Papers by Author: Byung Heum Song

Abstract: Ceramic coatings were synthesized on pure Mg and binary Mg-7.1wt%Al alloy by plasma electrolytic oxidation (PEO) technique, and the effect of current ratio, C2/C1, ranging from 0.2 to 0.85 on their mechanical and electrochemical properties was investigated. As the C2/C1 ratio increased, the thickness of the coating layer increased, while surface roughness was almost unchanged. The hardness and wear resistance had a marked tendency to increase with increasing C2/C1 ratio and Mg-Al alloy showed higher hardness and wear resistance at all C2/C1 ratios compared to pure Mg. The weight loss of the pure Mg and Mg-Al alloy in 3.5%NaCl solution was reduced by coatings. However, it had no dependence on the C2/C1 ratio. The wear resistance of the coated Mg-Al alloy was better than that of the coated pure Mg.

Abstract: Pure Mg, binary Mg-5.6wr%Al, Mg-1.0wt%Si and Mg-7.5wt%Zn alloys were coated by plasma electrolytic oxidation (PEO) method, and their wear properties were investigated and discussed based on surface roughness, thickness and component of coatings. All coatings showed porous layer with some volcano top-like pores on the surface and the non-uniform thickness. The coatings on Mg-Al, Mg-Si and Mg-Zn alloys were composed of primarily MgO and Al2O3, SiO2, ZnO, respectively. The coating layer on Mg-Si alloy was thicker than that of Mg-Al and Mg-Zn alloys, while it was less rough. The wear resistance of pure Mg and Mg alloys was improved by PEO method and the coated Mg alloys showed better wear resistance compared to the coated pure Mg. In particular, the coated Mg-Zn alloy revealed the best wear resistance, while the coated Mg-Si alloy had poor wear resistance despite much thicker coating layer.

Abstract: Ceramic coatings were synthesized on pure magnesium, binary Mg-Al and Mg-Zn alloys by plasma electrolytic oxidation (PEO) technique, and their mechanical and electrochemical properties were investigated. The coatings showed porous microstructure and some volcano top-like pores on the surface. The coatings on Mg-Al alloys consisted of MgO, MgAl2O4 and Al2O3. In the coatings on Mg-Zn alloys, MgO and ZnO were detected. The hardness and wear resistance showed slight dependence on Al content but no tendency to increase with increasing Zn content. The coated Mg alloys with Al, Zn showed better corrosion resistance in 3.5%NaCl solution but poor corrosion resistance in methyl alcohol, compared to the coated pure Mg.

Abstract: The bimodal-structured materials composed of Al-5wt%Mg alloy and its composites reinforced with SiC and Al2O3 particles were prepared by ball-milling and subsequent compaction under the pressure of 350MPa and sintering at temperatures ranging from 973K to 1173K for 1h, 3h and 5h. The macro-interface between Al-Mg and Al-Mg/ Al2O3 composite was macroscopically well-bonded compared to that between Al-Mg and Al-Mg/SiC composite under same sintering conditions. The bonding of macro-interface became better as the sintering time and temperature increased, resulting in that the bimodal-structured materials sintered at 1173K for 5h showed the relative density of nearly 100%. In addition, the higher sintering temperature was, the more irregular macro-interface was. The microhardness of macro-interface area was in between the Al- Mg and composites, which was independent of the sintering temperature.