Study on corrosion resistance of SZA-4 alloy

The samples of stress relieving annealing (SRA) and recrystallization annealing (RXA) tubes of SZA-4 zirconium alloy were tested in static autoclave in 360 ℃/18.6 MPa pure water, 360 ℃/18.6 MPa/0.01 mol/L LiOH aqueous solutions and 400 °C/10.3 MPa superheat steam.The characteristics of the microstructure were analyzed by TEM and SEM.lt was shown that the corrosion weight gain of RXA tube was lower than that of SRA tube after the longest 500 d corrosion test in three different corrosive mediums.The fine precipitates in the alloy were homogeneous and dispersed, mainly HCP-Zr (Nb, Fe, Cr)₂ and FCC-Zr₂ cFe, Cr). Compared with the RXA tube, the average diameter of SRA tube was relatively small, and there is a small amount of TET-Zr3Ge. The cracks paralleling to the interface of oxide/metal are formed in the fracture surface of the oxide film and the oxide film in the inner surface appears at the 'Cauliflower-like' morphology. With the increasing of corrosion rate, there were more cracks in the fracture surface of the oxide film and the size of 'Cauliflower-like' structure grows bigger. The main reason for the difference of the corrosion resistance of the alloy was the difference of the precipitated phases in the two kinds of annealing conditions. (authors)