The effect of thermal treatment on the corrosion properties of vapor deposited magnesium alloyed with yttrium, aluminum, titanium, and misch metal

The corrosion susceptibility of magnesium often limits the use of this important metal. Efforts to improve the corrosion resistance of magnesium through alloying are hindered by the limited solid solubility of most metals in magnesium. Moreover, the relatively high melting temperature of most of the less-common metals makes conventional alloying difficult. Vapor deposition has been used in this research to alloy magnesium with nonequilibrium concentrations of normally incompatible metals in an attempt to improve corrosion performance. Aluminum, titanium, yttrium, and misch metal were chosen as candidates likely to impart passivity on vapor deposited magnesium alloys. Although all of these metals afford some degree of corrosion resistance to magnesium, behavior is highly dependent on the thermal history of the alloys. Thermal effects, both during and after alloy deposition, alter the stress state of the alloys, precipitation of second phases, and the mechanical stability of the passive film. An optimal thermal treatment has been developed to maximize the corrosion resistance of vapor deposited magnesium–yttrium–titanium alloys.