Lightweight Magnesium Alloys Research Articles

Guiding severely anisotropic twinning bands in Magnesium: An in situ investigation by full-field microscopic image correlation

A critical issue for lightweight Magnesium alloys is their propensity for strain localization at the component scale, linked to the peculiar twinning phenomenon. For the (c-axes-aligned) rolling texture, highly compact coordinated twinning bands (CTBs) form that, uniquely, have a singular plane of shear. Normally, where these bands emerge, and progress are up to stochastic factors. Here, a cross-notched sample design is nominated to guide the bands of conjugate orientations into predetermined diagonal corridors and enforce their overlap at a prefixed location. The deformation fields in the Magnesium AZ31 sample are in situ monitored with an advanced microscopic image correlation (micro-DIC) variant that has a unique combination of extreme field coverage (∼1.5 ×105 grains), intragranular resolution (∼102 data points per grain) and very high time-step resolution (0.05–0.1% nominal strain increments over the twin plateau). The latter allows investigating the emergence, advance, lateral growth, and interaction of CTBs with extreme detail over absolute and sequential micro-DIC strain maps. The sample design is successful in guiding the CTB formations into the designated corridors. Seed segments of CTBs first make a cross connection across the sample, followed by lateral expansion that proceeds until the corridor is roughly filled. This happens sequentially for the two diagonal corridors, forcing the second band to pass through the first. The band strain is reduced by about 25% at the enforced overlap compared to the characteristic intensity it exhibits outside it (around 2.3%)—a direct measurement of the dilution of the strain activity of a CTB as it crosses another CTB. The uniqueness of this application in guiding severely anisotropic bands is contrasted with the micro-DIC fields of a transversely isotropic sample of the same material that is analogously put under a twin-dominated deformation.

LCF and HCF of Short Carbon Fibers Reinforced AE42 Mg Alloy.

Lightweight magnesium alloys and magnesium matrix composites have recently become more widespread for high-efficiency applications, including automobile, aerospace, defense, and electronic industries. Cast magnesium and magnesium matrix composites are applied in many highly moving and rotating parts, these parts can suffer from fatigue loading and are consequently subjected to fatigue failure. Reversed tensile-compression low-cycle fatigue (LCF) and high-cycle fatigue (HCF) of short fibers reinforced and unreinforced AE42 have been studied at temperatures of 20 °C, 150 °C, and 250 °C. To select suitable fatigue testing conditions, tensile tests have been carried out on AE42 and the composite material AE42-C at temperatures of up to 300 °C. The Wohler curves σa (NF) have shown that the fatigue strength of the reinforced AE42-C in the HCF range was double that of unreinforced AE42. In the LCF range at certain strain amplitudes, the fatigue life of the composite materials is much less than that of the matrix alloys, this is due to the low ductility of this composite material. Furthermore, a slight temperature influence up to 150 °C has been established on the fatigue behavior of the AE42-C. The fatigue life curves Δεtotal (NF) were described using the Basquin and Manson-Coffin approaches. Fracture surface investigations showed a mixed mode of serration fatigue pattern on the matrix and carbon fibers fracturing and debonding from the matrix alloy.

Nanomechanical and Electrochemical Corrosion Testing of Nanocomposite Coating Obtained on AZ31 via Plasma Electrolytic Oxidation Containing TiN and SiC Nanoparticles

Lightweight magnesium alloys offer excellent benefits over Al alloys due to their high specific strength and damping properties, but they are more prone to galvanic corrosion. Plasma electrolytic oxidation (PEO) coatings reinforced by nanoparticles have been shown to improve corrosion resistance and possess better mechanical properties. A lot of research has been published that focuses on the effect of nanoparticle concentration in the PEO electrolyte solution, and the type of nanoparticle, on the properties obtained. The aim of paper is to study the effect of processing time on the nanoparticle-reinforced PEO coating on AZ31 magnesium alloy. TiN and SiC nanoparticles were produced using plasma chemical synthesis and added to KOH-based electrolyte to develop PEO coatings. The concentration of nanoparticles was kept constant at 0.5 g/L and the treatment time was varied as follows: 1, 2, 3, 5, and 10 min. The coatings were tested for their microstructure, phase, chemical makeup, nano-mechanical properties, and corrosion resistance. Nanoparticles were found to be clustered in the coating and spread unevenly but led to a decrease in the size and number of pores on the PEO coating surface. The corrosion resistance and nano-mechanical properties of the coating improved with treatment time. The hardness and contact modulus of coatings with TiN particles were 26.7 and 25.2% greater than those with SiC particles. Addition of TiN nanoparticles resulted in improved corrosion resistance of the PEO coatings when the processing time was 5 or 10 min. The lowest corrosion rate of 6.3 × 10−5 mm/yr was obtained for TiN-added PEO coating processed for 10 min.

