Behavior Of AZ31 Magnesium Alloy Research Articles

Study of fractional softening of AZ31 magnesium alloy under multistage hot deformation

In the present study flow softening behaviour of AZ31 magnesium alloy was investigated by double hit compression tests in the temperature range 250–400°C and strain rate range 10–3–10–1 s–1. The tests were conducted with delay times varying 4–250 s after achieving the critical strain ϵc in each deformation condition. It has been found that static restoration processes (recovery and recrystallisation) were intensely depended on strain rate and deformation temperature. Fractional softening values increased with increasing strain rate and deformation temperature. Accordingly the softening curves were divided into three regions. The softening in the short interpass times was attributed to the occurrence of static recovery and followed by static recrystallisation and grain growth as dominant softening mechanisms for the second and third regions respectively. In addition static recrystallisation kinetics was interpreted by Avrami equation. Analysis of the results indicated that Avrami constant was changed by varying temperature.

Corrosion behaviour of AZ31 magnesium alloy with different grain sizes in simulated biological fluids

The corrosion behaviour of AZ31 magnesium alloy with different grain sizes immersed in simulated body fluids was compared in chloride solution (8 g l −1) and in phosphate-buffer solution (PBS). The influence of immersion time was also analyzed. Electrochemical techniques such as open circuit potential, polarization curves, transient currents and electrochemical impedance spectroscopy, complemented with scanning electron microscopy and energy dispersive spectroscopy, were used. Immediately after the immersion in the corrosive media the corrosion resistance was similar for both grain sizes of the AZ31 alloy and higher in NaCl solutions than in PBS. However, this corrosion behaviour was reversed after longer periods of immersion due to the stabilizing of the corrosion products of MgO by P-containing compounds. These P-compounds contribute to a higher level of protection by hindering the aggressive action of chloride ions. The best corrosion behaviour of the AZ31 alloy was obtained for the finest grain alloy associated with the highest transfer resistance value, after long periods of immersion in PBS.

Precipitation and responding damping behavior of heat-treated AZ31 magnesium alloy

Microstructure observation and dynamic mechanical analysis were carried out to investigate the precipitation and responding damping behaviors of AZ31 magnesium alloy. All the strain amplitude-dependent damping curves of the aged alloys are located between the curves of solutionized and as-cast alloys, although they have different critical strain amplitudes. The G-L theory is employed to explain the damping mechanism involving the interaction between the dislocation and the precipitated phase. In addition, a damping peak is observed at temperatures close to 330 °C for AZ31 magnesium alloy, which is related to the β-Mg 17 Al 12 phase dissolution.

Corrosion Behavior of AZ31 Magnesium Alloy in Dilute Sodium Chloride Solutions

Corrosion behavior of AZ31 magnesium alloy in dilute NaCl solutions was studied by electrochemical techniques. Its surface film was chemically characterized by X-ray diffraction (XRD). A corrosion map in terms of electrode potential and chloride concentration [Cl–] was obtained by using electrochemical measurements. With the map, passivation and corrosion zones were determined. The passivation zone was found to become narrow with the increasing of [Cl–] . The values of Eocp, open-circuit potential, in nondeaerated NaCl solutions were in the passivation zone when [Cl–] –] ≥0.2 M. The reduction reactions of dissolved oxygen and hydrogen evolution worked as cathodic reactions in nondeaerated solutions. By XRD analyses, Mg(OH)2, magnesium hydroxyl carbonate, and MgO were the dominant products in the corrosion zone, whereas magnesium hydroxyl carbonate and MgO were the main components in the passivated film.

Uniaxial tension and compression behavior of AZ31 magnesium alloy rolled and extruded materials

Mg alloy as a practical use metal is superior in specific strength and specific stiffness, and also exhibits eminent performance in heat discharging, electromagnetic wave shielding and vibration and shock absorption. Therefore, it is used for the components of cars, aircrafts, precision machines etc. and its applications are broadened to various fields. Mg alloy AZ31 rolled sheet and extruded sheet were considered in this study. It was the experimental observation and investigation of the deformation behavior about the materials manufactured different methods by uniaxial tensile test and compression test under the temperature range including high temperature range. It was also aimed at revealing and investigating the differences of material properties derived from different manufactured methods. A Siebel-type compression test was performed, which can compensate the deviation from a simple compression condition caused by the friction between interfacial surfaces of tools and materials, in order to perform the test based on ideal simple compression condition. The properties of material received by both tests were compared and important findings were obtained for Mg alloy AZ31 sheet.

