Electrodeposition of lead–tin alloy from methanesulphonate bath containing organic surfactants

The article discusses the process of electrodeposition of lead-tin alloy (tin content in the deposit up to 10–12 wt %) from methanesulfonate electrolytes. A composition was proposed of organic additives to the electrolyte providing attainment of high quality microcrystalline coatings with the alloy of predetermined composition at relatively low content of Sn²⁺ in the solution. It has been shown that the tin content in the deposit increases at an increase in current density and decrease in the electrolyte temperature. For production of anti-frictional Pb-Sn alloys with the tin content of about 10% the electrolysis should be performed at a current density of about 4 A/dm² and the temperature not exceeding 25°C. The effect of a decrease in the discharge rate of the Sn²⁺ ions into the alloy at deposition from electrolyte without organic additives was discovered, that is stipulated by deceleration of crystallization stage of tin on foreign substrate. When the alloy is deposited from electrolyte containing a composition of organic additives, the effect of super-polarization of discharge of Sn²⁺ ions is reduced.     

Influence of Na2TeO3 additive on electrodeposition of Zn–Mn alloy coatings from sulphate–citrate bath

The influence of Na₂TeO₃ additive in sulphate–citrate bath on electrodeposition of Zn–Mn alloy coatings was investigated by material characterisation methods and electrochemical techniques. The effects of small amounts (0·39–3·10 mM) of Na₂TeO₃ additive on cathode polarisation, composition and current efficiency were estimated. The crystal structure and surface morphology of Zn–Mn alloy coatings were studied by scanning electron microscopy (SEM) and powder X-ray diffraction spectroscopy (XRD) respectively. The SEM and XRD data showed that Na₂TeO₃ additive effectively accelerates phase transformation and reduces crystallite size.     

Characterization of nanocrystalline Co–W coatings on Cu substrate,electrodeposited from a citrate-ammonia bath

Cobalt–tungsten nanocrystalline coatings were electrodeposited on copper substrate using different current densities. The deposited coatings were single phase solid solution with an average grain size of about 18 nm, showing a nodular type of surface morphology. By increasing the deposition current density, the density of nodules was increased, with no obvious variation in grain size. Electrochemical impedance spectroscopy (EIS) confirmed the codeposition of tungsten through reduction of tungsten oxide film formed during the electrodeposition process. However, the role of ternary complexes in the bath cannot be ruled out, especially at lower cathodic potentials. The Co–W coating deposited at lower current densities showed higher tungsten content, microhardness, wear resistance and friction coefficient. However, this coating showed an inferior corrosion resistance. By increasing the deposition current density, a low tungsten coating with high corrosion resistant was obtained. This is attributed to the lower value of exchange current density of water reduction in the present of oxygen (i₀^H2O) achieved on the coating with lower tungsten content.     

Bright zinc–nickel alloy deposition from alkaline non-cyanide bath

Abstract

Zinc–nickel alloy deposition with polyvinyl alcohol and piperonal as bath additives has been investigated. The effects of additive concentration, triethanolamine concentration and other parametric variables on the deposit and solution properties have been studied. Polarisation studies were carried out under different conditions to understand the effect of triethanolamine and the brighteners on the co-deposition. Results indicated that the additives lead to bright alloy deposition containing ～10% nickel. The deposit produced at the optimum conditions with the additives has a nanograined structure with a γ phase.     

Electrochemical deposition of Fe–Mo–W alloy coatings from citrate electrolyte

Peculiarities of the electrochemical deposition of Fe–Mo–W coatings from citrate electrolyte containing iron(III) on the substrates of mild steel and gray cast iron are investigated. The effect of the salt concentration of alloying components and electrolysis modes on the quality, composition, and properties of the alloys is determined. It is shown that the alloys formed via nonstationary electrolysis exhibit a more uniform surface and lower content of impurities. The improved physical and mechanical properties as well as corrosion resistance of Fe–Mo–W coatings in comparison with the base metal can be considered as promising technologies for surface hardening and repair of worn items.     

