Conversion coatings on a magnesium alloy were obtained by dipping AZ31 specimens in aqueous solutions of sodium salts of mono-carboxylic acids (stearic, palmitic, myristic, lauric; mono-carboxylate ion concentration from 1 to 5 milli-molar, depending on the salt solubility) for 24 and 72 h at 22 °C, or 24 h at 70 °C. studied The influence exerted by the treatment time, bath temperature, alkyl chain length on the efficiency of these coatings was studied. The performances of the coatings were evaluated by potentiodynamic polarization curve recording after 1h immersion in the electrolytic solutions (0.05 M Na2SO4 and 0.1 M NaCl), while their temporal evolution was monitored by EIS spectra during 24 h. The efficiency of the coatings depended on the aliphatic chain length, and increased as the treatment time and the bath temperature were increased. The coating of lower homologue only hindered the cathodic process, while those of the higher homologues markedly inhibited the anodic process too. The best performances were displayed by 24h-50 °C stearic conversion coating, which maintained a very high efficiency for over 800 h immersion in 0.05M sulphate solution.
MONO-CARBOXYLATE CONVERSION COATINGS FOR AZ31 Mg ALLOY PROTECTION
FRIGNANI, Alessandro;GRASSI, Vincenzo;ZUCCHI, Fabrizio;ZANOTTO, Federica
2011
Abstract
Conversion coatings on a magnesium alloy were obtained by dipping AZ31 specimens in aqueous solutions of sodium salts of mono-carboxylic acids (stearic, palmitic, myristic, lauric; mono-carboxylate ion concentration from 1 to 5 milli-molar, depending on the salt solubility) for 24 and 72 h at 22 °C, or 24 h at 70 °C. studied The influence exerted by the treatment time, bath temperature, alkyl chain length on the efficiency of these coatings was studied. The performances of the coatings were evaluated by potentiodynamic polarization curve recording after 1h immersion in the electrolytic solutions (0.05 M Na2SO4 and 0.1 M NaCl), while their temporal evolution was monitored by EIS spectra during 24 h. The efficiency of the coatings depended on the aliphatic chain length, and increased as the treatment time and the bath temperature were increased. The coating of lower homologue only hindered the cathodic process, while those of the higher homologues markedly inhibited the anodic process too. The best performances were displayed by 24h-50 °C stearic conversion coating, which maintained a very high efficiency for over 800 h immersion in 0.05M sulphate solution.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
