Studies on spray casting of Al-alloys and their composites

A spray nozzle of convergent-divergent configuration was used for spray cas tings (SC) of A16061/M25 alloys and their composites. Both monolithic alloy s and composites showed equiaxed fine grained microstructure with a variati on in grain size from 20 to 30 mum. Some of the regions of the preform also showed cellular solidification structure with globularization of most of t he eutectic Si suggesting the effect of rapid solidification. High defect c oncentration in both SC matrix and their composites was observed with bulk SC samples showing uniformly distributed porosity, TEM studies showed decor ation of grain boundaries/presolidified droplets by some precipitates and a lso vacancy loops. Their aging characteristics indicated lowering of soluti onising temperature and aging time to get the same peak hardness: as obtain ed in the alloy produced by ingot metallurgy methods. An ordered phase with unit cell four times Larger than Al seems to form during the in situ heati ng of LM25-SiCp samples while dislocations seem to emerge from the interfac e between the particle and the matrix. The results are discussed in the lig ht of reported literature on spray casting/melt spinning of Al-alloys and c omposites. (C) 2001 Elsevier Science B.V. All rights reserved.