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In  order to improve  the  surface  quality  and  prevention  of  corrosion  and  reduction  of  wear  in  the  components  like  gears  and  bearings,  they  can  be  coated  with  phosphate coatings. SCH420H  alloy  steel  was  coated  with  manganese  phosphate  deposition. The  microstructure  and  corrosion  resistance  of  the  coating  was  studied  by  change  of  bath  temprature. In  order  to  investigate  the  phase  analysis  and  coating  microstructure, X-ray  diffraction (XRD)  and  scanning  electron  microscopy  (SEM)  were  used,  respectively. XRD  analysis  from  the  coated  surface  revealed  the  phases of  MnFe2(PO4)2(OH)2H2O,  Mn(PO)3, Fe(PO)3 and (Mn,Fe)5H2(PO4)4.4H2O. Results  showed  the  obtained  coating  at 90°C  was  uniform  and  continuous  and  no  crack  or  porosity  was  observed.  The  phosphate  surface  at  85°C  and  95°C  was  non-uniform  and  included  cracks.  In  order  to  investigate  the  corrosion  resistance,  potentiodynamic  polarization  and  electrochemical  impedance  spectroscopy  (EIS) tests  were  applied  on  coated  and  uncoated  specimens  in 3.5% NaCl  solution. The  results  of  potentiodynamic  polarization  and  electrochemical  impedance  spectroscopy  tests  were  in  agree  with  microscopic  images  and  results  showed  that  the  coated  specimen  at  90°C  has  higher  corrosion  resistance.

Keywords: Manganese phosphate coating, Temperature, Potentiodynamic polarization, Electrochemical impedance spectroscopy

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