The effect of the area fraction, size and distribution of model cathodic, intermetallic particles (IMPs) in an anodic Mg matrix on corrosion was investigated. Model Mg-Al electrodes were developed to study IMP effects in isolation from other metallurgical effects, with particles simulated by Al electrodes embedded in a Mg matrix. Arrays of model Mg-Al electrodes were constructed using high purity Al as a surrogate for Al-rich IMPs and flush mounted in commercial purity Mg. The area fraction, size and spacing of these electrodes each altered the corrosion rate and cathodic reaction kinetics assessed after a 24 and 48 hour immersion period at the open circuit potential. Corrosion rate increased with increasing area fraction of Al electrodes but decreased with increasing electrode spacing given a fixed area fraction. The affected zone around electrodes and at the Al/Mg interface was explored to ascertain its impact on the resultant global corrosion rate and kinetics. The effect of local pH at the Al electrode on the prospects for Al corrosion and chemical redeposition were also explored.