Optimization of the In-Situ Al-Si Base Functionally Graded Material Fabricated by Centrifugal Casting
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Optimization of the In-Situ Al-Si Base Functionally Graded Material Fabricated by Centrifugal Casting Yoshihiro Oya-Seimiya, Tetsumori Shinoda, and Yoshimi Watanabe1 Advanced Materials R & D Center, Meisei University, Tokyo, 191-8506, Japan 1 Department of Functional Machinery & Mechanics, Shinshu University, Ueda, 386-8567, Japan ABSTRACT The fabricating conditions for the in-situ Al-Si base composite by the centrifugal casting method (CCM) have been examined. The crystallized Si particles with a lower density distribute in a gradient fashion as densely on the inner and thinly on the outer side of the wall of the cylindrical CCM-composite. Synthetically, the 25 mol% Si composite is recommended for the application like the engine liner. INTRODUCTION The centrifugal casting method (CCM) is one of advantageous techniques to fabricate such a cylindrical composite as its main functions like strength and thermal expansion coefficient vary along the wall thickness of a cylinder in some conveniently gradient fashion. The functionally graded material (FGM) based on the CCM might be called the CCM-FGM. The previous studies on the CCM-FGM have mainly treated the case where dispersion-hardening (DH) particles in the composite have a higher density than that of the matrix substance, so that they segregate on the outer side of the cylinder wall [1-3]. The Al-Si base CCM-FGM studied in the present study is however different from the previous ones in the respect that Si particle as the DH phase have a lower density than that of the Al enriched matrix. So, Si particles are expected to concentrate towards the inner wall of the rotating cylinder and compose a light weighted cylindrical composite the inner wall side of which is more strengthened than the inner depth. EXPERIMENTAL PROCEDURE The raw material of some compositional Al-Si alloy (6-35mol%Si) is melted down in a furnace at 750℃, and then poured, by pulling a stopper rod up, to a metallic mold which is located below the furnace and rotating at a certain speed (1500-3000rpm) around a horizontal axis. The mold is preheated to 300℃ by a mold heater. The molten fluid is poured to the mold by way of a gate furnace also preheated at 300℃. All these casting tools are accommodated in an airtight chamber, which can be evacuated (until about 3x10-1 Pa) or made to an inert atmosphere if necessary. Rotational torque for the casting mold is transmitted from a motor outside of the chamber through a vacuum bearing. A cast cylindrical composite thus made (80mm the outer diameter, about 10mm the wall thickness and 180mm the cylinder length) is sliced at a cross section normal to the cylinder axis for the optical microstructure observation. The volume percent of the crystallized Si-particles is measured on the cross section by means of an electronic image analyzing technique on the optical microstructure photographed by a CCD camera. The Al-Si base CCM-FGM was assessed by measuring the changes of the wearing resistance along with the wall thickness of the cylindrical composite. RESULTS AND DIS
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