Kyung Chul Park

Microstructural characterisation and mechanical properties of Mg–xSn–5Al–1Zn alloys

Abstract In this study, the microstructure and mechanical properties of as cast Mg–x Sn–5Al–1Zn alloys were investigated. The microstructures of the alloys were characterised by the presence of Mg2Sn and Mg17Al12 precipitates. The greatest tensile strength and elongation were obtained at the alloy containing 5 wt-%Sn at room temperature. Microhardness of the alloys and volume fraction of the Mg2Sn precipitates increased with increasing Sn content. Fractographic analysis demonstrated that dimple and cleavage facet were dominant mechanisms of these alloys tested at room and elevated temperature. The portion of cleavage facet was increased with the increment of Sn at the room and elevated temperatures.

Influence of Sr and Zn additions on corrosion behaviour of Mg–6Sn–5Al–2Si alloys

Abstract In the present work, the effect of Sr and Zn additions on the corrosion behaviour of Mg–6Sn–5Al–2Si (TAS652) alloys was investigated. Microstructure, potentiodynamic polarisation, electrochemical impedance and immersion tests were carried out in 3˙5% NaCl solution to estimate the corrosion behaviour of TAS652 alloys. The TAS652, TAS652–Sr and TAS652–Zn alloys were fabricated by permanent mould casting. The addition of Sr was found to be efficient to modify and refine the microstructure of the TAS652 alloy. A morphology change in Mg2Si particles from Chinese script shape to a polygonal type was observed. Such modified microstructure resulted in significant improvement of the corrosion properties as compared to the TAS652 base alloy. On the other hand, Zn addition caused to slightly increase the volume fraction of Mg17Al12 phases. Since they are cathodic with the matrix, the galvanic corrosion was activated by Zn addition. The addition of small amount Sr was effective to the corrosion resistance of the TAS652 alloy, but the Zn addition was detrimental.

A PPAR Pan Agonist, MHY2013 Alleviates Age-Related Hepatic Lipid Accumulation by Promoting Fatty Acid Oxidation and Suppressing Inflammation

Nonalcoholic fatty liver disease (NAFLD) is frequently observed in obese and aged individuals. Peroxisome proliferator-activated receptors (PPARs) play a role in regulating hepatic lipid accumulation, a hallmark of NAFLD development. A PPAR pan agonist, 2-(4-(5,6-methylenedioxybenzo[d]thiazol-2-yl)-2-methylphenoxy)-2-methylpropanoic acid (MHY2013) has been shown to prevent fatty liver formation and insulin resistance in obese mice (db/db) model. However, the beneficial effects of MHY2013 in aged model remain unknown. In this study, we investigated whether MHY2013 alleviates hepatic lipid accumulation in aged Sprague-Dawley (SD) rats. We confirmed that MHY2013 increased the activities of three PPAR subtypes in HepG2 cells using luciferase assay. When administered orally in aged SD rats, MHY2013 markedly decreased the hepatic triglyceride levels without changes in body weight. Regarding underlying mechanisms, MHY2013 increased the mRNA levels of lipid oxidation-related genes, including carnitine palmitoyltransferase 1 (CPT1) and peroxisomal acyl-CoA oxidase 1 (ACOX1), without apparent change in the mRNA expression of lipogenesis-related genes. Furthermore, MHY2013 significantly increased systemic fibroblast growth factor 21 (FGF21) and adiponectin levels and suppressed inflammatory mRNA expression in the liver. In conclusion, MHY2013 alleviated age-related hepatic lipid accumulation, in part by upregulating β-oxidation signaling and suppressing inflammation in the liver. Therefore, MHY2013 is a potential pharmaceutical agent for treating age-related hepatic lipid accumulation.