Friction stir alloying of AZ61 and mild steel with Cu-CNT additive

Dissimilar joining between lightweight magnesium (Mg) alloys and steel is essential to produce lighter vehicles, improve vehicles’ fuel efficiency, and reduce carbon emissions. However, the joining of Mg to steel is impractical due to the immiscible properties between these metals. In this experiment, friction stir alloying (FSA) is proposed to solve this problem. The additive, consisting of different wt% of carbon nanotubes (CNT) in Cu powder was first added into the gap between the workpieces and then friction stir welding (FSW) was performed at varied traverse speed and constant rotational speed. After the joining, microstructure characteristics and mechanical properties of Cu-CNT reinforced Mg/steel joints were investigated. Transmission electron microscopy (TEM) analysis of the Mg/steel joint revealed the formation of IMC at the interface of the joint. Further analysis by X-ray diffraction (XRD) showed a dominant presence of Mg2Cu IMC which indicated the interdiffusion of Cu into Mg element to establish intermetallic bonding. The presence of CNT inside the Mg matrix was also confirmed by TEM which contributed to the strengthening effect of the joint. Tensile and microhardness results revealed a notable enhancement of joint mechanical properties when Cu-CNT additive was added as compared to specimens with only Cu additive, and specimens without additive. The enhanced tensile strength and microhardness of the Cu-CNT reinforced Mg/steel joint was attributed to the dispersion of CNT inside the Mg matrix, which induced multiple dislocations in the surface region, therefore improving the mechanical properties of the joint.

Study on energy absorption characteristics of expansion tube with light magnesium alloy

This paper proposed a lightweight magnesium alloy expansion energy-absorbing structure. The structure adopts lightweight materials, which can greatly reduce its own weight on the basis of ensuring energy absorption performance. Firstly, the geometric model of structure is designed and the corresponding physical prototype is processed. The theoretical model of magnesium alloy expansion tube is studied, and the main mechanical response is analyzed. Then the structural mechanical properties are studied by quasi-static compression test. Combined with the theoretical model, several typical deformation stages in expanding are analyzed. The effects of geometric parameters on the energy absorption performance are studied. The results show that with the increase of die angle, die expansion size and tube thickness, the maximum peak force, average force, energy absorption and specific energy absorption increase. Then the test results are compared with the corresponding theoretical steady force to verify the applicability of the theoretical model. The theoretical values are basically in good agreement with the experimental values. The error of all results is within 10%. Finally, comparing the characteristics of magnesium alloy, aluminum alloy and steel energy absorbing tube with the same quality, it is concluded that the specific energy absorption of magnesium alloy structure is 31.6% and 4.1% higher than that of steel and aluminum respectively, and magnesium alloy tube has higher specific energy absorption.

Selective laser melted AZ91D magnesium alloy with superior balance of strength and ductility

In the context of global carbon neutrality, the application of lightweight magnesium alloys is becoming increasingly attractive. In this study, selective laser melting (SLM) was employed to achieve nearly full dense and crack-free AZ91D components with fine equiaxed grain structure. The formation mechanism of typical pore defects (gas pore, lack-of-fusion pore and keyhole pore) and melting modes (keyhole mode and conduction mode) were systematically studied by varying the laser power and scanning speed. The morphology and volume fraction of the pores under different processing conditions were characterized. A criterion based on the depth-to-width ratio of the melt pool was established to identify different melting modes. The strength and ductility (tensile strength up to 340 MPa and uniform elongation of 8.9%) of the as deposited AZ91D are far superior to those of the casting components and are comparable to those of its wrought counterparts. The superior balance of strength and ductility of SLMed AZ91D, as well as the negligible anisotropic properties are mainly ascribed to the extremely fine equiaxed grain structure (with average grain size of ∼1.2 µm), as well as the discontinuous distribution of β-Al12Mg17 phases. It thus provides an alternative way to fabricate high-strength magnesium alloys with complex geometry.

