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The primary objective of this study is to investigate the microstructural, mechanical, and wear behaviour of AZ31/TiC surface composites fabricated through friction stir processing (FSP). TiC particles are reinforced onto the surface of AZ31 magnesium alloy to enhance its mechanical properties for demanding industrial applications. The FSP technique is employed to achieve a uniform dispersion of TiC particles and grain refinement in the surface composite. Microstructural characterization, mechanical testing (hardness and tensile strength), and wear behaviour evaluation under different operating conditions are performed. Response surface methodology (RSM) is utilized to optimize the wear rate by considering the effects of process parameters. The results reveal a significant improvement in hardness (41.3%) and tensile strength (39.1%) of the FSP-TiC composite compared to the base alloy, attributed to the refined grain structure (6–10 μm) and uniform distribution of TiC particles. The proposed regression model accurately predicts the wear rate, with a confirmation test validating an error percentage within ± 4%. Worn surface analysis elucidates the wear mechanisms, such as shallow grooves, delamination, and oxide layer formation, influenced by the applied load, sliding distance, and sliding velocity. The enhanced mechanical properties and wear resistance are attributed to the synergistic effects of grain refinement, particle-accelerated nucleation, the barrier effect of TiC particles, and improved interfacial bonding achieved through FSP. The optimized FSP-TiC composites exhibit potential for applications in industries demanding high strength, hardness, and wear resistance. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) and its alloys offer promise for aerospace, railway, and 3D technology applications, yet their inherent limitations, including inadequate strength, pose challenges. Magnesium matrix composites, particularly with metallic reinforcements like titanium (Ti) and its alloys, present a viable solution. Therefore, this study investigates the impact of Ti6Al4V reinforcement on AZ31 magnesium alloy composites produced using pulse plasma sintering (PPS). Results show enhanced microhardness of the materials due to improved densification and microstructural refinement. However, Ti6Al4V addition decreased corrosion resistance, leading to strong microgalvanic corrosion and substrate dissolution. Understanding these effects is crucial for designing Mg-based materials for industries like petrochemicals, where degradation-resistant materials are vital for high-pressure environments. This research provides valuable insights into developing Mg-Ti6Al4V composites with tailored properties for diverse industrial applications, highlighting the importance of considering corrosion behavior in material design. Further investigation is warranted to establish predictive correlations between Ti6Al4V content and corrosion rate for optimizing composite performance. [ABSTRACT FROM AUTHOR]

Electrochemical micromachining (ECM) is a nontraditional method used for machining operations in hard and light materials with fixed or varying parameters. In this study, magnesium AZ31 alloy was micro machined using two types of electrolyte supply systems, namely electrolyte flooding and minimum quantity electrolyte (MQE). Experimental investigations were performed using TOPSIS and artificial neural network (ANN) techniques with types of electrolyte supply system, electrolyte concentration (EC), duty cycle (%), and machining voltage (V) as the input parameters, and material removal rate (MRR) and over cut (OC) as the outputs. Single and multi-objective parameter optimization was performed using Taguchi, TOPSIS, and ANN techniques. The machined microholes were analyzed using scanning electron microscopy. According to the TOPSIS results, under optimal conditions, a high MRR value and minimum OC of 1.282 µm/s and 66 µm, respectively, were obtained. The results of TOPSIS were verified using the developed ANN architecture. [ABSTRACT FROM AUTHOR]

Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloy is an engineering material with tremendous application potential in fields such as transportation, aerospace, electronic instruments, and biomaterials. Nonetheless, the poor abrasion and corrosion resistance hinder the further application of Mg alloy in the field of industrial manufacturing. Solid - state thermal diffusion (SSTD) is regarded as an strategy for creating intermetallic thermal diffusion layers (TDLs) on the surface of Mg alloy, providing protection against wear and corrosion. However, traditional SSTD is a high - temperatures and time - consuming heat treatment process. During the process, Mg alloy may undergo grain coarsening and phase transformations, leading to a degradation in mechanical properties. Additionally, the long - term high - temperature heat treatment will inevitably increase energy consumption and production cost. The present study introduces a solid - state pressure - assisted thermal diffusion (SSPTD) process with the goal of efficiently fabricating Mg Zn intermetallic TDLs on the surface of AZ31 alloy at relatively lower temperatures. As a result, Mg Zn intermetallic TDLs with an outer diffusion layer (ODL) and an internal diffusion layer (IDL) were successfully fabricated on the AZ31 alloy at the average fabrication rate (AFR) of 0.6–3 × 103 μm/h. When the SSTPD treatment was conducted at 360 °C for 60 min under 10 MPa, the surface microhardness of the sample was increased by up to 3.6 times compared to that of the AZ31 alloy, and the corrosion current was reduced by about 74 %. However, the decline in the microhardness and corrosion resistance took place when the sample was subjected to the SSPTD treatment under the condition of higher temperature and pressure (e.g., 400 °C@30 MPa). The degradation in performance was primarily attributed to the increased formation of α - Mg phases and phase transition defects (e.g., cracks and shrinkage cavities) within the TDLs during the SSPTD treatment. • Developed a rapid process for fabricating TDLs on the surface of AZ31 alloy. • Clarified the formation mechanism for Mg Zn intermetallic TDLs. • SSPTD was used to harden surface and improve corrosion resistance of AZ31 alloy. [ABSTRACT FROM AUTHOR]

In the present work, AZ31 alloy is processed by WEDM process. The input machining variables of WEDM are designed according to Box-Behnken Design (BBD) of response surface methodology (RSM). The input machining variables considered in the present research are servo feed (SF), servo voltage (SV), pulse on-time (Ton), and pulse off-time (Toff), while the response characteristics evaluated in the present work are material removal rate (MRR), microhardness (MH), average surface roughness (Ra), and mean roughness depth (Rz). The analysis for each response is made with analysis of variance (ANOVA). The empirical models developed for each response are further utilized to get the Pareto fronts along various mutually conflicting process responses using improved multiobjective grey wolf optimization algorithm (MOGWO). In the present research, Levy flight algorithm has been used to improve the efficiency of MOGWO. It has been observed that the implemented multiple objective optimization approach is able to detect the uniformly distributed Pareto fronts very efficiently. The results obtained through the improved MOGWO are further validated through confirmation experiments which show a good agreement to the predicted results. The morphology of the machined surface is also evaluated using scanning electron microscopy, which depicts the microcracks, globules, micropores, and lumps. [ABSTRACT FROM AUTHOR]

