Additions of 1 wt.% Ca were made to Zn (Zn-1Ca) to generate favourable chemical conditions during corrosion for enhanced performance of phosphate inhibitors. Zn-1Ca displayed a reduced corrosion rate in 0.17 M NaCl measured using the Scanning Vibrating Electrode Technique and polarisation. In-situ timelapse microscopy and SEM-EDS demonstrated that intermetallic CaZn13 preferentially corroded releasing Ca2+ that increased corrosion product precipitation, cathodically deactivating the system. 1 × 10−3 mol dm−3 phosphate additions to 0.17 M NaCl decreased the corrosion rate of Zn and Zn-1Ca. Inhibition was greater for Zn-1Ca where uniform precipitation of mixed metal phosphates produced anodic and cathodic inhibition. •Addition of 1 wt.% Ca to Zn (Zn-1Ca) reduced its corrosion rate compared to Zn.•Distributed CaZn13 phases are preferentially corroded producing Ca2+ ions.•Zn-1Ca had increased corrosion products, cathodically deactivating the system.•Additions of phosphate ions inhibit the corrosion of both Zn and Zn-1Ca.•Inhibition is increased for Zn-1Ca due to precipitation of mixed metal phosphates.