• Corrosion Science and Technology
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• 제23권4호
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• pp.289-295
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• 2024

Zn-Mg-Al alloy hot-dip galvanized steel sheet has high corrosion resistance. Compared to conventional Zn coating with the same coating thickness, the high corrosion resistance Zn-Mg-Al coating is more corrosion-resistant. Various coating compositions are commercially produced and applied in diverse fields. However, these steel sheets typically contain up to 3 wt% magnesium. In recent years, there has been a growing demand for higher corrosion resistance in harsh corrosive environments. Therefore, variations in Mg and Al contents were investigated while evaluating primary properties and performance. As a result, we developed new alloy-coated steel with ultra-high corrosion resistance. A Zn-5 wt%Mg-Al coated steel sheet was evaluated for its corrosion resistance and various properties. As the amount of Mg added increased, the corrosion loss tended to decrease. The corrosion resistance of the coated steel sheet in a particular composition, the Zn-5 wt%Mg-Al coating sheet, was about 1.5 to 2 times higher than that of the conventional Zn-3 wt%Mg-Al coating sheet. Ultimately, this ultra-high corrosion-resistance coated steel sheet will provide a robust solution to conserve Zn resources and contribute to a low-carbon society.

• Transactions of Materials Processing
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• 제18권4호
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• pp.347-353
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• 2009

The apparent activation energy, the applied stress exponent, and rupture life have been measured from creep experiments over the range of $200^{\circ}C$ to $220^{\circ}C$ and the applied stress range of 64MPa to 94MPa. The materials were used AZ31 magnesium alloys treated by plasma electrolytic oxidation of $20{\mu}m$ and $40{\mu}m$ at surface to investigate the its influence on creep behavior, and creep tests were carried out under constant applied stress and temperature. The experimental results showed that the dipper the thickness of surface treatment the higher the activation energy and stress exponent. And the higher temperature and applied stress, the lower stress exponent and activation energy, respectively. Also the dipper the thickness of surface treatment the longer creep rupture time.

• Transactions of Materials Processing
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• 제33권3호
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• pp.178-184
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• 2024

In this study, we investigated the effects of extrusion ratio and extrusion temperature on the microstructure and tensile properties of extruded Mg-6Al-0.3Mn-0.3Ca-0.2Y (SEN6) alloy. As the extrusion ratio and temperature increase, dynamic recrystallization during extrusion is promoted, leading to the formation of a fully recrystallized microstructure with increased grain size. Additionally, the increases in extrusion ratio and temperature lead to texture strengthening, exhibiting a higher maximum texture intensity. The extruded materials contain three types of secondary phases, i.e., Al₈Mn₄Y, Al₂Y, and Al₂Ca, with irregular or polygonal shapes. The quantity, size, distribution, and area fraction of the second-phase particles are nearly identical between the two materials. Despite its larger grain size, the tensile yield strength of the material extruded at 450 ℃ and an extrusion ratio of 25 (450-25) is higher than that of the material extruded at 325 ℃ and an extrusion ratio of 10 (325-10), which is mainly attributed to the stronger texture hardening effect of the former. The ultimate tensile strength is similar in the two materials, owing to the higher work hardening rate in the 325-10 extrudate. Despite differences in grain size and recrystallization fraction, numerous twins are formed throughout the specimen during tensile deformation in both materials; consequently, the two materials exhibit nearly the same tensile elongation.

• Korean Journal of Materials Research
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• 제26권10호
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• pp.513-520
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• 2016

The effect of NaOH concentration on the properties of electrolytic plasma processing (EPP) coating formed on AZ61A Mg alloy is studied. Various types of EPP were employed on magnesium alloy AZ61A in a silicate bath with different concentrations of NaOH additive. Analysis of the composition and structure of the coating layers was carried out using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that the oxide coating layer mainly consisted of MgO and $Mg_2SiO_4$; its porosity and thickness were highly dependent on the NaOH concentration. The Vickers hardness was over 900 HV for all the coatings. The oxide layer with 3 g/l of NaOH concentration exhibited the highest hardness value (1220 HV) and the lowest wear rate. Potentiodynamic testing of the 3 g/l NaOH concentration showed that this concentration had the highest corrosion resistance value of $2.04{\times}10^5{\Omega}cm^2$; however, the corrosion current density value of $5.80{\times}10^{-7}A/cm^2$ was the lowest such value.

• Transactions of Materials Processing
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• 제21권1호
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• pp.49-57
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• 2012

It is difficult to estimate the properties of multilayered sheet because they are composed of one or more different materials. Plastic deformation behavior of the multilayered sheet is quite different as compared to each material individually. The deformation behavior of multilayered sheet should be investigated in order to prevent forming defects and to predict the properties of the formed part. In this study, the mechanical properties and formability of stainless steel-aluminum-magnesium multilayered sheet were investigated. The multilayered sheet needs to be deformed at an elevated temperature because of its poor formability at room temperature. Uniaxial tensile tests were performed at various temperatures and strain rates. Fracture patterns changed mainly at a temperature of $200^{\circ}C$. Uniform and total elongation of multilayered sheet increased to values greater than those of each material when deformed at $250^{\circ}C$. The limiting drawing ratio (LDR) was obtained using a circular cup deep drawing test to measure the formability of the multilayered sheet. A maximum value for the LDR of about 2 was achieved at $250^{\circ}C$, which is the appropriate forming temperature for the Mg alloy. Fracture patterns on a circular cup and thickness of formed part were predicted by a rigid-viscoplastic FEM analysis. Two kinds of modeling techniques were used to simulate deep drawing process of multilayered sheet. A single-layer FE-model, which combines the three different layers into a macroscopic single layer, predicted well the thickness distribution of the drawn cup. In contrast, the location and the time of fracture were estimated better with a multi-layer FE model, which used different material properties for each of the three layers.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.23-23
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• 2018

