Mechanical and bio-corrosion properties of quaternary Mg–Ca–Mn–Zn alloys compared with binary Mg–Ca alloys

Binary Mg–xCa alloys and the quaternary Mg–Ca–Mn–xZn were studied to investigate their bio-corrosion and mechanical properties. The surface morphology of specimens was characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results of mechanical properties show that the yield strength (YS), ultimate tensile strength (UTS) and elongation of quaternary alloy increased significantly with the addition of zinc (Zn) up to 4 wt.%. However, further addition of Zn content beyond 4 wt.% did not improve yield strength and ultimate tensile strength. In contrast, increasing calcium (Ca) content has a deleterious effect on binary Mg–Ca alloys. Compression tests of the magnesium (Mg) alloys revealed that the compression strength of quaternary alloy was higher than that of binary alloy. However, binary Mg–Ca alloy showed higher reduction in compression strength after immersion in simulated body fluid. The bio-corrosion behaviour of the binary and quaternary Mg alloys were investigated using immersion tests and electrochemical tests. Electrochemical tests shows that the corrosion potential (E_corr) of binary Mg–2Ca significantly shifted toward nobeler direction from −1996.8 to −1616.6 mV_SCE with the addition of 0.5 wt.% manganese (Mn) and 2 wt.% Zn content. However, further addition of Zn to 7 wt.% into quaternary alloy has the reverse effect. Immersion tests show that the quaternary alloy accompanied by two secondary phases presented higher corrosion resistance compared to binary alloys with single secondary phase. The degradation behaviour demonstrates that Mg–2Ca–0.5Mn–2Zn alloy had the lowest degradation rate among quaternary alloys. In contrast, the binary Mg–2Ca alloy demonstrated higher corrosion rates, with Mg–4Ca alloy having the highest rating. Our analysis showed the Mg–2Ca–0.5Mn–2Zn alloy with suitable mechanical properties and excellent corrosion resistance can be used as biodegradable implants.     

A high strength and ductility Mg–Zn–Al–Cu–Mn magnesium alloy

A high strength Mg–8.0Zn–1.0Al–0.5Cu–0.5Mn (wt.%) magnesium alloy with outstanding ductility was developed using a common casting technique and heat treatment. The microstructure of the as-cast alloy is composed of α-Mg, MgZn, MgZnCu and Al–Mn phases. After the solution treatment and subsequent two-step aging treatment, the yield strength (YS), ultimate tensile strength (UTS) and elongation of the alloy at peak hardness reach 228 MPa, 328 MPa and 16.0% at room temperature, respectively. The comprehensive mechanical properties of the alloy are superior to almost all other high performance casting Mg alloys.     

Effects of Ca addition on as-cast microstructure and mechanical properties of Mg–3Ce–1.2Mn–1Zn (wt.%) magnesium alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg–3Ce–1.2Mn–1Zn (wt.%) alloy were investigated by using optical and electron microscopes, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that the additions of 0.3–0.9 wt.%Ca to the Mg–3Ce–1.2Mn–1Zn alloy do not cause an obvious change in the morphology and distribution for the Mg₁₂Ce phase in the alloy. However, the grains and secondary dendrite arm spacings of the Ca-containing alloys are refined, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the grain size and secondary dendrite arm spacings to gradually decrease, respectively. In addition, the additions of 0.3–0.9 wt.%Ca to the Mg–3Ce–1.2Mn–1Zn alloy can effectively improve the as-cast tensile and creep properties of the alloy, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the as-cast tensile and creep properties to gradually increase, respectively.     

