Pure Al Coatings Research Articles

Study on Properties of Pure Al Coatings and Al/SiC Composite Coatings by Plasma Transferred Wire Spraying

Study on Properties of Pure Al Coatings and Al/SiC Composite Coatings by Plasma Transferred Wire Spraying

Microstructure and Properties of Al-Based Ceramic Coating Deposited on Magnesium Alloy Surface by Cold Spraying

In this study, pure Al and Al-Al2O3 composite coatings with a low porosity and high density were prepared on magnesium alloys by cold spraying. The surface morphology, component, hardness, interfacial bonding, wear and corrosion properties were investigated. Additionally, the relationship between the interface structure and the protective coatings’ quality was preliminarily established. Pure Al powder was used to create a coating with a homogeneous and dense microstructure. The hard-phase Al2O3 in the composite coatings was non-oxidized and would reduce the porosity of the coatings to improve their density and interfacial bonding by up to 55.82 MPa. The bonding mode of the pure Al coatings is primarily mechanical, whereas the bonding mode of the Al-Al2O3 mixed coatings is mechanical and metallurgical. The tough Al2O3 particles combined to form a layer of work-hardening reinforcement that resisted wear and effectively prevented it from spreading. The three Al-based coatings had excellent corrosion properties, as evidenced by their corrosion current being several orders of magnitude lower than that of the magnesium alloy substrates. The thick coating was significantly more corrosion-resistant than the thin coating and provided greater protection to the substrate. This study offers theoretical and technological assistance for the surface protection of magnesium alloy equipment in demanding conditions.

Effect of Si Content on Deposition and High-Temperature Oxidation of Al-Si Coatings Obtained by Magnetron Sputtering PVD Method

Intermetallic Al-Si-based coatings can greatly increase the oxidation resistance of γ-TiAl alloys. However, the effects of the Si addition are not fully understood. Therefore, it is difficult to determine the Si content that is optimal for oxidation resistance. Therefore, pure Al and several Al-Si coatings with varying Si contents between 1 and 81 at.% were studied. The coatings were produced using a combinatorial magnetron sputtering process. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used for structure and chemical analysis. The phases were identified by X-ray diffraction. Cyclic oxidation tests at 900 °C were conducted up to 5000 cycles of 1 h each and subsequently evaluated by thermogravimetric analysis. Si addition in the range of 1 to 12 at.% did not deteriorate the oxidation resistance compared to a pure Al coating up for 1000 cycles (1 h) of oxidation at 900 °C, while higher Si contents led to a high mass gain. For oxidation times up to 5000 cycles (1 h), a sufficient thickness of the coatings is crucial for good oxidation resistance. The main effect of Si addition is to enhance the transformation speed of the deposited Al and Si to the high temperature stable Ti(Al,Si)3 phase during the heat treatment. Si additions of up to 12 at.% led to increased initial mass gains and a decrease in the oxidation rates during subsequent exposures compared to pure Al coatings.

Effect of accelerating gas temperature on microstructure and properties of cold sprayed Al coating on polyether ether ketone (PEEK)

Cold spray (CS) is an emerging deposition technique for the metallization of polymer material to improve its thermal and electrical properties. In this study, pure Al coatings were deposited on polyether ether ketone (PEEK) substrate by CS. Further, the influence of accelerating gas temperature on microstructure and properties (i.e. deposition efficiency, adhesive strength, electrical conductivity, thermal diffusivity and hardness distribution) of the prepared coatings was systematically investigated. Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), the quantitative analysis of oxygen content and Raman spectra results revealed that the prepared coatings were composed of crystalline metallic Al without obvious oxide phases. Moreover, the polymer structure of PEEK substrate remained intact after high-velocity and high-temperature impact during the CS process. The adhesive strength, electrical conductivity and thermal diffusivity of the Al coating increased with increasing accelerating gas temperature. At the accelerating gas temperature of 380 °C, a dense and thick Al coating with high adhesive strength was obtained in just two deposition passes. Moreover, multi-pass tests (at high nozzle traverse speed) were performed to understand the deposition mechanism of Al coating on PEEK substrate through analyzing cross-section/surface morphology of samples with different thicknesses. Finally, the deposition mechanism of cold sprayed Al coating on PEEK was proposed.

