•Anodic behavior of Ti6Al4V in AlCl3-EMIC ionic liquid was studied through different methods and discussed afterwards.•Adhesive Al coating was electrodeposited on Ti6Al4V alloy from AlCl3-EMIC ionic liquid.•Electrolytic etching pretreatment of the substrates in AlCl3-EMIC ionic liquid was employed.•Adhesion strength of Al coatings reached values up to 11.5 MPa.•High adhesion strength is mainly due to complete removal of surface oxide layer by the pretreatment.In this paper, we studied the anodic behavior of Ti6Al4V electrode samples in 2:1 acidic AlCl3-1-ethyl-3methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid. Linear sweep voltammetry, chronoamperometry and galvanostatic polarization were carried under different conditions and the electrodes surfaces were analyzed with SEM and EDS. The passivation layers observed on the electrode were also analyzed through Raman spectroscopy. On the basis of these anodic behavior results, the electrodeposition of protective Al coating on Ti6Al4V alloys was performed after different electrolytic etching pretreatments and the results were discussed. The etching pretreatments resulted in the complete removal of surface oxides and an irregular surface morphology, which consequently increased the adhesion strength of the protective coatings to the substrates.

The passivation behavior of Fe in the acidic AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid was studied by linear sweep voltammetry and chonopotentiometry. Various approaches were used to characterize the composition and morphology of passive film formed on the Fe electrode, such as scanning electron microscopy (SEM), Raman spectra and X-ray Photoelectron Spectroscopy (XPS). The results showed that the critical passivation potential of Fe shifted to more negative when the molar ratio of AlCl3:EMIC changing from 2 to 1.3. A film with a light yellow color was observed on the surface of the Fe electrode after passivation. The composition of the passive film was demonstrated to be FeCl2. The passive film was composed of particulate FeCl2 with average diameter of about 500 nm. The formation of FeCl2 film was attributed to the variation of the electrolyte Lewis acidity from acidic to neutral at the interface during the dissolution process of Fe. The reason caused the variation of the electrolyte acidity was discussed.The FeCl2 passive film was observed in acidic AlCl3 -EMIC ionic liquid. The formation of FeCl2 film was attributed to the variation of the electrolyte Lewis acidity from acidic to neutral at the interface. Download high-res image (224KB)Download full-size image

The anodic behavior of neodymium in acidic AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid was investigated by conducting linear sweep voltammeter and chonopotentiometry. The viscosity of Nd dissolved ionic liquid and the surface morphologies of Nd were characterized using an Ostwald viscometer and a scanning electron microscope, respectively. The chemical composition of Nd surface was indentified by Raman spectra. The results showed that dissolution of Nd under anodic polarization occurred after the breakdown of oxide films. A viscous layer formed at the interface of Nd/ionic liquid during the galvanostatic process of 5 and 20 mA/cm2. The formation of viscous layer was attributed to the accumulation of Nd dissolved AlCl3-EMIC ionic liquid, which had high viscosity. The oxide films could be removed thoroughly and the surface of Nd was homogeneous without etching pits, when viscous layer formed in the anodic process. Otherwise, the surface showed a pitting morphology.Linear sweep voltammetry of Nd at different sweep rates

•A viscous layer formed at Mg/ionic liquid interface after the dissolution of Mg.•As direct evidence, photo of viscous layer at the interface was presented.•Viscous layer was resulted from accumulation of dissolved Mg(II) at interface.•Formation of viscous layer resulted in a homogenous etched Mg surface.•Dissolution model of Mg and formation mechanism of viscous layer was discussed.In this paper, anodic behavior of Mg in acidic AlCl3–1-ethyl-3-methyl-imidazolium chloride (AlCl3–EMIC) ionic liquid was investigated by conducting linear sweep voltammetry, chronoamperometry and chonopotentiometry. The viscosity of Mg dissolved ionic liquid and the surface morphologies of Mg were characterized using an Ostwald viscometer and a scanning electron microscopy, respectively. The results showed that the oxide film on the surface of Mg had great effects on the anodic behavior. The dissolution of Mg under anodic polarization occurred after the breakdown of oxide film. A viscous layer was observed forming at the interface of Mg/ionic liquid during the dissolution process. The formation of viscous layer was attributed to the accumulation of Mg dissolved AlCl3–EMIC ionic liquid at the interface, which was of high viscosity. With a viscous layer formed in the anodic process, the etched surface of Mg anode was homogeneous and flat without any etching pits. Otherwise, the Mg showed a morphology of pitting on the surface.

