Effect of brass interlayer on microstructure, mechanical and corrosion behaviour of friction stir welded AA6061-T6 alloy

In this study, friction stir welding (FSW) was performed on AA6061-T6 with and without brass interlayer. The FSW with interlayer was performed for various tool rotational speeds (600–1000 r/min) and at constant travel speed (25 mm/min). The defect-free joint with uniform distribution of brass particles in the stir zone (SZ) and formation of the uniform composite structure was observed at an intermediate optimized tool rotational speed of 800 r/min due to the proper material flow. A strong metallurgical bond between brass particles with aluminium alloy resulted in the formation of Al2Cu and Al4Cu9 strengthening intermetallic compounds (IMCs). The average grain size obtained for the weld with interlayer is smaller than weld without interlayer. The presence of the interlayer enhanced the hardness and the tensile strength compared to the weld without interlayer. This improvement in mechanical properties with interlayer is attributed to the formation and uniform distribution of strengthening IMCs. The corrosion analysis was carried out in 3.5% NaCl solution using immersion test and electrochemical polarization test. The weld with interlayer showed enhanced corrosion resistance than the weld without interlayer which is attributed to the formation of major Al2Cu IMC which has less activation energy for the corrosion process.

Corrosion and Biocompatibility of Pure Zn with a Micro-Arc-Oxidized Layer Coated with Calcium Phosphate

Recent studies have indicated a great demand to optimize the biocompatibility properties of pure Zn as an implant material. For this purpose, CaZn2(PO4)2·2H2O (CaZnP) was prepared using hydrothermal treatment (HT) combined with micro-arc oxidation (MAO) on pure Zn substrate to generate biodegradable implants. The polarization test and electrochemical impedance spectroscopy indicated that the MAO1−HT coating could modulate the corrosion behavior of MAO1 by filling the crevice between the coating and the substrate. Immersion test evaluation revealed that the osteogenic properties of MAO1−HT coating were better than that of pure Zn substrate, as evidenced by the molar ratio of Ca and P, which increased after soaking in simulated body fluid (SBF) for up to 10 days. In addition, L-929 cells cultured in the 100%, 50%, and 25% extracts of MAO1−HT coated samples exhibited excellent cytocompatibility. Meanwhile, cell adhesion was promoted on the surface with high roughness generated during MAO and HT processes. In summary, the calcified coatings improved biocompatibility and adjusted the degradation rates of pure Zn, broadening the application of Zn alloys.

Microbial fuel cell power overshoot studied with microfluidics: from quantification to elimination

Power overshoot can hinder determination of maximum power densities in microbial fuel cells (MFCs). In this work, a microfluidic approach was used to study overshoot in an MFC containing a pure culture of electroactive biofilms (EAB) containing Geobacter sulfurreducens. After 1-month operation under constant flow of an ideal nutrient medium, the MFC health began to degrade, marked by voltage loss and the appearance of anomalies in the power density curves. One such anomaly was a chronic power overshoot, accompanying a loss of both measured power and current density on the high-current side of the power density curve. The degree of power overshoot was quantified while certain flow-based interventions were applied, notably the shear erosion of the EAB outer layer. Next, two approaches to acclimation were demonstrated to treat the remaining overshoot. The standard approach, which acclimates the MFC to high currents before a standard polarization test, eliminated the remaining overshoot and returned maximum power densities to initial levels, but maximum current density remained lower than the initial level. A microfluidic-assisted “long-hold polarization test” enabled efficient in situ acclimation of each external resistor during the measurement. Despite the health-compromised MFC, this method provided long-term stability during the polarization test, resulting in power and current density measurements that exceeded those made on the healthy MFC using the standard polarization test. We conclude that slower electron transfer kinetics in unhealthy MFCs can provoke overshoot by prolonging the time to reach steady state during the polarization test, but a properly designed measurement overcomes this problem.

Studies on the Effects of NH3 in H2 and Air on the Performance of PEMFC

The effect of NH3 in H2 and in air was investigated at various concentrations ranging from 1.0 ppm to 100 ppm in air and ranging from 0.25 ppm to 10 ppm in fuel. The effect of NH3 on cathode caused an instantaneous decrease in cell voltage which dropped from 0.734 V to 0.712 V in 30 h and drop rates was 0.73 mV/h for 1 ppm; however, the cell voltage dropped to 0.415 V in 1 h for 100 ppm of NH3. The voltage could not be recovered after the polarization test (V-I test) but could be recovered to 84.4% after operation with neat air for 1.5 h and 98.4% after cycle voltammogram (CV). It was found that the voltage drop was obvious, and the drop rate increased with the NH3 concentration in H2. The voltage drop rates at 500 mA/cm2 were 0.54 mV/h for 0.5 ppm of NH3, 0.8 mV/h for 1 ppm, and 2 mV/h for 10 ppm. The voltage could be recovered from 70.6% to 77.3% after discharged with high purity H2 for 24 h, to 92.8% after being purged with clean air for 10 h and to 98.4% after CV scan. The tolerance concentration of NH3 in H2 for 1000 h was 40 ppb, for 2000 h was 20 ppb, and for 5000 h was 9 ppb.

Effect of Cu2+ on Corrosion Behavior of A106B Carbon Steel and 304L Stainless Steels in Seawater

The corrosion behaviors of A106B carbon steel and 304L stainless steel (SS) in seawater with different Cu2+ concentrations were studied by the immersion test and the potentiodynamic polarization test. The results showed that with the increasing Cu2+ concentration, the mass lot rates of A106B and 304L SS all increased in the immersion test, and compared with A106B, the mass lot rates of 304L SS were all smaller. In the potentiodynamic polarization test, following the concentration of Cu2+ increased, the corrosion potential of A106B firstly shifted negatively; then, when Cu2+ increased to 100 ppm, the polarization curve moved to the upper right direction; namely, both the corrosion potential and corrosion electrical density increased. The corrosion potential of 304L SS increased with the increasing Cu2+, and the passive region was reduced; the pitting sensitivity improved.

