Experimental Measurement and Computer Simulation of Galvanic Corrosion of Magnesium Coupled to Steel

The study of the galvanic corrosion of magnesium becomes increasingly important as the use of magnesium alloys increases rapidly in the auto and aerospace industries due to their advantages of light-weight, adequate mechanical properties and moderate cost. Corrosion, however, limits the application of magnesium alloys.[1–7] A number of different mechanisms are important for the corrosion.[8–14] But galvanic corrosion is probably the most important for magnesium because magnesium is the most active structural metal and consequently may suffer serious corrosion when joined to all other common metals of construction, such as aluminum or steel.[1,2,15] Fasteners and their galvanic corrosion is of major concern in automotive applications.[16–18] Skar[17] showed that6000 series aluminum alloy fasteners caused negligible galvanic corrosion of magnesium in the salt spray test.

However, steel fasteners are desired for many applications due to their inherently better mechanical properties. Poor compatibility with magnesium was shown by aluminium-coated steel fasteners[18] whereas steel fasteners with zinc or tin-zinc alloy coatings were compatible with magnesium in salt-water exposure.[16] To be able to design a structural component, incorporating galvanic corrosion, it is useful to be able to simulate the galvanic corrosion distribution qualitatively. The research presented in this paper has been undertaken as part of a program to explore that aim. The total corrosion in the area ofgalvanic corrosion can be considered to be made up of the following two components: (1) galvanic corrosion and (2) selfcorrosion. The galvanic corrosion is that part of the corrosion,which is directly caused by the coupling of the magnesium toa steel fastener. The self-corrosion is defined as the extra corrosion. Both the galvanic corrosion and the self-corrosionmay take the form of more or less general corrosion, or theform of localized corrosion or pitting corrosion