Influence of deposition time and surface roughness on microstructure and corrosion behavior of sputter-deposited pure Al coating on 4130 chromalloy steel

In the present investigation, a comparison of three sputter-deposited pure Al coatings on 4130-grade steel with different process parameters has been explored based on surface morphology and corrosion behaviour. In a natural environment, Al coatings are happened to be more corrosion resistant than Zn ccoatings owing to the formation of impervious Al2O3 layer on top of the substrate. Even at a temperature up to 180 °C, Al coatings are not corroded by distilled water. Al-coated steel can, therefore, be used for many applications like distilled water storage and handling, oven, heaters, car exhaust system, etc. Magnetron sputtering (MS) nowadays has gained a great deal of importance in developing different coatings. Al coatings with MS technique have emerged with uniform and contamination-free quality coating exhibiting high deposition rateandintensebonding with the substrate compared to other popular deposition processes. The influence of surface condition and deposition time on microstructure, thickness, corrosion behavior, adhesion and final surface roughness of the coated surfacehas been the topic of discussion in the current research. The surface morphology and composition were examined by Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-Ray Analysis (EDX), phase constitution by X-Ray Diffraction (XRD) and surface roughness by Optical Laser Spectroscopy (OLS spectroscopy). The effect of surface roughness on pitting potential was also discussed. Corrosion properties were evaluated by Electro-Chemical Impedance Spectroscopy (EIS), which revealed that the sample with 10 h of deposition time (sand blasted) has exhibited the bestcorrosion resistance property compared to the other two samples sand blasted for 5 h and without sand blasted for 10 h deposition time, respectively. This fact has been further corroborated by contact angle measurement tests. Glow discharge optical emission spectroscopy (GDOES) established the depth to depth profile of the coatings. The adhesion property for all three coatings was found good without any trace of pilling off in the bend test. Sand blasting operation before coatings also has a great effect on materials property basically roughness means smooth surface after coating with high resistance property.

Plasma electrolytic oxidation of cold spray kinetically metallized CNT-Al coating on AZ91-Mg alloy: Evaluation of mechanical and surficial characteristics

The cold-spray kinetically metallized (CS) carbon nanotube-aluminum (CNT-Al) and pure Al coatings were treated using plasma electrolytic oxidation (PEO) process to obtain CNT-Al+PEO and Al+PEO duplex coatings on AZ91 Mg alloy, respectively. The phase composition, microstructure, mechanical properties, wear and corrosion resistance of the PEO ceramic coatings were studied. The results showed that the PEO ceramic coating was mainly composed of α-Al2O3 and γ-Al2O3, moreover, the small amount of CNT was also retained during the PEO process. The mechanical properties and wear resistance of the PEO ceramic coatings were significantly improved compared to the respective CS coatings. In particular, the hardness and elastic modulus of the PEO-CNT coating reached 13.9 GPa and 185.4 GPa, which were 21.0% and 23.4% higher than the respective CS coating. Moreover, the wear rate of the PEO-CNT coating was only 4.83 × 10−5 mm3/N·m with a relatively low coefficient of friction of 0.65, which were 59.8% and 15.6% lower than the corresponding CS coating. The corrosion current density of the PEO-treated CNT-Al coating was 3.734 × 10−6A/cm2, which was similar to the untreated CS coating. In short, the PEO treatment greatly improves the mechanical properties and wear resistance of the CS CNT-Al coating.

Enhancement of Corrosion Resistance and Tribological Properties of LA43M Mg Alloy by Cold-Sprayed Aluminum Coatings Reinforced with Alumina and Carbon Nanotubes

