-Mn-Si, and Mg2Si intermetallic particles were detected in this alloy. In situ observation of a small electrode area was performed during potentiodynamic anodic polarization in naturally aerated 0.1 M NaCl at 298 K. For the Al-Fe-Mn particle, a trench was generated around the particle, and the trench increased as the electrode potential increased. However, no increase in size was observed at higher potentials. Then, a pit was initiated inside the trench. The same behavior was observed for the Al-Fe-Mn-Si particle. However, the trench growth stopped at a relatively low potential, and no pit was generated in the trench. There was no trench generated around Mg2Si. It appears that Si in the particles suppresses the trench formation and growth, which improves the pitting corrosion resistance of aluminum alloys.

Optimization of MAO Process Parameters and Effect of Subsequent Sealing Treatment on Corrosion Resistance of Aluminum Alloy

Micro-arc oxidation (MAO) coatings were obtained on the substrate of AlSi12Cu aluminum alloy in Na2SiO3 electrolyte. Then, the MAO coatings were sealed in stearic acid and sodium silicate solution, respectively. Experiments were conducted by varying current density, oxidation time and the frequency. L9 (33) of orthogonal experiments were chosen to optimize the processing parameters in the process of MAO technique. Through the above orthogonal experiments, the optimal process conditions were determined: the current density of 30 A/dm2, the oxidation time of 20 min, and the frequency of 600 Hz. The results showed that the MAO coating consisted of α-Al2O3 and γ-Al2O3. There were lots of pores and micro-cracks on the coating surface. The corrosion current of the aluminum alloy after MAO combination with stearic acid sealing treatments was significantly reduced, decreased 100 times more than the substrate and the corrosion potential increased 272 mV, signifying enhanced corrosion resistance. The corrosion rate of the aluminum alloy after MAO treatment in the washing powder solution decreased 25 times more than that of the substrate.

Corrosion resistance of 2524 Al alloy anodized in tartaric-sulphuric acid at different voltages and protected with a TEOS-GPTMS hybrid sol-gel coating

Corrosion is a major problem for high strength aluminium alloys. Thickening of the naturally formed oxide layer through anodizing is one of the main approaches to improve the corrosion resistance of these materials. Chromate anodizing is extremely efficient to produce anodized layers with good corrosion resistance and painting adhesion, however chromate based surface treatments must be banished from industrial use. The corrosion resistance of aluminium alloy 2524 (AA2524) anodized in tartaric/sulphuric acid (TSA) bath and protected with a hybrid sol-gel coating was evaluated by means of electrochemical impedance spectroscopy (EIS) and salt-spray tests. The morphologies of the obtained layers were characterized by SEM-FEG while the chemical in depth distribution of the hybrid layers was evaluated by means of Rf-GDOES. The effect of anodizing voltage on the sol-gel impregnation and the protection afforded by the layers was evaluated. Electrical equivalent circuit fitting of the EIS data has shown that the anodized layer thickness plays an important role in the protection mechanism of the sol-gel layer. Salt-spray tests highlighted the significant contribution of the sol-gel distribution in the anodized layer.

Alternative corrosion protection pretreatments for aluminum alloys

Aluminum alloys are extensively used in space programs for both structural and nonstructural applications. As is well known, the corrosion resistance of these alloys is quite limited and anticorrosion treatment is needed. Currently, the treatment most often used for improving the corrosion resistance of aluminum alloys is chromate (CrVI-based) conversion coatings (CCC). Due to the high environmental impact of these compounds, the REACH Regulation of the European Union decided to limit/restrict the use of hexavalent chromium. A sunset date of mid-2017 has been already set. For the time being, many chromate-free alternative products are available, but they have been found to be significantly inferior in terms of corrosion protection performances with respect to the chromate options. In this regard, there is a great need to develop high-performance hexavalent chromium-free anticorrosion coatings with low environmental impact and conformity with the EU regulations. The European Space Agency (ESA) is currently involved in a frame contract with Instituto de Soldadura e Qualidade (ISQ) that is currently ongoing. The objective of this study is to evaluate the anticorrosion behavior of the different alternative pretreatments applied to the most used aluminum alloys. The outcome of this activity will be the identification and the optimization of the most promising anticorrosion pretreatment. Several commercial Cr(VI)-free processes were applied onto aluminum alloys (2024-T3 and 2024-T81) used in the construction of ESA spacecraft in order to investigate their anticorrosive properties compared with Alodine 1200, a widely used conventional CCC. One of these commercial processes presented good anticorrosion performance, even better than Alodine 1200, and these results are presented in this paper. Salt spray resistance is included in the testing program as well as metallurgical coating evaluations that include microscopy observations before and after testing and electrochemical impedance spectroscopy in order to evaluate surface and microstructural modifications due to degradation mechanisms. Further studies must be performed with this promising alternative, modifying application parameters in order to achieve improved corrosion protection efficiency.

