Mg AZ80/SiC composite bars fabricated by infiltration of porous ceramic preforms
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1/8/04
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Mg AZ80/SiC Composite Bars Fabricated by Infiltration of Porous Ceramic Preforms V. KEVORKIJAN Semi-industrial samples of Mg AZ80/SiC/50p composites (machined bars with o.d. 80 mm and length 150 mm, having a maximum 2 vol pct of retained porosity) were successfully fabricated by pressureless, low-pressure (under overpressure of about 0.3 MPa) and moderate-pressure (under overpressure of about 0.8 MPa) infiltration. Pressureless infiltration was completed in 24 hours under the flowing atmosphere of nitrogen, whereas the moderate and low-pressure infiltrations were performed under a static atmosphere of pressurized nitrogen for 7 and 0.5 hours, respectively. The composite samples obtained by all applied infiltration paths posessed a homogeneous microstructure and superior mechanical properties as compared to the nonreinforced matrix. Due to the improved productivity of composite fabrication in comparison with the other two infiltration paths investigated in this work, the moderate-pressure infiltration process was recognized as the most competitive.
I. INTRODUCTION
THE use of magnesium alloys as the matrix phase in metal matrix composites (MMCs) is of interest as an alternative to aluminum-based composites for advanced structural applications and for components in engines, with the advantage of high specific strength and stiffness. As has been demonstrated,[1–5] magnesium MMCs (Mg MMCs) have mechanical properties basically similar to those of Al MMCs and can be used for similar lightweight structural and functional parts. The main advantage of Mg MMCs in comparison to Al MMCs and alloys is that they allow a weight savings of about 20 to 25 pct for the same structural resistance. The Mg MMCs also provide similar tribological performance and better machinability in comparison to aluminum alloys and Al MMCs.[6] Notwithstanding the current market dominance of casting Mg alloys, interest in the use of wrought magnesium alloys and composites is also continuously growing.[7] Magnesium wrought alloys and composites have a greater strength and ductility than their high-pressure die-cast or thixo-formed counterparts. However, despite the superior properties exhibited by wrought magnesium alloys and composites compared to cast products, lack of an adequate knowledge base still results in a low use level. In contrast to wrought aluminum alloys, which are extensively used in the form of forged, extruded, and rolled semifinished and finished products, wrought magnesium alloys are only applied in a very low percentage of applications, mostly in prototypes. The bulk workability of wrought Mg MMCs particularly is in an early stage of investigation.[1,8,9] Due to the presence of a ceramic reinforcement, these composites display marked increases in strength and stiffness. However, at the same time, the low ductility of the hcp magnesium lattice and the slipconstraining properties of the hard ceramic phases result in a significant reduction in toughness and ductility. In addition, many factors resulting
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