Fabrication of Al-3 Wt pct Mg matrix composites reinforced with Al 2 O 3 and SiC particulates by the pressureless infilt
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I.
INTRODUCTION
METAL matrix composites (MMCs) reinforced with ceramic reinforcements offer high strength and modulus, as well as good high-temperature properties, when compared to corresponding monolithic alloys and are promising materials for automotive and aerospace industry applications. Discontinuously reinforced MMCs containing particulates, short fibers, or whiskers offer isotropic properties and relative ease in fabrication when compared to continuously reinforced MMCs. Thus, various fabrication methods, including powder metallurgy (P/M), the traditional casting method, etc., have been developed.[1–4] However, since wetting between molten metal and reinforcements is often poor, improved wetting must be achieved to obtain a good bond between the matrix and reinforcements. This problem can be addressed, in part, through a strongly reactive alloying addition, such as Mg and Li, and through reinforcement coating. Also, mechanical stirring or pressure infiltration have been applied during fabrication. Other limitations, such as the distribution of reinforcements, interfacial reactions between the metal matrix and reinforcements, and control of volume fraction are often encountered during the fabrication of MMCs. Therefore, all such factors can affect the resultant properties of MMCs. Recently, Lanxide Inc. (Newark, DE) developed a new, innovative technique, known as the PRIMEX process, for fabricating MMCs. It employs the spontaneous infiltration
of a molten Al alloy containing Mg into a ceramic filler or preform, under a nitrogen atmosphere in a pressureless state and without the aid of vacuum or externally applied pressure.[5–10] The PRIMEX process has at least three advantages over conventional methods, because of the occurrence of spontaneous infiltration of molten metal in the pressureless state. First, the PRIMEX process is an economic process which does not require expensive equipment. Second, it is easy to control the volume fraction of reinforcements and, thus, MMCs with higher volume fractions of reinforcements over 50 vol pct. reinforcements can be incorporated to meet required properties, i.e., higher stiffness and wear resistance, or a low coefficient of thermal expansion. Third, the distribution of reinforcements is quite uniform. In addition, the resulting properties of MMCs can be tailored to the required properties via additions of appropriate additional alloying elements. It is also possible to fabricate net- or near-net-shaped MMCs, using suitable barriers to prevent the infiltration of molten metal. However, few publications on the PRIMEX process have appeared because of the existence of patents for this proprietary process. In this study, Al-3 wt pct Mg/Al2O3p (or SiCp) composites were fabricated by the pressureless infiltration method, and the infiltration behavior of molten metal, the mechanical properties, and the interfacial reactions were investigated. II.
KON BAE LEE, Postdoctoral Student, YOUN SU KIM, Graduate Student, and HOON KWON, Professor, are with the School of Metallurgical
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