Electrolytic phosphating potions are similar to chemical phosphating but need to be optimised for conductivity and current efficiency.
Electrolytic phosphating potions are similar to chemical phosphating but need to be optimised for conductivity and current efficiency.
(1) Anodic phosphating (workpiece as anode)
Composition of the potion:
Zinc dihydrogen phosphate (Zn(H₂PO₄)₂)
Zinc nitrate (Zn(NO₃)₂)
Nickel salt (NiSO₄)
Fluoride (NaF)
Conductive salts (e.g. Na₂SO₄ to increase electrolyte conductivity)
Process parameters:
Current density: 1~5 A/dm²
Voltage: 5~15 V
Time: 2~10 min
(2) Cathodic phosphating (workpiece as cathode)
Potion composition:
Manganese dihydrogen phosphate (Mn(H₂PO₄)₂)
Manganese nitrate (Mn(NO₃)₂)
Additives (e.g. molybdate to reduce hydrogen embrittlement)
Process parameters:
Current density: 0.5~3 A/dm²
Voltage: 3~10 V
Time: 1~5 min