Properties Of Mg Alloys Research Articles

Mechanical and physical properties of Mg alloys prepared by SPD methods

Magnesium alloys were prepared by severe plastic deformation (SPD). Three methods were used. The mechanical and thermal properties were estimated. The increase in strength could be attributed to the grain refinement and increased dislocation density. The thermal conductivity and expansivity was measured for samples prepared with different methods. Some examples are shown and discussed.

Enhanced ductility and strength of Mg-1Zn-1Sn-0.3Y-0.2Ca alloy achieved by novel micro-texture design

Texture weakening is generally adopted as one of the prominent methods to improve the ductility of Mg alloys. In this work, we designed and fabricated the Mg-1Zn-1Sn-0.3Y-0.2Ca (wt. % ZTWX1100) alloy with a novel basal-random heterogeneous (BRH) texture by precisely controlled high-reduction rolling, which contained both basal- and random-oriented grains with a uniform distribution. Compared with the basal-texture sample, the BRH texture improved the ductility and tensile strength simultaneously, due to the operation of non-basal slips within basal-oriented grains and the strong work hardening ability contributed by the basal-random grain boundaries. Besides, the basal-random grain boundaries in BRH texture were beneficial to improve the deformation compatibility by transforming the dominant carrier of local stress from original random-oriented grains to basal-oriented ones. This work aims to provide new insight into improving the mechanical properties of Mg alloys by texture coordinated deformation.

Novel multifunctional nanocomposites for superior barrier, hydrophobic and mechanical properties of Mg alloy in marine environment

The impact of surface functionalized titanium carbide (TiC) nanoparticles on the electrochemical and mechanical properties of epoxy nanocomposite was investigated. The functional TiC nanoparticles were synthesized using pyrrole (Py) and 2-amino-5-mercapto-1,3,4-thiadiazole (AMTD) and characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), and thermogravitric analysis (TGA) techniques. The resultant novel nanocomposite coating on Mg alloy in seawater was investigated by Tafel polarization, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) studies. Electrochemical studies revealed excellent corrosion protection performance and a decreased corrosion current density for the EP-AMTD/TiC (Rc = 4861.25 kΩ.cm2 and icorr = 3.75 μA/cm2) and the EP-Py/TiC nanocomposite coated Mg alloy (Rc = 3182.71 kΩ.cm2 and icorr = 5.65 μA/cm2) in comparison with the plain epoxy coated Mg alloy (Rc = 244.67.25 kΩ.cm2 and icorr = 9.55 μA/cm2) after 60 days of immersion. The results indicated that the functional TiC nanoparticles dispersed uniformly and retarded the propagation of aggressive ions to the coating/alloy interface. SECM observations confirmed the observation of least current at the scratched area of the EP-AMTD/TiC (2.1 I/nA) and the EP-Py/TiC (4.8 I/nA) coated alloy compared to pure epoxy coating (14.9 I/nA) even after 60 d immersion in seawater. SEM observations showed that reactive TiC nanofillers are dispersed uniformly. The changes in surface morphology, phase structure and composition were analyzed using SEM/EDX and XRD techniques. It was found that the intercalation of functional TiC nanoparticles in the epoxy coatings exhibited a smooth microstructure surface producing superior corrosion protection and mechanical properties. The mechanism of corrosion protection has been proposed.

Preparation and characterization of AZ91E/Al2O3 composites using hybrid mechanical and ultrasonic particle dispersion