In this study, new titanium alloys were prepared by adding elements such as tantalum (Ta), zirconium (Zr) and the like to complement the biological, chemical and mechanical properties of titanium alloys. The Ti-40Ta-xZr ternary alloy was formed on the basis of Ti-40Ta alloy with the contents of Zr in the contents of 0, 3, 7 and 15 wt. %. Plasma electrolytic oxidation (PEO), which combines high-voltage sparks and electrochemical oxidation, is a novel method to form ceramic coatings on light metals such as Ti and its alloys. These oxide film produced by the electrochemical surface treatment is a thick and uniform porous form. It is also composed of hydroxyapatite and calcium phosphate-based phases, so it has the characteristics of bone inorganic, non-toxic and very high bioactivity and biocompatibility. Ti-40Ta-xZr alloys were homogenized in an Ar atmosphere at $1050^{\circ}C$ for 1 hour and then quenched in ice water. The electrochemical oxide film was applied by using a power supply of 280 V for 3 minutes in 0.15 M calcium acetate monohydrate ($Ca(CH_3COO)_2{\cdot}H_2O$) and 0.02 M calcium glycerophosphate ($C_3H_7CaO_6P$) electrolyte. A small amount of 0.0075M zinc acetate and magnesium acetate were added to the electrolyte to enhance the bioactivity. The mechanical properties of the coated surface of Ti-40Ta-xZr alloys were evaluated by Vickers hardness, roughness test, and elastic modulus using nano-indentation, and the surface wettability was evaluated by measuring the contact angle of the coated surface. In addition, cell activation and differentiation were examined by cell culture of HEK 293 (Human embryonic kidney 293) cell proliferation. Surface properties of the alloys were analyzed by scanning electron microscopy(FE-SEM), EDS, and X-ray diffraction analysis (XRD).

• Advances in materials Research
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• 제8권1호
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• pp.47-73
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• 2019

Joining of Mg/Ti hybrid structures by welding for automotive and aerospace applications has attracted great attention in recent years due mainly to its potential benefit of energy saving and emission reduction. However, joining them has been hampered with many difficulties due to their physical and metallurgical incompatibilities. Different joining processes have been employed to join Mg/Ti, and in most cases in order to get a metallurgical bonding between them was the use of an intermediate element at the interface or mutual diffusion of alloying elements from the base materials. The formation of a reaction product (in the form of solid solution or intermetallic compound) along the interface between the Mg and Ti is responsible for formation of a metallurgical bond. However, the interfacial bonding achieved and the joints performance depend significantly on the newly formed reaction product(s). Thus, a thorough understanding of the interaction between the selected intermediate elements with the base metals along with the influence of the associated welding parameters are essential. This review is timely as it presents on the current paradigm and progress in welding and joining of Mg/Ti alloys. The factors governing the welding of several important techniques are deliberated along with their joining mechanisms. Some opportunities to improve the welding of Mg/Ti for different welding techniques are also identified.

• Korean Journal of Metals and Materials
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• 제50권6호
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• pp.463-468
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• 2012

A 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ (Mg-23.5Ni-$5Fe_2O_3$) sample was prepared by a quite simple process, reactive mechanical grinding, and its hydriding and dehydriding properties were then investigated. The reactive mechanical grinding of Mg with Ni and $Fe_2O_3$ is considered to facilitate nucleation and shorten the diffusion distances of the hydrogen atoms. After the hydriding-dehydriding cycling, the Mg-23.5Ni-$5Fe_2O_3$ sample contained $Mg_2Ni$ phase. Expansion and contraction of the hydride-forming materials (Mg and $Mg_2Ni$) with the hydriding and dehydriding reactions are also considered to increase the hydriding and dehydriding rates of the mixture by forming defects and cracks leading to the fragmentation of the particles. The temperature dependence of the hydriding rate of the sample is discussed.

• Transactions of Materials Processing
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• 제33권4호
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• pp.285-290
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• 2024

Electropulsing treatment (EPT) has been developed as an alternative to furnace heat treatment (FHT) to exploit its engineering advantages in rapidly annealing metallic materials. Conventionally, the separation of thermal and athermal effects of EPT has been attempted by comparing EPT and FHT specimens processed under identical temperature and duration. However, this method inherently introduces experimental and measurement errors. This study proposes a novel approach to distinguish the thermal and athermal effects of EPT-processed metals using T-shaped specimen with two observation points, namely 'C' and 'D'. For verification, the thermal gradient of T-shaped Mg alloys was examined under various EPT conditions. The points C exhibited higher temperatures compared to those at points D at a given electric current density, because only the former received both thermal and athermal effects. It was confirmed from twelve specimens that the point C at an electric current density of 65 A·mm^-2 and point D at 70 A·mm^-2 exhibited similar temperatures. This developed method is expected to reduce measurement errors in distinguishing thermal and athermal effects, thus providing a deeper understanding of their quantitative contributions in future studies.

• Journal of Hydrogen and New Energy
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• 제22권6호
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• pp.787-793
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• 2011

A 76.5wt%Mg - 23.5wt%Ni (Mg-23.5Ni) sample was prepared by reactive mechanical grinding (RMG) and its hydriding and dehydriding properties were then investigated. Activation of the Mg-23.5Ni sample was completed only after two hydriding (under 12 bar $H_2$) - dehydriding (under 1.0 bar $H_2$) cycles at 593K. The reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation and shorten diffusion distances of hydrogen atoms. After hydriding - dehydriding cycling, the Mg-23.5Ni sample contained Mg2Ni phase.