Display omitted •Al graded Mg-Al thin films were synthesized via combinatorial magnetron sputtering.•Al graded Mg-Al thin films were analyzed via in-situ electrochemistry.•The Mg-Al solid solution corrosion resistance increases with the Al concentration.•Exceeding cAl ∼ 4 wt% causes a distinct anodic current density decrease.•Exceeding cAl ∼ 4 wt% causes a predominant cathodic partial reaction on the surface. The effect of varying Al concentrations on the electrochemical corrosion resistance of binary Mg-Al solid solutions thin films under alkaline immersion conditions was investigated via a combination of in-situ flow-cell, scanning vibrating electrode technique and microscopy analysis. These spatially resolving characterization techniques are employed along the Al concentration gradient of the combinatorically grown thin films enabling efficient screening of the Al concentration dependent electrochemical corrosion behaviour. The analysis revealed an increasing corrosion resistance with increasing Al concentration, as a consequence of Al induced hydroxide reinforcement. Specifically, the addition of >4 wt.% Al decreases the corrosion current density in the range of 70–90 % compared to pure Mg.