Investigation on precipitation in Zircaloy-2 fuel cladding tube

The mechanical properties of an Al-25Si alloy fabricated through the spray forming route were studied in a wide range of temperatures covering from 370 to 500°C and the results were compared with those for the powder-metallurgy processed Al-Si alloys studied by other investigators. Superplasticity was observed at high-temperatures around 500°C at 5×10-4 s-1. The entire temperature range could be divided into two regions where grain boundary sliding and dislocation climb creep dictates plastic flow, respectively. The activation energies for effective plastic flow were measured in these two regions and found to be close to that for self-diffusion in pure aluminum. It was found that the present Al-25Si alloy almost behaves like superplastic aluminum matrix at elevated temperatures. Extensive whisker formation was observed and liquidation of grain boundary material during grain boundary sliding appears to be responsible for it.