Effect of an Mg-rich matrix on the corrosion behavior of as-cast magnesium-aluminum alloys

In the present study, the corrosion behavior of as-cast Mg-Al and Mg-Al-Zn alloys was studied as a function of the Al content in the matrix. Corrosion properties such as the corrosion rate, corrosion potential, and repassivation tendency were estimated through immersion and electrochemical tests. The corrosion potential and corrosion rate of a solutionized alloy depend mainly on the Al content of the as-cast alloy. The variation of Al content in the Mg-rich matrix influences the stability of the passive film and the repassivation tendency, i.e., as the Al content of the matrix increases, the repassivation tendency of the surface protective film after its breakage deteriorates. Also, it was proven that the enhancement of corrosion resistance by heat treatment, as in T6, is due to the decrease of solute concentration in the matrix, in addition to the effect of the precipitate, which plays the role of a barrier against corrosion.