In this study, graphene was incorporated into a micro-arc oxidation coating to improve the wear and corrosion resistance of AZ31 alloy. For this purpose, the different concentration of graphene particles was used as 0 g/l, 0.5, 1, and 2 g/l. The wear tests were performed under loads of 2, 4, and 8 N. The composition and morphology of the coatings were investigated by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The coating thickness increased with increasing graphene concentration. To evaluate the corrosion performance of the coatings, potentiodynamic polarization, and electrochemical impedance spectroscopy tests were performed after immersed samples for 0.5, 16, and 32 h. The wear test results show that wear rates significantly decreases with increasing graphene concentration. Corrosion tests showed that polarization resistance increased and corrosion current density decreased for the coatings with the graphene addition compared to substrate material. [ABSTRACT FROM AUTHOR]

Postweld plastic deformation was reported to be able to largely enhance the mechanical properties of friction stir‐welded (FSW) Mg alloys by changing microstructures in the regions with a soft‐oriented texture. However, few studies have concentrated on the effects of postweld plastic deformations on the corrosion behavior of FSW Mg alloys, which has an impact on their application. In the present study, electrochemical measurements, hydrogen evolution, and mass loss tests were used to study the influences of postweld compression along the transverse direction and subsequent annealing on the corrosion rate of FSW AZ31 Mg alloys. It was found that owing to the grain refinement in the weld zones, an improvement in the corrosion resistance and hardness was observed in the FSW AZ31 sample compared to the base metal (BM) sample. Postweld compression was very harmful to the corrosion resistance of the FSW AZ31 alloys. On the basis of the mass loss results, the corrosion rate of the compressed FSW sample was ~17.62 mm/year, which was ~8.99 times that of the FSW sample (~1.96 mm/year). Subsequent annealing could slightly reduce the corrosion rate of the compressed FSW AZ31 plates, whereas the corrosion rate of the FSW‐C‐T sample (~13.63 mm/year) was much worse than that of the BM sample (~4.73 mm/year). [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study is to evaluate the effect of pH treatment on the formation of hydroxyapatite (HA) coating layer and the biodegradation rate of hydroxyapatite coated AZ31 alloy for applications in biodegradable implants. Methods: HA was grown on the surface of AZ31 substrate at three different pH solutions of 7.5, 9.0, and 10.5 respectively by chemical solution treatment method. The coated samples were evaluated their biodegradation behavior by immersion test in the simulated body fluid (SBF) for 14 days. The biodegradation rate of the samples during immersion test was observed by Mg2+ ion quantification method and measuring the increase of pH of the medium. Results: HA coatings were successfully grown on the AZ31 substrate at three different pH conditions. The sample coated at pH 7.5 showed its uniform and dense coating layer resulted in highest corrosion resistance. While the highest biodegradation rate was observed for the sample coated at pH 10.5 due to many micro-cracks formed in the HA layer. After 14 days of immersion, Mg(OH)2 and calcium phosphate were corrosion products on the surface of the specimens coated at pH 10.5 and pH 9.0 respectively. While HA almost remained on the surface of sample coated at pH 7.5. Conclusion: AZ31 alloy coated with HA at pH 7.5 has lowest biodegradation rate and become suitable for applications in biodegradable implants. [ABSTRACT FROM AUTHOR]

Anti-corrosion and wear resistance of AZ31 alloy were enhanced through a three-stage surface treatment, which comprised surface micro-arc oxidation (MAO), sputtering and post supercritical CO 2 -assisted electroless plating (PSC–CO 2 -EP). In the MAO treatment, attempts were made to vary the F ion content in the electrolyte to investigate its impact on the morphology and composition of the oxide film. Subsequently, the MAO-treated AZ31 alloy underwent Ag sputtering, followed by the preparation of the Ni coating using the PSC-CO 2 -EP method (PSC–CO 2 –Ni). The SEM micrographs indicate that the addition of F ions to the electrolyte effectively improved the uniformity, thickness and compactness of the MAO-generated oxide film. Further modification with the sputtered Ag layer could enhance the adhesion between the Ni coating and the as-prepared oxide film. Additionally, the application of SC-CO 2 , with high diffusivity and low surface tension, significantly improved the anti-corrosion and wear resistance of the AZ31 alloy surface even after pressure release. The results demonstrate that the multilayer design proposed in this study addresses the vulnerability of the AZ31 alloy surface to corrosion. Furthermore, compared to the SC–CO 2 –assisted plating method, the PSC-CO 2 -EP technique offers greater process flexibility and exhibits high potential for practical applications. [Display omitted] • F ions included solution enhanced thickness of MAO-generated oxide film. • Sputtered Ag layer improved adhesion between Ni coating and MgO film. • MgO and PSC-CO 2 -Ni layers exhibited higher surface hydrophobicity than AZ31 alloy. • PSC-CO 2 -Ni/Ag/MAO/Mg alloy structure exhibited excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study is to evaluate the effect of pH treatment on the formation of hydroxyapatite (HA) coating layer and the biodegradation rate of hydroxyapatite coated AZ31 alloy for applications in biodegradable implants. Methods: HA was grown on the surface of AZ31 substrate at three different pH solutions of 7.5, 9.0, and 10.5 respectively by chemical solution treatment method. The coated samples were evaluated their biodegradation behavior by immersion test in the simulated body fluid (SBF) for 14 days. The biodegradation rate of the samples during immersion test was observed by Mg2+ ion quantification method and measuring the increase of pH of the medium. Results: HA coatings were successfully grown on the AZ31 substrate at three different pH conditions. The sample coated at pH 7.5 showed its uniform and dense coating layer resulted in highest corrosion resistance. While the highest biodegradation rate was observed for the sample coated at pH 10.5 due to many micro-cracks formed in the HA layer. After 14 days of immersion, Mg(OH)2 and calcium phosphate were corrosion products on the surface of the specimens coated at pH 10.5 and pH 9.0 respectively. While HA almost remained on the surface of sample coated at pH 7.5. Conclusion: AZ31 alloy coated with HA at pH 7.5 has lowest biodegradation rate and become suitable for applications in biodegradable implants. [ABSTRACT FROM AUTHOR]