Influence of Deaerated Condition on the Corrosion Behavior of AZ31 Magnesium Alloy in Dilute NaCl Solutions

The corrosion behavior of AZ31 Mg alloy in the nondeaerated and deaerated dilute NaCl solutions was investigated by electrochemical measurements. The cathodic reaction of AZ31 Mg alloy depends on the hydrogen evolution and the oxygen reduction in nondeaerated media, while that is dominanted by the hydrogen evolution in deaerated media. In the potentiostatic measurements in deaerated media, the current density reached a peak during the initial immersion and then showed a stepwise decrease getting into the passivation state by a homogeneous distribution of the Mg(OH)2 product with increasing polarization time. It revealed that AZ31 alloy has a better corrosion resistance in deaerated media after long immersion. In the 0.01 mol/L solution, passivation zone was observed in deaerated media polarization up to −1.35 V (vs. SCE) while the corrosion and passivation zones were occurred in nondeaerated media. Potentiodynamic measurements in the 0.01 mol/L NaCl solution containing various concentrations NaHCO3 showed that the corrosion behavior of AZ31 alloy depends on the NaHCO3 concentration. It means that the presence of CO2 naturally in nondeaerated media may affect the corrosion process.

Warm deformation mechanism of hot-rolled Mg alloy

Tension attachment of high temperature microscopy was proposed to research the microstructure evolution and plastic behavior of AZ31 magnesium alloy in a temperature range of 473–523 K and a load range of 80–160 N. Transmission electron microscopy(TEM) was utilized to observe the morphology of twins after deformation process. The results show that as Zener-Hollomon parameter Z increases (temperature falls, strain rate rises), the peak stress obviously increases, while the ductility tends to become worse. A great amount of twins can be found at moderate temperatures. Therefore, basal slip, a +c non-basal slipping and twinning are considered the dominant mechanisms at moderate temperatures. Some DRXed grains can be observed in the twinned regions and grain boundaries, suggesting both twinning-induced DRX and continuous DRX occurs in the deformation process.

Investigation of the effect of strain rate and temperature on the deformability and microstructure evolution of AZ31 magnesium alloy

Magnesium, being the lightest available structural material, is a primary candidate for automotive and aviation industries; however, the difficulty of deforming magnesium is a limiting factor. This research work aims to investigate the deformability of AZ31 magnesium alloy employing various deformation conditions. The results are used to correlate the effect of changing the deformation conditions on the resulting material behavior and microstructure. Tensile testing experiments were conducted at a wide variety of deformation conditions to determine the constitutive behavior of AZ31 magnesium alloy. The effect of changing the deformation conditions on the resulting microstructure is also examined and quantified by measuring the volume fraction and size of the dynamically recrystallized grains. Hardness measurements were employed to determine the softening behavior of the material during deformation due to dynamic recrystallization. The findings indicate a decrease in the peak stress and hardness and an increase in the fraction and size of dynamically recrystallized grains with decreasing strain rate and increasing deforming temperature. Temperature plays a major role in determining the fraction and size of dynamically recrystallized grain whereby, at a certain strain rate, an increase in temperature by 50 °C results in a change in the fraction of dynamically recrystallized grains by ∼30%. Further correlations were developed based on these findings to optimize the deformation behavior.

Biodegradable behaviors of AZ31 magnesium alloy in simulated body fluid

Magnesium alloys have unique advantages to act as biodegradable implants for clinical application. The biodegradable behaviors of AZ31 in simulated body fluid (SBF) for various immersion time intervals were investigated by electrochemical impedance spectroscopy (EIS) tests and scanning electron microscope (SEM) observation, and then the biodegradable mechanisms were discussed. It was found that a protective film layer was formed on the surface of AZ31 in SBF. With increasing of immersion time, the film layer became more compact. If the immersion time was more than 24 h, the film layer began to degenerate and emerge corrosion pits. In the meantime, there was hydroxyapatite particles deposited on the film layer. The hydroxyapatite is the essential component of human bone, which indicates the perfect biocompatibility of AZ31 magnesium alloy.

A study on the effect of thermo-mechanical parameters on the deformation behavior of Mg–3Al–1Zn

The flow behavior of AZ31 magnesium alloy was examined at high (250–450 °C) and ultra high (above 450 °C) temperatures. These were carried out using the hot compression testing method. For temperatures ranging from 250 °C to 450 °C, the peak flow stress was modeled using a power law expression with activation energy of 164 kJ/mol, a strain rate exponent of 0.14 (steady-state) stress exponent of 6.6. Also, a value of n = 5 was found for the “sinh” type of equation. The correlation between flow stress and thermo-mechanical parameters was described in terms of microstructural evolutions. The results also indicated that the presence of liquid at temperatures above 470 °C did change the deformation mechanisms, thereby affecting the flow behavior at ultra high temperatures.

