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Agitation leaching is a promising technology in hydrometallurgy for treating copper–cobalt oxide ores. In this work, the behavior of oxide ores containing around 2.3% Cu and 0.3% Co received from Congo was investigated for varying particle size, acidity, pulp density, temperature, leaching time, and reduction potential. XRD, optical microscopy (OM), and ICP-OES methods were used to examine the chemical composition, morphology, and metal content of the samples. The copper and cobalt recovery reached 88.2% and 82.5%, respectively, at room temperature, with a leaching time of 4 h, a pulp density of 33%, an acidity of 178 g/L, and no reductant. The Cu and Co remaining in the leaching residue were found to be in their sulfide forms and coated with dense and fine calcium sulfate. To improve the metal recovery, a combination of flotation and agitation leaching of the flotation tailings method was adopted, after which the Cu and Co recovery reached 96.6% and 86.0%, respectively.

This work highlights a new process for direct manufacturing of ductile iron that is based on the innovative combined technology of quenching and partitioning, and low-temperature-transformation of nano bainite as used for high strength steels. In this process, a commercial unalloyed ductile iron is austenitized at 890 °C for 20 min, then rapidly quenched to 180 °C for 5 s, and finally partitioned at 220 °C for 240 min. A maximum tensile strength of more than 1600 MPa, a hardness of 55 HRC at an elongation in excess of 5%, and the number of repeat tensile fatigue failure of 2.5 × 104 cycles at a stress amplitude of 600 MPa, are achieved. This is comparable to those of a high strength carbon alloy steel. These properties are due to the synergistic strengthening and toughening effects of a multiphase structure comprising tempered martensite, bainitic ferrite and retained austenite in the matrix, and a spherical graphite morphology. This work provides a guidance on how to produce unique steel-like ductile iron with a high level of strength and acceptable toughness.

The generation and microstructural characteristics of the surface layer formed during solution treatment at 1200 °C of a high nitrogen austenitic stainless steel, have been investigated using optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Contrasting with a bulk microstructure of austenite and ferrite, a multi-layer surface structure is obtained, which consists of a white outer-surface layer which is ferrite and a grey subsurface layer with austenite. Formation of the multi-layer structure occurs through phase transformations between austenite and ferrite due to the various levels of nitrogen diffusion. With increasing solution treatment time, the thicknesses of both the surface and the subsurface layer increase. Hardness tests show that the microhardness increases from the surface layer, to the subsurface layer and then to the bulk. This is attributed to the combined effects of solid solution strengthening from nitrogen and the grain size of austenite or ferrite. Keywords: High nitrogen austenitic stainless steel, Solution treatment, Multi-layer structure, Nitrogen diffusion

An unalloyed ductile cast iron with a multiphase structure is designed by a novel austempering process. The designed austempering treatment consists of initial rapid quenching to 180°C after austenizing at 890°C for 20min, and finally austempering at 220°C for 240min. A multiphase structure comprising lenticular/needle-like prior martensite, fine needle bainitic ferrite and film retained austenite is obtained. The excellent mechanical properties, with a tensile strength of 1530MPa and an elongation of 3.1% can be achieved by controlling the matrix microstructure of 12% prior martensite, 15% retained austenite with 1.64% carbon content, and 73% bainitic ferrite. This is mainly attributed to prior marteniste which can promote refinement of multiphase colonies.

High nitrogen stainless steel (HNSS) is becoming an increasingly important engineering material because of its excellent corrosion resistance and good mechanical properties. A hot rolled Cr19Mn19Mo2N0.7 HNSS, having a microstructure consisting of banded ferrite and dotted/dendritic nitrides dispersed in the austenite matrix, was solution treated at 1160oC for various times. It is shown that the nitride can be dissolved, and the shape of ferrite can be changed by the solution treatment. The microhardness of both austenite and ferrite decreases with increasing solution treatment time. This is attributed to an increased grain size and a homogeneous distribution of alloying elements. The results are helpful in controlling the thermomechanical processing of HNSSs in commercial practice.