As a light structural metal, magnesium (Mg) has been gaining increasing popularity in the transportation sector. However, widespread implementation of Mg is hindered by its low mechanical properties compared to aluminum and steel. A proven method to improve the mechanical properties of cast alloys is grain refinement. A finer grain size can be achieved through the addition of particle substrates to the liquid melt, where they can act as nucleation sites for the formation and growth of grains. Inoculants are typically added to the molten metal and dispersed using mechanical stirring (MS) with an impeller. However, achieving uniform dispersion of inoculants using this method is challenging. Alternatively, researchers have been investigating the potential of ultrasonic treatment (UST) to supplant MS. In this study, the dispersion of Al2O3 particle inoculants in AZ91E Mg alloy was investigated. Cast AZ91E + Al2O3 composites were prepared using MS or UST. The microstructure of the resultant castings were characterized using optical microscopy and scanning electron microscopy, while mechanical properties were evaluated through ambient temperature tensile tests and theoretical models. The specimens treated with UST displayed improved mechanical properties relative to the base alloy and the samples prepared with MS. This was attributed to the finer grain size, thermal expansion mismatch between the refiner and the matrix and improved inoculant distribution within the sonicated samples. This research resulted in a unique correlation between theoretical strengthening mechanism prediction models and experimental results achieved through sonication and grain refinement. Therefore, advances in the preparation of cast alloys and implementation of critical innovative technologies such as UST can improve the mechanical properties of Mg alloys.

Fabrication of cross-like ZIF-L structures with water repellency and self-cleaning property via a simple in-situ growth strategy

Inspired by the “lotus effect’’, more and more attention has been paid to the water repellent and self-cleaning surface. Due to its excellent properties, Mg alloy is considered to be one of the most promising engineering materials so far. However, the humid and corrosive environment makes Mg alloy susceptible to corrosion, which greatly limits its wide application. So it is very necessary to improve the properties of Mg alloy through surface treatment. Because of good chemical stability, thermostability and easy preparation, Zeolitic Imidazolate Frameworks (ZIFs) materials have been applied in the field of superhydrophobicity. In addition, in-situ growth has advantages of simple method, convenient operation and no need for expensive experimental equipment. Therefore, in this work, the superhydrophobic coating with cross-like Zeolitic Imidazolate Framework-L (ZIF-L) structure is fabricated on Mg alloy surface via a simple in-situ growth and low energy modification. The superhydrophobic ZIF-L coating on the Mg alloy substrate has excellent water repellency and self-cleaning property, and the stability test results show that it has good performance in thermostability and durability. Besides, the coating keeps superhydrophobic state after being immersed in an alkaline solution for 112 h, showing excellent resistance to alkaline solution. Therefore, the superhydrophobic coating prepared in this work can expand the application of Mg alloy in different service environments and provide a novel way for Mg alloy applying into more fields.

Research advances in magnesium and magnesium alloys worldwide in 2020

Research on magnesium alloys continues to attract great attention, with more than 3000 papers on magnesium and magnesium alloys published and indexed in SCI in 2020 alone. The results of bibliometric analyses show that microstructure control and mechanical properties of Mg alloys are continuously the main research focus, and the corrosion and protection of Mg alloys are still widely concerned. The emerging research hot spots are mainly on functional magnesium materials, such as Mg ion batteries, hydrogen storage Mg materials, and bio-magnesium alloys. Great contributions to the research and development of magnesium alloys in 2020 have been made by Chongqing University, Chinese Academy of Sciences, Central South University, Shanghai Jiaotong University, Northeastern University, Helmholtz Zentrum Geesthacht, etc. The directions for future research are suggested, including: 1) the synergistic control of microstructures to achieve high-performance magnesium alloys with concurrent high strength and superior plasticity along with high corrosion resistance and low cost; 2) further development of functional magnesium materials such as Mg batteries, hydrogen storage Mg materials, structural-functional materials and bio-magnesium materials; 3) studies on the effective corrosion protection and control of degradation rate of magnesium alloys; 4) further improvement of advanced processing technology on Mg alloys.

Microstructure, mechanical properties, cytotoxicity, and bio-corrosion of micro-alloyed Mg–xSn–0.04Mn alloys for biodegradable orthopedic applications: Effect of processing techniques

