Interface interactions during fabrication of aluminum alloy-alumina fiber composites

Abstract

The feasibility of fabricating fiber-reinforced aluminum alloys by addition of discontinuous fibers to vigorously agitated, partially solid metal slurries was investigated. In the first phase of the program, reported herein, emphasis was placed on the study of interface interactions between polycrystalline A1₂O₃ fibers and Al-2 to 8 pct Mg, Al-4.5 pct Cu and Al-4.5 pct Cu-1 to 2 pct Mg alloys. In general, it was observed that the incorporation of fibers could be readily achieved by this technique, and that fibers appeared wetted after a few minutes of contact with the melt. The composites produced exhibited an intimate, void free bond between the constituents. In addition, a region of significantly altered microstructure resulted from accumulation of oxide and/or aluminate particles which either formed within the melt and were attached to the moving fibers, or used the fiber surface as a substrate to grow on. Microscopic examination of this interaction zone and thermodynamic considerations indicate that it consists of fine α-Al₂O₃, aluminates, oxides of the alloying elements, and probably some intermetallic compounds. For example, it is shown that a stable MgAl₂O₄ spinel forms at the interface of A1₂O₃ fibers and Al-Mg alloys. Examination of composite specimens fractured under tension indicated that the interfaces produced were strong enough to permit the transfer of loads at strengths in the order of 250 to 350 MPa.