Macrosegregation and microstructure dendritic array affecting the electrochemical behaviour of ternary Al–Cu–Si alloys

The aim of the present study is to evaluate the electrochemical corrosion behaviour of ternary as-cast Al–Cu–Si alloys. Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that silicon and copper contents, which are affected by position in casting due to macrosegregation, and the dendrite arm spacing, can play an interdependent role on the corrosion behaviour. For the region with predominant Cu inverse segregation, i.e., close to the casting surface, the Cu content is the driving-force leading to a decrease in the corrosion resistance, but the favorable effect of the fineness of the dendritic array has also to be taken into account. However, from secondary dendrite arm spacings of about 15 μm up to coarser dendritic arrays, the Si particles seem to be the driving-forces related to the corrosion resistance and for these cases coarser microstructures were shown to improve the corrosion resistance.

► Electrochemical corrosion behaviour of AlCuSi alloys is affected by segregation.
► Si/Cu contents and dendritic spacing affect the corrosion behaviour of AlCuSi alloys.
► For fine dendritic arrays the local Cu content is decisive for corrosion resistance.
► For coarse dendritic arrays Si particles are determinant for corrosion resistance.