Al Alloy Coatings Research Articles

Wettability Behavior of Zinc-Based Alloys on Cast Iron

The wettability of two Zn–Al alloy coatings (called “McGill 2” and “McGill 3” with 27 and 10 wt% Al, respectively) on the compacted graphite cast iron substrate was studied using the static sessile drop method. The effects of wetting time and coating composition on the macrostructural and microstructural evolution of the system were investigated. It was found that although the contact angle was obtuse for both coating materials over the time, the interfacial reactions occurred between the drop and the substrate from the first stage of contact. The most significant result was the formation of a uniform and thick reaction layer (interlayer) with the diffusion-controlled property at the interface. The results showed that “McGill 2” coating is superior to “McGill 3” alloy as an intermediate material for the Al–Fe cast joining application. The “McGill 2” interlayer revealed a composite nature as it consisted of different layers of solid, in the form of stable AlxFeySiz intermetallic phases from the initial steps of the reactions.

Galvanic Attack of Coated Al Alloy Panels in Laboratory and Field Exposure

A galvanic test panel design incorporating a painted and scribed Al alloy panel and uncoated through-hole noble fasteners has recently been utilized to compare effects of different surface pretreat...

Evaluation of Coated Al Alloy Using the Breakpoint Frequency Method

Electrochemical Impedance Spectroscopy (EIS) was used to study coated Al alloys during long-term exposure in 5wt% NaCl solution. The breakpoint frequency extracted from Bode plots allows the determination of the electrochemically active area of the sample. It shifts from low to high frequency with increasing exposure time due to the enlargement of the active area. The appearance of a high breakpoint frequency fh, usually in the range of 102 to 103Hz, occurred after a certain exposure time associated with a sharp drop of open circuit potential and low frequency impedance, and was accompanied by the visual initiation of corrosion under the coating. The incubation time before fh appears can be used as a criterion to evaluate the performance of chromate primer combined with different surface pretreatments. Optical profilometry analysis was conducted to determine the corroded area of coated sample after long-term exposure. The corroded area of one coating system was very close to, but that of another coating system was much higher than, the electrochemically active area estimated by the breakpoint frequency method, due to the different extent of attack. This indicates that the breakpoint frequency may be only valid for the determination of defect area during the initiation of attack, but probably not for the propagation to large regions of attack.

Effect of Surface Pretreatment on Galvanic Attack of Coated Al Alloy Panels

A test assembly consisting of a coated and scribed aluminum alloy 7075-T6 panel galvanically connected to uncoated through-hole noble fasteners has recently been utilized to quantify corrosion attack during corrosion testing in laboratory chambers. In this work, the corrosion morphology and extent of attack of Al alloy panels with five different surface pretreatments prior to painting and scribing were compared after exposure to ASTM B117 with galvanic connection to uncoated stainless steel fasteners. The nature of the attack for samples with different surface pretreatment samples was found to exhibit two different trends: they either penetrated deeply into the substrate at the scribes or spread out under coatings. The galvanic currents between the coated Al alloy panel and the bare 316 stainless steel fasteners were monitored during 21 days exposure in an ASTM B117 chamber. The current trends measured for different surface pretreatment panels were consistent with optical profilometry (OP) results. However, the galvanic current and OP techniques both underestimated the extent of corrosion attack because of local H2 evolution and undercut attack, respectively. The results from both techniques were modified to compensate for these deficiencies. Acceleration factors associated with the galvanic interaction for the different surface pretreatment panels were determined.

709 A7075合金の疲労寿命に及ぼすDLC/AIN複合表面改質の影響(OS7-(3),OS7 オーガナイズドセッション≪精密/微細加工と評価≫)

In recent years, in the field of transportation equipment, the use of aluminum alloy having excellent lightweight, workability has increased from reducing the environmental impact. However, aluminum alloy has poor wear-resistance, so it has been important to improve tribology characteristics of Al alloy. Therefore, hard coatings such as DLC have been studied to protect Al alloys. We examined a DLC coating that have an interlayer of AlN having a continuous gradient structure of hardness from the bottom to top deposited by using Unbalanced Magnetron Sputtering (UBMS), in order to improve the adhesion between DLC film and Al alloy. DLC/AlN coated Al alloy indicated very low wear rates, excellent tribological properties. However, it has been reported that the hard film coated materials might be reduce the fatigue strength compared with the substrate. So, in this study, fatigue tests of DLC/AlN coated Al alloy were carried out. As a result, the fatigue strength of DLC/AlN coated Al alloy was not reduced compared with that of Al alloy substrate.