Optimizing mechanical properties of magnesium alloys by philosophy of thermo-kinetic synergy: Review and outlook

Although several strategies (including grain refinement, texture adjustment, precipitation hardening, etc.) have been verified to effectively improve the mechanical properties of lightweight magnesium (Mg) alloys, considerable efforts are still needed to be made to comprehensively understand the potential mechanisms controlling complex microstructures and deformation behaviors exhibited by the hexagonal close-packed host lattice of Mg, thus assisting the rational design of materials at a more physical level. As the cornerstone of this review, a universal rule, the so-called synergy of thermodynamics and kinetics (i.e., thermo-kinetic diversity, correlation and connectivity), including a recently proposed theory of generalized stability (GS), is introduced to deepen our understanding on common behaviors in Mg alloys (i.e., deformations (slip and twining modes), phase transformations (especially for precipitations) and interactions in between) at a new perspective. Guided by the GS theory, typical cases for Mg alloys design are qualitatively evaluated to reemphasize the traditional strengthening and toughening strategies mentioned above and to illuminate their exquisite coordination for breaking through the trade-off relationship between strength and ductility, corresponding to a typical thermo-kinetic pair (i.e., high driving force (∆ G ) - high GS). To produce the Mg alloys with superior strength-ductility balances, the potential capacity of this GS theory for guiding processing path design is discussed, finally.

A Prospective Way to Achieve Ballistic Impact Resistance of Lightweight Magnesium Alloys

The ballistic impact resistance of lightweight magnesium alloys is an eye-catching material for the military and aerospace industries, which can decrease the cost of a project and the fuel consumption. The shockwave mitigation ability of a magnesium alloy is 100 times stronger than an aluminum alloy; nonetheless, ballistic impact resistance has still not been achieved against blunt and API projectiles. The major obstacles are the low hardness, low mechanical strength, basal texture and strain hardening ability under loading along the normal direction of the sheet. The high yield strength and ultimate strength can be achieved for a specific loading condition (tensile or compression) by adjusting the texture in magnesium alloys. The projectile impact along the normal direction in a strong basal-textured magnesium alloy can only produce a slip-induced deformation or minor twinning activity. Here, we propose a practical technique that can be valuable for altering the texture from c-axes//ND to c-axes//ED or TD, and can produce high strain hardening and high strength through a twinning and de-twinning activity. Subsequently, it can improve the ballistic impact resistance of magnesium alloys. The effect of the technique on the evolution of the microstructure and possible anticipated deformation mechanisms after ballistic impact is proposed and discussed.

Synchrotron experiment and simulation studies of magnesium-steel interface manufactured by impact welding

The effective weight reduction in the automotive industry by the wide adoption of lightweight magnesium (Mg) alloys demands high-quality joint between magnesium alloys and massively-used steels in order to wring the excess weight with strength and safety assurance. However, Mg-steel joint is difficult to achieve because there is no mutual solubility between magnesium and steel and huge disparity in physical properties. An impact-based welding method recently showed successful Mg-steel joining. In this work, the characteristics of Mg-steel interface joined by the impact welding method were investigated. Synchrotron high-energy X-ray computed tomography and diffraction were applied to characterize the microstructure across Mg-steel interface. Results revealed a deposit layer formed at the joint interface where Fe-rich particles spread deep into the Mg matrix. High-resolution 3D morphology of Mg-steel interface demonstrated the trapped pores and cracks inside the deposit layer. The formation of the deposit layer and the void/cracking evolution were analyzed by using finite element models. These findings provide insights into the immiscible Mg-steel joining process.

Application of lightweight magnesium alloy in satellite antenna products

Combined with the actual work, the new metal matrix composite has the characteristics of light weight, low thermal expansion (CTE), ultra-high thermal conductivity, high specific strength, specific stiffness, good damping, etc. which is the key to realize the requirements of miniaturization, lightweight, long life and high reliability of aerospace products. This paper introduces the selection analysis and practical application of magnesium alloy in satellite antenna products. Antenna products based on magnesium alloy will be more and more widely used in aerospace field.

Increasing the Lightweight Potential of Composite Cold Forging by Utilizing Magnesium and Granular Cores

In this paper a process sequence, that uses forward rod extrusion with cold forged C15 steel cup billets to produce lightweight shafts, is presented. The steel cup billets feature either a lightweight magnesium alloy core or a granular medium core that is removed after forming to obtain hollow shafts without the need of complex tools and highly loaded mandrels. It is shown that composite shafts featuring magnesium cores can be produced for a wide range of extrusion strains. Due to high hydrostic pressures in forward rod extrusion, the forming limit of magnesium at room temperature can be expanded. The observed bond strength between core and sheath is below the shear yield strength of utilized magnesium AZ31 alloy. Hollow shafts are successfully produced with the presented process route by utilizing zirconium oxide beads or quartz sand as a lost core. As the law of constant volume in metal forming is violated by compressible granular media, a simulation approach using a modified Drucker-Prager yield surface to model these materials is validated to provide a tool for efficient process design. Granular cores and magnesium alloy cores offer new possibilities in production of lightweight shafts by means of composite cold forging. Both process variants allow for higher weight savings than composite shafts based on aluminum cores.

