The corrosion resistance of Mg–9 mass%Al alloys deteriorates significantly with increasing copper content. It is very important to prevent the deterioration with increasing copper content, because magnesium alloys easily become contaminated with copper in the process of recycling. We found that the corrosion resistance was obviously improved with increasing zinc content in copper-containing Mg–9 mass%Al alloys. In this study, copper intermetallic compounds and magnesium alloys of single phase including aluminum and zinc were produced. Moreover, their electrical characteristics were investigated in order to clarify the mechanism of the improvement of the corrosion resistance due to zinc addition. Adding zinc to copper-rich alloys made copper-based intermetallic compounds from Mg
6Al
7Cu
3 to Mg
32 (Al,Zn,Cu)
49, which is the compound based on Mg
32 (Al,Zn)
49 and includes copper. The cathodic current density of Mg
32 (Al,Zn,Cu)
49 was much smaller than Mg
6Al
7Cu
3. Therefore, the corrosion resistance was obviously improved with increasing zinc content of Mg–9 mass%Al alloys containing copper.
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