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This study investigates the effects of zinc (4 wt.%) and severe plastic deformation on the mechanical properties of AZ61 magnesium alloy through the stir-casting process. Severe plastic deformation (Equal Channel Angular Pressing (ECAP)) has been performed followed by T4 heat treatment. The microstructural examinations revealed that the addition of 4 wt.% Zn enhances the uniform distribution of β-phase, contributing to a more uniformly corroded surface in corrosive environments. Additionally, dynamic recrystallization (DRX) significantly reduces the grain size of as-cast alloys after undergoing ECAP. The attained mechanical properties demonstrate that after a single ECAP pass, AZ61 + 4 wt.% Zn alloy exhibits the highest yield strength (YS), ultimate compression strength (UCS), and hardness. This research highlights the promising potential of AZ61 + 4 wt.% Zn alloy for enhanced mechanical and corrosion-resistant properties, offering valuable insights for applications in diverse engineering fields. [ABSTRACT FROM AUTHOR]

AZ61 magnesium alloy metal matrix composites (MMCs) with different weight percentages (0, 1 and 2) of micro-silicon carbide particles (SiCp) were fabricated using stir casting method. Effects of SiCp on the microstructural distributions, mechanical and fatigue properties, and fracture surfaces have been investigated. The microstructural observations of as-cast MMCs unveil the existence of primary α-Mg phase and the presence of large amount of β-Mg17Al12 secondary phase at grain boundary. The specimens are subjected to homogenization heat treatment at 410 °C for 24 h; the β-Mg17Al12 phases are significantly dissolved in the matrix grain boundaries which enhance the ductility and decrease the hardness compared with the as-cast materials. The addition of SiCp reinforcement led to improved yield strength (YS) and ultimate tensile strength (UTS) of AZ61/SiCp composite compared to the unreinforced alloy. The maximum values of YS and UTS have been attained at AZ61/1wt%SiCp composites. The enhancement of YS and UTS was due to the presence of a uniformly distributed reinforced SiCp, which depends on grain refinement of the matrix and strong interfacial bonding between the matrix and reinforcement. In the case of fatigue test results, the addition of SiCp reduced the fatigue life and strength of AZ61 alloy composite. However, addition of 1wt%SiCp showed good mechanical and fatigue properties compared to pure AZ61 magnesium alloy and AZ61/2wt%SiCp composite. Furthermore, the effects of addition of SiCp on the mechanical and fatigue properties of the composite were confirmed by using the scanning electron microscope observation of fracture surfaces. [ABSTRACT FROM AUTHOR]

In this study, AZ61 alloy processed by equal channel angular pressing (ECAP) method, is presented. This research seeks to find out the relationship that exists between the microstructure of the AZ61-magnesium alloy doped with SiC and Ni and processed by ECAP in terms of hydrogen storage properties. The results indicate that grain size reduces nearly 10 times after 4 passes of ECAP. Homogeneous distribution of the SiC in the metal matrix composite (MMC) and dynamic recrystallization are also observed. There is a gradual reduction in the grain size when the number of ECAP passes are increased. This microstructural refinement induced by ECAP improves the storage capacity and reaction kinetics of the alloy. Besides, the addition of Ni catalyst achieves faster absorption and desorption kinetics. However, it does not change its capacity. Ni reacts with Mg to form an intermetallic, which is hydrogen-absorbing, which in turn, catalyzes the reaction. Apart from introducing defects, the ECAP process also produces Mg/Al intermetallic, which acts catalytically. It is shown that SiC-doped AZ61-magnesium alloy can absorb and desorb 6.8 wt% H 2 at 648 K and 50 atm. • AZ61 with SiC and Ni additives prepared by gravity stir casting method. • Dispersion characteristics of the particles influences the rate limiting factors. • AZ61-1 wt%SiC achieves a hydrogen capacity of 6.8 wt%. • Performance declines to 6.5 wt% when Ni catalyst is added. • Combining SiC and Ni shows improved kinetics. [ABSTRACT FROM AUTHOR]