Strengthening of an Al–Cu–Sn alloy by deformation-resistant precipitate plates

A variation of the Orowan equation is developed for aluminium alloys strengthened by dispersed, deformation-resistant {1 0 0}_α precipitate plates, and the quantitative effects of precipitate volume fraction, number density and aspect ratio on increments in Orowan strengthening are examined. The validity of the model is examined by a combination of mechanical property measurements and rigorous quantitative stereology of the size and distribution of {1 0 0}_α plates of θ′ phase in an Al–4Cu–0.05Sn (wt.%) alloy aged isothermally at 200 °C. For the ageing conditions selected, the predictions of the model for Orowan strengthening increments are in good quantitative agreements with those observed experimentally. The model predicts that, for a given volume fraction and number density of precipitate plates, an increase in plate aspect ratio can lead to a substantial increase in strength. In addition, it is not necessary to invoke a transition from precipitate deformation to Orowan strengthening to account for the form of the precipitation-strengthening response of the alloy. The maximum strengthening increment is associated with the minimum effective inter-particle spacing, rather than a critical thickness of the precipitate plates.     

Characterisation and corrosion resistance of Zn–Mn coatings electrodeposited from acidic chloride bath

Zn–Mn alloy coatings were galvanostatically electrodeposited from an acidic chloride bath. Effects of deposition current density, pH and temperature on surface morphology, microstructure and corrosion resistance of Zn–Mn coatings were studied. The coatings deposited at 10, 50 and 100 mA cm^?2 had a single η-Zn phase structure. However, a dual phase structure of η-Zn and ?-Zn–Mn with higher Mn content was found for the coatings deposited at 200 mA cm^?2. The dual structure degraded the corrosion resistance of the coatings. The highest corrosion resistance was achieved for the Zn–Mn coating deposited at 100 mA cm^?2, pH 4·9 and 25°C. This coating contained 4·1 wt-%Mn and showed a unique surface morphology consisting of randomly arranged packs of very thin platelets, laid perpendicular to the surface and provided a high compactness deficient free structure.     

Electrodeposition of high corrosion resistant Ni–Sn–P alloy coatings from an ionic liquid based on choline chloride

With the objective of obtaining corrosion resistant coatings, ternary Ni–Sn–P alloy coatings were electrodeposited from a deep eutectic solvent and their composition, morphology and corrosion resistance were investigated as a function of electrodeposition potential. A comparison was made with a Ni–P binary alloy coating electrodeposited under similar conditions. Cyclic voltammetry, energy dispersive analysis of X-rays, potentiodynamic polarisation, open circuit potential-time and electrochemical impedance spectroscopy techniques were used for studying the electrodeposition behaviour, chemical composition and coatings corrosion performances, respectively. The chemical compositions of the ternary Ni–Sn–P alloy films contained about 4.4–10.3?wt-% Sn, 7.2–8.1?wt-% P and Ni (balance). X-ray diffraction patterns of the ternary Ni–Sn–P deposits revealed a single and broad peak, becoming wide with an increase in Sn content, showing that the structures of all the deposits were nanocrystalline or amorphous. Corrosion tests showed that ternary Ni–Sn–P alloy coatings exhibited considerably better barrier corrosion resistance than binary Ni–P coatings, and their corrosion resistance improved with an increase in Sn content.     

Influence of organic additives on electrodeposition of Co–Cu alloys from sulphate bath

Abstract

In this work, the authors report on the influence of additives on the onset of deposition, the current efficiency (CE) and the nucleation growth mechanism of Co–Cu alloys electrodeposited on n-Si(100) substrate from sulphate solution with an addition of sodium citrate (SC) and citric acid (CA). The study was carried out by means of cyclic voltammetry, chronoamperometry methods using the Scharifker–Hills model for the determination of nucleation and growth mechanism and some kinetic parameters for nucleation. The CV curves indicate that the deposition potential of Cu(II) is shifted to more negative potentials while additive anion is added in the solution. Also, the results show that the additives do not improve the CE. For all baths, electrodeposited Co–Cu alloy follows instantaneous nucleation and three-dimensional (3D) diffusion limited growth. The nucleation density in the solutions without additive and with SC increases exponentially with the potential whereas in solution containing CA additive, it is no longer possible to consider exponential increase, indicating the existence of a reaction in addition to the 3D nucleation mechanism in the Co–Cu electrodeposition process.     

