Abstract
We have studied the microstructure of Si3N4-whisker(Si3N4w)-reinforced Al3 Mg-Si alloy (Al alloy 6061) composites, some of which show high-strain-rate superplasticity, by high-resolution and analytical electron microscopy, paying particular attention to the structure of the Si3N4w-Al-matrix interfaces. In the high-strain-rate superplastic composite, which was prepared by hot extrusion after hot-press sintering, a strong reaction occurs between the Al matrix and the Si3N4w crystals, and reaction phases at their interfaces with a definite crystallographic relationship to the Si3N4w crystals are formed. On the other hand, no evidence for an interfacial reaction between the Al matrix and the Si3N4w crystals was detected in the as-sintered material which was prepared without any subsequent extrusion and which shows no superplasticity.

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