Magnesium alloys have great potential for load-bearing biodegradable orthopedic implants. The mechanical properties and corrosion resistance depend on alloy composition and processing technique. Presently, the effect of processing techniques on the properties of Mg alloys containing small additions of Sn and 0.04Mn is investigated. Mg–xSn–0.04Mn alloys (x = 0.25 and 1.53wt%) were prepared by casting, heat treatment, hot extrusion, and hot rolling. Microstructure was investigated by optical microscopy, SEM, and XRD. The type, size, and volume fraction of precipitates were found to play the major role in determination of mechanical properties and rate of dissolution in Hank’s solution. A considerable rise in strength, ductility, and reduction in dissolution rate were obtained after thermomechanical treatment based on grain size, volume fraction, and distribution of precipitates. Extruded Mg–1.53Sn–0.04Mn alloy exhibited the best combination of strength, ductility and biodegradability by exhibiting a strength of 219.6 MPa, elongation of 7.9%, and corrosion rate of 0.71 mm/y, indicating that it is indeed a promising candidate for biodegradable orthopedic applications.

Microstructure and mechanical properties of the sub-rapidly solidified Mg―Zn―Y―Nd alloy prepared by step-copper mold casting

In this paper, the microstructure and compression mechanical properties of the sub-rapidly solidified Mg‒Zn‒Y‒Nd alloy cylinders with diameters of 2–8 mm prepared by step-copper mold casting were investigated. The cooling rate of samples increased gradually with decreasing the mold diameter. The ϕ2-mm sample consists of α-Mg with the smallest grain size of about 10 μm and spherical T-phase, rod-like I-phase, ribbon-like Mg7Zn3 phase, skeleton-like W'-phase. With a decrease in the cooling rate, the grain size of α-Mg increases and the secondary phases are coarsened. For the ϕ6-mm and ϕ8-mm samples, I-phase and W'-phase disappear, W-phase appears and tends to form network structures. Among these samples, the ϕ2-mm one exhibits the highest ultimate fracture strength of 384 MPa and the largest plasticity of 30 %. The good mechanical properties were attributed to the activation of non-basal <c + a> slips at the later stage of deformation. This result suggests that the sub-rapid solidification technique would be a promising way to improve the mechanical properties of Mg alloys, which can be used as biodegradable mini-implants.

A novel dynamic extrusion for microstructure tailoring and evading strength-ductility trade-off in AZ31 magnesium alloy

This study demonstrates that dynamic extrusion is a promising method for improving both strength and ductility in magnesium (Mg) alloy. The dynamic extrusion process introduces numerous {10-12} extension twins and high-density dislocation structures in the fine-grained AZ31 Mg alloy at high strain rate (~105 s−1) and room temperature. After annealing, we note that the high-density twins can effectively enhance the strain hardening and strength due to that twin boundary is inherently resistant to dislocation motion. Remarkably, the excellent ductility has been achieved because of high density deformation twins promote more dislocation to nucleate form twin boundaries, and offer more slip systems for dislocation motion. Our findings suggest dynamic extrusion increases the twin density of the initial microstructure, thereby simultaneously increasing both of the strength and ductility in Mg alloy. Ultimately, our work develops a novel strategy or technique to properly tailor microstructure to achieve a substantial improvement of mechanical properties in Mg alloys.

Tailoring bimodal grain structure of Mg-9Al-1Zn alloy for strength-ductility synergy: Co-regulating effect from coarse Al2Y and submicron Mg17Al12 particles

Grain boundary strengthening is an effective strategy for increasing mechanical properties of Mg alloys. However, this method offers limited strengthening in bimodal grain-structured Mg alloys due to the difficultly in increasing the volume fraction of fine grains while keeping a small grain size. Herein, we show that the volume fraction of fine grains (FGs, ∼2.5 µm) in the bimodal grain structure can be tailored from ∼30 vol.% in Mg-9Al-1 Zn (AZ91) to ∼52 vol.% in AZ91–1Y (wt.%) processed by hard plate rolling (HPR). Moreover, a superior combination of a high ultimate tensile strength (∼405 MPa) and decent uniform elongation (∼9%) is achieved in present AZ91–1Y alloy. It reveals that a desired bimodal grain structure can be tailored by the co-regulating effect from coarse Al 2 Y particles resulting in inhomogeneous recrystallization, and dispersed submicron Mg 17 Al 12 particles depressing the growth of recrystallized grains. The findings offer a valuable insight in tailoring bimodal grain-structured Mg alloys for optimized strength and ductility.