Improvement of Corrosion Resistance of Aluminum Alloy with Wettability Controlled Porous Oxide films

The combined process of porous type anodizing and desiccation treatment was applied to improve wettability of A1050 aluminum alloy. The water contact angles of anodized samples were increaseds considerably with desiccation treatment. However, there was no considerable effect of polishing and anodizing time on water contact angle. The corrosion behavior with the treatments was investigated electrochemically. The corrosion resistance of the samples in 3.5 mass% NaCl solutions increased with higher contact angle. Anodized and desiccated samples showed better corrosion resistance than un-desiccated samples around rest potential region.

Role of friction stir welding – Traveling speed in enhancing the corrosion resistance of aluminum alloy

The effect of friction stir welding (FSW) – traveling speed on the corrosion properties of 6061 aluminum alloy has been studied. The electrochemical tests indicate that an increase of FSW – traveling speed improves the corrosion resistance due to increased film and charge transfer resistances. In addition, the increase of FSW – traveling speed recrystallizes and refines the mean grain size from the initial 54.3 to 24.0 μm as well as increasing the homogeneity in microstructure.

Study on optimal surface property of WC-Co cutting tool for aluminium alloy cutting

The light weight property as well as high corrosion resistance of aluminium alloy has increased their demand especially in automobile industries. Aluminium alloy as a matter of fact has a low melting point and high ductility that severely adhere to the cutting tool surface and cause deterioration of chip evacuation. This problem often resulting in tools breakage. In this paper, in order to impart functions of anti-adhesion, we propose a technique by controlling the grinding marks micro texture on the tool surface by using the blast polishing treatment without any coating technologies. The results show that the tool which underwent polishing treatment reduces the cutting force as well as the aluminium adherence during the initial cutting process, and become worst as the process cutting continues. These results indicate that grinding mark texture improves the anti-adhesion by reducing the contact area during cutting and provide storage for the lubricant. In addition, too much polishing on the tool surface may remove these textures and resultantly worsen the tool performance.

КОРРОЗИОННАЯ СТОЙКОСТЬ АЛЮМИНИЕВЫХ СПЛАВОВ В УСЛОВИЯХ, ИМИТИРУЮЩИХ ФАКТОРЫ КОСМИЧЕСКОГО ПОЛЕТА

КОРРОЗИОННАЯ СТОЙКОСТЬ АЛЮМИНИЕВЫХ СПЛАВОВ В УСЛОВИЯХ, ИМИТИРУЮЩИХ ФАКТОРЫ КОСМИЧЕСКОГО ПОЛЕТА

Ultrasonic elliptical vibration texturing of the rake face of carbide cutting tools for adhesion reduction

Carbide tools are widely used to cut high-strength and corrosion-resistant aluminum alloys. However, aluminum chips tend to adhere to the cutting edge and rake face, influencing machined surface quality and even leading to tool failure. This paper proposes an innovative application of the ultrasonic elliptical vibration texturing (UEVT) process with properly selected elliptical locus for generating superior microgrooves on the carbide tool’s rake face using polycrystalline diamond (PCD) tools, in order to create a micropool-like lubrication effect at the chip-tool interface. Two microtextured carbide tools with a channel pitch of 400 and 200 μm and a depth of 12 μm were generated by UEVT. An experimental comparison between nontextured and UEVT tools in turning tubular aluminum alloy workpieces has demonstrated that microtextured tools with a pitch of 200 μm show a clear reduction in chip adhesion. The corresponding cutting performance is also improved due to the anti-adhesive property at the chip-tool interface. This work has demonstrated that ultrasonic elliptical vibration texturing has the potential for the mass production of microtextured tools for adhesion and friction reduction with high efficiency and accuracy.