Enhancing erosion-corrosion resistance of cupronickel alloys via Al-addition on microstructure and mechanistic

• 90/10 cupronickel alloy with Al addition was designed and investigated, in which enhanced mechanical properties and corrosion resistance were observed. • Al distribution in the matrix and corrosion product films was characterized via FIB and TEM. • Schematic diagram of the erosion-corrosion mechanism with Al addition was established. The influence of Al addition on the synergistic enhancement of erosion-corrosion resistance and mechanical strength of cupronickel alloys was systematically studied. The results demonstrated that the addition of 3 wt% Al increased the ultimate tensile strength by about 32.9% and reduced the average corrosion rate by 78.1% under artificial seawater erosion-corrosion condition. Al contributed to the strengthening of the matrix through solid solution and precipitation mechanisms, and the potential difference between this precipitated phase and the matrix was quite tiny, which did not cause significant micro-galvanic coupling corrosion. At the same time, Al reduced the stacking fault energy and thus increased the percentage of special grain boundaries, improving the alloy’s resistance to intergranular corrosion. Detailed characterization of the corrosion product film revealed that Al also minimized defects in the film and improved the electrochemical properties of the film, resulting in a more compact and tightly adherent layer. The dense Al 2 O 3 in the middle layer of the corrosion product film provided important protection against erosive ions corroding the matrix.