Papers by Author: Woo Jin Park

Abstract: The effect of warm rolling under various conditions on the microstructure and mechanical property was investigated using an AZ31 Mg alloy sheet. Several processing parameters such as initial thickness, thickness reduction by a single pass rolling, rolling temperature, roll speed, and roll temperature were varied to elicit an optimum condition for the warm rolling process of AZ31 Mg alloy. Microstructure and mechanical properties were measured for specimens subjected to rolling experiments of various conditions. Warm rolling of 30% thickness reduction per pass was possible without any side-crack at temperatures as low as 200oC under the roll speed of 30 m/min. The initial microstructure before rolling was the mixed one consisting of partially recrystallized and cast structures. Grain refinement was found to occur actively during the warm rolling, producing a very fine grain size of 7 µm after 50% reduction in single pass rolling at 200oC. Yield strength of 204MPa, tensile strength of 330MPa and uniform elongation of 32% have been obtained in warm rolled sheets.

Abstract: The spray forming process was used to produce Al-25Si alloy in this study. The microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles with average diameter of 5~7 µm. To deduce the extrusion condition, a series of compression tests has been conducted at temperatures ranging from RT to 500oC. The strain rate sensitivity parameter (m) of this alloy has been found to be very low ( ≤0.1) below 300oC and reached maximum value of about 0.13 at 500°C. The extrusion has been successfully conducted at the temperatures of 300°C and above with the ratio of area reduction of 28 and 40. The processing map for hot working has also been constructed.