Development of homogeneity in a Cu-Mg-Ca alloy processed by equal channel angular pressing

Abstract A Cu-0.41Mg-0.06Ca (wt.%) alloy was processed by equal channel angular pressing (ECAP) for up to 12 passes via Bc route at room temperature, and its homogeneity was evaluated from three aspects of hardness, microstructure and crystallographic texture. The hardness was measured in detail on the whole transverse planes, and the microstructure and the crystallographic texture in the central and bottom regions on the transverse planes were investigated by electron backscatter diffraction (EBSD) technique. After 1 ECAP pass, the hardness in the central region was 9.4% higher than that in the bottom region; the microstructure in the central region consisted of the elongated grains, while that in the bottom region was composed of the slightly distorted grains; the crystallographic texture in the central region followed the ideal orientations of the ECAP crystallographic texture, nevertheless the crystallographic texture in the bottom region obviously deviated from any ideal orientation of the ECAP crystallographic texture. Then, with the increase of ECAP passes, the hardness and microstructure differences between in the two regions gradually weakened, and the deviation of the crystallographic texture in the bottom region gradually decreased. After 8 ECAP passes, the both regions showed the same hardness, the similar ultrafine-grained microstructure and the similar crystallographic texture. The difference formation should be attributed to the non-uniform strain caused by the friction between the sample and the die wall, rather than caused by the corner gap. The difference weakening should be attributed to the strain hardening behavior of metals. The strength calculation showed that the Cu-Mg-Ca alloy after 8 ECAP passes had almost the same yield strengths where 593 MPa for the central region and 583 MPa for the bottom region, showing only 1.7% difference.