Enhanced Strength-Corrosion Synergy of 6061Al Casting Alloy Through Erbium Addition

The purpose of this work is to investigate the effect of Er on mechanical properties and corrosion behavior of 6061 alloys. The tensile strength and corrosion resistance of the 6061 alloys first enhanced and then declined synergistically with the increase of Er content. Microstructure analysis revealed that the morphology, composition, and potential of secondary phases changed significantly as Er content changed. When the Er content is 0.6 wt%, the needle-like beta-AlFeSi phases transformed into the granular AlFeSiEr phases, which led to an increase in the tensile strength of the 6061 alloys. At the same time, compared with the acicular beta-AlFeSi phases, the granular AlFeSiEr phases own a lower potential difference with alpha-Al, which weakened the corrosion of the micro-galvanic couples. However, as the Er content is higher than 0.6 wt%, the granular AlFeSiEr phases changed to block-shaped, which can adversely affect the tensile strength and corrosion resistance of the 6061 alloys. EIS results show that, compared with the acicular beta-AlFeSi phases, the 6061 alloys with granular AlFeSiEr phases form more uniform oxide films and exhibit better corrosion resistance. This study indicates that through appropriate Er addition, the synergistic enhancement of tensile strength and corrosion resistance of the 6061 alloys can be obtained, which is of great significance for the strengthening and long-term service of aluminum alloys.