Anisotropy of thermal conductivity and mechanical properties in Mg–5Zn–1Mn alloy

The microstructure, texture, thermal conductivity and mechanical properties of the as-extruded Mg–5Zn–1Mn (ZM51) magnesium alloy were investigated on specimens with the extrusion direction (ED), the transverse direction (TD) and the normal to the extrude plane (ND), respectively. The results indicated that the thermal conductivity of ZM51 alloy at room temperature is 125 (W/m K), almost twice as high as other conventional commercial magnesium alloys, such as Mg–Al series and Mg–RE series. The effect of texture on anisotropy of mechanical properties and thermal conductivity has been analyzed. The strong crystallographic texture typical of Mg alloys results in much higher yield strength and tensile strength (UTS) in the extrusion direction, but higher ductility and thermal conductivity in the transverse direction.     

Effect of Y on the bio-corrosion behavior of extruded Mg–Zn–Mn alloy in Hank's solution

The bio-corrosion properties of Mg–Zn–Mn alloys with and without Y in Hank's solution at 37 °C were investigated by using electrochemical test and electrochemical impedance spectra (EIS). The results of open circuit potential (OCP) and polarization tests indicated that Y could reduce the cathodic current density. A passivative stage appeared in the Tafel curve of the Y containing magnesium alloy, indicating that a passivative film was formed on the surface of the Y containing magnesium alloy. EIS results showed that the Y containing alloy had higher charge transfer resistance and film resistance, but lower double layer capacity than the alloy without the Y element. The surface reaction product identification by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the surface corrosion products were hydroxide and phosphate (Mg₃Ca₃(PO₄)₄) for Mg–Zn–Mn alloy and phosphate (MgNaPO₄) for the Y containing Mg–Zn–Mn alloys. The XPS results also showed that a Y₂O₃ protective film was formed on the surface of the Y containing magnesium alloy which contributed mainly to the low cathodic current density and the high resistance.     

Effect of Zn addition on hot tearing behaviour of Mg–0.5Ca–xZn alloys

The influence of Zn addition (0, 0.5, 1.5, 4.0 and 6.0 wt.%) on hot tearing behaviour of Mg–0.5 wt.% Ca alloy was investigated using a constrained rod casting (CRC) apparatus. The effects of mould temperature and grain refinement on the hot tearing susceptibility (HTS) were studied. Hot tears were observed with 3D X-ray tomography and the tear volumes were quantified. Results show that the Zn addition increases the HTS of Mg–0.5Ca alloys. At a mould temperature of 250 °C, all alloys investigated except Mg–0.5Ca–6Zn alloy show severe HTS. An increase in the mould temperature from 250 °C to 450 °C did not reduce the HTS in Mg–0.5Ca–1.5Zn and Mg–0.5Ca–4Zn alloys. Among all the investigated alloys, Mg–0.5Ca–4Zn alloy exhibits severe HTS as it completely broke away from the sprue–rod junction. The HTS of alloys was well correlated with the susceptible temperature range (ΔT_s). An increase in ΔT_s increased the HTS. The hot tears propagated along the grain boundaries through liquid film rupture. Grain refinement by Zr addition improved the hot tearing resistance of Mg–0.5Ca–4Zn alloy as the fine grain structure facilitated the easy feeding of liquid into the last area of solidification and accommodated the developed strain more effectively.     

Hot deformation and processing map of an as-extruded Mg–Zn–Mn–Y alloy containing I and W phases

The hot deformation characteristics of an as-extruded ZM31 (Mg–Zn–Mn) magnesium alloy with an addition of 3.2 wt.% Y, namely ZM31 + 3.2Y, have been studied via isothermal compression testing in a temperature range of 300–400 °C and a strain rate range of 0.001–1 s^− 1. A constitutive model based on hyperbolic-sine equation along with processing maps was used to describe the dependence of flow stress on the strain, strain rate, and deformation temperature. The flow stress was observed to decrease with increasing deformation temperature and decreasing strain rate. The deformation activation energy of this alloy was obtained to be 241 kJ/mol. The processing maps at true strains of 0.1, 0.2, 0.3 and 0.4 were generated to determine the region of hot workability of the alloy, with the optimum hot working parameters being identified as deformation temperatures of 340–500 °C and strain rates of 0.001–0.03 s^− 1. EBSD examinations revealed that the dynamic recrystallization occurred more extensively and the volume fraction of dynamic recrystallization increased with increasing deformation temperature. The role of element Y and second-phase particles (I- and W-phases) during hot compressive deformation was discussed.     

