Processing maps for hot-working of powder metallurgy 1100 Al-10 vol % SiC-particulate metal-matrix composite

Abstract

The hot-working characteristics of the metal-matrix composite (MMC) Al-10 vol % SiC-particulate (SiC_p) powder metallurgy compacts in as-sintered and in hot-extruded conditions were studied using hot compression testing. On the basis of the stress-strain data as a function of temperature and strain rate, processing maps depicting the variation in the efficiency of power dissipation, given by η = 2m/(m+1), where m is the strain rate sensitivity of flow stress, have been established and are interpreted on the basis of the dynamic materials model. The as-sintered MMC exhibited a domain of dynamic recrystallization (DRX) with a peak efficiency of about 30% at a temperature of about 500°C and a strain rate of 0.01 s⁻¹. At temperatures below 350°C and in the strain rate range 0.001–0.01 s⁻¹ the MMC exhibited dynamic recovery. The as-sintered MMC was extruded at 500°C using a ram speed of 3 mm s⁻¹ and an extrusion ratio of 10∶1. A processing map was established on the extruded product, and this map showed that the DRX domain had shifted to lower temperature (450°C) and higher strain rate (1 s⁻¹). The optimum temperature and strain rate combination for powder metallurgy billet conditioning are 500°C and 0.01 s⁻¹, and the secondary metal-working on the extruded product may be done at a higher strain rate of 1 s⁻¹ and a lower temperature of 425°C.