Austempered ductile iron (ADI) has been widely used in various industries due to its excellent combination of high strength, ductility and good wear resistance. The tensile behavior of an unalloyed commercial ADI with a multiphase structure designed by a novel multi-step austempering treatment is investigated. The developed austempering process consists of austenitizing at 890°C for 20min, then initial rapid quenching to 180°C, and isothermal holding at 190, 220, 250°Cfor 120min, and finally air cooling to room temperature. The optimum mechanical properties with an ultimate tensile strength of 1350MPa, a yield strength of 1090MPa, as well as an elongation of 3.5% is achieved at 220°C. This is attributed to a synergistic strengthening effect of multiphase structure including a prior martensite with fine needle bainitic ferrite and film retained austenite.

Compared with traditional stainless steels, high nitrogen stainless steels (HNSS), have been widely used due to their high strength, toughness along with excellent corrosion resistance and low cost, formed by partial replacement of Ni (austenite-forming element) by N. The evolution of the microstructure of a Cr19Mn19Mo2N0.7 stainless steel is investigated after solution treatment at 1010, 1060, 1200 or 1250°C for 30min. A complex multilayer structure has been found under a negative pressure vacuum. A white ferritic layer at the surface is formed, and a subsurface layer with full austenitic structure and a bulk microstructure comprising of austenite and ferrite are detected. With increasing solution temperature, the surface layer thickness increases. The formation of the multilayer structure is attributed to an outward diffusion, a diffusive retardation and an abnormal accumulation of nitrogen during solution treatment.

A commercial unalloyed ductile iron has been developed to produce a multiphase matrix microstructure consisting of lenticular prior martensite, feathery upper bainite and a nano-scaled super bainite of lath bainitic ferrite and carbon-enriched film retained austenite. Multi-step heat treatment composed of austenizing, rapidly quenching and isothermally holding at low temperature have been developed. A tensile strength of more than 1.6 GPa, a hardness higher than HRC 54, and an elongation in excess of 5%, are achieved. This is attributed to a synergistic multi-phase strengthening effect. The developed nano super bainite exhibits a good balance between strength and toughness. The presence of martensite formed during the quenching prior to the isothermal treatment, accelerates the kinetics of subsequent nano super bainitic transformation by bainitic laths nucleating quickly at the martensite-austenite interfaces.

A commercial ductile iron is treated by a novel austempering process to obtain a good combination of strength and ductility. The samples are austenitised at 890°C for 10 min, then quenched into patented quenching liquid, and austempered in an electric furnace at 220°C for 5, 10, 30, 60, 240 and 600 min, respectively, finally air cooled. The bending test and the tensile test are conducted and microstructural features are analysed on the austempered ductile iron. The optimum mechanical property is achieved at 220°C for 240 min. Main reason for high strength and ductility is the formation of a fine structure consisting of multiple phases of pre-formed martensite and lath bainitic ferrite with film retained austenite.

A quenching and partitioning process has been developed for an unalloyed ductile iron. The process includes austenitizing at 890 °C for 0.5 h, quenching to 180 °C below the Ms (the starting temperature of martensite transformation) for 5 s, with a controlled speed, then followed by a partitioning at 190 °C (10 °C lower than the Ms) for 8 h, and finally air cooling to the room temperature. A multiphase microstructure consisting of prior martensite (PM), bainitic ferrite (BF), and fresh martensite formed on final quenching (FM) with retained austenite (RA) is obtained through the microstructural evolution on quenching and partitioning steps. Further observation shows that a unique nano structure including lath BF and film RA with a width less than 100 nm nucleates around the PM. A strong influence of RA content and stability on both the tensile strength and the elongation is observed. In addition, the wear behavior is investigated under various loads without lubrication. A combined wear mechanism of abrasion and oxidation is found in a case of a low load. With increasing the load, the wear behavior correlates to a comprehensive strengthening and toughening effect of the multiphase microstructure in the matrix.