Mechanical properties and phase composition of potential biodegradable Mg–Zn–Mn–base alloys with addition of rare earth elements

Mechanical properties and creep resistance of the MgY4Zn1Mn1 alloy in the as cast as well as in the T5 condition were compared to those of the MgCe4Zn1Mn1 alloy in the same conditions. Yield tensile stress and ultimate tensile strength of the MgY4Zn1Mn1 alloy are slightly better in the temperature range 20 °C–400 °C than these of the MgCe4Zn1Mn1 alloy. Better thermal stability of ultimate tensile strength was observed in the T5 treated MgCe4Zn1Mn1 alloy than in this material in the as cast condition. An outstanding creep resistance at 225 °C–350 °C found in the MgY4Zn1Mn1 alloy is due to the existence of the 18R long period stacking structure persisting in this alloy even a long heat treatment of 500 °C/32 h. No similar stacking effects happen when Ce substitutes Y in approximately the same concentration. The creep resistance deteriorates considerably in the MgCe4Zn1Mn1 alloy. Rectangular particles of the equilibrium Mg₁₂Ce phase dominate in the microstructure of as cast as well as of high temperature heat-treated MgCe4Zn1Mn1 alloy. A population of small oval particles containing Mg and Zn develops additionally during annealing of this alloy. These particles pin effectively dislocations and can be responsible for the better thermal stability of the T5 treated material.     

Microstructure,mechanical and bio-corrosion properties of Mn-doped Mg–Zn–Ca bulk metallic glass composites

The effects of Mn substitution for Mg on the microstructure, mechanical properties, and corrosion behavior of Mg_69 ? xZn₂₇Ca₄Mn_x (x = 0, 0.5 and 1 at.%) 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 545 MPa to 364 MPa. 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. Mg_68.5Zn₂₇Ca₄Mn_0.5 exhibits the highest bio-corrosion resistance, biocompatibility and has desirable mechanical properties, which could suggest to be used as biomedical materials in the future.     

In situ synthesis method and damping characterization of magnesium matrix composites

Magnesium matrix composites reinforced with 8 wt% TiC was in situ synthesized using remelting and dilution technique. X-ray diffraction analysis revealed the presence of TiC phase in sintered block and magnesium matrix composites. Uniform distribution of fine TiC particulates in matrix material was obtained through microstructure characterization. The results of damping characterization revealed that damping capacity of materials is independent of frequency, but dependent on strain and temperature. There were damping peak in damping–strain curve, which is due to the foul and tangle of dislocations. There were two damping peaks at damping–temperature curve under respective temperature of 130 °C and 240 °C. The former damping peak of magnesium matrix composites is due to dislocation motion, and the latter is due to interface and grain boundary sliding. Generally, damping capacity of magnesium matrix composites is higher than that of AZ91 magnesium alloy, which is due to the addition of TiC particulates.     

Development of high-performance quaternary LPSO Mg–Y–Zn–Al alloys by Disintegrated Melt Deposition technique

In the present study, new quaternary MgY_1.65Zn_0.74Al_0.53 and MgY_3.72Zn_1.96Al_0.45 alloys (wt.%) were synthesized employing the Disintegrated Melt Deposition (DMD) casting technique followed by hot extrusion. Microstructural characterization revealed the presence of 14H long-period stacking ordered structure (LPSO) and Mg₄Y₂ZnAl₃ phases aligned along the direction of extrusion in both alloys. Refined grains (⩽5 μm) due to the effect of dynamic recrystallization (DRX) were also observed to co-exist with larger worked grains (⩾20 μm) in the extruded microstructures. Compared to monolithic Mg, significant increase in the microhardness (∼67–88%), tensile yield strength (∼245–290%) and ultimate tensile strength (∼113–144%) were observed in the Mg–Y–Zn–Al alloys. Despite the significant increase in strength of materials, failure strains of both Mg–Y–Zn–Al alloys were comparable to monolithic Mg. Ignition temperatures of both Mg–Y–Zn–Al alloys were found to outperform commercially available AZ31, AZ80 and WE43 (high-temperature) Mg alloys, and the highest ignition temperature of 770 °C was achieved in the MgY_3.72Zn_1.96Al_0.45 alloy.     

