In the present investigation, a comparative study on Alumina plus calcia stabilized Zirconia coatings applied on Al-6061, and cast iron substrates have been done and called coating system. The top coat thicknesses were varied in 100, 200, and 300µm for both the coating systems. The coating was achieved using Plasma Spray Technique (PST). The test was conducted as per ASTM B117 standard using Salt Fog Spray Technique. The samples were exposed to saline, aqueous NaCl solution at PH 6.7 for the duration of 24 hrs. Results obtained from SEM and EDX analysis found that as the coating thickness increases, the porosity of the top coat decreases and it also inhibits the corrosion phenomenon.The top coat of 100µm in the case of cast iron subjected to accelerated corrosion due to higher porosity and less thickness. The mechanism of corrosion has also been discussed in detail which may be helpful for the material scientist and researchers.