Ferritic nitrocarburizing offers excellent wear, scuffing, corrosion and fatigue resistance by producing a thin compound layer and diffusion zone containing e (Fe2-3(C, N)), γ′ (Fe4N), cementite (Fe3C) and various alloy carbides and nitrides on the material surface. It is a widely accepted surface treatment process that results in smaller distortion than carburizing and carbonitriding processes. However this smaller distortion has to be further reduced to prevent the performance issues, out of tolerance distortion and post grinding work hours/cost in an automotive component. A numerical model has been developed to calculate the nitrogen and carbon composition profiles of SAE 1010 torque converter pistons during nitrocarburizing treatment. The nitrogen composition profiles are modeled against the part thickness to predict distortion. Experimental composition profiles of torque converter pistons are reported for model validation and to determine the effect of nitrogen composition on distortion. The surface residual stresses predicted by the model are also compared to the measured residual stresses. The correlations between nitrocarburizing temperature, distortion and composition profiles are discussed using the modeling results. CITATION: Manivannan, M., Stoilov, V., and Northwood, D., "Ferritic Nitrocarburizing of SAE 1010 Plain Carbon Steel Parts," SAE Int. J. Mater. Manf. 8(2):2015, doi:10.4271/2015-01-0601. 2015-01-0601 Published 04/14/2015 Copyright © 2015 SAE International doi:10.4271/2015-01-0601 saematman.saejournals.org Downloaded from SAE International by Madhavan Manivannan, Tuesday, March 03, 2015

The Navy C-ring has been one of the most common types of specimen used for observing the dimensional changes (distortion) after heat treatment. The dimensional changes in the Navy C-rings are generally assumed to be comparable to those in an actual heat treated component. In this paper, we first review the various types of C-rings that have been used, and the results obtained for size and shape distortions for steels that have been carburised or nitrocarburised. An overview is then presented of the parameters that are included in simulation models to predict internal stresses and distortion. Finally, we present our own experimental and modelling results for the distortion in 1010 steel C-ring samples (three thicknesses) and an automotive component (torque converter piston) subjected to a gas ferritic nitrocarburising treatment. The predictions, on the basis of the nitrocarburised layer, and measured distortions were in better agreement for the thinner C-rings where the thickness was comparable to ...

The effect of unidirectional surface roughness on the corrosion behaviour of nickel in 0.5 M H 2 SO 4 solution was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The surfaces, both before and after corrosion, were characterized by scanning electron microscopy, profi lometry for roughness and energy dispersive spectroscopy for oxygen content. The results were compared with those for patterned samples consisting of an array of holes. For the unidirectional surface roughness samples, an increase in roughness gave rise to an increase in corrosion rate, refl ecting the decreased ability to form a stable passive fi lm. The patterned samples showed a higher corrosion resistance, which is attributed to a different corrosion protection mechanism, namely heterogeneous wetting.

The effects of heat treatment on distortion, residual stress, and retained austenite were compared for case-carburized 4320 steel, in both the austempered and quench-and-tempered condition. Navy C-ring samples were used to quantify both size and shape distortions, as well as residual stress. The austempering heat treatment produced less distortion and a higher surface residual stress. Both hoop and axial stresses were measured; the difference between them was less than seven percent in all cases. Depth profiles were obtained for residual stress and retained austenite from representative C-ring samples for the austempered and quench-and-tempered heat treatment conditions. Austempering maintained a compressive residual stress to greater depths than quench-and-tempering. Quench-and-tempering also resulted in lower retained austenite amounts immediately beneath the surface. However, for both heat treatments, the retained austenite content was approximately one percent at depths greater than 0.5 mm.

In the plasma electrolytic oxidation (PEO) coating of light metal alloys, changing the electrical parameters and electrolytic composition can change the discharge behaviour and, ultimately, the thickness, surface morphology and porosity of the coating. In the present study a combination of cathodic and anodic current pulses with suitable Ton and Toff periods were used to control the porosity and other structural defects of PEO coatings of an AM60B magnesium alloy. In order to investigate the effect of a current mode on the plasma discharge behaviour and coating microstructure during the PEO treatment of magnesium alloy, the emission intensities of six different spectral lines from the plasma species were recorded simultaneously as a function of both time and current mode using optical emission spectroscopy (OES) system. The fluctuations in signal intensities and temperature during the coating process reflect differences in location of both the discharge initiation, and discharge type. The coating surface morphology and microstructure that are obtained can be linked to the plasma discharge behavior. These results are discussed in relation to the discharge behaviour, and how such changes in discharge behaviour relate to the coating mechanisms.