Solidified structure control of Sn–10Pb alloy by imposing alternating current

Abstract

To control the solidified structure of an alloy, an alternating current imposing process on the alloy during its solidification has been examined. A Sn–10 mass-%Pb alloy was adopted as a model alloy in this experiment. The solidified structure with the alternating current was equiaxed structure while that without the alternating current was dendritic structure. The current imposing period of 1 s is enough for obtaining an equiaxed structure under this experimental condition. Imposition of the current in the initial stage of the solidification is essential to obtain an equiaxed structure in this process.     

Effect of bath stabiliser on performance of electrodeposited Ni–W coatings

Abstract

The paper describes the influence of the addition of a stabiliser agent on the composition of the bath and the performance of the electrodeposited nickel–tungsten (Ni–W) coatings under working conditions. The effects of the working temperature (65°C) and the addition of a stabiliser on the complexes of Ni and W present in a Ni–W electrolyte were analysed. It has been qualitatively demonstrated that an increase in temperature slightly modifies the speciation curves of Ni and W complexes, and the introduction of a stabiliser does not modify the formation of the metal complex, allowing the electrolyte to be stable during long periods of time. The deposit obtained in an aged electrolyte has a high resistance to corrosion and a good resistance to wear and the hardness can be elevated to ～1200 HV after the application of a heat treatment.     

Phase composition and structure of aluminum Al–Cu–Si–Sn–Pb alloys

The structure and phase composition of cast and heat treated Al–Cu–Si–Sn–Pb alloys containing 6 wt % Sn, 2 wt % Pb, 0–4 wt % Cu, 0–10 wt % Si have been studied using calculations and experimental methods. Polythermal and isothermal sections are reported, which indicate the existence of two liquid phases. It was found that the low-melting phase is inhomogeneous and consists of individual leadand tin-based particles.     

Electrochemical behavior of a lead-free Sn–Cu solder alloy in NaCl solution

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization techniques and an equivalent circuit analysis are used to evaluate the electrochemical corrosion behavior of Sn–Cu alloy samples in a naturally aerated 0.5 M NaCl solution at 25 °C. It has been found that a better electrochemical corrosion resistance is provided by a coarser cellular microstructure array. It has also been found that the corrosion current density (i_corr) is of about a quarter when compared with that of the finest microstructure examined. Such behavior is attributed to both localized strains between the Sn-rich phase and intermetallic (IMC) particles and the cathode/anode area ratios. The effect of copper alloying on i_corr is also discussed.     

Anomalous glass transition behavior in Cu–Zr–Sn alloy system

We discuss the effect of Sn addition on anomalous glass transition behavior in Cu–Zr bulk-forming metallic glasses. We found that an unusual endothermic reaction in Cu₅₅Zr₄₀Sn₅ ribbon can originate from the growth reaction of quenched-in nuclei from 0.4 nm to 3.7 nm in the supercooled liquid region. This anomalous devitrification may prove useful for the synthesis of a novel composite with uniform atomic/nanometer scale heterogeneity modulated by controlling cooling rate as well as by tailoring alloy composition.     

Comparison of the corrosion resistance of an Al–Cu alloy and an Al–Cu–Li alloy

ABSTRACT

In this study, the corrosion mechanisms of the AA2024-T3 and the AA2098-T351 were investigated and compared using various electrochemical techniques in 0.005?mol?L^?1 NaCl solution. The severe type of corrosion in the AA2098-T351 was intragranular attack (IGA) although trenching and pitting related to the constituent particles were seen. On the other hand, the AA2024-T3 exhibited severe localised corrosion associated with micrometric constituent particles, and its propagation was via grain boundaries leading to intergranular corrosion (IGC). Electrochemical techniques showed that the corrosion reaction in both alloys was controlled by diffusion. The non-uniform current distribution in both alloys showed that EIS was not a proper technique for comparing the corrosion resistance of the alloys. However, local electrochemical techniques were useful for the evaluation of the corrosion resistance of the alloys.     

