Study of aging and electrochemical behaviour of Al?Li?Cu?Mg alloys

Aging study of 1441 and 8090 Al? Li? Cu? Mg alloys exhibited characteristic precipitation hardening phenomena. Potentiodynamic polarisation studies carried out on various tempers of the 1441 and 8090 Al? Li? Cu? Mg alloys in 3.5% NaCl, with a small amount of H₂O₂, and in 3.5% NaCl solution with pH 10 and 12 showed the shifting of open circuit potential (OCP) towards more negative potential and higher corrosion rate, with the increase of aging time. The OCP value has shifted anodically with addition of H₂O₂ in 3.5% NaCl solution. Further, passivity phenomenon has been observed for all the alloy tempers in 3.5% NaCl solution at pH 10 and 12. The observation of OCP shift towards more negative potential and the higher corrosion rate with the increase of aging time has been attributed to the presence of higher amounts of anodic δ (AlLi), S′ (Al₂CuMg) and T₁ (Al₂CuLi) phases, studied by TEM, XRD and DSC methods.     

Effect of sulphate reducing bacteria on corrosion of Al?Zn?In?Sn sacrificial anodes in marine sediment

Microbiologically influenced corrosion (MIC) of Al? Zn? In‐Sn sacrificial anodes in marine sediment was investigated by exposing samples to sulphate reducing bacteria (SRB). Samples exposed to the sterile marine sediment were used as control. The results show that pitting corrosion occurs in both the sterile marine sediment and the SRB‐containing marine sediment. However, the corrosion can be increased sharply by the SRB metabolic activity due to the cathodic depolarization effect. In fact, the effect is based on the consumption of hydrogen which probably results in the acceleration of galvanic corrosion between corrosion products and metal substrate.     

Corrosion dependence of an Al?Mg?Si alloy under MgCl2 solution drop on initial concentration and humidity

The corrosion behavior of an Al–0.63Mg–0.28Si alloy under MgCl₂ solution droplets with different initial concentration in environments of 33, 75, and 88% relative humidity (RH) was studied using a Kelvin probe. The available cathodic limiting current associated with oxygen reduction was highly dependent on the environment RH and initial concentration. In the 33% RH environment, metastable pitting was the main form of corrosion. In some cases at 75 and 88% RH, the potential baseline decreased slowly by hundreds of mV and remained at the lower value, indicating stable filiform‐like corrosion grew. The initiation time of the stable corrosion was determined by the environment RH and initial concentration. With increasing initial concentration or decreasing environment RH, the available cathodic limiting current decreased, stable corrosion was difficult to occur. The stable corrosion could occur outside the drop and/or inside the drop, which was dependent on not only the cathodic limiting current but also the environment RH.     

Effect of heat treatment on corrosion behaviour of deposited Fe–40Al intermetallics

Abstract

A study using electrochemical techniques of the susceptibility to corrosion in 0·1M NaCl solution (pH 3) of atomised and deposited Fe–40Al (at.-%) intermetallic material at room temperature is reported. Specimens were heat treated at temperatures of 600 and 900°C for 24 and 72 h. Potentiodynamic polarisation, linear polarisation resistance, potential–time, and electrochemical current noise data were collected. The untreated material displayed higher corrosion resistance than the heat treated material. In the treated material, the corrosion resistance increased with both the time and temperature of heat treatment. Also, untreated material was more susceptible to pitting corrosion than heat treated material. As the temperature or the time of heat treatment was increased, the material became more resistant to pitting. This improvement in resistance to pitting was related to a decrease in surface defects, such as pores and cracks, and an increase in grain size. Thus, heat treatment lowered the number of active sites and helped the material to establish a more protective film.     

Relationship between heat treatment and corrosion behaviour of Mg-3.0%Nd-0.4%Zr magnesium alloy

The corrosion behaviour of Mg-3.0Nd-0.4Zr （NK30） magnesium alloy was investigated in as-cast （F）, solution treated （T4） and peak-aged （T6） conditions in 5% NaCI solution by immersion tests and electrochemical measurements. The results of immersion test show that NK30 alloy exhibits better corrosion resistance in F condition than it does in the other two conditions due to the more compact corrosion film formed on alloy in F condition. The potentiodynamic polarization curves show that the overpotential of cathodic hydrogen evolution reaction on NK30-F is much higher than that on NK30-T4 and NK30-T6. The corrosion potentials of NK30 increase in the following order： F〈T4〈T6. The results of electrochemical impedance spectroscopy （EIS） also confirm that the corrosion film of NK30-F plays a more protective role than that of NK30-T4 and NK30-T6.     