A new die-cast magnesium alloy for applications at higher elevated temperatures of 200–300 °C

The development of lightweight magnesium (Mg) alloys capable of operating at elevated temperatures of 200–300°C and the ability of using high pressure die casting for high-volume manufacturing are the most advanced developments in manufacturing critical parts for internal combustion engines used in power tools. Here we report the microstructure and mechanical properties of a newly developed die-cast Mg–RE(La,Ce,Nd,Gd)–Al alloy capable of working at higher elevated temperatures of 200–300°C. The new alloy delivers the yield strength of 94 MPa at 300°C, which demonstrates a 42% increase over the benchmark AE44 high temperature die-cast Mg alloy. The new alloy also has good stiffness at elevated temperatures with its modulus only decreasing linearly by 13% from room temperature up to 300°C. Thermal analysis shows a minor peak at 364.7°C in the specific heat curve of the new alloy, indicating a good phase stability of the alloy up to 300°C. Nd and Gd have more affinity to Al for the formation of the minority of divorced Al–RE(Nd,Gd) based compounds, and the stable Al-poor Mg12RE(La0.22Ce0.13Nd0.31Gd0.31)Zn0.39Al0.13 compound acts as the continuous inter-dendritic network, which contribute to the high mechanical performance and stability of the new die-cast Mg alloy at 200–300°C.

Effects of aligned graphene sheets on mechanical properties of ZK61 alloy

Lightweight magnesium (Mg) alloys suffer from their relatively low strength and limited ductility. The addition of graphene can effectively improve the strength and ductility of Mg alloys. However, the mechanism of improving ductility by graphene in Mg alloys has been generally neglected, as evidenced by a lack of studies. To reveal the mechanism, ZK61 alloys reinforced with reduced graphene oxide (rGO) are fabricated by spark plasma sintering (SPS). After compressive tests in the direction of the axial pressure in SPS (Z direction) and the direction perpendicular to the axial pressure (X/Y direction), the rGO/ZK61 composites exhibit high ductility in the Z direction. Transmission electron microscopy (TEM) reveals that some of the aligned rGO sheets are parallel to the X/Y direction. The aligned rGO sheets show a high ability to suppress deformation twinning in the Z direction and provide high strain hardening. This activates the non-basal slip system to improve ductility, thereby leading to highly uniform elongation and good ductility.

Optimization of plasma nitrided, liquid nitrided & PVD TiN coated H13-D2 friction drilling tool on AZ31B magnesium alloy

This study investigates the effects of input parameters and coating techniques for realizing smooth surface finish on AZ31B magnesium alloy. Response surface methodology was used for predicting the best input parameters. Three kinds of coating parameters were adopted on a H13-D2 friction drilling tool. Lightweight magnesium alloy (AZ31B) of less than 4 mm commonly used in automotive and aeronautical sectors was used as working material in this research. Plasma nitriding, Liquid nitriding and PVD- Titanium coating techniques were used for increasing the tool life. The main focus of this research was to find an optimized coated tool. Surface roughness and time consumption during friction drilling technique was focused in this research. Using ANOVA, it was established that PVD Titanium Nitrided H13-D2 tool is best suited for machining AZ31B alloy realizing a surface roughness of 0.43 µm at 4000 rpm & 50 mm/rev.

Fabrication and Numerical Analysis of Friction Stir Back Extruded Lightweight Magnesium Alloy Heat Pipes

Heat pipes are used for a variety of cooling applications and the major users are the aerospace and electronics industries. The ideal requirement for efficient heat pipes is that they be as light as possible while still maintaining a very good thermal conductivity. In this research work, Magnesium alloy ZE41 was tested as a competent material for the manufacturing of heat pipes. The Magnesium alloy heat pipes with improved grain structure, homogeneous distribution of rare earth elements, better strength were manufactured by Friction Stir Back Extrusion (FSBE). The heat pipes were tested for compatibility with varying mixtures of working fluids namely Acetone and Ethanol by performing Immersion corrosion test. The thermal efficiency of the heat pipes was also determined from simulations by employing suitable properties of the working fluids and the component.

