抄録
The effect of Cr additive on the threshold stress in region I superplastic behavior of Al–Cu eutectic alloy is investigated using high-purity alloys with various Cr contents ranging from 0.002 to 0.26 mass%. The threshold stress increased largely with increasing Cr content up to 0.05 mass% and exhibited a tendency toward a possible saturation. It decreased with increasing temperature and grain size. The temperature dependence was similar to that of grain boundary segregation of impurity atoms. Transmission electron microscopy did not reveal the presence of fine precipitates at the grain and phase boundaries. Therefore, it was proposed that segregating Cr atoms are pinning grain boundaries, inhibiting grain boundary migration that accompanies grain boundary sliding and bringing about the threshold stress.
