Development of conversion coating on mild steel prior to sol gel nanostructured Al2O3 coating for enhancement of corrosion resistance

► Sol-gel Al2O3 coating on mild steel (MS) substrate with a prior conversion coating. ► Conversion coating on MS consists of Al2O3, SiO2, α-Fe2O3 and Fe3O4. ► Amorphous Al2O3 coating on MS reduces icorr by 5 orders of magnitude. ► Al2O3 coating produces barrier type protection in 3.5 wt.% NaCl up to ≥ 1.0 VSCE.