Magnesium alloys are considered one of the more promising materials for future use in many engineering applications. However, due to their high chemical and electrochemical reactivity, magnesium alloys have poor corrosion resistance in aqueous environments. Improving their corrosion resistance by coating can greatly extend their application. One promising coating method is plasma electrolytic oxidation (PEO). The nature of the coating formed, and the ultimate corrosion performance depends on the both the processing parameters (electrolyte, current density, current mode, processing time) and specific Mg-alloy substrate. In the present study, PEO coatings were produced on three different Mg-alloys (AJ62, AM60B and AZ91D) using different processing parameters. Scanning electron microscopy was used to characterize the coatings. The corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in an aqueous 3.5% NaCl solution. Relationships are drawn between PEO processing parameters, substrate composition and corrosion performance. Electrochemical impedance spectroscopy data indicate that the bipolar PEO coated AZ91D Mg alloy demonstrates a higher corrosion resistance when compared to coated AM60B, AJ62 and pure Mg.

To further our understanding of the plasma electrolytic oxidation (PEO) process, and to aid in the optimization of the process, it is important to identify the mechanisms of coating formation. In the present work, coatings up to 110 μm thick were produced on an AJ62 Mg-alloy substrate using the PEO process. Optical emission spectroscopy (OES) was employed to follow the microdischarges and substrate and electrolyte elements present in the plasma discharge during the coating growth, and to determine plasma electron temperatures. During PEO processing of magnesium, some of the metal cations are transferred outwards from the substrate and react with anions to form ceramic coatings. Also, due to the high electric field in the discharge channels, oxygen anions transfer toward the magnesium substrate and react with Mg 2+ cations to form a ceramic coating. In PEO process, the ceramic coating grows inwards to the alloy substrate and outwards to the coating surface simultaneously. The total coating thickness variation compared with the geometrical dimensions of the uncoated and coated samples were investigated. For the coating growth, there are three simultaneous processes taking place, namely the electrochemical reactions, the plasma chemical reactions and thermal diffusion. Oxygen diffusion occurring during PEO processing is discussed in terms of coating growth mechanisms.

In this study a new approach that is based on creating surface patterns on metallic surfaces has been used to decrease corrosion in nickel. Patterns of holes with specific diameters ( D ) and inter-hole spacings ( L ) were created by laser ablation on nickel and potentiodynamic polarization corrosion tests were carried out in a 0.5 M H 2 SO 4 solution. The corrosion potential, E Corr , and current density ( I Corr ) were determined and compared for different ratios of ( D / L ). Energy dispersive spectroscopy (EDS) was performed on the surface of the samples to investigate the chemical composition, specifically the oxygen content of different regions of the patterned area before and after corrosion testing. By creating such patterns we are able to produce a surface with heterogeneous wetting properties, to decrease the surface energy and to decrease the contact area between the liquid and the substrate. As a result of the surface patterning a significant improvement of corrosion properties of nickel surface has been achieved. Patterned surfaces showed better corrosion resistance compared to the polished reference samples. In addition, it has been shown that for a few specific patterns the corrosion resistance can be increased by orders of magnitude.

