Rapid solidification processing of some aluminium alloys

Abstract

In the past thirty years since the introduction of the "Splat Cooling" technique by Duwez et. al., the science and technology of rapid solidification have made tremendous progress culminating in the commercialization of several processes like melt spinning, planer flow casting and centrifugal atomization and products like metallic glass ribbons, and high strength, high temperature, super plastic etc. alloys, some of them not amenable to processing by conventional ingot metallurgy route. Among the several aluminium based alloys systems, three categories of alloys have attracted greater commercial interest, viz. (a) the high strength hardening alloys (b) low-density aluminium-lithium alloys and (c) dispersion strengthened elevated temperature alloys. These alloys are of interest to the aerospace industries as they can contribute to 15-25% weight reduction on account of their superior properties. In this paper, after briefly reviewing rapid solidification processing of high strength aluminium alloys, some aspects of the RSP research in National Metallurgical Laboratory (NML) dealing with centrifugal atomization and rapid solidification processing of some non heat-treatable alloys of the Al-Si and Al-Ni systems and heat treatable alloys of the 7075 type are presented. RSP has been found to result in considerable refinement of the size of the second phase particles in the non heat-treatable alloys resulting in considerable improvement in their properties. The conventional high strength aluminium alloys subjected to RSP exhibit a moderate improvement in properties. Some novel microstructures observed in the rapidly solidified alloys are also presented.