Investigation on Microstructure of Weld Zone of R60702 Zirconium Laser Welded Joint and Its Corrosion Resistance in Sulfuric Acid

Abstract

In order to explore the corrosion resistance of different structures in the weld zone of R60702 laser welded joints under different welding processes (Process 1: laser power 1 600 W，welding speed 1 600 mm/min，linear energy 60 J/mm，gas flow 20 L/min，defocus amount 0 mm；Process 2: laser power 1 800 W，welding speed 1 200 mm/min，linear energy 90 J/mm，gas flow 20 L/min，defocus amount 0 mm)，metallurgical microscope (OM)，X-ray diffractometer (XRD)，electrochemical tester，scanning electron microscope (SEM)，threedimensional profilometer and energy spectroscopy (EDS) were used to analyze the metallographic structure，phase composition，corrosion resistance and its mechanism，corrosion morphology and elemental composition of corrosion products.Results showed that the weld zone exhibited different microstructures under two welding processes.Under the condition of process 1，the weld zone was a mixture of basket-like structure and a small amount (26.7%) of parallel lath-like Widmanstatten structure.Under the condition of process 2，the weld area displayed a typical Widmanstatten structure.After being immersed and corroded in 20%sulfuric acid at 100 ℃for 72 h，the mixed structure welds showed galvanic corrosion，and the parallel lath Widmanstatten structure welds showed uniform corrosion.In addition，the parallel lath Widmanstatten structure welds had better corrosion resistance.The inhomogeneity of the microstructure of the mixed-structure weld created a potential difference，which caused the oxide film to rupture due to galvanic corrosion，and so the mixed structure held the poorer corrosion resistance.On the contrary，the parallel lath Widmanstatten structure weld had good electrochemical uniformity and no significant difference in self-corrosion potential，which was beneficial to inhibit galvanic corrosion.

Keywords

• laser welding|industrial pure zirconium|structure|corrosion resistance