EFFECT OF BURNISHING ON THE CORROSION PROPERTIES OF Ni-5%Al AND Ni-5%Al-15%Al2O3 COATINGS OBTAINED BY PLASMA SPRAYING

The Ni-5%Al alloy coatings and Ni-5% Al-15%Al2O3 composite coatings were obtained by plasma spraying method. The PN120 gun was used. The coatings onto a shaft made of austenitic stainless steel (X5CrNi 18-10) were sprayed. The coatings were subjected to turning, burnishing. The evaluation of corrosion properties were based on the measurements of corrosion current density and corrosion potential (polarization method), the charge transfer resistance and exponent of constant phase element impedance (electrochemical impedance spectroscopy method). Corrosion tests were performed in replacement seawater (3.5% sodium chloride solution). On the basis of studies, the effect of finishing type on the corrosion properties of plasma sprayed coatings has been demonstrated. The lowest corrosion current density was found for Ni-5% Al coatings after burnishing, icorr value equal to 0.96 A/cm 2 , and the charge transfer resistance was 27007 Ωcm 2 . The lowest resistance to corrosion of turned Ni-5%Al-15%Al2O3 composite coatings was observed. These coatings were characterized by the following parameters of corrosion process: icorr = 17.64 A/cm 2 , Rct = 2137 Ωcm2. Burnishing caused increased corrosion resistance of coatings. Due to reduced roughness and waviness are obtained reduction of the area of the actual burnished coatings compared to turned coatings. Thus, it is resulting in reduced values of corrosion current density. After finishing treatment, the plasma sprayed Ni-5%Al-15%Al2O3 coatings characterized by lower corrosion resistance compared to the alloy coating. The presence of the reinforcing phase in the coating promotes the increase of the porosity. The plasma sprayed coatings on nickel matrix had a tendency to localized corrosion in sodium chloride solution.

Influence of yttrium on microstructure and properties of Ni–Al alloy coatings prepared by laser cladding

Ni–Al alloy coatings with different Y additions are prepared on 45 # medium steel by laser cladding. The influence of Y contents on the microstructure and properties of Ni–Al alloy coatings is investigated using X-ray diffraction, scanning electron microscopy, electron probe microanalyzer, Vickers hardness tester, friction wear testing machine, and thermal analyzer. The results show that the cladding layers are mainly composed of NiAl dendrites, and the dendrites are gradually refined with the increase in Y additions. The purification effect of Y can effectively prevent Al 2 O 3 oxide from forming. However, when the atomic percent of Y addition exceeds 1.5%, the extra Y addition will react with O to form Y 2 O 3 oxide, even to form Al 5 Y 3 O 12 oxide, depending on the amount of Y added. The Y addition in a range of 1.5–3.5 at.% reduces the hardness and anti-attrition of cladding layer, but improves obviously its wear and oxidation resistances.

Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2—Measurement of Galvanic Interaction

A test sample incorporating a painted Al alloy panel, uncoated through-hole fasteners, and scribes has recently been shown to provide an accelerated response during atmospheric corrosion testing in...

Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 1—Concept

A test sample incorporating a coated and scribed Al alloy panel and uncoated through-hole fasteners was designed to provide accelerated response during atmospheric corrosion testing in the field or in laboratory chambers. Protective coatings that would take many months to show signs of degradation on normal scribed samples with no galvanic connection exhibited corrosion in much shorter times when uncoated Ti alloy or stainless steel fasteners were used, particularly in conjunction with scribes through the coating. The results after three weeks of exposure to ASTM B117 correlated well with long-term beach exposure, allowing rapid ranking of different coating systems. Of the fastener materials studied, visual observation indicated that the worst attack occurred near Type 316 (UNS S31600) stainless steel (SS316) fasteners even though Ti-6Al-4V fasteners are more noble. The volume of AA2024-T3 (UNS A92024) lost during the exposure, as determined by an optical profilometer, was also largest for samples with SS316 fasteners. Scanning Kelvin probe measurements across the scribes on one of the coating systems showed that, after exposure in an ASTM B117 salt fog chamber, the potential was lowest for scribes next to SS316 fasteners. The difference between SS316 and Ti-6Al-4V was explained by the available cathodic current, which was measured in chloride solution.

