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2 Archives of Materials Science and Engineering

2 2008

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Thermal residual stress investigation in AS52/ Al18B4O33 magnesium matrix composite by thermal cycling test

Lee W., Park Y., Park B., Park I., Park Y.

Archives of Materials Science and Engineering

2008

Vol. 32, nr 1

17-20

Purpose: MMCs have microscopic scale thermal residual stress that is generated after cooling from high temperature Because of the difference of thermal expansion coefficient between the matrix and reinforcement. Because of their high service temperature, automobile parts experience thermal cycling between room and service temperature. Those thermal cycles can vary the properties of the MMCs by changing residual stress field. In this study, the relations between residual stresses and hardness were investigated. Design/methodology/approach: For the residual stress investigations, thermal cycling test was performed. After thermal cycling testing, the thermal residual stress of the MMC was investigated using high resolution Xray diffraction test. On the other hand, the residual stress was calculated by the finite elements method and it was compared to the experimental results. Findings: The residual stress relaxed in the matrix with thermal cycling. With the relaxation of the residual stress, the hardness of the composite was decreased. Research limitations/implications: In this study, the relaxation of residual stress of MMCs was observed with thermal cycling. Further investigations for the mechanical properties, like tensile behaviour and wear properties, should be needed in next study. Originality/value: In this study, numerically calculated residual stress in magnesium matrix MMCs was compared with experimental results.

Microstructural characterization and mechanical properties of Mg-xSn-Al-Zn alloys

Kim B., Jeon J., Park K., Park B., Park Y., Park I.

Archives of Materials Science and Engineering

2008

Vol. 30, nr 2

93-96

Purpose: In this study, the microstructure and mechanical properties of as-cast Mg-xSn-Al-Zn alloys were investigated. Design/methodology/approach: Ingot was fabricated by a squeeze cast. The alloys were induction melted at 750stopniC in a mild steel crucible under CO2+2%SF6 mixed gas atmosphere and cast into a permanent mould coated with boron nitride spray held at approximately 350 stopniC . Tensile tests were carried out at room temperature in a screw-driven tensile testing machine and crosshead speed was 0.2 mm/min. Microstructural observation was carried out using a optical microscope (OM) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDS). Findings: It is found that the tensile strength and elongation decreased at room temperature increased with Sn concentration. As a consequence, 5wt% Sn addition was the one exhibiting the best tensile properties at room temperature. The micro-hardness of the alloy continuously increased with increasing the Sn concentration. Practical implications: The investigations of microstructure of commercially magnesium alloys are important for achieving desired mechanical behaviour of the material. Originality/value: The fracture behaviors of magnesium alloys are investigated.