Interface microstructure and mechanical properties of zinc–aluminum thermal diffusion coating on AZ31 magnesium alloy

The zinc–aluminum (Zn–Al) alloy coating with excellent wear and corrosion resistance was fabricated on the surface of magnesium substrate (AZ31) using thermal diffusion technique. The microstructure, phase constitution and chemical composition were investigated. The experimental observation exhibited that the interfacial microstructures were composed of network eutectic structures and lamellar eutectoid structures at heating temperature of 350 °C for holding time of 30 min under 0.1 MPa in a vacuum of 10⁻³ Pa. X-ray diffraction (XRD) pattern analysis identified that α-Mg, Mg₇Zn₃ and MgZn phases were formed in the diffusion layer. The interdiffusion of Mg and Al atoms were restricted by Mg–Zn intermetallic compounds (IMCs). The value of microhardness at the diffusion layer increased due to the formation of Mg–Zn eutectic phases. This technique is beneficial to improving poor wear and corrosion resistance of magnesium alloy.     

Microstructural change and precipitation hardening in melt-spun Mg–X–Ca alloys

Mg–Al–Si–Ca and Mg–Zn–Ca base alloys were rapidly solidified by melt spinning at the cooling rate of about a million K/s. The melt-spun ribbons were aged in the range 100–400°C for 1 h. The effect of additional elements on microstructural change and precipitation hardening after heat treatment was investigated using TEM, XRD and a Vickers microhardness tester. Age hardening occurred after aging at 200°C in the Mg–Al–Si–Ca alloys mainly due to the formation of Al₂Ca and Mg₂Ca phases, whereas in the Mg–Zn–Ca alloys mostly due to the distribution of Mg₂Ca. TEM results revealed that spherical Al₂Ca precipitate has the coherent interface with the matrix. Considering the total amount of additional elements, Mg–Zn–Ca alloys showed higher hardness and smaller size of precipitates than Mg–Al–Si–Ca alloys. With the increase of Ca content, the hardness values of the aged ribbons were increased. Among the alloys, Mg–6Zn–5Ca alloy showed the maximum value of age hardening peak(H_v:180) after aging at 200°C for 1 h.     

Structural characteristics and elevated temperature mechanical properties of AJ62 Mg alloy

Structure and mechanical properties of the novel casting AJ62 (Mg–6Al–2Sr) alloy developed for elevated temperature applications were studied. The AJ62 alloy was compared to commercial casting AZ91 (Mg–9Al–1Zn) and WE43 (Mg–4Y–3RE) alloys. The structure was examined by scanning electron microscopy, x-ray diffraction and energy dispersive spectrometry. Mechanical properties were characterized by Viskers hardness measurements in the as-cast state and after a long-term heat treatment at 250 °C/150 hours. Compressive mechanical tests were also carried out both at room and elevated temperatures. Compressive creep tests were conducted at a temperature of 250 °C and compressive stresses of 60, 100 and 140 MPa. The structure of the AJ62 alloy consisted of primary α-Mg dendrites and interdendritic nework of the Al₄Sr and massive Al₃Mg₁₃Sr phases. By increasing the cooling rate during solidification from 10 and 120 K/s the average dendrite arm thickness decreased from 18 to 5 μm and the total volume fraction of the interdendritic phases from 20% to 30%. Both factors slightly increased hardness and compressive strength. The room temperature compressive strength and hardness of the alloy solidified at 30 K/s were 298 MPa and 50 HV 5, i.e. similar to those of the as-cast WE43 alloy and lower than those of the AZ91 alloy. At 250 °C the compressive strength of the AJ62 alloy decreased by 50 MPa, whereas those of the AZ91 and WE43 alloys by 100 and 20 MPa, respectively. The creep rate of the AJ62 alloy was higher than that of the WE43 alloy, but significantly lower in comparison with the AZ91 alloy. Different thermal stabilities of the alloys were discussed and related to structural changes during elevated temperature expositions.     

