Characterization of cast AlSi(Cu) alloys by scanning Kelvin probe force microscopy

The aluminum cast alloys undergo surface treatments involving micro-electrochemistry for improved hardness, wear and/or corrosion resistance. The susceptibility to local galvanic coupling for three different permanent mold cast aluminum alloys, i.e. 99.8 wt.%Al, Al–10 wt.%Si and Al–10 wt.%Si–3 wt.%Cu was investigated using the scanning Kelvin probe force microscopy (SKPFM) technique. All the particles detected in the alloys (i.e. Al–Fe, Al–Fe–Si, Si, Al2Cu) revealed a positive Volta potential difference relative to the matrix. However, the nobility depended on particles composition. The highest Volta potential differences were determined in the Al–10 wt.%Si–3 wt.%Cu alloy between the copper containing intermetallics and the aluminum matrix whereas the lowest differences were detected for the Al–Fe particles in the 99.80 wt.%Al specimen. Further, the matrix of the 99.8 wt.%Al specimen showed Volta potential differences possibly due to compositional gradients following casting.