Extending the Lifetime of Weldable Primers by Means of Chemical Inhibitors
Pre-painted metal sheets (coil-coatings) are widely used in casings of household appliances, roofs and side walls in buildings and body parts for the automotive industry. One of the main problems of this type of material is the difficulty to weld it. In an attempt to overcome this problem weldable organic coatings are being experimented. Primers with heavy loads of zinc powder are being employed with success to spot-weld different components of an article. These primers may also present an anticorrosive effect through the galvanic protection offered by the zinc powder. However in aggressive conditions the zinc containing primers can corrode very fast and be consumed in a short period of time. Work has been undertaken in order to extend the lifetime of these primers but maintaining the welding and anticorrosive capabilities. The approach followed here was the modification of primers by corrosion inhibitors that can provide additional active protective effect. A set of organic and inorganic corrosion inhibitors was tested in order to partially passivate the primer. The inhibition of corrosion of zinc and iron was also investigated. Electrochemical testing was done with Electrochemical Impedance Spectroscopy (EIS) and the Scanning Vibrating Electrode Technique (SVET). Results showed that soluble inorganic salts of Ce(III) and La(III) and organic inhibitors like benzotriazole and mercaptobenzothiazole are good candidates to increase the service life of weldable primers.
António Torres Marques, António Fernando Silva, António Paulo Monteiro Baptista, Carlos Sá, Fernando Jorge Lino Alves, Luís Filipe Malheiros and Manuel Vieira
A.C. Bastos et al., "Extending the Lifetime of Weldable Primers by Means of Chemical Inhibitors", Materials Science Forum, Vols. 587-588, pp. 1003-1007, 2008