In recent years, many researchers have been focusing on improving the discharge properties of AZ31 magnesium alloy for battery applications. In this paper, the equal‐channel angular pressing (ECAP) is used as a preferred way of refining the microstructure to enhance the discharge characteristics of AZ31 alloy as the anode for seawater batteries. The electrochemical discharge behaviors of ECAP‐processed AZ31 alloy are investigated along extrusion surfaces, normal cross‐sections, and transverse cross‐sections and compared with as‐cast and homogenized samples. On the basis of the findings, the anode efficiency is improved effectively through the ECAP method, with approximate isotropy in the discharge behaviors of refined AZ31 alloy. The enhanced discharge performance can be attributed to the refined grains, uniform grain sizes, and dispersed β‐Mg17Al12 after ECAP processing. [ABSTRACT FROM AUTHOR]

Evaluation of the possibility of substitution of steel part in the car body by the one made of AZ31 alloy was the main objective of the whole project. The objective of this paper was to determine the flow stress model, which accounts for the difference in the behavior of magnesium alloys during tension and compression. Tension tests on Zwick machine and compression tests on Gleeble 3800 were performed. Inverse analysis was applied to interpretation of the results of the tests. Separate numerical models for tension and compression were implemented into Abaqus software and simulations of the stamping were performed. Sensitivity of the results to the flow stress model was evaluated. [ABSTRACT FROM AUTHOR]

Multipass friction stir processing (FSP) is an effective method to produce a homogeneous microstructure and enhance the mechanical properties of magnesium (Mg) alloys. However, few studies have concentrated on the variation of corrosion resistance of Mg alloys during multipass FSP. Electrochemical alternating current (AC) impedance, polarization behavior, hydrogen evolution, and corrosion morphology were used to investigate the effects of subsequent passes on the corrosion resistance of FSP AZ31 plates. A quasi‐in‐situ observation of the growth of corrosion products was carried out to further study the corrosion behaviors of FSP AZ31 alloy. It is found that subsequent passes could further reduce the grain size of FSP AZ31 alloy and result in an increase in the hardness compared with the first pass. Moreover, subsequent passes are beneficial to the improvement in the corrosion resistance of AZ31 alloy. Pitting corrosion occurs in FSP AZ31 plates, which has not changed after subsequent passes. [ABSTRACT FROM AUTHOR]

In the present work, effects of the hot spinning process on the spinnability of AZ31 blank to a tubular shape are investigated. The hot spinning process was carried out by an electrical heating system embedded inside the mandrel. Based on the results, the hot spinning below 250 °C led to fracture. At 250 °C, although deformation imposed no fracture, localized thinning limited the spinnability of the alloy. The spinnability was, however, quite well at the temperature range of 300–450 °C. At this range of temperature, it was found that despite different initial microstructures, the initial conditions of the material, i.e., annealing and as-received conditions, have no significant effect on the spinnability. This was attributed to the complete dynamic recrystallization above 300 °C. Regarding the roller path, two paths of linear and nonlinear paths were implemented. The results show that the nonlinear path of the roller failed to produce a sound tube even above 300 °C. Finite element simulations in combination with a ductile fracture criterion were employed to analyze the low spinnability of the AZ31 blank through this path. Based on the results, this path introduces higher longitudinal strain along with the combination of intensive tensile hydrostatic and longitudinal stresses within the workpiece wall. Such deformation conditions, therefore, cause circumferential cracks at the workpiece wall. [ABSTRACT FROM AUTHOR]

Effects of various friction stir processing (FSP) variables on the microstructural evolution and microhardness of the AZ31 magnesium alloy were investigated. The processing variables include rotational and travelling speed of the tool, kind of second phase (i.e., diamond, Al2O3, and ZrO2) and groove depth (i.e., volume fraction of second phase). Grain size, distribution of second phase particle, grain texture, and microhardness were analyzed as a function of the FSP process variables. The FSPed AZ31 composites fabricated with a high heat input condition showed the better dispersion of particle without macro defect. For all composite specimens, the grain size decreased and the microhardness increased regardless of the grooved depth compared with that of the FSPed AZ31 without strengthening particle, respectively. For the AZ31/diamond composite having a grain size of about 1 μm, microhardness (i.e., about 108 Hv) was about two times higher than that of the matrix alloy (i.e., about 52 Hv). The effect of second phase particle on retardation of grain growth and resulting hardness increase was discussed. [ABSTRACT FROM AUTHOR]

The present study deals with the microstructural evolution and mechanical properties of AZ31 magnesium alloy processed throughout the novel hot constrained compression (HCC) method. AZ31 core specimens constrained by steel sleeves were compressed in the temperature range of 100 to 600 °C at 0.1 s−1 strain rate, up to true strain of 0.6 mm/mm. Similarly, simple compression (SC) tests were carried out on the AZ31 specimens to compare with the HCC ones. The AZ31 specimens failed under SC while the HCC process was successfully conducted without any sign of failure. This phenomenon is attributed to the hydrostatic pressure imposed by the sleeve steel. Moreover, microstructure characterization revealed that the greater strain accommodation in the HCC case is a result of grain refinement due to severe twinning and preceded dynamic recrystallization (DRX) at low and high temperatures, respectively. Nonetheless, the HCC process beyond 460 °C led to grain growth and coarser microstructure as compared to the SC counterparts. Mechanical properties of processed specimens were investigated at room temperature using shear punch tests. Results indicated that while shear strength and formability of HCC products are premier at low temperature deformation, they are attenuated by increasing the temperature beyond 460 °C. This phenomenon is mainly attributed to the different grain size distribution and the effects of γ precipitants. [ABSTRACT FROM AUTHOR]

