Galvanic corrosion behaviour of magnesium alloy in contact with coated components

Electrochemical investigations were carried out to examine galvanic corrosi on in preparation for the use of steering gear made from a magnesium, press ure die-casting. The aim was to characterize various joining elements of th e steering gear (e.g. hold-down devices, threaded bushings, plugs, screws) with different types and qualities of protective coating with regard to the risk of galvanic corrosion in magnesium alloy AZ91. In addition the change in the polarization resistance was determined for one coating system after contact with AZ91 and compared with data without contact. The quality of the coatings is very important to prevent galvanic corrosion . This was demonstrated using as an example, KTL coated systems of various quality. The evaluation of current density potential curves of the coatings only all ows a gradation of the top coat qualities in relatively short time, but the problems which can actually appear at contact to AZ91 aren't recognized.