Tensile properties of hot rolled Mg–3Sn–1Ca alloy sheets at elevated temperatures

Mechanical behavior of hot rolled Mg–3Sn–1Ca (TX31) magnesium alloy sheets were studied in the temperature range 25–350 °C. The microstructure of the alloy consisted of the eutectic structure of α-Mg + Mg₂Sn and a dispersion of needle-like CaMgSn. The highest room-temperature ductility of 18% was obtained by hot rolling of the cast slabs at 440 °C, followed by annealing at 420 °C. The high temperature tensile deformation of the material was characterized by a decrease in work hardening exponent (n) and an increase in strain rate sensitivity index (m). These variations resulted in respective drops of proof stress and tensile strength from 126.5 MPa and 220 MPa at room temperature to 23.5 MPa and 29 MPa at 350 °C. This was in contrast to the ductility of the alloy which increased from 18% at room temperature to 56% at 350 °C. The observed variations in strength and ductility were ascribed to the activity of non-basal slip systems and dynamic recovery at high temperatures. The TX31 alloy showed lower strength than AZ31 magnesium alloy at low temperatures, while it exhibited superior strength at temperatures higher than 200 °C, mainly due to the presence of thermally stable CaMgSn particles.     

Notch tensile behavior of extruded Mg–Y–Zn alloys containing long period stacking ordered phase

The notch tensile behavior of extruded Mg–6RY–4Zn and Mg–9RY–4Zn (RY: Y-rich misch metal) alloys containing long period stacking ordered (LPSO) phase tested from room temperature to 250 °C was investigated. LPSO long-strips crack more severely in notch samples compared with that in smooth samples. The UTS values are above 300 MPa and the notch sensitivity ratio (NSR) values are larger than 1 in both alloys because the severe crack of LPSO phase costs more energy in notch samples. Furthermore, the NSR value rises with increasing the RY content or elevating the test temperature. The strengthening effect of LPSO phase is more remarkable at high temperatures. The notch leads the fracture mode of the two alloys changing from ductile fracture to brittle fracture. Designing complex shape components should consider the NSR and plasticity of Mg–Y–Zn alloys together.     

A new resource-saving,low chromium and low nickel duplex stainless steel 15Cr–xAl–2Ni–yMn

A new family of resource-saving, low Cr and low Ni duplex stainless steels, with compositions of 15Cr–xAl–2Ni–yMn (x = 1.2–2.8, y = 8–12, wt.%) has been developed by examining the effect of Al and Mn on microstructure, mechanical property and corrosion property. The results show that 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn alloys have a balanced ferrite–austenite relation and that 15Cr–2.8Al–2.0Ni–12Mn alloy has a primary ferrite phase structure. The ferrite volume fraction increases with the solution treatment temperature and Al content while decreases with Mn content. No precipitate was found after solution-treated at 750 °C for 30 min. 15Cr–1.2Al–2.0Ni–8Mn alloy has a strong strain hardening effect, and 15Cr–2.0Al–2.0Ni–10Mn alloy has a good TRIP effect. Both of the 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn alloys have excellent impact toughness at low temperature with the impact energy higher than 125 J at −40 °C. The pitting corrosions always occur in austenite phase. Among the designed alloys, 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn are found to be excellent alloys with a proper phase proportion and a better combination of superior mechanical property and good pitting corrosion resistance.     