Abstract The influence of VN particles on the grain refinement and mechanical properties of AZ31 magnesium alloy was investigated and the refining and reinforcing mechanisms were also discussed. These particles present remarkable grain refining efficiency on AZ31 alloy. Addition of 0.5 wt% VN into AZ31 alloy led to decreasing the average grain size from 115.7 μm to 62.4 μm. X-Ray Diffraction and energy dispersive spectroscopy showed the existence of AlN, which was in situ produced through the reaction of VN and Al. Based on the phase identification and disregistry calculation, it was confirmed that the refinement of AZ31 alloy was mainly ascribed to duplex phase composed of AlN and VN acting as nucleating substrates of α-Mg during solidification. Improved mechanical properties were achieved after addition of VN. Yield strength (YS) increased from 39.5 MPa to 50.3 MPa with addition of 1 wt% VN. 0.5 wt% VN into AZ31 alloy exhibited the best mechanical properties with a YS of 47.1 MPa, an ultimate tensile strength (UTS) of 197.4 MPa and an elongation (EI) of 17.8%, enhancing the AZ31 alloy by about 19.2%, 40.3% and 67.9%, respectively. Highlights • Remarkable refinement was achieved by adding VN particles into AZ31 alloy. • AlN were in situ produced through the reaction of VN and Al. • Duplex phases composed of AlN and VN act as nucleation substrates of α-Mg. • 0.5 wt% VN into AZ31 alloy exhibited the best mechanical properties. [ABSTRACT FROM AUTHOR]

Effect of electromagnetic stirring and solution treatment on the microstructural evolution and mechanical properties of AZ31 alloy are investigated in this study. Results show that the mechanical properties of AZ31 alloy are substantially increased after electromagnetic stirring and solution treatment. The tensile strength and elongation are 178 MPa and 19.6 % for AZ31 alloy prepared by electromagnetic stirring after solution treatment. A large number of twins and low angle boundaries are observed in the specimen after heat treatment, since the compressive stress on (101‾0) crystal plane become larger during quenching. The dislocation arrays, which produced by slip or climbing of dislocations, join together to form low angle boundaries. [ABSTRACT FROM AUTHOR]

Abstract In the present study, wear and friction behaviour of Magnesium(Mg) Metal Matrix Composite(MMC) reinforced with Silicon carbide(SiC) doped reduced graphene oxide (r-GO) nanosheets is carried over. In addition, a mathematical model is developed to predict the influence of various control factors of the Mg composites fabricated through Solvent-based powder metallurgy process. Herein SiC is doped with varying wt. % (10, 20, 30) into r-GO nanosheets and its effect over dry sliding wear is studied at constant control parameters like that of load (10N), sliding distance (1000m) and sliding velocity (1 m/s). Optimal parameter for specific wear rate (SWR) is attained by Taguchi method and the mathematical model was developed using Artificial Neural Network in order to understand the wear behaviour of developed MMC under varying parametric condition. Analysis of variance result reveals that wt.% of r-GO have major influence on SWR and sliding velocity have least effect. Occurrence of delamination wear could also be notified over the worn out surface. [ABSTRACT FROM AUTHOR]

Abstract The effects of a micro-twin lamellar structure on the mechanical properties and fracture morphology of AZ31 Mg alloy have been investigated through impact test, tensile test, and SEM observation of the failure surface. A hot-rolled AZ31 Mg alloy sheet was subjected to dynamic plastic deformation with the aim of introducing a {10 1 ¯ 2} twin lamellar structure prior to tee tensile test, because dynamic plastic deformation with a high strain rate (4–6 × 102 s–1) can activate a greater number of deformation twins in AZ31. Compared with the mechanical properties of hot-rolled and annealed Mg alloy before dynamic plastic deformation, it was found that the tensile yield stress and maximum flow stress of the AZ31 Mg alloy increase after dynamic plastic deformation, and ductility improves under tension in the range 0–30°. Based on the analyses of microstructure and fracture morphology, the phenomenon can be ascribed to the fact that the micro-twin lamellar structure can refine the matrix grain and render the microstructure more homogeneous. [ABSTRACT FROM AUTHOR]

Magnesium alloys have been used in a wide range of lightweight applications in industries such as aerospace, automotive, and personal computing due to their high strength to weight ratio; however, high chemical reactivity, poor corrosion and wear resistance limit their widespread uses in many fields. The plasma electrolytic oxidation (PEO) process can produce a protective oxide layer on the magnesium alloy to improve the mechanical properties that limit more widespread application of magnesium alloys. In this work, molybdenum disulphide (MoS 2 ) nanoparticles in concentrations ranging from 0 to 10 g/L were added into the PEO electrolyte. The aim of this study is to investigate the influence of incorporating MoS 2 nanoparticles on the microstructure, phase, as well as short- and long-term corrosion resistance, and other mechanical properties of PEO grown oxides. While the MgAl 2 O 4 phase was formed for all PEO grown oxide, the addition of MoS 2 nanoparticles in the electrolyte reduced the formation of MgAl 2 O 4 phase and enhanced the growth of MgO phase in the oxide coating. A higher hardness, 16.6 GPa, was obtained for the oxide layer grown with 10 g/L MoS 2 nanoparticles added. The corrosion resistance, wear resistance, and adhesion of the PEO grown oxide layer were strongly influenced by the porosity defect, phase, and microstructure of the coating. It appears that the addition of 2.5 g/L MoS 2 nanoparticle in electrolyte provided an oxide layer with the best short-term corrosion resistance, excellent adhesion, and the lowest wear rate; however, the addition of MoS 2 nanoparticles to the PEO electrolyte was disadvantageous to the long-term anticorrosion performance of an oxide layer because of its reduced formation of MgAl 2 O 4 phase. [ABSTRACT FROM AUTHOR]