Analytical characterisation and corrosion behaviour of bis-aminosilane coatings modified with carbon nanotubes activated with rare-earth salts applied on AZ31 Magnesium alloy

The present work investigates the corrosion behaviour of AZ31 Magnesium alloy (Mg AZ31) substrates pre-treated with a water soluble bis-aminosilane modified with multiwall carbon nanotubes (CNTs). Prior addition to the silane solution, the CNTs were submitted to a treatment in an aqueous solution containing cerium nitrate or lanthanum nitrate. The chemical composition of the treated CNTs and of the modified silane coatings was assessed by X-ray Photoelectron spectroscopy (XPS). The thickness and the morphology of the silane coatings were investigated by scanning electron microscopy (FEG/SEM). The pre-treatment of the Mg AZ31 was performed by dipping the metallic coupons in the silane solution modified with the CNTs. The electrochemical behaviour of the silane coated coupons was studied during immersion in 0.05 M NaCl solutions, using the scanning vibrating electrode technique. The electrochemical investigation showed that the activation of the CNTs with the rare-earth salt delays the corrosion activity of the Mg AZ31 substrates. The analytical and microscopic study suggested that the CNTs are homogeneously dispersed in the silane coating and that the CNTs act as support for inhibitor storage.

The relation between severe plastic deformation microstructure and corrosion behavior of AZ31 magnesium alloy

Abstract The quest for ever, higher performance in structural applications has resulted in the outgoing development of new or improved materials with novel crystallographic textures, microstructures, and compositions. However, commercial applicability of such materials depends heavily on the development of economical and robust manufacturing methods. Due to the promise of excellent properties, such as superplasticity, high strength, good ductility, enhanced high cycle fatigue life, and good corrosion resistance, interest has grown in nanostructure bulk materials. Those materials are defined most often as materials exhibiting nanocrystalline grain structures and particle sizes below 100 nm in at least one dimension. In recent years, bulk nanostructure materials processed by methods of severe plastic deformation (SPD) such as equal channel angular extrusion (ECAE) have attracted the growing interest of specialists in materials science. The main object of this research is to compare the microstructural changing and corrosion behavior of magnesium alloy AZ31 after extrusion and severe plastic deformation by ECAE process. The ECAE process can produce intense and uniform deformation by simple shear and provides a convenient procedure for introducing an ultra fine grain size into a material. The samples were prepared by using hot extrusion methods. Hardness and AC and DC polarization tests were carried out on the extruded rods, and the microstructure was examined using optical, electron microscopy (SEM, TEM) and EDS. The results showed that the severe plastic deformation process affected both the microstructure and the corrosion behavior of AZ31 Mg alloy. These results can be explained by the effects of the process on microstructure of AZ31 Mg alloy such as grain size and dislocation density caused by the change in recrystallization behavior.

Corrosion Behavior of AZ31 Magnesium Alloy with Microarc Oxidation Film Irradiated by High-Intensity Pulsed Ion Beam

The microarc oxidation (MAO) films on AZ31 magnesium alloy were modified by high-intensity pulsed ion beam (HIPIB) at an ion current density of 200 A/cm2 with 1-5 shots. The modified MAO films presented a corrosion resistance superior to that of the original films. Scanning electron microscopy (SEM) observation revealed that a sealing layer was formed on the MAO films by HIPIB irradiation. The corrosion behaviors of the MAO films in 3.5 % NaCl solution were characterized by using electrochemical impedance spectroscopy (EIS). The noticeable improvement in the corrosion resistance of MAO films is attributed to the blocking effect of the sealing layer that hinders the process of electrolyte penetrating the MAO films to the magnesium alloy.

Deformation and fracture during equal channel angular pressing of AZ31 magnesium alloy

The deformation and fracture characteristics of AZ31 magnesium alloy during equal channel angular pressing (ECAP) were established. The isothermal behavior of AZ31 magnesium alloy was determined at temperatures between 150 and 250 °C and ram speeds producing average effective strain rates between 0.001 and 0.25 s −1. AZ31 magnesium alloy was particularly susceptible to shear localization during ECAP, uniform flow occurred only at high temperatures and low strain rates. Observations of shear banding and shear fracture were interpreted in terms of the tendency for strain concentration as quantified by the flow localization ‘ α’ parameter, or the ratio of the normalized flow softening rate to the strain-rate sensitivity. These understandings of the effect of material properties on flow localization tendency are helpful for the selection of processing parameters with uniform flow during ECAP.

