Influence of Heat Treatment on Corrosion Behavior of Mg-Al Alloy

초록

Influences of heat treatment and Mg17Al12 precipitate on the corrosion behavior of AZ91 magnesium alloy were investigated in as-cast, homogenized(T4), and artificially aged(T6) conditions in deaerated chloride solutions. The result of corrosion test showed that T6 alloy has much better corrosion resistance than as-cast or T4 alloy. Heat treatment influences mainly precipitation and distribution of Mg17Al12 phase in Mg-Al alloy. At T6 conditions Mg17Al12 phase precipitates along the grain boundaries and Al concentration of matrix decreases to 3%. The open circuit potential of Mg17Al12 intermetallic compound was mesured more noble than that of Mg-3Al matrix composition alloy. But, it was obtained from the galvanic corrosion test and potentiostatic test that the galvanic coupling of Mg17Al12 and Mg-3Al matrix gave little effect on the corrosion of AZ91-T6 alloy, as the effect of cathodic polarization of Mg17Al12 was smaller than that of Mg-3Al. It was also found that the corrosion resistance of Mg-Al alloy increased as the concentration of Al in matrix decreased resulting from the precipitation of Mg17Al12 phase. From the result of the corrosion morphology investigation, filiform attack was preferential than pitting in AZ91-T6 alloy. And it was considered that Mg17Al12 precipitates play a role of physical barrier against the propagation of the filiform corrosion.