The application of magnesium alloys in the automotive industry has been limited by their inferior corrosion and wear properties. PEO (plasma electrolytic oxidation) is an electrochemical process that uses a non-hazardous aqueous electrolyte to oxidize the metal surfaces to form oxide coatings which impart high corrosion and wear resistance. In this study we investigated the effect of current mode (unipolar, bipolar or hybrid (combination of both)) on the corrosion and wear properties of PEO coatings formed on an AM60B magnesium alloy (mass fraction: Al 5.6–6.4%, Mn 0.26–0.4%, Zn ≤ 0.2%, balance Mg). Changing the current mode produces changes in the PEO process characteristics, including the breakdown voltage and discharge events, both in terms of discharge intensity and density. The morphology and microstructure of the coatings were investigated using scanning electron microscopy (SEM). PEO-coated materials tested using a pin-on-disk tribometer under dry sliding conditions show a higher coefficient of friction (COF) but a lower wear rate than the uncoated alloy. It was also found that the coatings formed using a bipolar or hybrid (unipolar + bipolar) current mode showed lower COF values and wear rates due to their modified coating microstructure and surface morphology. Inclined impact–sliding wear tests, which allow the simulation of a combination of impact fatigue failure and sliding wear failure under repetitive high local loads, also demonstrated the superior tribological properties of coatings produced using either a bipolar or a hybrid current mode.

Plasma electrolytic oxidation (PEO) is an electrochemical process uses an environmentally-friendly aqueous electrolyte to oxidize the metal surfaces to form ceramic oxide coatings which impart a high corrosion and wear resistance. In this study we investigated the effect of current mode on the properties of PEO coatings formed on an AM60B magnesium alloy. Unipolar, bipolar and hybrid (combination of both) current modes were used in this work. Optical emission spectroscopy (OES) was employed to investigate the PEO plasma. Coatings prepared using a hybrid current mode had a dense inner layer with fewer defects. The order of the applied current modes (unipolar and bipolar modes) had a significant effect on the coating morphology and corrosion resistance. The effects of the negative current part of the pulses on the coating were studied by using a unipolar current mode with different pulse timings. Coatings produced with a longer off-time had more porosity, and hence lower corrosion resistance. The corrosion protection efficiency of these coatings are compared to those produced by PEO coatings on a AJ62 Mg-alloy.

In this study, we have used PEO (plasma electrolytic oxidation) for the production of oxide coatings on a Ti–6Al–4V alloy at two different current modes, namely pulsed unipolar and bipolar. Optical emission spectroscopy (OES) in the visible and near UV band (280–800 nm) was used to characterize the PEO plasma. The emission spectra were recorded and the plasma temperature profile versus processing time was constructed using a line intensity ratios method. The aim of this work was to study the effect of the process parameters, including current mode and pulse duration time, on the plasma characteristics, surface morphology and microstructure and corrosion resistance of oxides grown on Ti–6Al–4V by PEO process. Scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD) were used to study the coating microstructure, morphology and phase composition. The corrosion resistance of the coated and uncoated samples was examined by potentiodynamic polarization in a 3.5% NaCl solution. It was found that the plasma temperature profiles are significantly influenced by changing the current mode from unipolar to bipolar. The strongest discharges that are initiated at the interface between the substrate and the coating can be reduced or eliminated by using a bipolar current mode. This produces a thinner, denser and more corrosion-resistant coating.

Magnesium alloys are increasingly being used as lightweight materials in the automotive, defense, electronics, biomaterial and aerospace industries. However, their inherently poor corrosion and wear resistance have, so far, limited their application. Plasma electrolytic oxidation (PEO) in an environmentally friendly aluminates electrolyte has been used to produce oxide coatings with thicknesses of similar to 80 mu m on an AJ62 magnesium alloy. Optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285 nm-800 nm) was employed to characterize the PEO plasma. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the coated materials, and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution were used to determine the corrosion behavior. It was found that the plasma discharge behavior significantly influenced the microstructure and the morphology of the oxide coatings and, hence the corrosion resistance. The corrosion resistance of the coated alloy was increased by changing the current mode from unipolar to bipolar, where the strong plasma discharges had been reduced or eliminated. (C) 2011 Elsevier B.V. All rights reserved.

Carbonitriding is a widely accepted method of heat treatment used by North American manufacturers for plain carbon steel. While the process imparts a hard, wear resistant case, it is also associated with both size and shape distortion, which can be problematic for components in tight fitting assemblies. This research compares the effects of the carbonitriding and nitrocarburising processes on SAE 1010 steel with respect to residual stress and distortion. Results indicate that the two processes develop residual compressive stresses and are associated with both size and shape distortion. Although the magnitude of the compressive stresses in nitrocarburised steels is lower, this process was noted to give rise to overall smaller dimensional changes than the carbonitriding process. The findings from this study are applied to a manufacturing application involving the surface treatment of a thin shelled automotive component in a light loading application.