•Adhesive Al coating was electrodeposited on Mg alloy from AlCl3–EMIC ionic liquid.•Electrolytic etching pretreatment in AlCl3–EMIC ionic liquid was employed.•Adhesion strength of Al coating was higher than 4 MPa.•High adhesion is due to complete removal of surface oxide layer by the pretreatment.•Uniform dissolution of α and β phases in pretreatment also improves coating adhesion.In this paper, electrolytic etching pretreatment of AZ91D Mg alloy in AlCl3–1-ethyl-3-methyl-imidazolium chloride (AlCl3–EMIC) ionic liquid was employed for the electrodeposition of well adhesive Al coatings. The quantitative measurement of coating adhesion was carried out and the mechanism of electrolytic etching on the improvement of coating adhesion was studied through Scanning Electron Microscopy (SEM), energy dispersive X-ray (EDS), X-ray Photoelectron Spectroscopy (XPS) and Grazing Incidence X-ray Diffraction (GIXRD). With electrolytic etching pretreatment at 25 mA/cm2, the adhesion of subsequently electrodeposited Al coatings on AZ91D was higher than 4 MPa. The improvement of adhesion strength was attributed to both the complete removal of oxide layers on the surface and the uniform dissolution of Mg solid solution phase (α phase) and intermetallic phase Mg17Al12 (β phase). Meanwhile, further electroless replacement of metallic Al was observed at the position of α phase. In the case of 5 mA/cm2 electrolytic etching pretreatment, only partial surface oxide layers were removed and etching grooves formed on the surface, which resulted in a low adhesion strength of 0.5–1 MPa.

Amorphous Al–Mn coating was electrodeposited on NdFeB magnets from AlCl3–EMIC–MnCl2 ionic liquid with the pretreatment of anodic electrolytic etching in AlCl3–EMIC ionic liquid at room temperature. The microstructure, composition and phase constituents of the coatings were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The corrosion resistance of the coatings was tested by means of potentiodynamic polarization and immersion test in 3.5 wt. % NaCl solution. The results show that anodic electrolytic etching in AlCl3–EMIC ionic liquid is a satisfactory pretreatment to remove the surface oxide film and favor the adhesion of the Al–Mn alloy coating to the NdFeB substrate. The amorphous Al–Mn alloy coating provides sacrificial anodic protection for NdFeB. It exhibited good corrosion resistance and significantly reduced the corrosion current density of NdFeB by three orders of magnitude at potentiodynamic polarization.Highlights► Amorphous Al–Mn alloy coating was electrodeposited on NdFeB magnet from ionic liquid. ► To remove the surface oxides of NdFeB, anodic etching pretreatment is used. ► The deposited Al–Mn alloy coating shows high adhesion to the NdFeB substrate. ► Corrosion tests show that amorphous Al–Mn alloy coating is anodic coating for NdFeB magnet.

In this study, we proposed a two-step approach to prepare aluminide coatings, namely electrodepositing Al from AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid at room temperature and subsequent heat treatment at low temperature. The adherence of the coating was checked by a simple mechanical scratch test. The surface and cross-sectional morphologies, phase structures and chemical compositions of the coatings after heat treatment were characterized by scanning electronic microscope (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX), respectively. The deposited Al coatings were in homogenous and controllable thickness with excellent adherence to the substrate. The coatings were brittle Fe2Al5 and FeAl3 phase after 5 min heat treatment at 670 °C, which transformed into ductile FeAl phase after 16 h heat treatment. The advantages of this method in eliminating the brittle Fe2Al5, cracks and pores in the aluminide coatings were discussed.