Magnesium is a suitable material for structural and aerospace applications owing to its high strength to weight ratio, yet the wide usage of Mg alloys is restricted due to their poor corrosion and mechanical properties. In this study, cold gas spraying method was used to produce pure Al, Al-Al2O3 and Al-Al2O3-CNTs coatings with feedstock powder containing Al admixed with 5 wt.% Al2O3 and 1 wt.% CNTs to improve electrochemical and tribological properties of Mg-LA43M alloy. X-ray diffraction spectroscopy and scanning electron microscopy were performed for compositional and microstructural analysis of feedstock powders as well as coatings. Furthermore, corrosion properties of coatings were examined by photodynamic polarization, electrochemical spectroscopy and long-term immersion test in 3.5% NaCl solution. The obtained results were correlated with microstructural analysis and we found that reinforcement of hard particles, especially CNTs, resulted in better corrosion resistance of MMC coatings as compared to Mg substrate and pure Al coatings. Reinforcements of Al2O3 and CNTs also improved the sliding wear resistance of the coatings. Al-Al2O3-CNTs exhibited lower coefficient of friction and wear rate than the Mg substrate, pure Al, and Al-Al2O3 coatings due to the denser microstructure.

Effect of titanium addition on structure, corrosion resistance and mechanical properties of aluminum coatings on NdFeB by ion-beam-assisted magnetron sputtering

Titanium has been added in the Al coatings on sintered NdFeB magnets by ion-beam-assisted magnetron sputtering to improve the mechanical properties of coatings without corrosion resistance deterioration. The effect of Ti addition on structure, mechanical and electrochemical properties of Al coatings has been investigated, complemented by x-ray diffraction and transmission electron microscopy. The results show that the ion-beam-assisted magnetron co-sputtering of Al and Ti obtains a single-phase polycrystalline structure of Al–Ti solid solution. With the increasing Ti content, the coating structure becomes denser and the grain size is reduced. Both the mechanical and wear properties of the coatings are improved with the addition of Ti where the hardness of the Al–Ti coating increases with the increasing amount of Ti. Polarization and EIS testing results show that the titanium-doped coatings have an enhanced corrosion resistance by comparison with pure Al coatings when Ti content is lower than 4.3 at.%.

Tribological and corrosion behavior of flame sprayed Al–10 wt% Ti3SiC2 composite coating on carbon steel

Pure Al coatings are extensively used in various industries but their poor wear resistance has introduced as the main drawback of them. In this study, the effect of the addition of Ti3SiC2 on the tribological and corrosion behavior of Al coating was investigated. The morphological and phase evolution of coating and powders was analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) patterns. The corrosion behavior of samples was investigated by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). The wear behavior of coating and substrate studied by the pin-on-disc test. The results indicated that the wear resistance of Al coating in terms of friction coefficient and wear rate was significantly improved by the presence of Ti3SiC2 inclusions. According to the result of potentiodynamic polarization tests in simulated 3.5% NaCl solution, the corrosion potential of the Al/Ti3SiC2 coating is nobler than that of the pure Al one. The electrochemical impedance spectroscopy (EIS) tests indicated that corrosion resistance of Al/Ti3SiC2 coating was increased as compared with pure Al coating.

The deposition, microstructure and properties of Al protective coatings for NdFeB magnets by multi-arc ion plating

Herein, pure Al coatings have been deposited on sintered NdFeB via multi-arc ion plating method. The effect of target current and working pressure on the microstructure and properties of these coatings have been investigated using scanning electron microscopy, laser scanning confocal microscopy, X-ray diffraction, tensile testing, electrochemical tests and neutral salt spray. The results showed that the Al coating on NdFeB magnets achieved higher deposition rate of 4.85 μm/h, a maximum adhesive strength of 24 MPa and a corrosion current density of two orders of magnitude less than that of bare NdFeB substrates when processed using a target current of 60 A and a working pressure of 1.0 Pa. Electrochemical impedance spectroscopy and neutral salt spray tests further proved the excellent corrosion protection performance of such thin films with a thickness of 5 μm without any significant perturbation on the magnetic properties of the substrate.

Effect of powder size on the long‐term corrosion performance of pure aluminium coatings on mild steel by cold spraying

To achieve the long‐term corrosion protection of mild steel under corrosive environment, pure aluminium coatings were cold sprayed (CS) on mild steel with three different powder sizes, namely within the three following classes 85–100, 60–75 and 40–50 µm. The as‐sprayed samples were exposed to the atmosphere for 11 years. The long‐term corrosion behaviour of the sprayed steels was studied by atmospheric exposure, immersion tests as well as electrochemical measurements in 3.5 wt% sodium chloride (NaCl) solution. It was found that the coatings with coarse powder reduced the long‐term corrosion resistance of the samples. The deteriorated corrosion resistance of the sprayed samples was ascribed to the penetration of the corrosive medium (oxygen, water and electrolyte) through the porosity defects of coatings and with coarse powder. These results provide a guide for the design of cold sprayed corrosion‐resistance pure Al coatings for engineering applications.

