STP890

    Rapid Solidification of Highly Undercooled Aluminum Powders

    Published: Jan 1986


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    Abstract

    The amount of liquid undercooling attained during rapid solidification processing (RSP) is an important factor in determining microstructural development. An effective experimental method that may be applied in assessing undercooling potential involves the examination of a dispersion of stabilized, fine (5 to 20-µm) liquid droplets. Substantial undercoolings (ΔT ≥ 160°C) have been measured by differential thermal analysis for slowly cooled (30°C/min) droplet emulsions of aluminum alloys. Results from Al-Si and Al-Fe alloys indicate that undercooling is a function of droplet size, melt super-heating, and material composition. Comparison studies have also been conducted relating the amount of undercooling to microstructural refinement in alloys prepared as droplet emulsions and by air atomization. The results indicate that at large undercooling (ΔT > 260°C) droplet solidification can yield a microstructure similar to that formed in atomized powder. Microstructural variations with powder size are related not only to a changing cooling rate but also to a modified undercooling behavior. These observations highlight the role of undercooling in RSP and indicate that the droplet approach can be effective in examining potential aluminum powder metal alloys and in optimizing processing procedures for rapid quenching treatments.

    Keywords:

    aluminum alloys, powder metallurgy, liquid undercooling, nucleation kinetics, solidification, powder microstructure, aluminum-silicon alloys, aluminum-iron alloys


    Author Information:

    Perepezko, JH
    Professor of metallurgical engineering and graduate research assistant, University of Wisconsin at Madison, Madison, WI

    LeBeau, SE
    Research engineer, Research and Development Division, Babcock and Wilcox, Alliance, OH

    Mueller, BA
    Professor of metallurgical engineering and graduate research assistant, University of Wisconsin at Madison, Madison, WI

    Hildeman, GJ
    Section head, Alloy Technology Division, Alcoa Laboratories, Alcoa Center, PA


    Paper ID: STP33026S

    Committee/Subcommittee: B09.03

    DOI: 10.1520/STP33026S


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