EFFECT OF BURNISHING ON THE CONTACT FATIGUE OF REGENERATIVE THERMALLY SPRAYED COATINGS

This study of the resistance to contact fatigue of Ni-5%Al alloy coatings and Ni-5%Al-15%Al2O3 composite coatings were evaluated. The coatings were prepared by flame spraying (Casto-Dyn DS 8000 torch) and plasma spraying (PN 120 plasma jet). The coatings were subjected to a finishing treatment: turning, burnishing and grinding. Depending on coatings phase composition and finishing treatment, the parameter mean values of surface roughness (Ra) were in the wide range of 0.28 to 2.61 Pm. The coatings after burnishing characterized by smallest of surface roughness. The largest value of the parameter Ra was observed in the case of coatings after turning. The presence of the reinforcing phase in the coating increases the surface roughness of thermally sprayed composite coatings. The hardness of coatings also depends on the finishing methods. The minimum hardness equal to 192 HV2 was found in the case of coatings of Ni-5%Al obtained by using a Casto-Dyn DS 8000 gas torch. Burnished Ni-5%Al-15%Al2O3 coatings obtained by plasma spraying characterized by hardness 291 HV2. Resistance of fatigue surface of thermally sprayed coatings on a SCF (standing contact fatigue) test stand was assessed. The test was designed based on the guidelines of the PN-80/H-04324 Polish standard. During the fatigue tests were provided constant contact of co-acting parts, without slipping. Based on the survey it was found that the plasma sprayed coatings (PN120 plasma-jet) have a greater resistance to fatigue then the coatings obtained by flame spraying Casto-Dyn DS 8000 torch. Composite coatings of Ni-5%Al15%Al2O3 are more resistant to contact fatigue, compared to the alloy coatings of Ni-5%Al. Burnishing increases the fatigue resistance of coatings when compared to turning. Burnished and polished surfaces are characterized by a similar contact fatigue resistance.

Development of Al-Alloy Coating for Advanced Nuclear Systems Using Lead Alloys

Small and medium reactors using lead alloys as coolants are one of the promising reactor concepts with improved safety because of their thermal-physical and chemical properties. This paper focuses on the development of Al-alloy coating for nuclear systems using liquid lead-bismuth eutectic (LBE). Since corrosion attack becomes severe against structural steels at high temperatures in liquid LBE, it is necessary to improve the corrosion resistance of steels. An Al-alloy coating method using Al, Ti, and Fe powders, and laser beam heating has been developed. The main defects formed in the Al-powder-alloy coating process are surface defects and cracks. The conditions required to avoid these defects are the employment of the laser beam scanning rate of 20 mm/min and the adjustment of the Al concentration in the coating layer. According to the results of the corrosion tests at 550 °C in liquid LBE, the Al-alloy coating layers on 316SS prevent severe corrosion attack such as grain boundary corrosion and LBE penetration observed in the 316SS without coating. The good corrosion resistance of the Al-alloy coating is based on the thin Al-oxide film, which can be regenerated in liquid LBE. From the viewpoint of the soundness of the produced Al-powder-alloy coating layers and the preservation of their corrosion resistance, it is estimated that the range of adequate Al concentration in the coating layer is from 4 to 12 wt. %.

Cold sprayed copper coatings on ASTM B 221 alloy - characterisation and corrosion study in simulated marine and industrial environment

In the current investigation copper powder was deposited on ASTM B 221 aluminium alloy by low pressure cold spray process. The coating deposition was carried out by varying process parameters. The corrosion performance of bare and coated aluminium alloy was evaluated in aggressive simulated marine (NaCl) and industrial (Na2SO4) environments. The kinetics of the corrosion was approximated by the weight change measurements made after every 24 hrs for a total period of 30 days. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis/electron probe micro analysis (SEM/EDAX/EPMA) techniques were used to analyse the corrosion products. The copper coated Al alloy showed lesser weight change and the coating remained intact till the end of the experiment. The phases revealed in the scales of coated specimens were mainly copper and aluminium copper, which are reported to be conductive and protective against corrosion.