Abstract The response surface methodology in the design of experiments (DOE) wizard and Gurson-Tvergaard-Needleman (GTN) model were employed to estimate the optimum GTN damage parameters and to validate their significant effects respectively on the ductile fracture behavior of ECAP deformed AZ61 magnesium alloy. Hollomon's flow stress was applied to identify uniform deformation and non-uniform deformation regions to investigate the void nucleation and coalescence processes separately. The significance of statistical results was evaluated with the analysis of variance (ANOVA) based on P-values and coefficients of determination (R 2). Correspondingly, the contributions of ECAP plastic deformation and the corresponding local plasticity (damage progresses) on the progress of GTN ductile fracture damage parameters were studied. Desirability function was used to show the significance of individual and interaction effects of optimum initial damage parameters on the respective response variables. By using response surface methodology, the optimum GTN damage parameters were determined at the corresponding positions of each critical response variables. Results also showed that varying both stress triaxiality and damage variables simultaneously can greatly affect the curve fitting process of experimental, simulation and GTN model curves. However, at constant stress triaxiality condition, the GTN model curve was observed perfectly fitting with the tensile test curve. [ABSTRACT FROM AUTHOR]

Cast commercial AZ61 magnesium alloys were processed through equal channel angular pressing (ECAP) and were comminuted into chips by filing with a rasp in order to measure their hydrogen storage properties. The effects of the number of ECAP passes and the processing route of ECAP on the hydrogen storage properties of AZ61 magnesium alloys were investigated. ECAP processing led to severe dynamic recrystallization and grain refinement of the AZ61 alloys. Of the analyzed samples, the AZ61 alloy processed via the Bc ECAP route with eight passes exhibited the smallest grain size, the fastest hydrogen absorption and desorption rates, and the highest gravimetric hydrogen storage capacity of 6.2 wt%. [ABSTRACT FROM AUTHOR]

In this paper, solution and ageing heat treatment processes were used to improve microplastic deformation behaviors of as-cast SiCp/AZ61 magnesium metal matrix composites (Mg MMCs) fabricated by stir casting method. Higher percentages of SiC particle reinforcements showed higher microhardness values. Ageing heat treatment process was seen significant on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC which induced lower microhardness value. At the 12 h ageing of 2 wt% SiCp/AZ61 Mg MMC the formations of particle free regions and discontinuous secondary phases were observed. For a higher ageing time, the secondary phases distribution became continuous and laminar structure. The addition of 5 wt% SiC particles resulted in the formation of Mg 2 Si phase throughout the whole heat treatment processes. The addition of SiC particles reinforcements increased the phase heterogeneity during ageing heat treatment processes. XRD patterns revealed the presence of nanocrystalline MgSiO 3 phase on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC. Using reference intensity ration (RIR) method a 51.6% of MgSiO 3 phase was determined which can cause the formation of microplastic deformation behavior. And also, the maximum average crystallite size, compressive microstrain and microcrack-free phase boundaries were observed on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC. [ABSTRACT FROM AUTHOR]

We studied the hydrogen storage properties of commercial AZ31 and AZ91 magnesium alloys with refined microstructure. Various processing techniques, such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM), were utilized to modify the microstructure and phase composition of the alloys. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical digital microscopy (ODM) were utilized to characterise the microstructure and phase transformations during the hydrogen absorption/desorption processes. The isothermal kinetics are measured by a Sieverts'-type apparatus at the temperature of 350 ℃. In the ECAP process, the AZ31 alloy had a slightly higher storage capacity and faster absorption kinetics, absorbing 6.0 wt% (6.6 wt% - maximum) of hydrogen in less than 12 min. In the HEBM process, AZ91 absorbed 6.5 wt% of hydrogen and desorbed it in 347 ± 13 s, a faster rate than AZ31. The pressure–composition isotherms of all studied alloys at a temperature of 300 °C were determined. The processed alloys exhibited no pressure hysteresis. The microstructure of bulk samples and the morphology of prepared powders were shown to affect their hydrogenation behaviour. The activation energies for hydrogen desorption were 119 ± 2 kJ/mol for AZ31 alloy processed by ECAP and 128 ± 3 kJ/mol for AZ91 alloy processed by HEBM, which are significantly lower than the activation energy values of pure Mg hydride. • Hydrogen storage properties of commercial AZ31 and AZ91 alloys are studied. • The ECAP and HEBM processes were employed to enhance hydrogen storage performance. • Both processes significantly improved the kinetic and thermodynamics properties. • The processed alloys exhibited no pressure hysteresis • The activation energies reduced to 119 ± 5 kJ/mol for AZ31-ECAP and 128 ± 5 kJ/mol for AZ91-HEBM. [ABSTRACT FROM AUTHOR]