Bonding, Reactivity, and Mechanical Properties of the Kinetic-Sprayed Deposition of Al for a Thermally Activated Reactive Cu Liner

Pure Al coatings were fabricated on Cu substrates via kinetic spraying to produce a thermally activated reactive Cu liner. The coatings need to endure high-strain rate severe plastic deformation and react with oxygen during penetration or after penetration of the liner. In this study, the Al powder underwent large exothermic reactions with a small particle size and fast heating rate, as determined from the differential scanning calorimetric analysis. Process optimization of the Al deposition was facilitated by defining the “critical velocity” of an Al particle in the kinetic spraying process based on numerical modeling and computations using ABAQUS finite element codes. The simulation results revealed that the critical velocity of an Al particle at room temperature (RT) is 780 m/s and it decreases as the particle temperature increases. Certain process conditions resulted in improved coating properties as the temperature of the particles was affected by the process gas temperature and pressure. The mechanical properties such as the bond strength of the coatings formed under various process conditions were evaluated and compared. The relationships between the resulting properties, processing conditions, and the structures of the coatings are discussed.

Effect of surface composition and microstructure of aluminised steel on the formation of a titanium-based conversion layer

The presented work aims at determining the influence of surface composition and microstructure of hot dip aluminium–silicon coated steel on the formation characteristics and mechanism of a titanium-based conversion layer. Varying the amount of silicon in the molten aluminium bath changes the surface nature which in turn affects the subsequent pre-treatment process. Different phases in the layer formation process were identified in the open circuit potential evolution as a function of immersion time in the conversion solution. The homogeneity and the thickness of the conversion layer in each of these regions were evaluated using secondary electron images, Auger elemental surface maps and depth profiles. While intermetallic precipitates (FeAl3) act as nucleation centres in pure Al coatings, eutectic Si is responsible for the deposition process in a Si-rich coating. A continuous surface conversion layer is formed after 45s of immersion in the conversion bath. Also, the presence of silicon in the coating leads to the deposition of a thicker conversion layer. A model for build-up of the conversion layer is proposed based on these observations.

Pure Al Coatings Prepared by Arc-Added Glow Plasma Depositing Technique and Subsequence Plasma Oxidation

Al coatings were prepared on 316L stainless steel substrate by arc-added glow plasma depositing technique and then plasma oxidized. The influences of bias voltage and arc source current on both the thickness and surface roughness of Al coatings were investigated respectively. Then, the microstructure and the composition of Al and Al2O3 coatings were characterized. Finally, the bonding force and the corrosion resistance of as-prepared alumina coatings were discussed. The results indicated that nanostructured pure Al coatings with surface roughness (Ra) of 267.93 nm were obtained when the bias of the substrate was-300V and the arc current was 70A. The Al2O3 coatings oxidized from nanoAl coatings were dense and uniform, with a bonding force of 37.4 N, an excellent corrosion potential of-0.202V and corrosion current of 0.197 μm·cm-2 in 3.5% NaCl solution.

Residual stresses in cold spray Al coatings: The effect of alloying and of process parameters

Al and Al alloy cold spray coatings were deposited on Mg substrates using two different cold spray systems – a Kinetic Metallization system (convergent barrel, sonic nozzle) and a CGT system (convergent-divergent barrel, supersonic nozzle). The residual stress profiles in the coatings were measured using neutron diffraction with high spatial resolution. In the first part of the study, the residual stress profile in pure Al coatings was compared when sprayed using the Kinetic Metallization system (using both helium and nitrogen as the driving gas), and with the CGT system using nitrogen gas. In this way the effect of impact velocity and process temperature was studied. In the second part of the study, the residual stress profile was compared in coatings of pure Al, 7075 Al and 6061 Al sprayed using the same process conditions in the CGT system. The residual stress profiles depend more on the alloy content, i.e. intrinsic resistance to plastic deformation, than on the processing conditions, and this is interpreted using a simple model that incorporates the effect of peening stresses in the cold spray process.