On Stability and Ice-Releasing Performance of Nanostructured Fluoro-Alkylsilane-Based Superhydrophobic Al alloy2024 Surfaces

Atmospheric icing occurs when surface of exposed structures come into contact with supercooled water droplets and/or snow particles. Ice and wet-snow adhesion and excessive accumulation on exposed structures and equipment is well known as a source of numerous types of failures and malfunctions in power transmission lines, aircrafts, boats etc. in many cold-climate regions. Hydro-/superhydrophobic coatings have been developed over the past few decades as a passive technique to reduce or prevent ice accumulation on outdoor structures. In this study, superhydrophobic Al alloy (AA2024) substrates with static water contact angle values of (CA)>163o and water contact angle hysteresis values of (CAH)≤5o were prepared by etching aluminium alloy substrate in hot water followed by further surface hydrophobization with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS-17) using wet-chemistry technique. The prepared coated Al alloy samples showed good superhydrophobic and self-cleaning properties. Systematic study of both waterand ice-repellent behaviour of such organic coatings terminated by alkyl groups and expected to reduce ice adhesion, were then conducted. The stability tests of the coated surfaces with CA>150o in water resulted in a gradual loss of their superhydrophobic properties after ~1280 h of immersion. Artificially created glaze ice, similar to the naturally accreted one, was deposited on the nanostructured surfaces by spraying supercooled water micro-droplets with the average size of ~80 μm in a wind tunnel at subzero temperature (−10 oC) and a wind speed of 11 m/s. The ice adhesion strength was evaluated by spinning the samples in a centrifuge at constantly increasing speed until ice delaminating occurred. While the uncoated as-received Al alloy samples were found to have an average ice detachment shear stress of ~445±20 kPa, their counterparts coated with a thin layer of FAS-17 showed a lower value of ~65 kPa. This reduction is attributed to the presence of engineered micro/nano-hierarchical surface asperities and to applying low surface energy layers on the sample surfaces. However, the results show that the anti-icing properties of the tested samples deteriorate over time.

Phase Stability of Al-5Fe-V-Si Coatings Produced by Cold Gas Dynamic Spray Process Using Rapidly Solidified Feedstock Materials

In this study, aluminum alloy Al-5Fe-V-Si (in wt.%) feedstock powder, produced by rapid solidification (RS) using the gas atomization process, was selected to produce high-temperature resistant Al-alloy coatings using the cold gas dynamic spraying process (CGDS). The alloy composition was chosen for its mechanical properties at elevated temperature for potential applications in internal-combustion (IC) engines. The CGDS spray process was selected due to its relatively low operating temperature, thus preventing significant heating of the particles during spraying and as such allowing the original phases of the feedstock powder to be preserved within the coatings. The microstructure and phases stability was investigated by means of Scanning Electron Microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetery techniques. The coatings mechanical properties were evaluated through bond strength and microhardness testing. The study revealed the conservation of the complex microstructure of the rapid solidified powder during the spray process. Four distinct microstructures were observed as well as two different phases, namely a Al13(Fe,V)3Si silicide phase and a metastable (Al,Si) x (Fe,V) Micro-quasicrystalline Icosahedral (MI) phase. Aging of the coating samples was performed and confirmed that the phase transformation of the metastable phases and coarsening of the nanosized precipitates will occurs at around 400 °C. The metastable MI phase was determined to be thermally stable up to 390 °C, after which a phase transformation to silicide starts to occur.

Study on Corrosion-Resisting Properties of High-Speed Arc Sprayed Zn-Al Alloy Coating in Caverns

Zn、Al alloy coatings were prepared by high velocity arc spraying technology on 16MnR steel substrates, With the design salt spray test, Study on the corrosion resistance of the Zn、Al alloy coating in the grotto environment. The porosity of the metal coating and the compact of the corrosion are infection on the corrosion resistance of the coating. Al coating and Zn/Al(300/100) coating corrosion resistance better than others on 16MnR steel.

에어로졸 증착법에 의한 YSZ 코팅된 AA1050 알루미늄 합금의 전기화학적 부식 특성

Yttria stabilized zirconia (YSZ) coating was formed on AA1050 Al alloys by aerosol deposition (AD), and its electrochemical corrosion properties were investigated in 3.5 wt% NaCl and 0.5M H 2 SO 4 solutions. The crack-free, dense, and ~5 μm thick YSZ coating was successfully obtained by AD. The as-deposited coating was composed of cubic-YSZ nanocrystallites of ~10 nm size. The potentiodynamic test indicated that the YSZ coated Al alloy had much lower corrosion current densities (2 nA/㎠) by comparison to uncoated sample and exhibited a passive behavior in anodic branch. Particularly, a pitting breakdown potential could not be identified in H 2 SO 4 . EIS tests revealed that the impedance of YSZ coated sample was ~10 6 Ω㎠ in NaCl and ~10 7 Ω㎠ in H 2 SO 4 , which was about 3 or 4 orders of magnitude higher than that of uncoated sample. Consequently, the corrosion resistance of Al alloy had been significantly enhanced by the YSZ coating.