In this study, a plasma electrolytic oxidation process (PEO) was used to produce oxide coatings on commercially pure aluminum (Al 1100) at two different current modes, pulsed unipolar and bipolar modes. Optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285 nm–800 nm) was employed to investigate the PEO plasma. The emission spectra were recorded and plasma temperature profile versus processing time was constructed using line intensity ratios method. Scanning Electron Microscopy (SEM) with energy dispersive x-ray analysis (EDS) was used to study the coating microstructure and coating cross section. It was found that the plasma discharge behavior significantly influenced the microstructure and the morphology of the oxide coatings. The main effect came from the strongest discharges which were initiated at the interface between the substrate and the coating. Through manipulation of process parameters to control or reduce the strongest discharge, the density and quality of the coating layers could be modified. This work demonstrated that by adjusting the ratio of the positive to negative pulse currents as well as their timing in order to eliminate the strongest discharges, the quality of the coatings was considerably improved.

A Plasma Electrolytic Oxidation (PEO) process was used to produce thin oxide coatings on a Zr–2.5 wt% Nb alloy. Effects of current density on surface morphologies and wear properties of PEO coatings were investigated and compared to the uncoated substrate and a commercially used black oxide coating. Corrosion properties at ambient and high temperature/pressure conditions were studied using potentiodynamic polarization tests and autoclave tests, respectively. Up to 30-day autoclave experiments were carried out in an aqueous condition of 300 °C and 10 MPa in 0.05 M LiOH solutions. It was found that most of the micro-pores which were produced during the PEO treatment were closed after the autoclave experiments. PEO coatings had larger weight gains in the first 10 exposure days than the black oxide coating. However, after 10 days, the corrosion rate of black oxide coating accelerated and exhibited a similar weight gain to PEO coatings after 30 days. PEO coatings prepared at low current densities had lower weight gains. Although the black oxide coating exhibited a good corrosion resistance, it had a much lower wear resistance than the PEO coatings. Compared with the uncoated substrate, all PEO coatings had a higher corrosion resistance, lower weight gain during autoclave tests and better wear resistance.

In this study, aluminum oxide was deposited on an Al alloy substrate to produce hard ceramic coatings using a plasma electrolytic oxidation (PEO) process working at atmospheric pressure. The process utilizes dc and unipolar pulsed dc in the frequency range 0.2–20 kHz. Optical emission spectroscopy was employed to study the species and electron temperature of the plasma. The morphology and microstructure of the coatings were investigated using scanning electron microscopy. It was found that in the first 12 min of the PEO process, the plasma electron temperature increased with the applied voltage during the experiments, the plasma electron temperature was found to be in the range 4000–9000 K, and the applied voltage to the electrodes ranged up to 550–600 V for the different current modes. The plasma temperature profile exhibits a wider peak temperature spike for the dc power mode than for the pulsed dc mode, indicating that the dc plasma discharges would provide longer sintering time. The pulsed dc mode inc...

In this study, the contact resistance (CR) and electrochemical properties of TiN, CrN and TiAlN electron beam physical vapor deposition (EBPVD) coatings and their stainless steel 316L (SS316L) substrate were investigated in a simulated proton exchange membrane (PEM) fuel cell environment. The potentiodynamic polarization corrosion tests were conducted at 70 °C in 1 M H 2 SO 4 purged with either O 2 or H 2 , and the potentiostatic corrosion tests were performed under both simulated cathodic (+0.6 V vs. Ag/AgCl reference electrode purged with O 2 ) and anodic conditions (−0.1 V vs. Ag/AgCl reference electrode purged with H 2 ) for a long period (4 h). SEM was used to observe the surface morphologies of the samples after corrosion testing. All the TiN-, TiAlN- and CrN-coated SS316L showed a lower CR than the uncoated SS316L. While the corrosion performance of the coatings was dependent on the cathodic and anodic conditions, the CrN coating exhibited a higher (in the anodic environment) or similar (in the cathodic environment) corrosion resistance to the uncoated SS316L. Thus, the CrN-coated SS316L could potentially be used as a bipolar plate material in the PEM fuel cell environment. Although the EBPVD process greatly reduced number of pinholes in the coatings compared to other plasma enhanced reactive evaporations, future research efforts should be directed to eliminate the pinholes in the coatings for long-term durability in fuel cell applications.

