Improved Corrosion Resistance of La0.8Ce0.2Fe9.2Co0.6Si1.2 Magnetocaloric Alloys for Near-Room-Temperature Applications

Rare earth-rich NaZn13-type La-Fe-Si-based alloys are promising candidates for near-room-temperature magnetocaloric applications. However, their poor corrosion resistance limits practical applications. The microstructure, corrosion behavior and magnetic entropy change of La0.8Ce0.2Fe9.2Co0.6Si1.2 alloys after annealing were systematically investigated. Annealing treatments were conducted at 1423 K for durations of 4–24 h. As annealing time increased, the α-Fe phase content decreased monotonically from ~7.81wt% to ~2.92wt%, accompanied by significant microstructural evolution. For the 4 h-annealed sample, extensive and large corroded spots were observed, attributed to micro-galvanic corrosion where the α-Fe phase (cathode) and 1:13 matrix phase (anode) formed active electrochemical pairs. Prolonged annealing reduced the corrosion current density by ~50%, directly correlating with the α-Fe phase reduction and improved microstructural homogeneity. Notably, corrosion exhibited a negligible effect on the magnetic entropy change of the alloys. This study confirms that optimizing annealing time to decrease α-Fe content and enhance microstructural uniformity represents an effective strategy to improve corrosion resistance without compromising magnetocaloric performance.