Papers by Keyword: Magnesium Alloy

Abstract: Magnesium (Mg) alloy sheets are expected to contribute to the lightweighting of structural components, owing to their inherent benefits of low density and high specific strength. However, the limited room-temperature press formability exhibited in Mg alloy sheets remains a barrier to their expanded use. A significant factor contributing to the limited formability is the strong basal texture. To improve the room-temperature press formability, ZX series Mg alloy sheets that weakened the basal texture have recently been developed. In our previous study [Hama et al., Mater. Res. Proc., 28(2003), 711-716], cup drawability of a Mg-1.5mass%Zn-0.1mass%Ca (ZX10Mg) alloy sheet was investigated at room temperature. The obtained cup exhibited that the cup height and thickness strains differed significantly in the circumferential direction of the cup. However, a more detailed discussion on the mechanisms of this anisotropic deformation was hampered by a reliance solely on experimental observations. Therefore, in this study, crystal plasticity finite-element simulations of cup drawing of the ZX10Mg alloy sheet were performed. The simulation results qualitatively reproduced macroscopic and microscopic deformation behaviors during cup drawing. Numerical studies showed that the anisotropic deformation during drawing was primarily induced by the texture of the material, suggesting that anisotropic deformation is inevitable unless the anisotropic c-axes distribution remains in the initial texture.

Abstract: In response to the growing trend of miniaturization in electronic products, there is an increasing focus on temperature control and material selection in the manufacturing process. Dissimilar joining of magnesium alloys, commonly used in electronics, has gained significant attention. This study investigates friction stir welding of thin dissimilar magnesium alloy sheets using a micro five-axis milling machine. AZ31 and LZ91 alloys were joined, and the welding parameters, including rotational speed and traverse speed, were carefully designed and monitored. Surface imaging, microstructure, tensile strength, and microhardness were analyzed to assess the results. The findings revealed that due to the rapid heat dissipation of the materials, temperature increases were minimal. At a rotational speed of 15,000 rpm and a traverse speed of 10 mm/min, optimal surface structure, hardness 77 HV, and tensile strength 151 MPa were achieved. The study successfully demonstrated the potential of using friction stir welding for joining thin dissimilar magnesium alloy sheets in industrial applications.

Abstract: In recent years, the weight reduction of components in the automotive and aircraft industries has become a major issue in achieving sustainable development goals (SDGs), as it is critical to reducing fuel and energy consumption. Magnesium (Mg) alloys have the lowest density among all practical metals and have attracted attention as lightweight materials. For weight reduction, rims and wheels are fabricated by the hot forging of Mg alloys, and the shortening of the die life is a problem because of the high load on the die and the tendency to burn and wear caused by adhesion in the hot forging of Mg. The T-shape compression test (TSCT) can evaluate friction in complex deformations involving both extrusion and compression and can achieve a surface area enlargement greater than 50%. In this study, a hot V-groove friction test based on the TSCT is proposed as a friction test that simulates hot extrusion and forging. The friction coefficient is identified from the aspect ratio of the product after compression, as either longitudinal extrusion or transverse compression is the preferred deformation due to the effects of friction. The proposed test combines extrusion and compression deformation, has a high surface area expansion ratio of a greater than 50%, and produces a two-dimensional deformation in which the circle collapses. In addition, the dimensions and compression ratio can be easily changed. In this study, as part of the development of a V-groove friction test, we examine the tool dimensions and mechanism of adhesion under different temperatures and compression ratios. Using the AZ80 alloy as experimental material and varying the temperature and stroke amount, we investigate the effects of the working temperature on adhesion growth during hot forming.