In this study, commercial AZ31 Mg alloys were processed by equal channel angular pressing (ECAP) to study the effects of processing route and numbers of passes on hydrogen storage properties of AZ31 alloys. Furthermore, Mg-based metal matrix composites (MMCs) were fabricated by gravimetric casting of AZ31 alloy, activated carbon and Ni to investigate the effect of additives on hydrogen storage properties. The results indicated that kinetics of hydrogen uptake increased with the increasing number of pass. AZ31 processed by ECAP route B c with 8 passes had hydrogen capacity of 7.0 wt%, and demonstrated the highest grain refinement and the fastest hydrogen absorption kinetics. With the addition of 5 wt% of activated carbon and 0.5 wt% Ni, the hydrogen sorption kinetics of MMCs was enhanced and was comparable to that of the AZ31 processed by ECAP with 8 passes; however, in exchange for the improved kinetics, the hydrogen storage capacity was lowered to 6.3 wt%. To enhance hydrogen absorption kinetics, adding catalysts in the casting process could be more efficient than post-casting ECAP treatment if saving processing time is the priority. [ABSTRACT FROM AUTHOR]

The extrusion experiments were carried out under various temperatures to study the formation of longitudinal weld seams (L-seams) during porthole die extrusion process of AZ31 alloy. Moreover, 3D transient numerical modeling was established to verify the experimental findings. The results indicated that the cross section of profile can be divided into three distinct zones, namely, welding zone, transition zone, and matrix zone, and the fraction of dynamic recrystallization varied in these zones. The average grain size in welding zone increased with increasing temperature, and the profile front had coarser grains in comparison with the other parts. The profile extruded at 380 °C exhibited the highest tensile strength and elongation. Moreover, the profile front always had poor tensile properties in comparison with the other parts. Q criterion is inadequate to describe the welding quality of L-seams, while J criterion shows higher prediction accuracy. Finally, it was demonstrated that the mechanical properties of profile containing L-seams were determined not only by the welding quality but also by the microstructure near L-seams. [ABSTRACT FROM AUTHOR]

The effect of pre-strain on extension twinning behavior in an extruded AZ31 Mg alloy was investigated in this study. Pre-compression along the radial direction (RD) and subsequently compression along the extrusion direction (ED) were carried out with quasi-static strain at room temperature. The twinning evolution was observed by in-situ electron backscatter diffraction (EBSD). The results showed that profuse basal and pyramidal dislocations were introduced after a 5% strain pre-compression along the RD. The pre-strain along the RD significantly hindered the nucleation of 10 1 ¯ 2 extension twins during subsequent compression along the ED, but had little effect on the growth of 10 1 ¯ 2 extension twins. The nucleation of 10 1 ¯ 2 extension twinning at a twin boundary facilitated by twin-twin interaction was confirmed. The increase of dislocation density of twinned area was more depended on basal slip inside twins rather than twin-dislocation interaction, and the twin-twin interaction was an important source of dislocation multiplication. • The profuse dislocations are introduced into an extruded AZ31 bar by pre-compression along the radial direction. • The main dislocation types caused by pre-compression are basal and pyramidal dislocations. • The pre-introduced dislocations can hinder the nucleation of 10 1 ¯ 2 extension twins other than their growth. [ABSTRACT FROM AUTHOR]

A new organic-inorganic composite coating was generated on AZ31 alloy surface with sol-gel method to improve the anti-corrosion performance and biocompatibility of AZ31 alloy in the physiological environment. The results of electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, pH variations in modified-simulated body fluid (m-SBF) demonstrated that the silane/Mg(OH) 2 composite coating significantly enhanced the anti-corrosion ability and slowed down the degradation of AZ31 alloy under in vitro condition. Fourier-transform infrared spectroscopy (FTIR) showed that the major composition of in-situ formation layer was Mg(OH) 2 . The surface morphology, chemical and phase constitutions of the composite coating were detected using scanning electron microscopy (SEM). The results demonstrated that the composite coating was uniform and defect-free. X-ray diffraction analysis (XRD) was also employed to characterize the corrosion products of all specimens immersed in m-SBF after 30 days. MTT and ALP tests indicated that the composite coating greatly enhanced the cell proliferation and osteogenic differentiation of osteoblasts on the AZ31 alloy surface. [ABSTRACT FROM AUTHOR]

The electrochemical polymerization of polypyrrole (Ppy) films on AZ31Mg alloys was carried out using cyclic voltammetery in 0.5 M sodium salicylate solution containing 0.25 M pyrrole and different concentration of sodium fluoride (NaF). Corrosion performance of the Ppy film was assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 % NaCl solution. It was observed that Ppy coatings doped in the presence of 100 ppm NaF provide the best corrosion protection for magnesium and the corrosion potential shifted about 290 mV toward nobler potentials and decrease the corrosion current density about one order of magnitude. The surface analysis of the coatings showed that the addition of F dopant anions led to an improvement in the smoothness, thickness, and adhesion quality of the synthesized Ppy coating on the Mg surface. The scanning electron microscopy (SEM) studies of the fluoride-doped Ppy films revealed that the synthesized coating has a closely packed globular structure which was composed of nanoparticles of Ppy. [ABSTRACT FROM AUTHOR]

Traditionally, emphasis has been placed on durable, long-lasting electronics. However, electronics that are meant to intentionally degrade over time can actually have significant practical applications. Biodegradable, or transient, electronics would open up opportunities in the field of medical implants, where the need for surgical removal of devices could be eliminated. Environmental sensors and, eventually, consumer electronics would also greatly benefit from this technology. An essential component of transient electronics is the battery, which serves as a biodegradable power source. This work involves the fabrication, characterization, and modeling of a magnesium-based biodegradable battery. Galvanostatic discharge tests show that an anode material of magnesium alloy AZ31 extends battery lifetime by over six times, as compared to pure magnesium. With AZ31, the maximum power and capacity of the fabricated device are 67 μW and 5.2 mAh, respectively, though the anode area is just 0.8 cm 2 . The development of an equivalent circuit model provided insight into the battery's behavior by extracting fitting parameters from experimental data. The model can accurately simulate device behavior, taking into account its intentional degradation. The size of the device and the power it produces are in accordance with typical levels for low-power transient systems. [ABSTRACT FROM AUTHOR]