Fabrication of Zn?Ni/Ni?P compositionally modulated multilayer coatings

Zn? Ni/Ni? P compositionally modulated multilayer (CMM) coatings which have a novel three‐dimension (3d) latticed multilayer structure were prepared by dual‐bath technique. The formation of the special 3d latticed structure was investigated. The adhesion and corrosion resistance of the CMM coatings were studied. The results showed that the special 3d latticed multilayer structure, which was different from the structure of traditional CMM coatings, was formed during Ni? P electroless plating. The 3d latticed structure benefited the adhesion and corrosion resistance of the novel CMM coatings. The barrier effect of the 3d latticed structure is enhanced.     

Influence of heat treatment on high frequency soft magnetic properties of Finemet amorphous alloy

In order to study high-frequency soft magnetic properties of Finemet amorphous alloy, the microstructural change and nanocrystallization under different heat treatment conditions were investigated by XRD and TEM. The crystallite size of α-Fe was calculated from the XRD pattern using the Scherrer formula, while the high frequency magnetic properties were measured at room temperature by TPS-200SA exchange tester. The results of XRD and TEM indicate that the nanocrystallization occurs at 500 ℃. When the annealing temperature increases to 560 ℃, the amorphous alloy becomes totally nanocrystallized and the crystallites distribute homogeneously, thus an excellent combination of soft magnetic properties is obtained.     

Electrochemical behavior of Ni?P?SiC composite coatings: Effect of heat treatment and SiC particle incorporation

This paper describes the effects of heat treatment and of SiC particle incorporation on the electrochemical behavior and physical structure of Ni? P (17 at% P) composite coatings. The deposits were obtained by electrodeposition with various contents of SiC particles in the plating bath and heat treated at 420 °C. The physical structure was investigated by inductively coupled plasma atomic emission spectrometry (ICP‐AES), X‐ray diffraction (XRD), and scanning electron microscopy (SEM – image analysis). The electrochemical behavior of the resultant composite coatings was determined by chronopotentiometry, electrochemical impedance spectroscopy, and potentiodynamic measurements in 0.6 M NaCl solution at pH 6. Heat treatment showed a positive effect on the electrochemical behavior of Ni? P coatings, shifting the open circuit potential toward less active potentials. The incorporation of SiC particles inhibited pit nucleation on the Ni? P composite coating, with or without post‐heat treatment. However, heat treatment in the Ni? P? SiC seemed to induce cracks in the metallic matrix, initiating at the SiC particles, possibly caused by the contraction in the metallic matrix. The cracked structure promoted localized corrosion, while coatings without heat treatment resulted in a general and uniform corrosion.     

Influence of heat treatment regimes on microstructures and fracture characteristics of 7055Al alloy containing Ag

Tensile properties, fracture characteristics and microstructures of 7055 aluminum-based alloy containing Ag after T6, T73 and RRA treatment were investigated. The results show that RRA treatment retains strength of 7055-T6 with higher electrical conductivity close to that of 7055-T73 alloy, but its elongation decreases greatly.SEM fractographs reveal that intergranular cracking and shear-type transgranular cracking are both presented on the fracture appearance of 7055-T6 specimen. After T73 treatment, the fractographs mainly consist of dimple-type transgranular cracking with minor intergranular cracking. For 7055-RRA specimen, intergranular cracking domi-nates with minor dimples on the fracture surface. The type and size of precipitates, width of grain boundary and the ability of precipitates to impede dislocation motion vary with heat treatment regimes. Three frature models were built on the basis of microstructural analyses.     

Effect of heat treatment on thermal stability of Ti40 alloy

Five new heat treatment processes were designed, which were divided into three groups by their characteristics. The microstructures and mechanical properties of the alloy after the five heat treatments and thermal exposure at 500, 550℃ for 100 h were tested. The results indicate that a little differences exist in the performance of mechanical properties at room-temperature after the five heat treatments, and the thermal stability is the key factor for determining heat treatment process. Among the three groups of heat treatment processes, the best thermal stability is achieved after the first group of heat treatment. After annealing treatment at intermediate temperature, some defects and uneven grain boundaries are remained, which leads to the reduction fractions of precipitations on unit grain boundary and the harmful effect of precipitations on grain boundary is weakened. The process of annealing at 650 ℃for 4 h is recommended the best heat treatment process for Ti40 alloy.     

Influence of yttrium on microstructure and properties of Ti-23Al-25Nb alloy after heat treatment

The existence of yttrium in Ti-23Al-25Nb alloy and its influence on the microstructure after heat treatment of Ti-23Al-25Nb alloy were investigated using thermal analysis（DTA）, EPMA, XRD and SEM. The heat treatment was determined based on DTA measurements. The compression tests at room temperature were performed on a Instron-569 universal tester. The results show that yttrium exists as the Y2O3 alloy. The addition of Y doesn＇t affect the characteristic phase transformation temperature At lower quenching temperature, Y strengthens the XRD peaks of O phase by improving the decomposition of B2 phase. Yttrium addition enhances the compression properties with the compression strength, yield strength and compression ratio increasing. The strengthening is attributed to the second phase strengthening of Y2O3 particles and the grain refinement.     