THE EXTRACTION OF EUCALYPTUS AS A NATURAL INHIBITOR FOR MILD STEEL IN HCL MEDIUM

This work concern with the electrochemical study related to eucalyptus leaves extract utilized as inhibitor towards mild steel' corrosion in various concentrations of HCl, at a temperature comparable to the average temperature in Iraq, at a temperature of 25°C.Electrochemical impedance spectroscopy and electrochemical polarization test methods were used to investigate this. The extract inhibition efficiencies and mild steel corrosion rate were calculated. The results show that the extract may be utilized as one of the effective inhibitors to prevent mild steel corrosion. The maximal efficiency of inhibition has been 99.77% at a concentration of 0.5 molarity, and the inhibition efficiency decreased with the increase in HCl concentration.

Psidium guajava Leaves as Corrosion Inhibitor of Al-6061

The anti-corrosion characteristic of the extract of Psidiumguajava leaves on aluminum in 3.5 wt% sodium chloride were examined using electrochemical measurement. The thermodynamic factors such as the free energy adsorption, change in enthalpy, and entropy was also analyzed. The adsorption isotherm was detail described to study the adsorption of the inhibitor on the aluminum surface with various concentrations of the inhibitor. The electrochemical measurement was done through the potentiodynamic polarization test. The results show that the inhibitor act as the mixed type inhibitor and its adsorption on the aluminum surface obeys Temkin adsorption isotherm. The study suggests that the use of Psidium guajava leaves extract for the food industrial application is eco-friendly and safe, especially in salt solution medium.

Electrochemical Analysis of Nano- and Micro-Sized Pore Formed Ti–6Al–4V Alloys in Solution Containing Ca, P, Mn, and Si Ions via Plasma Eletrolytic Oxidation for Bio-Implant Materials

The purpose of this study was to investigate electrochemical analysis of nano- and micro-sized pore formed Ti–6Al–4V alloys in solution containing Ca, P, Mn and Si ions via plasma eletrolytic oxidation for bio-implant materials. The coatings were produced on Ti–6Al–4V alloy for dental implant using the plasma electrolytic oxidation (PEO) method in electrolytes with the various concentration of 0, 5, and 20% Mn and Si, respectively. Electrochemical potentiodynamic polarization and AC impedance behaviors were carried out in 0.9% NaCl solution at 36.5 ± 1 °C using potentiostat (Potentiostat, EG&G, 362) and electrochemical impedance spectroscope (EIS, EG&G, 1025). The potentiodynamic polarization test with a scan rate of 1.667 mV s-1 was carried out from –1500 mV to 2000 mV. The frequency range used for EIS was 102–105 Hz. The amplitude of AC signal was 10 mV and 5 points per decade was used. From the potentiodynamic polarization test, PEO treated alloy in electrolyte containing Ca, P, Mn, and Si show a lower corrosion potential than that on the bulk surface. In the case of Mn and Si doped surface, the corrosion resistance increase compared to non-doped surface with Mn and Si elements, and the current density was lower than that of the bulk surface. From the AC impedance test, in the case of Mn and Si doped surface, polarization resistance values were higher than other specimens, and nano- and micro-sized pores were covered with corrosion product consisted Mn and Si elements.

Corrosion behavior of the heat affected zone in a 316 L pipeline weld

On-site investigation, scanning electron microscope, energy dispersive X-ray spectroscopy, and cyclic potentiodynamic polarization test were carried out for failure analysis of the 316 L pipeline in this paper. The visual inspection revealed that the inner wall was covered with severe rust, and obvious misalignment and poor appearance were found in the weld. The energy dispersive X-ray spectroscopy result identified the presence of Cl in the inner wall of the pipeline. Some carbides of Cr and Mo precipitated in the heat affected zone, which partially deteriorated the corrosion resistance. The cyclic potentiodynamic polarization curve proved that the heat affected zone is not only sensitive to pitting corrosion, but also has inferior repassivation ability. Finally, the pitting preferentially occurred in the heat affected zone and gradually developed to leakage.

Enhance corrosion behavior of AZ31 magnesium alloy by tailoring the anodic oxidation time followed by heat treatment in simulated body fluid

Purpose This paper aims to investigate the impact of anodizing time and heat treatment on morphology, phase and corrosion resistance of formed coating. To characterize the anodic oxide layer, X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) that was equipped with energy dispersive spectroscopy (EDS) was hired. The corrosion behavior of oxide-coated samples was estimated by electrochemical polarization test in simulated body fluid (SBF). Design/methodology/approach Anodic oxidation method is applied to reinforce the corrosion and biological properties of biomaterials in the biomedical industry. In this paper, the alkaline NaOH (1 M) electrolyte was used for AZ31 magnesium alloy anodizing accompanied by heat treatment in the air. Findings It can be concluded that the best corrosion resistance belongs to the 10 min anodic oxidized sample and among the heat-treated samples the 30 min anodized sample represented the lowest corrosion rate. Originality/value In this study, to the best of the authors’ knowledge for the first time, this paper describes the effect of anodizing process time on NaOH (1 M) electrolyte at 3 V on corrosion behavior of magnesium AZ31 alloy with an alternate method to change the phase composition of the formed oxide layer. The morphology and composition of the obtained anodic oxide layer were investigated under the results of SEM, EDS and XRD. The corrosion behavior of the oxide coatings layer fabricated on the magnesium-based substrate was studied by the potentiodynamic polarization test in the SBF solution.