Byeong Ho Kim

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.

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.