Enhanced Precipitation and Recrystallization in a Mg-Zn Alloy During Low-Temperature Extrusion

Lightweight magnesium (Mg) alloys have great potential to be used in a variety of structural applications. However, Mg’s hexagonal crystal lattice and the limited number of deformation slip systems create fundamental challenges during forming. Furthermore, the selection and amounts of alloying additions can lead to complex phases and transformations or location-sensitive precipitate reactions (i.e., in grain or grain boundary regions). Mg-Zn alloys are promising candidates for applications requiring high strength due to their high hardening response. In this study, we processed solution treated Mg-3Zn (wt.%) using equal channel angular extrusion (ECAE) along the Bc route at 150 oC. The microstructure of the extruded material showed two distinct regions. The grain interior showed a dense distribution of nano precipitates. The grain boundary region contains recrystallized ultrafine grains with some reprecipitation occurring inside them. We employed the Lukác-Balík strain hardening model to estimate the dislocation density evolution during the processing, and we linked these dislocations to the high density of precipitates seen in the grain interiors.

Effect of Rotational Speed on Microstructure and Mechanical Properties in Submerged Friction Stir Welding of ME20M Magnesium Alloy

Submerged friction stir welding of magnesium alloys has not been well investigated to date. ME20M is an important lightweight magnesium (Mg) alloy with enhanced yield strength and heat resistance that merits further research. In this paper, submerged friction stir welding of the ME20M Mg alloy was carried out using different parameters for the underwater cooling. Defect-free weld joints were produced, and the macrostructure, microstructure, tensile properties, and hardness were investigated. The results show that by increasing the rotational speed, the grain size of the weld nugget increased, the tensile strength of the joint decreased, and the microhardness of the different weld zones decreased. The finest obtained grain size was about 3.5 µm in the weld nugget at a rotational speed of 1100 rpm. The highest tensile strength achieved was 183.2 MPa, which was ~ 76.32% of the base metal. The highest and lowest hardness values of the weld joint were obtained at rotational speeds of 1100 and 1600 rpm, respectively, in the weld nugget and heat-affected zones.

Smaller but more ductile

Light Metals Poor ductility is one limiting factor in widespread use of strong but lightweight magnesium alloys in cars, trains, and planes. The usual way to try to circumvent this poor ductility is by adding other elements, which can be costly. Liu et al. show that very small samples of pure magnesium are much more ductile than previously believed (see the Perspective by Proust). The small samples suppress the deformation twinning that causes fractures in larger samples. Avoiding this mechanism should allow development of high-ductility magnesium and other metal alloys. Science , this issue p. [73][1]; see also p. [30][2] [1]: /lookup/doi/10.1126/science.aaw2843 [2]: /lookup/doi/10.1126/science.aax9732

Large plasticity in magnesium mediated by pyramidal dislocations.

Lightweight magnesium alloys are attractive as structural materials for improving energy efficiency in applications such as weight reduction of transportation vehicles. One major obstacle for widespread applications is the limited ductility of magnesium, which has been attributed to [Formula: see text] dislocations failing to accommodate plastic strain. We demonstrate, using in situ transmission electron microscope mechanical testing, that [Formula: see text] dislocations of various characters can accommodate considerable plasticity through gliding on pyramidal planes. We found that submicrometer-size magnesium samples exhibit high plasticity that is far greater than for their bulk counterparts. Small crystal size usually brings high stress, which in turn activates more [Formula: see text] dislocations in magnesium to accommodate plasticity, leading to both high strength and good plasticity.

The effect of an MgO intermediate layer on a nanostructured HA coating fabricated by HVOF on an Mg alloy

Lightweight magnesium alloys are currently being investigated as implants due to their biodegradability and mechanical properties. However, their clinical applications are limited by their high corrosion rate in the physiological environment. Coating Mg-based alloys is an approach that is used to delay primary corrosion and increase their lifetime. Therefore, hydroxyapatite was coated on anodized and non-anodized magnesium substrates using high-velocity oxy-fuel spraying. This study aimed to evaluate the effect of the MgO intermediate layer between the hydroxyapatite coating and Mg alloy substrate. The microstructure and corrosion behaviour of the coated samples are the main focuses of this study. X-ray diffraction spectroscopy was used to analyse the phases. Electrochemical impedance spectroscopy was performed in simulated body fluid. The results revealed that the presence of an anodized layer increased corrosion resistance.