Strength and plasticity of lamellar vs. fibrous eutectic Mg-Al nanocomposites: An in-situ microcompression study

Owing to their low density and high strength-to-weight ratio, Mg alloys are attractive for automotive and aerospace applications. However, the current use of magnesium in the industry is limited due to the low strength and poor formability at ambient temperatures. Two-phase nanostructured materials are a promising solution to improve the mechanical properties of Mg alloys. Depending on processing parameters, either fibrous or lamellar morphologies can be formed via the eutectic transformation. In this work, the mechanical behavior of these two different morphologies were examined by in-situ SEM microcompression tests. The lamellar morphology exhibited a superior combination of strength and plasticity with respect to the fibrous morphology, and both showed superior strength relative to pure Mg, up to five-fold in the former and 12-fold in the latter. However, the higher strength in the fibrous eutectic was obtained at the expense of a low plasticity. According to the HR/TEM analyses of the deformed micropillars, the relatively high plasticity of the lamellar morphology was attributed to the two reasons; on the one hand, high dislocation activity was observed in both α and β phases and resulted in plastic co-deformation of the layers. On the other hand, the α layers played a significant role in restricting the shear instabilities that initiated in the β layers. Such an effect was not observed with the fibrous morphologies, and thus, they failed by cleavage along the closest-packed planes in the β crystal.

The high-temperature oxidation resistance properties of magnesium alloys alloyed with Gd and Ca

This work studied the high-temperature oxidation resistance properties of Mg alloys with Gd and Ca. The oxidation property of Mg-3.5Gd-xCa (x = 0, 0.5, 1.0 and 3.0 wt%) alloys followed parabolic oxidation kinetics at 500 °C. A stable oxide film was formed on the alloy surface and limited further oxidation. The oxide film was composed of Gd2O3, MgO and MgCO3 for Mg-3.5Gd and was mainly CaO and CaCO3 with increasing Ca content for Mg-3.5Gd-xCa alloys. The high oxidation affinity of Ca caused it to be oxidized preferentially and the fast diffusion of Ca in Mg alloys provided a source for the continuous oxidation of Ca at the surface. The parabolic rate constant, grains size and surface roughness of the oxide film increased with the increasing Ca content in Mg-3.5Gd-xCa alloy. The understanding of multi-element alloying on the oxidation behavior of Mg alloy is helpful for the design of multi-element oxidation-resistant Mg alloys.

Significant improvement in yield stress of Mg-Gd-Mn alloy by forming bimodal grain structure

Fabricating bimodal grain structure is an effective way to improve the mechanical properties of Mg alloys. In present work, the various Mn contents (0, 0.5, 1.0, 1.5 wt%) are added in Mg-1.0Gd alloy to fabricate bimodal grain structure and improve the mechanical properties. After extrusion at 300 °C, bimodal grain structure is obtained in the Mg-1.0Gd-1.0Mn and Mg-1.0Gd-1.5Mn alloys. With the increment of Mn content, the average grain sizes of dynamic recrystallization (DRX) grains are refined from 8.6 to 1.2 μm. The mechanical properties are significantly improved. The Mg-1.0Gd-1.5Mn alloy exhibits the best tensile yield stress (TYS) and ultimate tensile stress (UTS), which is 280 MPa and 293 MPa. Comparing with the Mg-1.0Gd alloy, the improvement of TYS and UTS are 165 MPa (143%) and 98 MPa (51%). The enhancement of the strength is mainly attributed to the bimodal grain structure. The formation of the bimodal grain structure and the strengthening mechanisms are also discussed.

Improvements of Corrosion Resistance and Antibacterial Properties of Hydroxyapatite/Cupric Oxide Doped Titania Composite Coatings on Degradable Magnesium Alloys.

