Microstructural Heterogeneity and Ti-Rich Interfacial Regions in a Commercial AA1100–B4C Aluminum Matrix Composite

The microstructure of a commercially produced AA1100 aluminum matrix composite reinforced with 25 vol.% B 4 C particles has been characterized. The composite contained broadly distributed irregular and angular B 4 C particles, with a measured area fraction of 26 ± 6% and local variations in particle size, morphology, and spacing. The aluminum-rich matrix exhibited local grain-size heterogeneity, with finer grains in regions without immediately adjacent former particle sites (9.5 ± 2.8 µ m) and coarser grains in regions surrounding former B 4 C particle locations (22.9 ± 4.6 µ m). A chemically and structurally distinct Ti-rich interfacial region was identified between the B 4 C particles and the surrounding aluminum matrix. X-ray diffraction confirmed the presence of crystalline TiB 2 in the recovered material containing the Ti-rich phase, while transmission electron microscopy and selected-area electron diffraction revealed a crystalline interfacial region. The recovered material exhibited a type IV(a) N 2 adsorption–desorption isotherm with an H3 hysteresis loop, consistent with mesoporosity associated with slit-like pore spaces formed between lamellar or plate-like features. The crystallographic texture was weaker and more diffuse in the composite, with the maximum orientation distribution function density decreasing from 12.3 m.r.d. in the unreinforced AA1100 reference material to 5.1 m.r.d. in the composite. The relationship between the interfacial regions associated with the reinforcement and the microstructural heterogeneity of the aluminum matrix is discussed.