The process engineering of Mg alloys is nevertheless compromised due to their relatively poor mechanical properties. To address some of these difficulties, metal-matrix composites (MMCs) of Mg-alloys have been investigated for sometime. In the present work, small amounts (up to 1 wt%) of WS 2 nanotubes are mixed with Mg-alloy (AZ31) using melt-stirring process above 700 °C. The new MMC nanocomposites exhibit much superior mechanical properties vis a vis the pristine alloy. Metallographic investigation demonstrates that the average grain size has been reduced in inverse proportion to the added amounts of nanotubes up to 1 wt%. Physical considerations suggest that the main mechanism responsible for the reinforcement effect lies in the mismatch between the thermal expansion coefficients of the metal and the nanotubes. This mismatch induced large density of dislocations in the grain boundaries in the vicinity of the nanotube-matrix interface, which obstruct the crack propagation. [ABSTRACT FROM AUTHOR]

The influence of trace amounts of Sn on the formation of the LPSO phase and mechanical properties of Mg–RE–Zn alloys is discussed. Results show that trace Sn has no effect on the phase category of the alloy. After annealing, however, Sn-doped alloys show a high density of the lamellar-shaped LPSO phase. After Sn addition, the strength of the alloy is enhanced but its elongation is reduced. [ABSTRACT FROM AUTHOR]

Magnesium alloys are attractive for the production of lightweight parts in modern automobile and aerospace industries due to their advanced properties. Their mechanical properties are usually enhanced by the incorporation with reinforcement particles. In the current study, reinforced AZ31 magnesium alloy was fabricated through the addition of bulk Al and the incorporation of SiC nanoparticles using a stir casting process to obtain AZ31-SiC nanocomposites. Scanning electron microscope (SEM) investigations revealed the formation of Mg17Al12 lamellar intermetallic structures and SiC clusters in the nanocomposites. Energy dispersive spectroscopy (EDS) detected the uniform distribution of SiC nanoparticles in the AZ31-SiC nanocomposites. Enhancements in hardness and yield strength (YS) were detected in the fabricated nanocomposites. This behavior was referred to a joint strengthening mechanisms which showed matrix-reinforcement coefficient of thermal expansion (CTE) and elastic modulus mismatches, Orowan strengthening, and load transfer mechanism. The mechanical properties and wear resistance were gradually increased with an increase in SiC content in the nanocomposite. The maximum values were obtained from nanocomposites containing 1 wt% of SiC (AZ31-1SiC). AZ31-1SiC nanocomposite YS and hardness were improved by 27% and 30%, respectively, compared to AZ31 alloy. This nanocomposite also exhibited the highest wear resistance; its wear mass loss and depth of the worn surface decreased by 26% and 15%, respectively, compared to AZ31 alloy. [ABSTRACT FROM AUTHOR]

Abstract: The effects of Mn substitution for Mg on the microstructure, mechanical properties, and corrosion behavior of Mg69−xZn27Ca4Mnx (x=0, 0.5 and 1at.%) alloys were investigated using X-ray diffraction, compressive tests, electrochemical treatments, and immersion tests, respectively. Microstructural observations showed that the Mg69Zn27Ca4 alloy was mainly amorphous. The addition of Mn decreases the glass-forming ability, which results in a decreased strength from 545MPa to 364MPa. However, this strength is still suitable for implant application. Polarization and immersion tests in the simulated body fluid at 37°C revealed that the Mn-doped Mg–Zn–Ca alloys have significantly higher corrosion resistance than traditional ZK60 and pure Mg alloys. Cytotoxicity test showed that cell viabilities of osteoblasts cultured with Mn-doped Mg–Zn–Ca alloys extracts were higher than that of pure Mg. Mg68.5Zn27Ca4Mn0.5 exhibits the highest bio-corrosion resistance, biocompatibility and has desirable mechanical properties, which could suggest to be used as biomedical materials in the future. [Copyright &y& Elsevier]

This study involves the investigation of the mechanical properties of the extruded tube products with reinforced silicon carbide particulates (SiCp). Finite element analyses are firstly conducted to analyze the plastic flow of the magnesium alloy AZ61 within the die and to investigate the effects of initial billet temperatures on the extrusion loads and final product temperatures. AZ61/SiCp composite ingots reinforced with different weight fractions of SiCp are fabricated by a melt stirring technique. A specially designed die set is used in the extrusion experiments to obtain tubes with uniform thickness distribution in the circumferential direction. The extruded tubes are also heat treated to obtain even better mechanical properties. Finally, tensile tests, Vickers microhardness, tests and microstructure observation are performed on the billets and extruded tubes of AZ61 monolithic alloys and AZ61/SiCp composites. A much smaller grain size and higher tensile strength and hardness are achieved for the extruded AZ61/SiCp composite tubes. [ABSTRACT FROM AUTHOR]

