High corrosion resistance of La1.4Fe11Co0.8Si1.2 magnetocaloric alloy

The microstructure, phase constitution and corrosion behavior of non-stoichiometric LaxFe11Co0.8Si1.2 (x = 1.0, 1.2, 1.4, 1.6) magnetocaloric alloys were investigated. Annealed LaxFe11Co0.8Si1.2 compounds, containing the desired NaZn13-type matrix phase (1:13 phase), as well as a small α-Fe and La-rich phase content, exhibited high micro-galvanic corrosion in deionized water. The size of the La-rich phase in the LaxFe11Co0.8Si1.2 alloys varied with the La content. The refined La-rich phase in the La1.4Fe11Co0.8Si1.2 alloy led to reduced galvanic corrosion and a more protective corrosion layer. Due to the internal stress of the corrosion product, the corrosion product of the coarse La-rich phase in the La1.6Fe11Co0.8Si1.2 alloy easily cracked, leading to higher corrosion. Among these alloys, the La1.4Fe11Co0.8Si1.2 alloy with a high content of the 1:13 phase and a small finer La-rich phase content, exhibited strong corrosion resistance.