Microstructure and Erosion-Corrosion Behavior of Hot-Dipping Al-Mn Alloy Coatings on Low Carbon Steel

Low carbon steel was coated by hot-dipping into a molten bath containing Al-2 wt.%Mn. The phase composition, morphology and the erosion-corrosion behavior of the aluminide layer were characterized by XRD, OM, SEM and erosion-corrosion tester, respectively. The results show that the coatings are mainly composed of Al, FeAl3, Fe2Al5 and MnAl6 phase. The coatings consist of two-layer structure, i.e., toplayer Al-Mn alloy layer and tongue-like intermetallic compound. The thickness of the coating layer is about 800 μm and all the coating layers show good adhesion to the steel substrate. Compared with the pure Al coatings, the Al-Mn alloy coatings exhibit lower wear rate irrespective of the rotation speed. The hot-dipped Al-Mn coatings possess considerable erosion-corrosion resistance.

Corrosion properties of aluminium coatings deposited on sintered NdFeB by ion-beam-assisted deposition

Pure Al coatings were deposited by direct current (DC) magnetron sputtering to protect sintered NdFeB magnets. The effects of Ar+ ion-beam-assisted deposition (IBAD) on the structure and the corrosion behaviour of Al coatings were investigated. The Al coating prepared by DC magnetron sputtering with IBAD (IBAD-Al-coating) had fewer voids than the coating without IBAD (Al-coating). The corrosion behaviour of the Al-coated NdFeB specimens was investigated by potentiodynamic polarisation, a neutral salt spray (NSS) test, and electrochemical impedance spectroscopy (EIS). The pitting corrosion of the Al coatings always began at the voids of the grain boundaries. Bombardment by the Ar+ ion-beams effectively improved the corrosion resistance of the IBAD-Al-coating.

Micro Arc Oxidation of Wire Arc Sprayed Al-Mg6, Al-Si12, Al Coatings on Low Alloyed Steel

Micro arc oxidation of wire arc sprayed Al-Mg6, Al-Si12 and Pure Al coatings on low carbon steel has been performed. The coatings have been analyzed using optic microscope, scanning electron microscopy, X-ray diffraction and surface roughness tester. At the same time, voltage and current regimes are investigated during the process. Then after MAO process, uniform Al2O3 ceramic coatings have been deposited on surface of Al-Mg6, Al-Si12 and Al coated steel. The ceramic coatings are mainly composed of Al2O3 phase. The compound coatings show high hardness and significant improvement of corrosion resistance property.

Influence of Pre-Heated Al 6061 Substrate Temperature on the Residual Stresses of Multipass Al Coatings Deposited by Cold Spray

In this work, the influence of the substrate temperature on the deposition efficiency, on the coating properties and residual stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using a CGT Kinetics 3000 cold spray system. The substrate temperature was in a range between 20 (room temperature) and 375 °C and was kept nearly constant during a given deposition while all the other deposition parameters were unchanged. The deposited coatings were quenched in water (within 1 min from the deposition) and then characterized. The residual stress was determined by Almen gage method, Modified Layer Removal Method, and XRD in order to identify both the mean coating stress and the stress profile through the coating thickness from the surface to the coating-substrate interface. The residual stress results obtained by these three methods were compared and discussed. The coating morphology and porosity were investigated using optical and scanning electron microscopy.

Microstructure and wear resistance of Al–SiC composites coatings on ZE41 magnesium alloy

Al and Al–SiC composites coatings were prepared by oxyacetylene flame spraying on ZE41 magnesium alloy substrates. Coatings with controlled reinforcement rate of up to 23 vol.% were obtained by spraying mixtures containing aluminium powder with up to 50 vol.% SiC particles. The coatings were sprayed on the magnesium alloy with minor degradation of its microstructure or mechanical properties. The coatings were compacted to improve their microstructure and protective behaviour. The wear behaviour of these coatings has been tested using the pin-on-disk technique and the reinforced coatings provided 85% more wear resistance than uncoated ZE41 and 400% more than pure Al coatings.