Eok-Soo Kim

A Study on the Microstructure Change with Modification and Cast-forging in Hypereutectic Al-Si Alloys

For application of cast-forging process with Al-Si hypereutectic alloys, casting experiments are carried out by adding P and Sr to Al-Si hypereutectic alloys for eutectic and primary Si refinement treatment. We experimented on the mechanical properties according to microstructural changes, forging ability test and also investigated the mechanical properties after forging. The finest microstructure could be observed respectively when 0.075 wt.% Sr and 0.1 wt.% P were added. In this case, tensile strength and elongation increased much more than no addition as casting. After high temperature deformation simulation test with grain refinement specimens was carried out about 60 N/mm of specimen was confirmed. After hot forging, tensile strength and elongation wear increased. It was considered that casting defect was removed by compressive working.

A Study of the Development of a High-Strength Al-Zn Based Alloy for Die Casting I

Al-Zn based alloys are the most common types of wrought Al alloys. Although Al-Zn alloys have high strength, they cannot be applied to a conventional casting process. In this study, Al-Zn-based alloys applicable to a die casting process were developed successfully. The developed Al-45 wt% Zn-based alloys showed a fine equiaxed grain structure and high strength. A fine equiaxed grain having an average size of 25 μm was obtained by the die casting process. The UTS and elongation of the new alloy are 475 MPa and ~3.5%, respectively. In addition, we elucidate the effect of a Zn addition on variations in different mechanical properties and the microstructure characteristics of (Al96.3-xZnxCu3Si0.4Fe0.3) x=20, 30, 40, and 45 wt% alloys fabricated by a die casting process. (Received July 2, 2010)

Characterization of Partial Squeeze and Vacuum Die Casting Process in Fabricating Automobile Parts

A functional automotive part, reaction shaft support, was fabricated by partial squeeze and vacuum die casting (PSVD) with light-weight Al-15% Si hypereutectic alloy which has good fluidity and excellent wear resistance. The effects of partial squeezing pressure and time-lag of PSVD process on the microstructure of the product were investigated. Measurement of specific gravity with the change of partial squeeze pressure and time-lag showed that the partial squeezing effect can be increased by increasing squeeze pressure and decreasing time-lag. However, too high a squeeze pressure and too a low time-lag brought about insufficient squeezing effect due to instant movement to the squeeze plunger stroke end point. Through the combination of vacuum suction before melt injection and partial squeezing after melt injection in PSVD process, light-weight Al-15% Si alloy reaction shaft support was successfully developed, resulting in excellent microstructural and mechanical properties.