In this work, AZ91 magnesium alloy reinforced with a low fraction (0–1) wt.% tungsten disulfide(WS 2) microparticles have been fabricated using stir casting method. Effects of WS 2 microparticles on mechanical properties, microstructure, and their correlation have been analyzed. The microstructure of composites has been investigated by scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffractometer. Results indicate that density, hardness, ultimate tensile strength (UTS), and tensile ductility have a direct relation with reinforcement (WS 2) contents and has optimal value for 0.6 wt% WS 2 /AZ91 composites then slightly decrease afterward. The UTS and hardness of 0.6 wt%WS 2 /AZ91 were increased by 23.23% and 10.65% respectively with respect to monolithic AZ91. The ultimate compressive strength(UCS) is directly related with WS 2 concentration and 10.07% enhancement in UCS for 1 wt%WS 2 /AZ91 composites have been noted. The trend is interlinked with density and hardness of composites. SEM images depict, WS 2 micro-particles suppress β-Mg 17 Al 12 precipitates, refine the microstructure and enhance the grain size resulting in an increase in mechanical properties. The improvement in microstructure and mechanical properties is attributed to the dispersion of WS 2 particles which hinder the grain growth. The increase in porosity has causes the decrease in mechanical behavior of 1 wt%WS 2 /AZ91. Twin boundary fracture has been found major fracture phenomenon in fractured WS 2 /AZ91 surfaces. • WS 2 /AZ91 metal matrix composites have been manufacture by stir casting method. • Density and porosity of WS 2 /AZ91 composites has been assessed. • Mechanical behavior under compression and tension has been analyzed. • Effect of WS 2 on microstructure has been investigated. • Fracture behavior of composites has been studied. [ABSTRACT FROM AUTHOR]

The tribological behavior of AZ31 Mg alloy reinforced with multiwall carbon nanotubes (MWCNTs) was studied through experiments on a ring-on-block wear testing apparatus against 45C steel. The composites were successfully fabricated using stir-casting processing with different percentages of MWCNTs and then age hardened for 10 h. The effect of the various concentrations of MWCNTs on the microstructures, tribological properties, and wear mechanisms of the composites were systematically examined by scanning electron microscopy (SEM). With increasing percentage content of MWCNTs, the wear rate and the coefficient of friction decreased, which is attributed to the microhardness and self-lubricating properties of the MWCNTs. The microstructure characterization results established different mechanisms—specifically, abrasion, oxidation, and delamination—and very small plastic deformation. • Magnesium alloy AZ31 reinforced with multiwalled carbon nanotubes was fabricated using stir casting method. • Samples were homogenized for 24 h at 400C0 and then aged for 10 h at 200C0 temperature. • Wear tests for as-cast and aged composites were performed using Ring on Block wear apparatus under dry and wet conditions and mass wear loss and coefficient of friction was determined. • Worn surfaces were analyzed using scanning electron microscope for wear mechanism analysis. [ABSTRACT FROM AUTHOR]

The large differential-thermal extrusion (LDTE) process, a novel approach for efficiently fabricating a high-strength Mg-10.3Gd-4.4Y-0.9Zn-0.7Mn (wt.%) alloy, is introduced in this work. Unlike typical isothermal extrusion processes, where the ingot and die temperatures are kept the same, LDTE involves significantly higher ingot temperatures (~120 °C) compared to the die temperature. For high-strength Mg-RE alloys, the maximum isothermal extrusion ram speed is normally limited to 1 mm/s. This research uses the LDTE process to significantly increase the ram speed to 2.0 mm/s. The LPTE-processed alloy possesses a phase composition that is similar to that of isothermal extruded alloys, including α-Mg, 14H-type long-period stacking ordered (LPSO) and β-Mg5(Gd, Y) phases. The weakly preferentially oriented α-Mg grains in the LDTE-processed alloy have < 10 1 ¯ 0 > Mg//ED fibrous and <0001>Mg//ED anomalous textures as their two main constituents. After isothermal aging, high quantitative densities of prismatic β′ and basal γ′ precipitates are produced, which have the beneficial effect of precipitation hardening. With a yield tensile strength of 344 MPa, an ultimate tensile strength of 488 MPa, and an elongation of 9.7%, the alloy produced by the LDTE process exhibits an exceptional strength–ductility balance, further demonstrating the potential of this method for efficiently producing high-strength Mg alloys. [ABSTRACT FROM AUTHOR]