The excellent biocompatibility of calcium phosphate (CaP) coatings makes them widely used in magnesium (Mg) alloy orthopedic implant materials. However, the porous morphology of CaP coatings limits their corrosion resistance. A cupric oxide (CuO) doped titania (TiO2) sol-gel coating is prepared on a porous hydroxyapatite (HA) coating. According to electrochemical test results, the HA/CuO-TiO2 coating obtains a current density of 6 × 10-4 mA/cm2, lower than that of the Mg alloy (2.6 × 10-2 mA/cm2). The hydrogen evaluation of the HA/CuO-TiO2 coating is only 1/12 that of the Mg alloy after immersion for 7 days. In addition, the HA/CuO-TiO2 coating has an antibacterial rate of 99.5 ± 0.4% against Staphylococcus aureus, significantly higher than that of the HA coating (19.8 ± 0.3%) and HTC0 coating (38.4 ± 0.5%). The CuO doped composite coating has no adverse effect or cytotoxicity on cell proliferation (cell viability ≥79.6%). Hence, the HA/CuO-TiO2 composite coating is useful for enhancing the corrosion resistance and antibacterial properties of Mg alloys while ensuring cytocompatibility. The HA/CuO-TiO2 coated AZ60 Mg alloy can meet the requirements of clinical application.

Towards developing Mg alloys with simultaneously improved strength and corrosion resistance via RE alloying

Magnesium (Mg) alloys have received an increasing interest in the past two decades for their tremendous application potential. The strength and corrosion resistance levels of common Mg alloys are still relativity low, and especially they are to be improved simultaneously. The addition of rare earth (RE) to Mg alloys is believed to be beneficial for both the strength and corrosion resistance, and some RE-modified traditional Mg alloys have been studied and some new RE-containing Mg alloys have been developed by now. However, further simultaneous improvements in both strength and anti-corrosion require a better understanding of the behavior and mechanism of RE in Mg alloys. In this review, the common influence mechanisms of RE on mechanical and anti-corrosion properties of Mg alloys are summarized, and the latest research progress of RE-containing Mg alloys with simultaneously improved strength and corrosion resistance are introduced. It is demonstrated that the research on high-strength and high corrosion resistant RE-containing Mg alloys is still immature, and some opinions and suggestions are put forward for the synergetic improvement of the strength and corrosion resistance of Mg alloys, so as to contribute to the further development of Mg alloys with higher performance.

Microstructure Evolution and Mechanical Properties of AQ80 Alloy During Forward Extrusion and Twist Deformation

A new severe plastic deformation technique, forward extrusion and twist deformation, was adopted to manufacture magnesium (Mg) alloys at different temperatures. The microstructure evolution and mechanical properties of extruded AQ80 alloy were investigated. The strain distribution in FETD extrusion was simulated with finite element simulation software. The extruded samples exhibit finer grain sizes, weaker basal textures, higher recrystallized volume fractions and higher strengths than the traditional forward extrusion samples. This technology can refine the microstructure and improve the mechanical properties of Mg alloys. At lower temperatures, the grain size is smaller with a finer second phase, which is detected as Mg17AL12. Mg17AL12 has a particle-stimulated nucleation effect and a retarding effect on grain growth, resulting in much finer DRXed grains. Due to the effects of fine-grained strengthening and second phase strengthening, the strength and elongation of AQ80 alloy can be improved significantly.

Enhanced surface properties of Mg alloy via coupling porous substrate and Al coating

The poor wear resistance has been a main challenge for extensive application of Mg alloy. The method of coupling porous flexible Mg alloy-substrate and hard Al alloy-coating was studied in this paper to improve the wear resistance. Nano-indentation and scratch tests were performed on pure Mg, coating deposited on porous substrate for 2 h (Po-Mg-Al-2 h), coating deposited on substrate for 2 h (Mg-Al-2 h) and 4 h (Mg-Al-4 h) to make a direct comparison. Po-Mg-Al-2 h exhibited the highest hardness and elastic modulus, followed by Mg-Al-2 h, Mg-Al-4 h and Mg. Corresponding Coefficients of Friction (COFs) from scratch tests of aforementioned specimens were 0.224, 0.232, 0.234 and 0.308, respectively. Additionally, the scratched morphologies of Po-Mg-Al-2 h showed a relatively smooth groove and short residual scratch without debris and flakes observed in other specimens. A better capability of wear resistance, significantly enhanced hardness and modulus were obtained through coupling porous substrate and Al coating.

