Inhibition of precipitation structure transformation and enhancement of hardness by trace La addition in Cu-1Cr-0.1Zr alloy sheets

Abstract

Cu-1Cr-0.1Zr and Cu-1Cr-0.1Zr-0.07La alloy sheets were prepared by the following process: vacuum casting– homogenization treatment– hot forging– solid solution treatment– cold rolling– aging treatment. The effect of trace La on the aging behavior and mechanical properties of Cu-1Cr-0.1Zr alloy was investigated. Compared to the Cu-1Cr-0.1Zr (0La) alloy, the Cu-1Cr-0.1Zr-0.07La (0.07La) alloy exhibited a significant increase in hardness and a slight decrease in electrical conductivity due to larger number of finer and coherent f.c.c Cr-rich precipitates. It was found that trace La can affects the evolution of precipitation phases. The thermodynamics calculation indicates that with La addition, the Cr-rich precipitates were much more inclined to nucleate with f.c.c structure, and the precipitation growth kinetics results indicate that the addition of La can reduce the activation energy of precipitation, promote the precipitation of f.c.c Cr phase and form Cr-poor zones, making it more difficult to form bcc nuclei. Thus, the transformation of nanoscale Cr-rich precipitates from f.c.c structure to bcc structure was inhibited due to trace La addition, causing higher hardness with appropriate conductivity.