C. Xu, T. G. Langdon, University of Southern California, Los Angeles, CA; Z. Horita, Kyushu University, Fukuoka, Japan
Equal-channel angular pressing (ECAP) is a useful tool for achieving exceptional grain refinement in bulk metallic alloys. Typically, the grain sizes produced through ECAP processing are in the submicrometer range. Thus, ECAP processing has the potential for producing materials having grain sizes up to an order of magnitude smaller than those generally attained through typical thermo-mechanical treatments. The development of these small grain sizes means that the as-pressed alloys have a considerable potential for exhibiting extensive superplastic ductilities and these ductilities will occur both at faster strain rates and at relatively lower temperatures then in conventional superplasticity. These two characteristics are both favorable for making use of these alloys in superplastic forming operations.
This paper concentrates on two separate aspects of processing by ECAP. First, it describes the application of ECAP to a representative commercial Al-2024 alloy. This alloy was selected because it contains no minor additions of either zirconium or scandium to assist in preventing grain growth. The experiments show that good superplastic ductilities can be achieved in this alloy under conditions that are appropriate for forming operations. Second, it examines the potential for achieving a superplastic capability through the pressing of samples in the form of plates instead of the more conventional bars or rods that are generally used in ECAP. Using an Al-Mg-Sc alloy, it is demonstrated that the ECAP processing of plate samples can be conducted successfully to produce an as-pressed material that exhibits good superplastic characteristics. The direct pressing of plate samples is an attractive feature for the future utilization of this technology in industrial applications.