Al-Mn Thermally Sprayed Coatings as Replacement of Cd-Based Coatings

Cadmium coatings are used in aerospace and offshore industries for parts in corrosive environments. Since cadmium is a highly toxic heavy metal, it is subject to strong restrictions. Alternatives include Al-based alloys. The present work describes preliminary results for Cd substitution by using Al-Mn with 25 at.-% Mn deposited on 42CrMo4 steel by atmospheric plasma spraying (APS). The prepared alloy powder for the APS process was characterized by laser granulometry, SEM/EDX, and STA. A fraction with particle sizes ranging from 20 µm to 45 µm was used for the thermal spraying process. The APS coating and an Al reference sample were characterized by image analysis, Vickers hardness, and Standard Salt Spray (SSP) testing. The Al-Mn coating exhibits a significantly higher hardness in comparison to pure Al. In both cases, red iron corrosion did not appear during SSP testing. The Al coating was partially covered by a thick oxide film, whereas Al-Mn showed only moderate oxidation but lower adhesion to the substrate