Dissolution of secondary phases during thermal treatment in cast magnesium alloys influences their engineering properties. In this study, a kinetic model based on a Kissinger-type method has been developed for describing dissolution of secondary phases in the high pressure die cast magnesium alloy AM50 during a thermally activated heating process. Also, differential scanning calorimetry (DSC) was effectively used for investigating the dissolution kinetics of secondary phases in the AM50 alloy. By fitting a kinetic model to the DSC results, the activation energy of the dissolution of the secondary phases can be determined. In parallel, the microstructure of the alloy was analyzed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). It was found that the distribution of secondary phases and the concentration of alloying elements both at the grain boundaries and in the grains play an important role in the solid-state transformation kinetics of die cast magnesium alloy AM50.

Carbonitriding is a metallurgical surface modification technique that is widely used in the automotive industry to increase surface hardness and wear resistance. Given the problems associated with carbonitriding, such as dimensional distortion, oxidation and non-uniform surface hardness, nitrocarburizing has been proposed as an alternative heat treatment method to improve the surface characteristics. The major advantages of ferritic nitrocarburizing are the minimal dimensional changes and distortion due to the low process temperature at which no phase transformations occur. This increases productivity and product quality, and decreases costs. The focus of this study was to determine the effects of carbonitriding and ferritic nitrocarburizing processes on the dimensional changes and residual stresses in a steel used for automotive applications. Navy C-ring specimens and prototype stamped parts made from SAE 1010 plain carbon steel were used in the testing. Gas, vacuum and ion ferritic nitrocarburizing processes with different heat treatment parameters were investigated. X-ray diffraction techniques were used for the residual stresses evaluation and surface phase analysis of the specimens.

Magnesium is subject to severe galvanic corrosion attack in a commercially available engine coolant, when in contact with stainless steel and an Al alloy. Thin oxide coatings with different coating thicknesses were produced using a Plasma Electrolytic Oxidation (PEO) process to protect Mg against the corrosion attack. The galvanic corrosion properties of the PEO coatings were investigated using immersion corrosion testing. The test results showed that the anti-corrosion properties of the PEO coatings increased with increasing coating thickness. PEO coatings with a thickness of several micrometers effectively prevented the galvanic corrosion of Mg, without significantly reducing the heat conductivity of the Mg.

A series of casting experiments were carried out with Mg–5.0 wt.% Al–2.0 wt.% Ca (AC52) alloy with different cooling rates from 0.5 to 65.0 °C/s. A significant refinement of the grain size of the alloy had been achieved at higher cooling rates of 20.0–65.0 °C/s. The decrease in cooling rates resulted in continuous coarsening of the eutectic phases from nanoscale particle to microscale needle within the primary grain of the alloys. EDS results showed that there were the higher solute content of alloying elements (Al and Ca) within the primary grain of the alloys resulting from the quenching effect of fast cooling. The nanoscale creep resistance of the as-cast AC52 alloys increased with an increase in cooling rate except that the alloy cast at 20 °C/s showed the highest creep resistance. The creep curves indicated that the interaction between the dramatically increased dislocations and the surrounding solute and dispersed fine eutectics caused a high plastic penetration depth in the primary stage after loading. Then creep deformation changed from the high stress exponent regime ( n ≈ 7) to the low stress exponent regime ( n ≈ 3) at a threshold stress (∼140 MPa) controlled by the dislocation and twining controlled mechanisms. The creep behavior was correlated with the microstructure including solute content of alloying elements and dispersed eutectic phases within the primary grain to explain the underlying creep mechanisms.