Papers by Author: Zhi Chao Duan

Abstract: Experiments were conducted to evaluate the feasibility of using a new ECAP die configuration in which there are arcs of curvature at the intersection of the two channels at both the outer and inner points. The experiments used a configuration in which the radii of curvature were identical at both the outer and inner points since calculations suggest this corresponds to an optimum configuration. High-purity aluminum was pressed using this special die and hardness measurements were taken on cross-sectional planes after pressing. The results show the new die configuration leads to less homogeneity than with conventional ECAP dies.

Abstract: The processing of bulk metals through the application of severe plastic deformation provides an opportunity for achieving exceptional grain refinement to the submicrometer or even the nanometer range. This paper examines the characteristics of metals processed by equal-channel angular pressing with special emphasis on the levels of ductility that may be attained. It is shown that the amount of ductility is dependent not only upon the composition of the material but also, and to a major extent, upon the testing temperature. Specifically, the ductilities are often low at ambient temperatures where the strength of the as-processed material is relatively high but, by contrast, exceptionally high superplastic ductilities may be achieved over short ranges of strain rate when testing at elevated temperatures.

Abstract: Equal-channel angular pressing (ECAP) is a convenient processing method for refining the grain size of bulk materials to the submicrometer level. Metallic alloys processed by ECAP often exhibit excellent superplastic characteristics including superplasticity at high strain rates. This paper summarizes recent experiments designed to evaluate the occurrence of superplasticity in representative aluminum and magnesium alloys and in the Zn-22% Al eutectoid alloy.