Novel PPARα agonist MHY553 alleviates hepatic steatosis by increasing fatty acid oxidation and decreasing inflammation during aging

Hepatic steatosis is frequently observed in obese and aged individuals. Because hepatic steatosis is closely associated with metabolic syndromes, including insulin resistance, dyslipidemia, and inflammation, numerous efforts have been made to develop compounds that ameliorate it. Here, a novel peroxisome proliferator-activated receptor (PPAR) α agonist, 4-(benzo[d]thiazol-2-yl)benzene-1,3-diol (MHY553) was developed, and investigated its beneficial effects on hepatic steatosis using young and old Sprague-Dawley rats and HepG2 cells. Docking simulation and Western blotting confirmed that the activity of PPARα, but not that of the other PPAR subtypes, was increased by MHY553 treatment. When administered orally, MHY553 markedly ameliorated aging-induced hepatic steatosis without changes in body weight and serum levels of liver injury markers. Consistent with in vivo results, MHY553 inhibited triglyceride accumulation induced by a liver X receptor agonist in HepG2 cells. Regarding underlying mechanisms, MHY553 stimulated PPARα translocation into the nucleus and increased mRNA levels of its downstream genes related to fatty acid oxidation, including CPT-1A and ACOX1, without apparent change in lipogenesis signaling. Furthermore, MHY553 significantly suppresses inflammatory mRNA expression in old rats. In conclusion, MHY553 is a novel PPARα agonist that improved aged-induced hepatic steatosis, in part by increasing β-oxidation signaling and decreasing inflammation in the liver. MHY553 is a potential pharmaceutical agent for treating hepatic steatosis in aging.

Mechanical and Creep Properties of the Cast Magnesium Alloy

Currently most commercial magnesium alloys are based on the Mg-Al system and it is reasonably well developed. Although the Mg-Al based alloy system has excellent castability and adequate ambient temperature mechanical properties, it shows poor creep resistance. Therefore, our group has focused on finding the way to improve the creep properties of Mg alloys. This paper presents a brief summary of the research achievements in this area recently made by AFML(Advance Functional Materials Lab in PNU, Korea). The properties of newly designed Mg alloys in our group are presented and compared with the properties of commercial A356 alloy.

THE ELECTROCHEMICAL BEHAVIOR OF Mg-Ce-Zn SYSTEM

In the present work, the electrochemical behavior of Mg-xCe-1Zn (x = 3, 8 and 13wt.%) alloys have been investigated. The alloys were fabricated by using a vacuum induction melting method under an argon atmosphere. Potentiodynamic polarization was carried out in 3.5% NaCl solution of pH 7.2 at room temperature to evaluate the corrosion properties of Mg-xCe-1Zn (x = 3, 8 and 13wt.%) alloys. The microstructure of the Mg-(3, 8 and 13wt.%)Ce-1Zn alloys were mainly consisted of α-Mg and eutectic Mg12Ce phase. With the increase of Ce contents, the volume percent and size of the eutectic Mg12Ce phase were increased. Results indicated that the corrosion rate of Mg-xCe-Zn alloy was increased by the excessive Ce addition.

In Situ Fracture Behavior of AZ51 and AZT513 Alloy

The fracture behavior of Mg-5Al-1Zn and Mg-5Al-1Zn-3Sn alloy was investigated by direct observation of microfracture process using an in-situ loading stage installed inside a scanning electron microscope chamber. Crack was initiated at the interface of Mg/second-phase particles or second-phase particles. Fracture of the alloys was predominantly dimple or/and quasi-cleavage failure. The improvement of what could be explained by mechanisms of blocking of crack or shear band propagation, formation of multiple shear bands, crack blunting and shear band branching.

The Influence of Sn Addition on the Corrosion Behavior of Mg-5Al-1Zn Alloy

In the present work, the effect of Sn addition on the corrosion behavior of Mg–5Al–1Zn alloys was investigated. Microstructure, potentiodynamic polarization and immersion tests were carried out in 3.5% NaCl solution of pH 7.2 to estimate the corrosion behavior of AZ51 alloys with and without Sn addition. Mg17Al12 and Mg2Sn phases were mainly precipitated in inter-dendrite structures. With increasing the Sn content, the volume fraction of the Mg2Sn phase was increased and coarsening tendency was observed. The corrosion resistance was increased by Sn addition. Especially, the AZ51-5wt.%Sn alloy characterized the superior corrosion resistance among the four alloys. The Sn is known for a high hydrogen overvoltage and the secondary phases effectively formed the network structure, resulting in a drastically decreasing corrosion rate of AZ51 alloy.