Corrosion behavior of Zn?Ni?Al2O3 nanocomposite coatings obtained by electrodeposition from alkaline electrolytes

The aim of this work was to investigate the anti‐corrosive properties of nanocomposite Zn? Ni coatings containing Al₂O₃ nanoparticles, prepared from alkaline commercial electrolytes (pH 13), (PERFORMA 280.5, COVENTYA S.A.S, France), by electrodeposition on carbon steel (OL37). The corrosion resistance of the coatings prepared with different concentrations of Al₂O₃ (5, 10, and 15 g/L) was evaluated in 0.2 g/L Na₂SO₄ solution (pH 5) by open circuit potential (OCP) measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of electrochemical measurements were corroborated with those obtained by using X‐ray diffraction analysis. The obtained results show that the introduction of Al₂O₃ nanoparticles in the plating bath generally brings an increase in corrosion resistance of Zn? Ni layers and put in evidence the existence of an optimal Al₂O₃ concentration. Under the examined conditions, the optimal concentration determined from polarization measurements was proven to be 5 g/L Al₂O₃. The highest value of the polarization resistance, R_p, obtained from impedance measurements corresponds also to Zn? Ni with 5 g/L Al₂O₃, which is in agreement with the results obtained from polarization and XRD measurements.     

Generation of nanocrystalline NiO particles by solution combustion method and its Zn?NiO composite coating for corrosion protection

The nanocrystalline nickel oxide (NiO) particles have been successfully prepared by a simple, fast, economical, and eco‐friendly solution‐combustion method using Ni(NO₃)₂ · 6H₂O (oxidizer) and sugar (dextrose as fuel). The as‐prepared compound was calcined for an hour at different temperatures. The synthesized NiO was characterized by XRD, TGA, SEM/EDX, TEM, XPS, FT‐IR, and UV–Vis spectral methods. The crystallite sizes of the NiO particles were measured. Rietveld refinement of X‐ray data matches the cubic structure with space group of Fm3m (No. 225). The thermal behavior of as‐prepared compound was examined. Scanning electron micrographs show uniform cubic like morphology of NiO and its chemical composition was measured. The TEM results reveal that the particle sizes were in the order of 70–80 nm. The red shift was noticed in UV–Vis absorption spectra. As an application part the Zn? NiO composite coating was prepared by electrodeposition method and its corrosion behavior was analyzed by Tafel, impedance and anodic polarization in aggressive medium.     

Influence of process paameters on thermal-rate treatment of ZA42 alloy

Sand casting process ad directional solidification technique combining thermal-rate treatment(TRT) were used.The influence of process parameters on TRT was investigated according to the values of impact toughness.At the same time,the mechanism of TRT was discussed.The results showed that TRT can improve the impact toughness of this alloy,while the hardness is basically constant.The time of heat preservation should not be more than 5 min.Different forms of cooling intensification additive have different effects among which the zinc ingot solidified in graphite mold is the best one that can improve impact toughness of samples by more than 80%.With increasing the cooling temperature,the value of α(Al)crystal lattice constant increases.The element Sb has negative effect on TRT.     

Influence of process parameters on thermal-rate treatment of ZA42 alloy

Sand casting process and directional solidification technique combining thermal-rate treatment(TRT) were used. The influence of process parameters on TRT was investigated according to the values of impact toughness. At the same time, the mechanism of TRT was discussed. The results showed that TRT can improve the impact toughness of this alloy, while the hardness is basically constant. The time of heat preservation should not be more than 5min. Different forms of cooling intensification additive have different effects among which the zinc ingot solidified in graphite mold is the best one that can improve impact toughness of samples by more than 80%. With increasing the cooling temperature, the value of α(Al) crystal lattice constant increases. The element Sb has negative effect on TRT.     

Effects of heat treatment process on stress corrosion cracking and microstructures of 7A05 A1 alloy plate

In order to improve the stress corrosion cmcking（SCC） resistance of 7A05Al alloy, four different heat treatment processes were performed. After the heat treatments, the stress corrosion cracking resistance, mechanical properties and microstructures of 7A05Al alloys were studied. The results show that the retrogression and reaging（RRA） treated specimens possess the highest SCC resistance with slightly reduced strength compared with the other specimens. Thus RRA is the best process in terms of the optimal combination of SCC resistance and strength. Further TEM observation reveals that the RRA treated specimens are characterized by the fine equiaxed grains, dispersed second phase and wide PFZ. The pre-aging treated specimens show lower SCC resistance but higher strength as compared with the RRA treated ones. Equiaxed grains are also observed in the pre-aging treated samples by TEM, indicating that the anisotropy is eliminated. However, the dual aging and deformation plus aging treated specimens are demonstrated by large anisotropy.