Study On The Corrosion Resistance Of Ni-Sn-P Alloy Deposits

Ni-Sn-P alloy coating has been widely applied in the industries because it has good properties in corrosion resistance conductivity and reparability, etc. And as its corrosion process is typical and systemic, it has been usually used as the model to study the corroding system. So it is valuable to study the Ni-Sn-P alloy coating.In this paper, the electrochemical methods and corrosion weight loss methods were used to research the corrosion resistance of Ni-Sn-P alloy coating in 10%H₂SO₄ and artificial sea water. SEM, XPS, XRD and EDS were used to analyze the crystal structure and corrosion products of Ni-Sn-P alloy coating.Results of the study have shown that Ni-Sn-P alloy coating with high content of Sn has batter corrosion resistance than Ni-P alloy coating and SUS304 stainless steel, and the corrosion resistance of Ni-Sn-P alloy improved as the Sn content increased.In 10%H₂SO₄, the uniform corrosion can take place on the surface of Ni-Sn-P alloy coating. The element of Ni dissolved preferentially, with the element of P, Sn enriched on the surface of Ni-Sn-P alloy coating. As a result of this, a layer of passive film composed of SnO₂ and Ni₃(PO₄)₂ formed on the surface of Ni-Sn-P alloy, which can protect the alloy from corrosion. In artificial sea water, also the uniform corrosion can take place on the surface of Ni-Sn-P alloy coating. But the element of Ni and Sn dissolved preferentially, with the element of P enriched on the surface of Ni-Sn-P alloy coating. Then a layer of passive film composed of SnO₂,Ni₃(PO₄)₂,NiO and Ni₂O₃ formed on the surface of Ni-Sn-P alloy, of which, SnO₂ can resist the penetration effect of Cl- effectively.Besides of this, we have researched the influence of heat treatment with different atmosphere and temperatures on the corrosion resistance of Ni-Sn-P alloy coating. The results have shown that as the heat treatment temperature increased in nitrogen atmosphere, the corrosion resistance of Ni-Sn-P alloy coating in 10%H₂SO₄ was reduced. In artificial sea water, the corrosion resistance of Ni-Sn-P alloy coating was improved with low temperature (200℃) heat treatment, and then as the heat treatment temperature increased, its corrosion resistance reduced. But when the heat treatment temperature was 500℃, the corrosion resistance of Ni-Sn-P alloy coating was improved effectively.The corrosion resistance of Ni-Sn-P alloy coating was reduced with low-temperature (200℃, 300℃) heat treatment in air atmosphere; But high-temperature (400℃, 500℃) heat treatment in air atmosphere will lead to a layer of thick and dense oxide film composed of SnO, SnO₂, NiO, Ni₂O₃ and P₂O₅ formed on the surface of Ni-Sn-P alloy coating, which can separate the corrosive solution and the Ni-Sn-P alloy, protecting the alloy from corrosion.