Microstructural refinement in AI alloys by impulse atomization

As aluminum alloy usage in automobiles grows, there are ever-increasing dem ands on recycling processes and facilities to deal with mixed alloy automot ive aluminum scrap. Recycling strategies using simple and cost effective pr ocessing routes must produce high quality aluminum stock, which can be rela tively costly and difficult. An alternative is to use physical processing m ethods to upgrade the scrap properties instead of refining the chemistry. T o this end, impulse atomization (1A), a single fluid atomization technique, is used to generate a range of microstructures under varying solidificatio n cooling rates. Atomized and quenched AA6061 aluminum and scarp Al droplet s were produced with d(50) of about 550 mum and a geometric standard deviat ion of about 1.4. The particles are spheroidal in shape and are thus in a c onvenient form for consolidation. This study compares and contrasts the mic rostructural features of IA and quenched-IA powders, for AA6061 and a scrap aluminum alloy composition. It is shown that microsegregation of alloying elements such as copper has occurred in all samples and that solidification nucleation commenced within a distance of 9cm of the atomizing nozzle, des pite the high solidification cooling rates which range from 400 to 6,000 de greesC/s.