Thin film aluminum electrodes were sputter-deposited onto quartz resonators for the electrochemical quartz crystal microbalance technique. The aluminum electrodes were then photolithographically patterned and decorated with arrays of Cu islands or Al-Cu-Mg islands mimicking cathodic and anodic phases in commercial Al alloys. Open circuit exposure to 0.5 M NaCl of different pH was performed, and the resonance frequency of the quartz measured in parallel. In the beginning of the experiments a frequency increase due to loss of Al by corrosion was observed. Later on the deposition of corrosion products with a large roughness caused the frequency to decrease.