Abstract: Alloys of Magnesium metal have attracted the attention of the automobile industries in the past two decades due to their greater specific strength as well as stiffness. However, increasing the corrosion performance of alloys of magnesium has remained a prime concern in order to attain better performance without using expensive rare-earth elements. In this study, the result of Sn addition (0%, 2%, 4%) to hot rolled binary Mg-2Zn alloy was examined in terms of their corrosion and microstructural properties. To understand microstructural features, optical micrography, and SEM-EDX study were conducted. SEM and EDX analysis confirmed the presence of Sn phase after 2% and 4% addition of Sn. The number of particles increased with the gradual increase in the addition of Sn. However, Sn lowered the melting point of Zn precipitates. Thus, the presence of Zn particles was reduced with the addition of Sn. Electrochemical analyses were conducted in order to study the corrosion performance of the selected alloys by submerging it in NaCl (3.5 wt.%) solution, supported by the SEM micrographs of the corroded surface. It was found that adding tin up to 2% increases corrosion resistance. The addition of 4% Sn, on the other hand, introduced large-size particles of Mg₂Sn, leading to local corrosion initiation sites, micro galvanic in nature, and hence, reducing corrosion resistance.

Abstract: Lightweight metallic alloys in the transport sector are the essential choice to reduce carbon monoxide emissions. Magnesium (Mg) can serve this purpose appreciably because it has a low density compared to other metallic metals and a high strength in a small portion of metals. The reason behind this is having very low weight. Notwithstanding the alloys exhibit high susceptibility to corrosion especially galvanic corrosion, which impedes it from its various applications. The corrosion resistance of magnesium alloy depends largely on the surface film whether it can protect well and the corrosion due to galvanic effect between the second phase particles or microstructures and the magnesium matrix. Role of second phase particles eventually improves the corrosion property by enhancing its resistance to corrosion. Mg-4Zn being a promising alloy, 3 wt% Gd has been added further to investigate the corrosion resistant properties of Mg-4Zn-3Gd alloy. After preparing the alloys by casting method in induction furnace followed by homogenization at 410°C, the sample was hot rolled at 400°C. Preparation of the samples has been verified by EDS, XRF and XRD analysis. Corrosion study has been done for 1 hour, 24 hours and 72 hours. Microstructures have been taken for as cast, homogenized, and as rolled condition before corrosion test. The analysis shows a large difference in the grain size and phase distribution. Due to dynamic recrystallization during rolling hardness also shows differences compared to as cast and homogenized sample. The corrosion test is performed by weight loss test, electrochemical measurement, and immersion test. In the results, it has been seen an increase in corrosion rate at the initial stage, however it came to a constant rate after some time. After corrosion test, optical micrographs (OM) and scanning electron microstructures (SEM) images show typical morphology of corroded surface with some micro cracks. The presence of Gd in Mg-4Zn alloy enhanced the corrosion performance when it is done for longer time.

Abstract: The microstructure of AZ91 (Mg-Al) alloy is comprised of α-Mg and β-Mg₁₇Al₁₂ massive phase. The lower melting point associated with the β-Mg₁₇Al₁₂ phase results in poor creep resistance of the alloy. In the present study, the AZ91 alloy with the addition of calcium (Ca, 1wt%) and cerium (Ce, 1wt%) is cast, and their effect on the microstructure and creep behavior of AZ91 alloy have been investigated. Thermally stable phases such as Al₂Ca and Al₁₁Ce₃ are introduced in the AZ91 alloy through the addition of Ca and Ce elements. Energy dispersive spectroscopy (EDS) and x-ray diffraction analysis confirmed the presence of these intermetallic phases in the microstructure. Tensile creep tests on the as-cast samples were performed at 175^°C temperature under 50 MPa stress. The study shows that the creep resistance of AZ91 alloy is greatly improved with the presence of Al₂Ca and Al₁₁Ce₃ intermetallic phases because of their better thermal stability than β-Mg₁₇Al_12.

Abstract: Mg-Li system alloys also has excellent cold-workability compared to commercial hcp-structured Mg alloys. However, Mg-Li alloys have poor corrosion resistance because not only that is Mg-based alloy but Li as a major alloying element is a less noble metal. For example, Mg-Li alloy sheet indicates high corrosion rate and exfoliation corrosion as a result of long-term corrosion test. The authors reported Mg-14 mass%Li-3 mass%Al alloy has the highest corrosion resistance in β-type solid solution alloy. Even though the optimized alloy composition, the alloy does not have enough corrosion resistance for practical use. In this study, anodized coating on Mg-Li alloy using phosphate solution was investigated. Anodizing of Mg-Li alloy facilitates the dissolution of substrate because of high Li concentration in this alloy. Therefore, the anodizing conditions were widely examined. As a result, the coating with approximately 15-20 μm of the surface layer was successfully formed. The surface layer was composed of MgAl₂O₄ and some phosphorus compounds. The thickness of anodized layer varied with the anodizing conditions. The dense surface layer was formed at a certain anodizing voltage and the corrosion resistance of anodized Mg-Li alloys was improved. However, the surface has some cracks and large flaky compounds. The formation mechanism of dense layer during anodizing were discussed.