Influence of solution and aging on the microstructures and mechanical properties of complex deformed WE93 alloy

Optical microscopy, scanning electron microscopy, transmission electron microscopy, hardness testing, and mechanical property testing were performed to study the influence of solution (T4) and aging (T6) on the microstructures and mechanical properties of the WE93 magnesium alloy. A reasonable solution treatment and an aging regime were developed, and the fracture features of the alloy in different states were analyzed. Results show that complex deformation produces microstructures that are largely characterized by deformation-precipitated Mg–Y phase (Mg₂₄Y₅), in addition to those with cubic Mg–Y and Mg–MM phases, which are both undissolved after homogenization. The optimum solution treatment condition for the alloy is a holding temperature of 490 °C for 2 h. After solution treatment, the precipitated Mg–Y phase re-dissolves and grain size grows to a limited extent, which may be attributed primarily to the pinning effect of the Mg–MM phase on the grain boundary. The reasonable aging regime was maintained at 225 °C for 40 h. After the solution and aging treatments, the ultimate tensile strength of the alloy at room temperature reaches 375 MPa but the elongation is only 3%. As indicted by the fracture behavior of the alloy, the secondary cracks of the extruded alloy and the solid-solution alloy occur mainly in the Mg–MM phase with few transcrystalline fractures. After peak aging, however, transcrystalline cracks appear on the grains at room and high temperatures. Under a multi-strengthening mechanism, the mutual coordinating effect may depend primarily on service temperature.     

Development of Al–Mn–Mg 3004 alloy for applications at elevated temperature via dispersoid strengthening

In this study, the potential applications of Al–Mn–Mg 3004 alloy at elevated temperature have been evaluated through the systematic study of the precipitation behavior of α-Al(MnFe)Si dispersoids and their effect on material properties during precipitation treatment and long-term thermal holding. The results demonstrate a significant dispersion strengthening effect caused by the precipitation of fine uniformly distributed dispersoids during precipitation treatment. The peak compression yield strength (YS) at 300 °C of the experimental 3004 alloy can reach as high as 78 MPa due to a large volume fraction (~ 2.95 vol.%) of α-Al(MnFe)Si dispersoids. The dispersoids are found to be thermally stable at 300 °C for up to 1000 h of holding, leading to consistently high mechanical performance and creep resistance. The superior and stable YS and creep resistance at 300 °C enables the 3004 alloy to be applied to weight-sensitive applications at elevated temperatures.     

Development and evaluation of a magnesium–zinc–strontium alloy for biomedical applications — Alloy processing,microstructure, mechanical properties,and biodegradation

A new biodegradable magnesium–zinc–strontium (Mg–Zn–Sr) alloy was developed and studied for medical implant applications. This first study investigated the alloy processing (casting, rolling, and heat treatment), microstructures, mechanical properties, and degradation properties in simulated body fluid (SBF). Aging treatment of the ZSr41 alloy at 175 °C for 8 h improved the mechanical properties when compared to those of the as-cast alloy. Specifically, the aged ZSr41 alloy had an ultimate tensile strength of 270 MPa, Vickers hardness of 71.5 HV, and elongation at failure of 12.8%. The mechanical properties of the ZSr41 alloy were superior as compared with those of pure magnesium and met the requirements for load-bearing medical implants. Furthermore, the immersion of the ZSr41 alloy in SBF showed a degradation mode that progressed cyclically, alternating between pitting and localized corrosion. The steady-state average degradation rate of the aged ZSr41 alloy in SBF was 0.96 g/(m²·hr), while the pH of SBF immersion solution increased. The corrosion current density of the ZSr41 alloy in SBF solution was 0.41 mA/mm², which was much lower than 1.67 mA/mm² for pure Mg under the same conditions. In summary, compared to pure Mg, the mechanical properties of the new ZSr41 alloy improved while the degradation rate decreased due to the addition of Zn and Sr alloying elements and specific processing conditions. The superior mechanical properties and corrosion resistance of the new ZSr41 alloy make it a promising alloy for next-generation implant applications.