This work aims to investigate the corrosion resistance of AZ31 magnesium alloy protected by hybrid films based on tetraethylorthosilane (TEOS) and (3-glycidoxypropyl)trimethoxysilane (GPTMS) with the addition of different amounts of SiO 2 nanoparticles. The electrochemical techniques used to evaluate the corrosion resistance in 0.1 mol l l− 1 NaCl electrolyte were open circuit potential (EOC) measurements and electrochemical impedance spectroscopy (EIS), which diagrams were fitted using equivalent electrical circuits (EEC). Surface and cross-section analyses of the bare and coated samples were performed by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) before and after electrochemical studies. The results showed that the coatings protected the Mg alloy against corrosion, and that the addition of the nanoparticles improves the corrosion resistance. The morphological characterization showed, for the coated systems, the presence of corrosion products adhered to the metal surface, a process that seems to be hindered in the presence of the SiO 2 nanoparticles. The results demonstrate that an optimum amount of nanoparticles must be added to the coating in order to optimize the anticorrosion protection and that only early stages protection can be achieved. [ABSTRACT FROM AUTHOR]

The variation induced in the microstructural inhomogeneity of AZ31 alloy subjected to indirect extrusion was studied using tool steel dies with angles of 30°, 60° and 90°. Finite element modeling (FEM) of this extrusion process was also carried out to determine the metal flow, temperature evolution and effective strain distribution, which were then correlated with the observed microstructural changes. Although all extruded samples were found to have a bimodal microstructure consisting of equiaxed fine recrystallized (DRXed) grains and elongated coarse unDRXed grains, the inhomogeneity of their microstructural characteristics (i.e., DRX fraction and texture intensity) decreased in cross section with an increase in the die angle. The FEM analysis also demonstrated that a faster metal flow, higher temperature, and larger effective strain are generated in an alloy extruded with a 90° die angle, and that this enhances DRX behavior during extrusion and ultimately results in a homogeneously DRXed microstructure. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of AZ31–1Ca magnesium alloy prepared by disintegrated melt deposition (DMD) technique is compared with that in as-cast (AC) condition. The microstructure of the DMD-processed material exhibited fine grain structure with fibering and intense basal texture along the extrusion direction unlike the AC material which had large grains and near random orientation. The processing maps developed on DMD-processed alloy exhibited three domains within the following ranges of temperature/strain rates: (1) 250–360 °C/0.0003–0.01 s −1 , (2) 430–500 °C/0.0003–0.1 s −1 ; (3) 325–400 °C/0.3–10 s −1 . In the map for the AC alloy, Domain 1 occurred at higher temperature and Domain 3 was absent. Domain 1 in both conditions represents dynamic recrystallization (DRX) which is nucleated by basal+prismatic slip along with simultaneous recovery by dislocation climb controlled by lattice self-diffusion. In Domain 2 of DMD-processed alloy, grain boundary sliding and wedge cracking occurred leading to intercrystalline fracture in tension while in the AC alloy DRX has occurred to enhance the workability. In Domain 3 of DMD-processed alloy, DRX is nucleated by basal+prismatic slip with climb occurring via grain boundary self-diffusion. In the AC alloy, Domain 3 is absent since the large grain size reduced the grain boundary self-diffusion. Hot working DMD-processed alloy is best done at lower temperatures and higher strain rates (350 °C and 10 s −1 ) while the AC alloy may be processed at higher temperatures and lower strain rates (475 °C and <0.1 s −1 ). [ABSTRACT FROM AUTHOR]

Deep drawing process of AZ31 alloy sheet was conducted under crank press, which is different from conventional drawing on hydraulic press with a lower speed. The optimum drawing condition was determined by the orthogonal test to improve the drawability of AZ31 alloy. Good formed specimens were obtained and their mechanical behaviours after drawing were investigated from the point of view of microstructure evolution, texture evolution and fracture appearance. The results showed that fine grain microstructure and weaken basal texture after deformation is attributed to the twin induced dynamic recrystallisation. [ABSTRACT FROM AUTHOR]

The influence of carbon content on Al–Ti–C master alloy prepared by self-propagating high-temperature synthesis (SHS) in melt method was investigated. The results indicate that when the carbon content in the preform is insufficient, the master alloy mainly contains TiAl 3 and TiC phases. With the increasing of carbon content, the TiAl 3 phase transforms into TiC particles gradually. Further increase the carbon amount results in the formation of Al 4 C 3 phase. The master alloy with sufficient carbon, which contains Al 4 C 3 and TiC phases, is the most excellent refiner and exhibits satisfactory performance in refining AZ31 alloy. With 1.5% master alloy addition, the grain size reduced from 280 μm to 109 μm. The tensile properties were dramatically enhanced with the refinement of grain structure. The ultimate tensile strength increased from 105 MPa to 156 MPa while the elongation increased from 8.4% to 13.6%. [ABSTRACT FROM AUTHOR]

Abstract: The Taylor–Lin polycrystal elasto-viscoplastic model was employed to simulate the fatigue behavior of a strong basal textured Mg alloy (AZ31) at room temperature. Extensive tensile twinning in a compression–compression cycling mode was shown though no strain hardening occurred in the stress–strain cyclic curves. Using a volume transfer scheme, twinning was simulated where the twin variants were predefined as grains. Parts of the volumes of the mother grains were transferred to the twins by employing the minimum elastic energy criterion for selecting the two least-energy twin variants. Massive detwinning was shown by simulating through transferring parts of the volumes of the twins back to the mother grains. The modeling approach led to fair agreement with experimental twin activity measured by electron backscatter diffraction. The texture changes due to twinning were well reproduced by the model. Additionally, the stress distribution was examined in the polycrystal in the loaded and unloaded (residual) states, separately for the mother and twin grain populations. It has been found that the twins had large residual stresses which deviated in sign and distribution considerably from the residual stresses in the mother grains. This deviation is caused by the different orientations of the twins and the kinematic hardening obtained naturally with crystal plasticity. The crystal plasticity-induced kinematic hardening offers a good interpretation of the large Bauchinger effect observed in low cyclic fatigue of polycrystalline magnesium alloys. [Copyright &y& Elsevier]