Abstract: Laser beam welding is still the focus of research all over the world since new laser sources with more brilliance, higher power, or higher efficiency are being developed. High brilliance leads to thinner fibers when solid-state lasers are used. For welding applications, a thin beam, respective a small focus spot is recommended for low heat input resulting in less deformation. The edge preparation of the welding pieces must be as accurate as possible, and a zero gap is recommended. In earlier research, it was shown, that the gap bridging capacity could be enhanced by the wobbling of small focus spots, as well as refining the grain size in the weld zone by decreasing the focus diameter. Inventions in the optics, like the beam splitting into a core and a ring part, avoid the use of a scanner and can lead to better gap bridging. Nevertheless, the use of a brilliant beam, resulting in a small focus in combination with high power can result in very high welding velocities, just limited by the used machinery. In the present study, a disk laser with 4 kW maximum power and 100 μm focus spot was used to weld 2 mm thick magnesium AZ31 sheets at speeds up to 20 m/min. As expected, the seam width becomes smaller with raising velocity, and some underfill and access material occurred on the surface and the root of the welded sheets. Surprisingly, the texture of the weld seam changed from random at low velocity to a more pronounced texture at high speed with respect to the basal texture of the plate base material. This influences the mechanical behavior, namely the strain to fracture, of the welded joints positively. The high-speed weldments are compared to state-of-the-art weldments of magnesium AZ31, in terms of mechanical strength and elongation to fracture, based on the texture analysis.

Abstract: Magnesium (Mg) alloys are promising biodegradable implant materials. If successful, they do not require second surgical operation for their removal. However, the focus of this study is to address the limitation of fast degradation rate (DR) which hinders the clinical application of Mg alloys. The bio-corrosion rate of any intermetallic alloy is related to its beta (β) phase volume fraction. Thus, homogenization heat treatment (HHT) was carried out to reduce the β phase. The influence of β phase and the hydroxyapatite powders (HAp) was employed to slow down the initial DR of Mg AZ91 alloy. Samples were cut from Mg grade AZ91 alloy ingot in 10mm x 10mm x 3mm dimension. The samples were prepared and divided into two; the first part was classified as as-received sample (sample a) while the second one was processed for HHT. HHT was carried out at 410°C/10h, cooled inside the furnace and named as homogenized sample (sample b). The HAp was synthesized using a simple wet chemical precipitation technique (SWCPT) and deposited on sample b via electrophoretic deposition (EPD) at different voltages with different deposition times. The HAp, uncoated and coated samples were characterized. Potentiodynamic polarization (PP) and immersion tests were carried out in stimulated body fluid (SBF) to estimate the DR and in vitro bioactivity of Mg AZ91 respectively. The results revealed a significant drop in DR from sample a (1.421 mm per year) to coated sample h (3.73 x 10^-4 mm per year). Keywords: Magnesium alloy, biodegradable implants, beta phase, homogenization heat treatment, hydroxyapatite, electrophoretic deposition.

Abstract: With the development of the material databases’ construction, the use of machine learning methods to process data mining to discover new materials has gradually become a hot topic. The mechanical properties of Mg alloys are related to their components and processing technologies, therefore, it is possible to build prediction model between components, processing technologies and mechanical properties. In order to improve the design efficiency of Mg alloys, using machine learning methods to build a prediction model for the mechanical properties of Mg alloys is of vital importance. To achieve efficient material design, this paper proposed an improved random forest (RF) method based on the Particle Swarm Optimization (PSO) algorithm, and built a Mg alloy performance prediction model. Experiments showed that the accuracy was greatly improved compared with the original RF model, and the prediction accuracy of mechanical properties can reach more than 90%.