Suk Bong Kang

Bio: Suk Bong Kang is an academic researcher. The author has contributed to research in topics: Microstructure & Alloy. The author has an hindex of 17, co-authored 49 publications receiving 939 citations.

Enhanced plasticity of twin-roll cast ZK60 magnesium alloy through differential speed rolling

Abstract: ZK60 magnesium alloy strips were produced by twin-roll cast (TRC) and then subjected to differential speed rolling (DSR) with a velocity ratio of 1:1.2 and 1:1.5. Microstructures, textures and mechanical properties of the DSR-processed sheets were compared with those of equal speed rolling (ESR) to examine the effects of velocity ratio. The sheets processed by DSR showed significantly higher elongation and slightly lower tensile strength than those of the ESR-processed sheet, which can be attributed to the inclination and weakening of the basal fiber texture. Combining the DSR and TRC techniques is suggested to be an effective way of plasticity enhancement of the magnesium alloys, in additional to apparent advantages in energy saving.

Thermal decomposition of silicon carbide in a plasma-sprayed Cu/SiC composite deposit

Abstract: A functionally graded SiC/Cu metal matrix composite (MMC) produced by plasma spray has been studied. The phase constituents of Cu, Cu2O, CuO, Cu3Si, Si, and SiC in the plasma-sprayed deposits were analyzed by XRD. The SiC was decomposed into Si and C, and copper silicide was then formed. Most pores were found in the vicinity of SiC due to the decomposition of the SiC and thermal expansion mismatch between SiC and Cu during rapid solidification. From the thermodynamic consideration, the overall decomposition of SiC during plasma spray process occurs as follows: (1) SiC(s) = Si(s) + C(s); (2) SiC(s) + CO2(g) = Si(s, l) + 2CO(g) and SiC(s) + 2CO(g) = SiO2(s) + 3C(s); (3) SiO2(s) + CO(g) = Si(s, l) + 2CO2(g). Based on the analyses of the electron probe X-ray microscope analyzer (EPMA) and X-ray photoelectron spectroscopy (XPS), it was revealed that dissociated carbon was present in the deposits.

Microstructure and mechanical properties of twin-roll cast Mg–4.5Al–1.0Zn sheets processed by differential speed rolling

Abstract: The microstructure and mechanical properties of the twin-roll cast (TRC) Mg–4.5Al–1.0Zn alloy sheets produced by differential speed rolling (DSR) were investigated by optical microscopy, transmission electron microscope and electron backscattered diffraction. The results are compared with those of the sheet processed by equal speed rolling (ESR). It is shown that twining played an important role at the initial stage of rolling. With the increase of the rolling reduction, the microstructures in the processed sheets become more homogeneous and they are more refined by DSR than by ESR. After annealing, the sheet processed by DSR shows a higher elongation and slightly lower yield strength than those of the ESR-processed sheet, which could be attributed to grain refinement and texture weakening. These results suggest that, in comparison with conventional casting and rolling, the combined technology of TRC and DSR is a more effective way to process magnesium sheets with enhanced formability after final annealing.

Deformation textures of AA8011 aluminum alloy sheets severely deformed by accumulative roll bonding

Abstract: A fully annealed AA8011 aluminum alloy sheet containing a number of large particles (∼5 µm) was severely deformed up to an equivalent strain of 12 by an accumulative roll-bonding (ARB) process. The texture evolution during the ARB process was clarified, along with the microstructure. The ARB-processed aluminum alloy sheets had a different texture distribution through the sheet thickness, due to the high friction between the roll and the material during the ARB process. The shear textures composed of {001} 〈110〉 and {111} 〈110〉 orientations developed at the sheet surface, while the rolling textures, including Cu {112} 〈111〉 and Dillamore {4,4,11} 〈11,11,8〉 orientations, developed at the sheet center. The textural change from a shear texture to a rolling texture at the sheet center during the ARB process contributed to an increase in the fraction of high-angle boundaries. Also, a large number of second-phase particles in the AA8011 alloy sheets weakened the texture. Up to the medium strain range (below ɛ=6.4), relatively weak textures developed, due to the inhomogeneous deformation around the second-phase particles; after the strain of 6.4, strong rolling-texture components, such as the Dillamore and Cu orientations, developed. This remarkable textural change can be explained by the reprecipitation of fine particles in grain interiors.

Microstructure and mechanical properties of Mg–4.5Al–1.0Zn alloy sheets produced by twin roll casting and sequential warm rolling

Abstract: Microstructure and mechanical properties of Mg–4.5Al–1.0Zn (designated as AZ41M in short) alloy sheets produced by twin roll casting, sequential warm rolling and post annealing at 350 °C were studied in this paper. Microstructure of twin roll casting strip consisted of dendrite structure, eutectics and intermetallic compounds located in the interdendritic region. AZ41M alloy sheets showed higher strength and lower elongation after sequential warm rolling, while post annealing after warm rolling induced the decrease of strength and increase of elongation. This results in the balance of strength and elongation in AZ41M alloy sheets. The grain refinement during manufacturing processes was attributed to the formation of heavy shear bands, high dislocation density, twinning, and precipitates of Al 2 Ca/Mg 2 Ca or Al 8 Mn 5 and the Ca dissolution into Mg 17 Al 12 phase.