Semisolid rheoforming (SSR) is a promising technology for the production of Mg wrought alloy in foundry settings. In order to realize SSR, it is necessary to characterize the grain structure evolution during slurry preparation. In this paper, slurry of AZ31 alloy was produced by a novel rheocast process known as self-inoculation method (SIM). Interrupted quenching technology was applied to investigate the primary a-Mg evolution during continuous cooling and isothermal holding. Results indicate that the initial microstructure of slurry produced by SIM is a mixture of irregular grains, which becomes ideally globular when the slurry slowly cools to 620 °C and isothermally held for at least 30 s. The local solute diffusion leads to dendritic fragmentation and forms separated particles. During prolonged holding, the particle surface gradually becomes smooth because of protuberance melting and groove advancement. Coarsening of a-Mg grains in isothermal holding was analyzed using Lifshitz-Slyozov-Wagner theory. Results suggest that coalescence is most likely the dominant coarsening mechanism in the early stage while Ostwald ripening tends to be the principal one later. The EDS results indicate that a longer holding time leads to Al solute element segregation at the grain boundaries, but Zn distribution within liquid matrix has no obvious change. [ABSTRACT FROM AUTHOR]

Abstract: Creep behavior of AZ31 magnesium alloy was investigated in temperature range of 423–498K by the localized impression creep and the conventional tensile creep testing methods, in order to evaluate the correspondence of the creep results obtained by these two testing techniques. Impression creep tests were conducted under punch stresses in the range of 125–600MPa, while tensile creep tests were performed under tensile stresses in the range 35–140MPa. According to the obtained results, the creep behavior could be divided into two stress regimes with different stress exponents and activation energy values. Based on the steady-state power-law creep relationship, the average stress exponents of about 3 and 6 were, respectively, obtained at the low- and high-stress regimes in both impression and tensile creep tests. The respective average impression creep activation energies of 96.9 and 139.2kJ/mol, at the low- and high-stress regimes, were close to 93.8 and 126.6kJ/mol determined in the tensile creep tests. Based on the obtained stress exponents and activation energies, it is suggested that the dominant creep mechanism is pipe-diffusion-controlled dislocation viscous glide in the low-stress regime, and dislocation climb in the high-stress regime. The achievement of similar creep characteristics in the employed tests implies that the localized impression creep test is capable of acquiring reliable information on the creep behavior of the present wrought Mg alloy. [Copyright &y& Elsevier]

Introducing a volume transfer scheme to handle twinning, the elasto-viscoplastic Taylor–Lin model was employed for the first time to investigate the effect of tensile twinning on the low cyclic deformation behavior of a strong basal textured Mg alloy at room temperature. tensile twinning was predominately activated together with massive de-twinning. The numerical simulation reproduced the experimental cyclic stress–strain curve and twinning activity in good agreement with experiments obtained by orientation mapping and suggested Taylor deformation mode. [ABSTRACT FROM AUTHOR]

Pre-stretching and annealing treatment was carried out to modify the microstructure of Mg–3Al–1Zn (AZ31) alloy to enhance its formability. The pre-stretched and annealed specimens exhibited lower basal texture intensities and coarser grain sizes and their Erichsen values were increased up to 65% compared with the as-received sheet. The microstructure, macrotexture, mechanical properties and formability of specimens before and after pre-stretching followed by annealing were characterized and compared. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical properties of deformed AZ31 Mg alloy at high temperature of 450–600°C with a strain rate of 3s−1 were investigated by tensile tests. The zero strength of AZ31 Mg alloy was emerged at a mushy state (600°C), while the zero ductility was appeared at 575°C, just below the solidus temperature. The abnormal coarsening of the grains happened at the temperature of 525–575°C and some molten grain boundaries were observed at 600°C. Finally the morphology and crack propagation of fracture surface were also discussed. [Copyright &y& Elsevier]

Abstract: Spark plasma sintering (SPS) technology was used to determine the appropriate conditions for SPS sintering of commercially pure magnesium as well as the magnesium alloy AZ31. It was found that the sintering temperatures of 585°C and 552°C were the most suitable sintering temperatures for the magnesium and the AZ31 alloy, respectively. Magnesium matrix and AZ31 alloy matrix composites reinforced with SiC particles were then successfully fabricated by the SPS method at sintering temperatures of 585°C and 552°C, respectively. A uniform distribution of SiC particles was observed along the boundary between matrix particles. The mechanical properties, i.e. hardness and tensile strength increased with increasing SiC content up to 10wt%. However, when the SiC content was larger than 10wt%, the tensile strength decreased due to the agglomeration of SiC particles. The agglomeration of SiC particles was found to lead to the degradation of the interfacial bonding strength between matrix and reinforcement. [Copyright &y& Elsevier]

Abstract: Very high-cycle fatigue behaviors of extruded Mg–12Gd–3Y–0.5Zr (GW123k) magnesium alloy have been investigated and compared to that of conventional extruded AZ31 magnesium alloy. Typical post-fatigue microstructure and surface morphology features are presented for both the GW123k and the AZ31 alloy in order to stand out the uniqueness of GW123k alloy. Respective fatigue damage mechanisms for both alloys were also proposed in accordance. It is found that GW123k alloy contains a large amount of precipitated particles and possesses a relatively weak texture, which give rise to its much relieved tension–compression yield asymmetry and enhanced fatigue failure resistance. The much homogenized deformation mechanism in GW123k alloy is considered the underline reason for the improvement of material''s fatigue performance. [Copyright &y& Elsevier]

Abstract: The ultra-fine grained materials produced by severe plastic deformation (SPD) methods have been widely investigated in the last decades due to the enhanced material properties such as improved tensile strength, hardness, toughness, fatigue life, and the optical and electrical related properties. The microstructure and mechanical properties of the deformed materials are strongly dependent on the amount and the homogeneity of strain achieved during the SPD processes. Accumulative back extrusion (ABE) method is a novel severe plastic deformation (SPD) technique which has been recently developed for fabrication of bulk ultra-fine structured materials. The knowledge of strain distribution and deformation behavior during ABE processing may assist the better understanding of the whole process. Therefore the present work has been conducted to examine the strain distribution and deformation behavior during ABE process through applying 3D finite element simulations with Abaqus/Explicit for different stages of deformation. In order to validate the simulation results, a grid method assessment was employed. The results demonstrated that a homogenous equivalent plastic strain of 4–5 has been gained after applying one pass ABE. In addition the results indicate that the distribution of normal strain is inhomogeneous. The microstructural observations have revealed a proper structural homogeneity after completion of an ABE cycle. [Copyright &y& Elsevier]

