With suitable pretreatment, a compact and even nickel-phosphorus alloy coating was
obtained on W-Cu alloy by electroless deposition from solutions containing nickel sulphate as a
source of nickel and sodium hypophosphite as the reducing agent and a source of phosphorus. The
Ni-P coating was normally prepared from acidic baths at high temperature of the order of 90oC with
the pH of 4.8 and it was smooth and uniform and exhibited high crystal refinement and high
microhardness and superior corrosion resistance. The microhardness, adhesion and corrosion
resistance mechanism of Ni-P deposit were studied. The microhardness of the Ni-P alloy deposit
increases greatly by tempering at various temperatures. The Ni-P deposit has a strong adhesive force
with W-Cu alloy substrate checked by thermal shock test and scribe test. The anti-corrosion ability of
Ni-P coating and its anti-corrosion mechanism were measured using immersion experiment and
potentiodynamic polarization techniques. The results showed that the corrosion resistance of Ni-P
coating was higher than that of W-Cu alloy substrate in the 10vol.% sulfuric acid, monitoring sweat
solution and 3.5wt.% sodium chloride solution. The anti-corrosion mechanism of electroless Ni-P
coating immersed in 3.5wt.% sodium chloride solution was studied using potentiodynamic
polarization techniques. The surface micromorphological morphology and structure of the Ni-P
coating were investigated using Scanning Electronic Microscope (SEM) and X-ray Diffraction
(XRD). The results indicated that the Ni-P alloy coating consisted of microcrystals and it was
amorphous in structure, and the electrochemical measurement showed passive film formed on Ni-P
coating during immersion test in the 3.5wt.% sodium chloride solution.
Study on Corrosion Resistance of Anodized 6463 Aluminum Alloy as Construction Material in 3.5% Sodium Chloride Solution