Towards magnesium alloys for high-volume automotive applications

Abstract: Reducing vehicle weight is an important approach for increasing fuel economy, addressing regulatory requirements, and meeting consumer needs. Magnesium alloys are among the lightest structural metals and offer tremendous weight saving potential; however, many technical and commercial barriers limit their use in today's cars and trucks. Following a brief review of historical trends in vehicle weight and automotive magnesium, we describe key barriers to wider adoption of magnesium in high-volume vehicle applications. A discussion of manufacturing and processing, in-service performance, and cost requirements identifies specific development needs and opportunities while framing promising paths forward.

A selective laser melting and solution heat treatment refined Al-12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

Abstract: This study shows that a eutectic Al–12Si alloy with controllable ultrafine microstructure and excellent mechanical properties can be achieved by using selective laser melting and subsequent solution heat treatment. This provides a novel and promising approach to the refinement of eutectic Al–Si alloys. Unlike Al–12Si alloys fabricated and refined by traditional methods, the as-fabricated Al–12Si in this study contains nano-sized spherical Si particles surrounding a supersaturated Al matrix. During solution heat treatment, precipitation and coalescence of the Si particles occur, which decreases the Si concentration in the matrix and sub-micron to micron-sized spherical particles embedded in an Al matrix form. The as-fabricated Al–12Si exhibits significantly better tensile properties than the traditionally produced counterparts; while the solution treated Al–12Si has an extremely high ductility of approximately 25%. Importantly, the mechanical properties of the Al–12Si can be tailored through controlling the precipitation and coalescence of the Si particles by varying the solution heat treatment time. A detailed transmission electron microscopy study was conducted to investigate this Al–12Si alloy with ultrafine eutectic microstructure. The excellent tensile properties have been attributed to the refined eutectic microstructure containing spherical Si particles. The formation of this unique microstructure is due to the super heating and an extremely high cooling rate during selective laser melting and the subsequent solution heat treatment, which enables Si to grow along its most stable plane {1 1 1}Si.

Study on mechanical and wear properties of Al 7075/Al2O3/graphite hybrid composites

Abstract: This work investigated the influence of graphite on the wear behavior of Al 7075/Al 2 O 3 /5 wt.% graphite hybrid composite. The investigation reveals the effectiveness of incorporation of graphite in the composite for gaining wear reduction. The Al 7075 (aluminium alloy 7075) reinforced with Al 2 O 3 –graphite were investigated. The composites were fabricated using liquid metallurgy route. Ceramic particles along with solid lubricating materials were incorporated into aluminium alloy matrix to accomplish reduction in both wear resistance and coefficient of friction. The Al 7075/Al 2 O 3 /graphite hybrid composite was prepared with 5 wt.% graphite particles addition and 2, 4, 6 and 8 wt.% of Al 2 O 3 . The hardness, tensile strength, flexural strength and compression strength of the Al 7075–Al 2 O 3 –graphite hybrid composites are found to be increased by increased weight percentage of ceramic phase. The wear properties of the hybrid composites containing graphite exhibited the superior wear-resistance properties.

Nanostructured aluminium alloys produced by severe plastic deformation: New horizons in development

Abstract: In recent years, much progress has been made in the studies of nanostructured Al alloys for advanced structural and functional use associated both with the development of novel routes for the fabrication of bulk nanostructured materials using severe plastic deformation (SPD) techniques and with investigation of fundamental mechanisms leading to improved properties. This review paper discusses new concepts and principles in application of SPD processing to fabricate bulk nanostructured Al alloys with advanced properties. Special emphasis is placed on the relationship between microstructural features, mechanical, chemical, and physical properties, as well as the innovation potential of the SPD-produced nanostructured Al alloys.

Texture evolution in equal-channel angular extrusion

Abstract: The focus of this article is texture development in metals of fcc, bcc, and hcp crystal structure processed by a severe plastic deformation (SPD) technique called equal-channel angular extrusion (ECAE) or equal-channel angular pressing (ECAP). The ECAE process involves very large plastic strains and is well known for its ability to refine the grain size of a polycrystalline metal to submicron or even nano-size lengthscales depending on the material. During this process, the texture also changes substantially. While the strength, microstructure and formability of ECAE-deformed metals have received much attention, texture evolution and its connection with these properties have not. In this article, we cover a multitude of factors that can influence texture evolution, such as applied strain path, die geometry, processing conditions, deformation inhomogeneities, accumulated strain, crystal structure, material plastic behavior, initial texture, dynamic recrystallization, substructure, and deformation twinning. We evaluate current constitutive models for texture evolution based on the physics they include and their agreement with measurements. Last, we discuss the influence of texture on post-processed mechanical response, plastic anisotropy, and grain refinement, properties which have made ECAE, as well as other SPD processes, attractive. It is our intent to make SPD researchers aware of the importance of texture development in SPD and provide the background, guidance, and methodologies necessary for incorporating texture analyses in their studies.