Corrosion Inhibition of Rapidly Solidified Mg-3% Zn-15% Al Magnesium Alloy with Sodium Carboxylates

• Published in: Corrosion (Houston, Tex.) Vol. 54; no. 6; pp. 444 - 450
• Main Authors: Daloz, D., Rapin, C., Steinmetz, P., Michot, G.
• Format: Journal Article
• Language: English
• Published: Houston NACE International 01.06.1998; NACE
• Subjects: Aliphatic compounds; Anions; Aqueous solutions; Carboxylates; Corrosion; Corrosion currents; Corrosion inhibitors; Corrosion rate; Corrosion resistance; Corrosion resistant alloys; Electrochemistry; Magnesium; Magnesium alloys; Magnesium base alloys; pH effects; Rapid solidification; Sodium; Spectrometry; Submerging; Zinc
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3284872

ABSTRACTThe ability of sodium linear-saturated carboxylates to protect magnesium alloys against aqueous corrosion was characterized. Electrochemical measurements of polarization resistance (Rp) and corrosion current (Icorr) showed the inhibition efficiency of these compounds is a function of their concentration and of the length of the aliphatic chain. In every case studied, the efficiency increased with immersion time. At pH 8, the best inhibiting behavior was observed with 0.05 M sodium undecanoate. The potential-pH diagram of magnesium in an aqueous solution containing undecanoate anions was generated based upon the solubility determined for magnesium undecanoate (Mg[CH3(CH2)9COO]2). According to this diagram, the very low corrosion rate was suspected to result from formation of Mg(CH3[CH2]9COO)2. Infrared spectrometry carried out on both the synthesized magnesium carboxylate and the product from the magnesium alloy surface after inhibitive treatment confirmed this hypothesis. INTRODUCTIONMagnesium alloys have great potential applications as structural materials because of their good mechanical properties, low densities, and excellent casting properties.1-2 However, before their use becomes widespread, their corrosion properties must be improved. In that regard, new alloys have been developed from highly-pure elements, such as AZ91HP (9 wt% Al, 1 wt% Zn). Rapid solidification (RS) also has been explored. RS leads to corrosion behaviors comparable to that of classical aluminum alloys.3-4 However, these good properties do not exclude an additional surface treatment, the first step of which generally is chromating,5 which results in very high corrosion resistance but which has the inconvenience of toxicity. Surface treatment, for storage or prepainting of magnesium alloys, can be carried out with environmentally safe corrosion inhibitors. The present work focused on a family of organic compounds, linear sodium monocarboxylates, used as corrosion inhibitors. The evolution of their inhibition efficiency as a function of the alkyl chain length was studied using electrochemical methods.