Nanosized Al2O3 particles were introduced into an epoxy adhesive to improve the adhesion strength of bonded steel utilizing both modified and unmodified epoxy adhesive. The adhesion strength was measured by pull-off adhesion test as a function of nano-Al2O3 amount and interface roughness. The results indicated that the adhesion strength was increased dramatically by addition of nano-Al2O3 into the epoxy adhesive compared with that of pure epoxy adhesive. The highest adhesion strength was obtained with 2 wt% nano-Al2O3 in epoxy adhesive, being almost four times higher than that of the unmodified. As the adhesion strength increased, the locus of failure changed from interfacial to the mixture of interfacial and cohesive.Scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) were used to investigate the interface morphology and chemical composition of steel and epoxy adhesive. TEM proved that nano-Al2O3 was finely dispersed in the epoxy adhesive. The results of SEM and EDX showed little difference between unmodified and modified samples. The XPS results showed that a new chemical group, identified as a carboxyl group, was formed at the interface between the steel and epoxy adhesive after modification by nano-Al2O3. Thus, the enhancement in adhesion strength was correlated with the introduction of this new polar group.

In this investigation, the influence of different nanoparticles and surface roughness on the adhesion between epoxy adhesive and steel substrate was primarily investigated. The results of pull-off adhesion tests indicated that nano-Al2O3 of the three kinds of nanoparticles had the most influence on adhesion strength, which was the optimal additive for the epoxy adhesive to improve the adhesion strength. Also, it was found that modified by 2% nano-Al2O3, the strength multiplication on the surface abraded with silicon carbide paper of 150 grits (150#) was the highest, of three different surface roughness. So, as the results showed that modified by 2% nano-Al2O3, the adhesion strength of epoxy adhesive on the surface abraded with 150# was visibly improved by about 5 times. Transmission electron microscope (TEM) displayed nano-Al2O3 homogeneously dispersed in epoxy adhesive. Field emission scanning electronic microscope (FE-SEM) revealed that the surface morphology of steel well coincided with that of epoxy adhesive.

The uniform nano-sized copper layer has been electroless plated on Al2O3 nanoparticles by feeding the solution containing copper-complex or formaldehyde or NaOH to suspending solution containing Al2O3 particles. The principal influencing factors on the uniformity of copper layer has been investigated by field-emission scanning electron microscope and laser diffraction particle size analysis. Feeding the copper-complex solution in suspending solution containing formaldehyde, NaOH and Al2O3 particles were found to be appropriate to achieve copper completely coated Al2O3 powders. The proper NaOH content in suspending solution prevents the Al2O3 nanoparticles from aggregation. The uniformly copper coated nano-sized Al2O3 composite powder can be produced at the optimazed NaOH content.

Al-Cr-Fe coatings have been widely used in the surface engineering field of materials, due to their excellent corrosion resistance to water vapor and fused salt deposits. In this study, a new two-step approach was developed to prepare Al-Cr-Fe coatings on surfaces of SUS430 stainless steels. First, the Cr/Al composite coatings were prepared by electrodepositing Cr from aqueous solution then electrodepositing Al from AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid on SUS430 stainless steel substrate. In the second, heat treatment of the Cr/Al composite coatings was carried out to acquire Al-Cr-Fe coatings. Effects of the thickness of Cr/Al composite coatings, the time and temperature of heat treatment on composition and phase structure of alloy layers were studied by using scanning electron microscope (SEM), backscattered electron (BSE), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The structure transformation process and formation mechanism of Al-Cr-Fe coatings were discussed.