Influence of the Copper Content on Microstructure and Corrosion Resistance of AZ91 Based Secondary Magnesium Alloys

Copper is one of the critical elements that can enrich in Mg alloys during recycling of post consumer scrap. Sources of copper are coatings on used magnesium parts or aluminium alloy contaminations in Mg scrap. Therefore, it is important for the development of secondary magnesium alloys to understand the effects of copper in the microstructure of magnesium AZ based alloys and how this influences the corrosion resistance.

Copper contents have been varied between 0 and 2 wt% in gravity die cast AZ91D alloy. The resulting microstructures were studied by LM, SEM + EDX and XRD. Already at low Cu contents (0.25 wt% Cu) ternary Mg-Al-Cu intermetallic phases were observed. Further increasing Cu concentrations resulted in more copper-rich phases, and a significantly reduced corrosion resistance was found. By correlating microstructure and corrosion properties, critical Cu concentrations were defined and corrosion minimising strategies for AZ based secondary alloys were developed.