Thermally sprayed Al-Mn coatings for wet corrosion protection as alternative to cadmium

摘要

Cadmium coatings are still used in aerospace industry for parts in corrosive environments such as actuators or landing gears. Since cadmium is a highly toxic heavy metal, it is subject to strong restrictions, namely REACh. Alternatives include aluminum-zinc alloys which possess a similar electronegative potential and act as sacrificial anode on steel. The present work describes preliminary results for cadmium substitution by using an aluminum-manganese (Al-Mn) system with 25 at.% manganese deposited on 42CrMo4 steel by atmospheric plasma spraying (APS). The prepared alloy powder for the APS process was characterized by laser granulometry and SEM/EDX. A fraction with particle sizes ranging from 10 to 60 urn was used for thermal spray process. The APS coatings were characterized by optical image analysis, Vickers hardness and tested in Standard Salt Spray (SSP). The Al-Mn coatings exhibited significantly higher hardness in comparison to pure aluminum. Red iron corrosion appeared during SSP testing after 240 h but remained moderate even after 1000 h. The Al-Mn material itself showed only a low oxidation rate but worsened adhesion to the substrate if compared to as-coated state. Future work will mainly focus on the material composition to achieve more ductile coatings.