Interfacial reactions of Sn–Zn–Ag–Cu alloy on soldered Al/Cu and Al/Al joints

This work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3?min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn₃ and Cu₅Zn₈ were observed.     

Formation and study of the properties of finishing coatings of a circuit board with tin–zinc alloy instead of tin–lead alloy coatings

A formation technique of electroplating coatings of tin–zinc alloy (50) based on using low-toxicity lactic acid as surfactant, ligand, and buffer addition was developed. The dependences of alloy composition and cathodic yield on the alloy current and the coating quality on the concentration of tin and zinc ions in the solution, the content of lactic acid, the solution acidity (pH), the temperature, and the current cathodic density were investigated. The optimum conditions of the process carrying out were determined. The performance characteristics of obtained coatings were investigated. It was proven that the coating with this alloy meets the requirements of GOST (State Standard) 23752–79 “Circuit Boards. General Technical Specifications” and can be used for the circuit boards of products of the instrument-making industry instead of tin–lead alloy, which will make it possible to reduce the environmental risk of production, as well as increase the efficiency and maintainability of devices and systems.     

Influence of pulse parameters on electrocodeposition of Cr–Al2O3 nanocomposite coatings from trivalent chromium bath

Abstract

Cr and Cr–Al₂O₃ coatings were electrodeposited from Cr(III) bath with both pulsating and direct current onto copper substrates. Pulsating current resulted in homogeneous films of higher Al₂O₃ content and lower particle agglomeration than the direct current. Differences were more tangible at shorter duty cycles and pulse frequencies. Pulsating current improved both microhardness and corrosion resistance. The presence of alumina nanoparticles resulted in greater current efficiency, higher film microhardness and better corrosion resistance. Maximum current efficiency, highest microhardness and densest electrodeposited coatings were achieved at current density of 20 A dm^?2, duty cycle of 40% and pulse frequency of 10 Hz.     

Phase transformation of Cu precipitates from bcc to fcc in Fe–3Si–2Cu alloy

Phase transition of Cu precipitates during aging of an Fe–3Si–2Cu alloy was studied by transmission electron microscopy. The precipitation of 3–5-nm-sized body-centered cubic (bcc) Cu in ferrite matrix was confirmed by high-angle annular dark-field scanning transmission electron microscopy imaging. The bcc Cu precipitates transformed to 9R Cu as they grew. Many 9R Cu precipitates were twinned, but untwinned 9R Cu particles were also observed. The 9R Cu transformed to twinned face-centered cubic (fcc) Cu by the glide of ±a/3 [1 0 0]_9R Shockley-type partial dislocations. Formation of the 3R structure previously reported could not be confirmed in this study. Finally, twins in fcc Cu precipitates disappeared to form stable fcc Cu particles. The importance of electron beam-orientation-dependent moiré fringes in the correct identification of Cu structure is discussed in detail.     

Shape memory properties and oxidation behaviour of a rapidly liquid quenched Cu–Sn alloy

Rapidly liquid quenched Cu–Sn ribbons were produced and their shape memory properties and oxidation behaviour investigated using thermal analysis, metallography and X-ray diffraction methods. During the heating regime from −70°C to room temperature in a DSC instrument, martensite → austenite transformation was performed and the A_s and A_f temperatures were determined as −16.4°C and −8.4°C respectively. The oxidation behaviour was also determined using TGA. The total oxidation percentages decreased with increasing heating rate, whereas the oxidation rate increased with the heating rate during the heating and cooling times. The shape memory behaviour of the ribbon samples were also seen after bending in liquid nitrogen and reheating to room temperature.