CORROSION BEHAVIOUR OF THE AZ31 MAGNESIUM ALLOY AND SURFACE TREATMENTS FOR ITS CORROSION PROTECTION

Nowadays environmental conservation forces the transportation industry to manufacture lighter and low emissions transport vehicles. In this contest, magnesium alloys have found increasing attention by the automotive industry because of their low density associated with good mechanical properties. However the low corrosion resistance of magnesium alloys in wet environments is still a limiting factor against their widespread diffusion. The aim of this research is both studying the correlation between microstructure and corrosion behaviour of a AZ31 magnesium alloy and developing eco-friendly protective technologies. In particular inhibitors and surface pretreatments with different organic compounds have been investigated. The effect of microstructure on corrosion resistance of AZ31 alloy has been analyzed through a comparative study between the electrochemical behaviour of as-cast and hot rolled AZ31. Environmentally friendly sodium salts of mono-carboxylic acids have been studied as inhibitors of AZ31 alloy corrosion in a standard saline solution. Moreover, long chain sodium mono-carboxylates have been tested as promoters of conversion coatings for this alloy. Finally, significant improvements have been achieved by modifying the protective coatings obtained by 3-mercapto-propyl-trimethoxysilane through cerium nitrate or oxide nanoparticle additions.