Abstract: Influence of chloride, sulfate and bicarbonate anions on the corrosion behavior of AZ31 magnesium alloys in dilute solutions was investigated by electrochemical measurements, whereby corrosion maps in terms of electrode potential and solution concentration were obtained. AZ31 alloy exhibited corrosion and passivation zones in those dilute solutions. The passivation zone was strongly influenced by the kinds of the solution used and the broadest zone was obtained in Na2SO4, followed by NaCl and NaHCO3. AZ31 alloy had a better corrosion resistance in Na2SO4, attributing to the lowest attack by SO4 2− and a thick corrosion product covering the surface which inhibited the corrosion attack. However, despite a much lower passivation zone in NaHCO3 as compared to the other two solutions, the corrosion rate in NaHCO3 was found to be the lowest. The values of open-circuit potential were in the passivation zone when [Cl−] was less than 0.2mol/L in NaCl, and [SO4 2−] and [HCO3 −] were both less than 0.3mol/L in Na2SO4 and NaHCO3. In the passivation zone, the formation of surface films or corrosion products on the material surface retarded further corrosion in dilute solutions. In the corrosion zone, pits grew continuously in depth and diameter in NaCl and Na2SO4 resulting in the localized corrosion through the agglomeration of pits. The formation of crystalline-like MgCO3 products exhibited the general corrosion in NaHCO3. [Copyright &y& Elsevier]

Abstract: The present work studied the formation of new phases by adding alloying additions (Ca, Sr, and Ce) in AZ31 alloy at micro-levels (approximately 0.2wt.% per element). Quantitative electron probe micro-analysis (EPMA) was used to identify the compositions of these phases; a comparison in the morphology and distribution of an identical phase in different alloy systems was made; and the thermodynamic software of FactSage™ was utilized to calculate the possible intermetallic phases during solidification. The results of EPMA showed the existence of phases other than Mg17(Al, Zn)12 and Al8Mn5 in AZ31 alloy, namely: Al2Ca, Al2Sr, Al11Ce3, Al8CeMn4, and Al2(Ca Sr); and these new phases were thermally stable at 450°C for 10h. The morphology and distribution of second phases in different alloy systems were self-consistent. These phases were well predicted by FactSage™ with recent light alloy database. [Copyright &y& Elsevier]

Abstract: Neutron diffraction data was collected, showing the strain distributions along radial, axial and hoop directions in a direct chill cast billet of AZ31 magnesium alloy. Strain measurement by neutron diffraction is a non-destructive technique that uses the diffraction of a beam of thermal neurons to determine the atomic spacing within a small gauge volume inside polycrystalline materials. The benefits of using neutrons versus X-rays lie in the increased penetration depth achieved with neutrons, which can allow measurement of the internal strains several centimeters away from the material surface. A data-processing technique was proposed to assess and remove the irregular points, and the point-to-point fluctuations were evaluated. Residual strain measurements on the as-cast billet contribute direct observation of the stress/strain state in the billet. And the results also provide the data necessary to validate a thermo-mechanical model that predicts the evolution of stress/strain during the DC casting and subsequently to investigate the cracking defects in the billets. [Copyright &y& Elsevier]

Abstract: AZ31–Ce–Gd alloys were studied and the influence of cerium (Ce) and gadolinium (Gd) on the microstructure and rolling capability of AZ31 alloy was investigated. The results indicated that the grains of AZ31 alloy were refined with Ce and Gd addition. Ce and Gd addition resulted in the formation of Al4Ce, Al2Gd and Mg3Gd. After homogenization and rolling, the Al4Ce, Al2Gd and Mg3Gd still existed. The rolling capability of AZ31 alloy was improved obviously with Ce and Gd addition. However, once Gd content increased to a certain value, the rolling capability of the modified alloy declined but still better than that of AZ31 alloy. [Copyright &y& Elsevier]

Abstract: AZ31–x gadolinium (Gd) magnesium alloys were studied and the influence of Gd on the microstructure and rolling capability of AZ31 alloy were investigated in this paper. The results indicate that the grains of AZ31 alloy are refined with Gd addition. Gd addition results in the formation of Al2Gd. After homogenization, Al2Gd still exists and it plays an important role in improving the rolling capability of alloys. The rolling capability of AZ31 alloy is improved obviously with Gd addition. After Gd was added, the homogenization time shorten more than half, with better rollability. However, once Gd content increases to a certain value, the rolling capability of AZ31 will decline. [Copyright &y& Elsevier]

Abstract: TiO2 layer was prepared as a protective coating for AZ31 magnesium alloy by the liquid phase deposition (LPD) method followed by an annealing treatment. The structural evolution and crystallization of coating brought by annealing were investigated by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD), respectively. The corrosion protection performance was evaluated in a three-electrode electrochemical examination system. The anatase TiO2 layer shows evident corrosion resistance. With the increase of the annealing temperature and prolongation of annealing time, the anticorrosion property was improved. The improvements of the anticorrosion properties were related with the structural evolution of the coating brought by the annealing treatment. [Copyright &y& Elsevier]

Abstract: Thermal behavior and heat transfer during equal channel multi-angular pressing process of AZ31 alloy at room temperature were analyzed by using the 3-dimensional finite volume method. The simulations were carried out at different frictional conditions (friction factor m =0, 0.1 and 0.2), pressing speeds (v =2 and 20mm/s), and pressing routes (A, B and C). The pressing speed influences more on the temperature rise of the AZ31 sample than the pressing route and friction condition. The initial temperature 293K of the AZ31 alloy was increased up to 395K for 20mm/s pressing speed during the pressing. [Copyright &y& Elsevier]