PROCESSING MAPS FOR HOT-WORKING OF POWDER-METALLURGY 1100 AL-10 VOL-PERCENT SIC-PARTICULATE METAL-MATRIX COMPOSITE

The hot-working characteristics of the metal-matrix composite (MMC) Al -10 vol % SiC-particulate (SiC(p)) powder metallurgy compacts in as-si ntered and in hot-extruded conditions were studied using hot compressi on testing. On the basis of the stress-strain data as a function of te mperature and strain rate, processing maps depicting the variation in the efficiency of power dissipation, given by eta = 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-degr ees-C and a strain rate of 0.01 s-1. At temperatures below 350-degrees -C and in the strain rate range 0.001-0.01 s-1 the MMC exhibited dynam ic recovery. The as-sintered MMC was extruded at 500-degrees-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-degrees-C) and hi gher strain rate (1 s-1). The optimum temperature and strain rate comb ination for powder metallurgy billet conditioning are 500-degrees-C an d 0.01 s-1, and the secondary metalworking on the extruded product may be done at a higher strain rate of 1 s-1 and a lower temperature of 4 25-degrees-C.