Abstract:The cladding tubes of a newly designed SZA-4 zirconium alloy of Zr-Sn-Nb system were hydrided using electrolytic hydrogen charging technique. The effect of electrolytic hydrogen charging time on the hydrogen absorption amount and the type and the distribution of hydrides, as well as the effect of homogenization annealing time on the type and the distribution of hydrides in SZA-4 zirconium alloy were investigated. The results showed that the hydrogen absorption amount of samples increased with the hydrogen charging time, and a parabola relationship between hydrogen absorption amount and hydrogen charging time was found. Microstructure analysis showed that the hydride layers were formed on the surface of the samples after electrolytic hydrogen charging, while the inner part remained the zirconium alloy matrix. And the thickness of the hydride layers increased with the increase of hydrogen charging time. The phase structure analysis showed that the hydride layer was merely composed of δ-ZrH1.66 at the beginning and increased with hydrogen charging time. When hydrogen charging time reached 24 hours, the hydride layer was composed of ε-ZrH1.801 and δ-ZrH1.66 phase. After 400 ℃/6 h homogenization annealing, the thickness of the hydride layer of hydriding samples further increased, and platelet-like hydrides precipitates within the tubes along the circumferential direction were found. The phase structures analysis of the homogenization annealing of hydriding samples showed that ε-ZrH1.801 disappeared and the original δ-ZrH1.66 hydride transformed into δ-ZrH1.5 hydride in hydride layers. And after 400 ℃/96 h homogenization annealing treatment, all of hydride layers disappeared, and thin platelet-like hydrides were evenly distributed in the samples.