Corrosion behavior of mold-cast Mg alloy AZ91 is investigated in as-cast (F), homogenized (T4), and artificially-aged (T6) conditions in chloride media. Heat treatment influences mainly the distribution of intermetallic β-phase (Mg17Al12) in the alloy. Aging to T6 temper causes precipitation of the phase as a nearly continuous network of secondary particles along the grain boundaries. The alloy exhibits much better corrosion resistance in the T6 temper than it does in the other two conditions. It is observed that the β-phase is inert to the chloride solution in comparison to the magnesium matrix and acts as a corrosion barrier. The mechanism responsible for this behavior is investigated by studying the electrochemical properties of synthetically prepared β-phase and solid-solution alloys representative of the magnesium matrix.

Subject
Materials, Corrosion rate, Metal surfaces, Precipitates, Aluminum, Magnesium alloys, Sodium chloride, Acidity, Sodium chloride solution, Magnesium, Aluminum alloys, Alloys, Corrosion potential
National Association of Corrosion Engineers
1989
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