Improvement of tribological, mechanical and chemical properties of Mg alloy (AZ91D) by electrophoretic deposition of alumina/GO coating

Although Mg alloys are excellent structural materials but their weak tribological and corrosion properties limit their widespread applications. In the present study we aimed to enhance the tribological, surface mechanical and corrosion properties of AZ91D Mg alloy by electrophoretic deposition of alumina/GO coatings (with 0.0, 0.5, 1.0, and 2.0 wt% of GO). The phase composition and microstructural features of the coatings were studied by X-ray diffraction and scanning electron microscopy techniques. Hardness, drop contact angle, and electrochemical impedance tests were conducted to investigate the various properties of the coatings. Our results show that electrophoretic deposition technique is capable of preparation of coatings with very low number of cracks, particularly when higher content of GO (2 wt%) is used. Although coating of only alumina already improved the alloy properties, but incremental addition of GO demonstrated significant improvement in hardness, scratch and corrosion resistances of the coatings. According to our results, the improvement in mechanical properties is mainly due to the effect of GO nanoplatelets in bridging between alumina nanoparticles. On the other hand, GO considerably boosts the corrosion resistance due to its effect in removing the cracks and open spaces from the microstructure. Overall, alumina/GO nanocomposite coatings prepared by electrophoretic deposition demonstrates comparable-level properties with those prepared in the previous researches by thermal spraying methods.

Simultaneously improved mechanical and thermal properties of Mg-Zn-Zr alloy reinforced by ultra-low content of graphene nanoplatelets

Mg-Zn-Zr (ZK60) alloys reinforced by ultra-low content (<0.1 wt%) of graphene nanoplatelets (GNPs) were fabricated via stirring cast and extrusion processes. In composites, GNPs thoroughly dispersed and continuously combined with Mg matrix at the interface, beneficial for the load and heat transfer of composites. The static and dynamic mechanical properties of GNP/ZK60 composite were investigated and respectively compared with those of ZK60 alloy. With only 0.04 wt% addition, GNP nanofillers improved the impact toughness twice that of ZK60 matrix up to 17 J cm-2. In tensile test, GNP(0.04)/ZK60 composite performed enhanced tensile yield strength of 256 MPa, improved by 62% than ZK60 alloy. Although grain boundary is commonly considered as defect to deteriorate transport property, GNP(0.04)/ZK60 composite with largely refined grain size conducted superior thermal conductivity of 139.4 W·(mK)-1 than ZK60 alloy (132.2 W·(mK)-1) at room temperature. The dispersed GNPs in matrix provide beneficial networks for efficient load and heat transfer. This work explores that graphene reinforcement is an effective way to simultaneously improve the mechanical and thermal properties of Mg alloys for enlarged applications.

Mechanical properties and deformation mechanisms of a novel fine-grained Mg-Gd-Y-Ag-Zr-Ce alloy with high strength-ductility synergy

Grain boundary precipitation and segregation play an important role in determining mechanical properties of Mg alloys. In the present work, we studied work focuses on the strengthening and deformation mechanism of coarse-grained (CG) and fine-grained (FG) Mg-Gd-Y-Ag-Zr-Ce alloy. The CG alloy is strengthened by means of age-strengthening with the formation of both basal plate γ′′ and prismatic plate β′ precipitates in the grain interior. While the strengthening of FC alloy is completed by intergranular alloying segregation and intragranular precipitates γ′′ and β′. The segregation of alloying elements at the grain boundary and formation of sub-micron particles can stabilize the grain boundary and suppress the intergranular deformation. Consequently, dislocations could be trapped near γ′′ and β′ precipitates in the grain interior. Unlike CG alloys, the FG alloys exhibit a heterogeneous transition from elastic to plastic deformation via the Lüders plateau. The rapid gliding dislocation multiplications and fine-grained size are necessary and sufficient conditions for the Lüders strains. Our work provides the insights on the evolution of fine-grained microstructure and helps for the design of Mg alloys with good mechanical properties.