Influence of prior corrosion on the high cycle fatigue behavior of microarc oxidation coated 6061-T6 Aluminum alloy

The objective of this study is to evaluate the influence of prior immersion of microarc oxidation coated and uncoated Al alloy in 3.5% NaCl solution up to 168 h on their high cycle fatigue behavior. The prior immersion caused pitting on uncoated Al alloy while in the case of MAO coated Al alloy no pits were observed. Electrochemical impedance spectroscopy revealed progressive degradation of the MAO coated Al alloy with increasing duration of immersion. The fatigue life of MAO coated Al alloy decreased with increasing duration of immersion but at a significantly lower rate than in the case of the uncoated Al alloy. Thus, MAO coatings provided a measure of protection under corrosion fatigue conditions as compared to the uncoated Al alloy.

Morphology and properties of hot dip Zn–Mg and Zn–Mg–Al alloy coatings on steel sheet

Hot dip coating on low carbon steel sheet samples by binary Zn–Mg alloy with low and high Mg and a ternary Zn–Mg–Al alloy, and their characterization and property evaluation have been described in this article. A good quality coating with respect to surface quality, coating structure and anti-corrosion properties was achieved at a lower bath temperature than in conventional galvanizing. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction studies have revealed the presence of eutectic phase mixtures in these coatings. Formation of MgZn2 has been observed on the top surface and through the cross-section of coating made from higher Mg bath. The hardness of the top surface of Zn–Mg and Zn–Mg–Al coating layers was found to be higher than Zn coating layer due to the presence of MgZn2 and other intermetallics. Steel samples coated in Zn–Mg–Al bath show better corrosion resistance properties than the ones coated in pure zinc and Zn–Mg binary baths. The correlation of these improved properties with the coating morphology has been discussed.

Fabrication of porous Al alloy coatings by cold gas dynamic spray process

Al alloy coatings (Al–Mg binary) were prepared by cold gas dynamic spray and characteristics of the porous Al alloy coatings were examined after post-annealing. The coatings of composites (Al–Mg and Al–AlMg) were annealed in a nitrogen atmosphere for four hours. Post-annealing caused Mg in the coatings to diffuse into the Al matrix by eutectic reaction between Al and Mg. For Al/AlMg multicoatings, porous layers in the coatings were formed by post-annealing (diffusion of Mg into the Al matrix). Therefore, processing parameters such as particles and coating method can be used for controlling the size and distribution of pores in cold sprayed coatings.

Microstructure and mechanical properties of magnetron co-sputtered Ni–Al coatings

Binary Ni–Al alloy coatings were fabricated by magnetron co-sputtering with dual targets of pure Ni and Al metals. The chemical composition variation, microstructure evolution and related properties of the coatings caused by sputtering power modulation were investigated. The Ni–Al coatings with Al contents ranging from 2.7 to 24.9 at.% were manipulated through dual-gun sputtering. The as-deposited Ni–Al films revealed crystalline and nano-crystalline microstructures with respect to sputtering powers. Microstructure consisting of a significant crystallization feature of a metastable (Ni,Al) matrix and Ni 3Al precipitations was observed for the coatings under high sputtering powers, while coatings deposited at lower sputtering powers exhibited a (Ni,Al) solid solution polycrystalline structure with (111) preferred orientation. The coatings with (Ni,Al) matrix and Ni 3Al precipitations exhibited a higher hardness than those with a single (Ni,Al) phase. The formation of (Ni,Al) nano-crystallites and Ni 3Al phases was the strengthening mechanism for Ni–Al coatings deposited under high energy input during sputtering. With the increase in Al sputtering power, a slight decrease in grain size due to a higher Al concentration in the Ni–Al coatings was observed. The variation in hardness of the magnetron co-sputtered Ni–Al coatings could be attributed to the grain size and microstructure evolution.