The corrosion behavior of Ce-implanted magnesium alloys

The aim of this study was to investigate the effect of cerium ion implantation on the corrosion behavior of AZ31 magnesium alloys. Samples were implanted with doses of 5 × 10 16, 1 × 10 17 and 5 × 10 17 ion/cm 2, respectively, using a metal vapor vacuum arc (MEVVA) source at an extraction voltage of 45 kV. Auger electron spectrometry (AES) and X-ray photoelectron spectroscopy (XPS) were used to analyze the depth distribution and the valence states of elements in the implanted layer, respectively. The potentiodynamic polarization technique was applied to evaluate the corrosion resistance of the implanted samples in a 3.5 wt.% NaCl solution saturated with Mg(OH) 2. The results showed that under an optimal dose the corrosion resistance of the implanted sample was improved compared with that of the bare sample. Finally, the corrosion mechanism of the Ce-implanted samples was discussed.

Creep behavior of AZ31 magnesium alloy in low temperature range between 423 K and 473 K

The deformation behavior of coarse-grained AZ31 magnesium alloy was examined in creep at low temperatures below 0.5 T m and low strain rates below 5 × 10−4 s−1. The creep test was conducted in the temperature range between 423 and 473 K (0.46–0.51 T m) under various constant stresses covering the strain rate range 5 × 10−8 s−1–5 × 10−4 s−1. All of the creep curves exhibited two types depending on stress level. At low stress (σ/G 4 × 103), the creep curve was typical of class II. At the low stress level, deformation could be well described by solute drag creep whereas at the high stress level, deformation could be well described by dislocation climb creep associated with pipe diffusion or lattice diffusion. The transition of deformation mechanism from solute drag creep to dislocation climb creep, on the other hand, could be explained in terms of solute-atmosphere-breakaway concept.

The effects of cerium implantation on the oxidation behavior of AZ31 magnesium alloys

Implantation of cerium ions into the surface of AZ31 magnesium alloys was performed with fluences of 5 × 10 16, 1 × 10 17 and 5 × 10 17 ions/cm 2, respectively. Auger electron spectrometry (AES), X-ray photoelectron spectroscopy (XPS) and glancing angle X-ray diffraction (GAXRD) were used to characterize the implanted surface. The results showed that after treatment a pre-oxidation layer with a duplex structure was formed. The outer layer was mainly composed of MgO, while the inner layer consisted of MgO, Ce 2O 3 and CeO 2. The influence of cerium implantation on the oxidation behavior of AZ31 magnesium alloys was investigated at 773 K in pure O 2 for 90 min. The results indicated that the oxidation resistance of the implanted sample was improved with optimal fluence. The corresponding mechanism of the oxidation behavior was also discussed.

P036 二軸圧縮試験機を用いた種々のひずみ経路におけるAZ31マグネシウム合金の塑性挙動に関する検討(フェロー賞表彰対象ポスターセッション)

P036 二軸圧縮試験機を用いた種々のひずみ経路におけるAZ31マグネシウム合金の塑性挙動に関する検討(フェロー賞表彰対象ポスターセッション)

Effect of temperature on mechanical behavior of AZ31 magnesium alloy

Strain rate sensitivity and tension/compression asymmetry of AZ31 magnesium alloy at different temperatures and strain rates were investigated. Both of mechanical behaviors are temperature dependent. Strain rate sensitivity increases with increasing temperature. Thermally activated slip is the source of strain rate sensitivity. At the temperature below or near 373 K, strain rate sensitivity is very little. Tension/compression asymmetry in yielding decreases with increasing temperature. Twinning is the reason of tension/compression asymmetry. At the temperature above or near 573 K, the material shows little tension/compression asymmetry of the flow stress.

The effect of Y-ion implantation on the oxidation of AZ31 magnesium alloy

The beneficial effect of Y-ion implantation on the oxidation behavior of AZ31 magnesium alloy was investigated. Yttrium ions having energy of 90 keV were implanted with a concentration of 5 × 10 17 ions/cm 2. Isothermal oxidation tests have been conducted at 773 K in pure O 2. The experimental results indicated that after treatment the oxidation resistance of AZ31 was significantly improved. AES, XRD and SEM revealed that the pre-oxidation layer could play an important role in further oxidation of the alloys. Finally, cyclic-oxidation test was performed at 773 K in air for 96 h. The implanted AZ31 showed an improved oxidation resistance. With longer oxidation time the beneficial effect of Y-ion implantation vanished gradually.