A high-strength Mg-8.8Gd-3.8Y-1.0Zn-0.7Mn (wt%) alloy hollow profile with complex cross-section was successfully fabricated through porthole die extrusion, and its weld seam was analyzed for microstructure and element distribution to investigate the impact of solid-state bonding. The weld seam displayed a homogeneous magnesium grain structure and a precipitation-free zone. The diffusion behavior of alloying elements during solid-state bonding significantly affected the microstructure of the weld seam, with Gd and Y atoms diffusing towards the outside of the weld region. The hollow profile exhibited favorable mechanical properties, with an ultimate tensile strength (UTS) of 470 MPa, a tensile yield strength (TYS) of 309 MPa, and an elongation (EL) of 7.4%, and showed a minor negative effect from the weld seam. • High-strength Mg-Gd-Y-Zn-Mn alloy hollow profiles showed a favorable metallurgical bond in the weld seam with a homogeneous magnesium grain structure and no microvoids. • Alloying element diffusion influenced the weld seam microstructure, resulting in lower concentrations of Gd and Y in the weld region, while Zn and Mn showed a more uniform distribution. • The presence of the weld seam had minimal impact on the overall mechanical properties of the hollow profiles, which retained superior mechanical performance. [ABSTRACT FROM AUTHOR]

High-performance as-extruded and peak-aged Mg-9.2Gd-3.3Y-1.2Zn-0.9Mn (wt%) alloys have been fabricated by semi-continuous casting, heat-treating, extruding and ageing processes. The effects of different heat treatments on the microstructure and mechanical properties have been investigated. Lamellar and bulk-shaped 14H-type long-period stacking ordered (LPSO) phase and few RE-rich (RE: rare earth element) particles form by different heat treatments. After hot extrusion, the heat-treated alloy with bulk-shaped LPSO phase exhibits an equal-axial microstructure, while the heat-treated alloy with lamellar LPSO phase across the grains shows bimodal grain microstructure consisting of fine equal-axial grains and coarse deformed grains. The more profuse lamellar LPSO phase in heat-treated alloy generates higher volume fraction of deformed grains and finer equal-axial grains, hence leads to higher strength but lower ductility. After ageing, the alloy with profuse LPSO and β′ phases achieves the superior mechanical properties with ultimate tensile strength (UTS) of 525 MPa, tensile yield strength (TYS) of 420 MPa and elongation to failure (EL) of 6.3%. The alloy strengthening is mainly attributed to the bimodal grain microstructure, LPSO phase, Mg 5 Gd (β) phase and β′ phase. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and mechanical properties of Mg–8.40Gd–5.30Y–1.65Zn–0.59Mn (wt%) alloy were investigated in this study. The phase composition of the alloy involved an α-Mg matrix and long-period stacking ordered phases of Mg12Zn(Y,Gd) with some eutectic phases. After aging at 200°C for 50h following extrusion (extrusion ratio= 11:1, extrusion temperature=400°C), the alloy achieved high strength (ultimate tensile strength=∼500MPa, tensile yield strength=∼322MPa) and good ductility (elongation=∼10.0%) and exhibited excellent comprehensive mechanical properties. These properties could be attributed to the numerous plate-shaped β′ phase precipitates in the α-Mg matrix, as well as the small dispersed block-shaped long-period stacking ordered phases along the grain boundaries. [Copyright &y& Elsevier]

Abstract: This study investigates the effects of heat treatment on the morphology of long-period stacking ordered phase (LPSO) and the corresponding mechanical properties of Mg–9Gd–xEr–1.6Zn–0.6Zr (1–4wt%) using optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, and tensile tests. The microstructure analysis of the as cast alloys showed that the volume fraction of the (Mg, Zn)3(Gd, Er) phase increased with increasing Er content. The (Mg, Zn)3(Gd, Er) phase in grain boundaries transformed into the 14H-LPSO phase Mg12Zn(Gd, Er) after heat treatment between 400°C and 515°C. The bulk shaped LPSO phases distributed along the grain boundaries produced isometric crystal grains in and enhanced the ductility of the as-extruded alloys. However, the lamellar LPSO phases precipitating in the grain interior induced strip-shaped grains in and improved the strength of the as-extruded alloys. [Copyright &y& Elsevier]