PARTICLE WEAKENGING IN HIGH-STRAIN-RATE SUPERPLASTIC POWDER-METALLURGY PROCESSED 2124 AND 6061 ALUMINUM COMPOSITES

摘要

High-strain-rate superplastic behaviors of powder-metallurgy processed 2124 and 6061 Al alloys, and SiC/2124 Al and SiC/6061 Al composites reinforced by SiC particulate were studied over a wide temperature and strain rate ranges. The matrix alloys and composites showed large tensile elongations above 10~(-2) s~(-1). The strengths of both composites are unexpectedly lower than that of the Al matrix alloys in the temperature range where grain boundary sliding dominates the plastic flow. Their difference in strength is also temperature dependent, increasing with increase in temperature. Abnormally high activation energy for plastic flow, being considerably higher than those for the matrix alloys, is another important feature of the composites. High-resolution transmission electron microscopy indicates that solutes such as Mg and Si strongly segregate at interfaces between SiC and Al matrix. Particle weakening, possibly with some liquid formation at the interfaces, is discussed qualitatively and partially quantitatively by adapting the concept of effective diffusivity considering mass flow through liquid phase formed at interfaces between reinforcement and Al matrix.