Organic and inorganic passivation performance on electroless nickel (LP)

Abstract

Passivation is a very important process after Electroless Nickel (EN-P) plating where it serves to protect the nickel surface against further dissolution or corrosion. Passivation will reduce the reactivity of chemically active metal surface by immersion in a passivation solution. The objectives of this study were to investigate and analyse the organic and inorganic passivation on EN low phosphorous (LP) of the characteristics and corrosion performance on the aluminium alloy component. There are two types of passivation solution that had been used which were chromic acid based solution (inorganic type) and silicate based solution (organic type) and it was found that their optimum passivation time were 210 sec and 90 sec respectively. FESEM (EDX) was used to characterize the surface of EN-P layers with both passivation types. XRD was also used to characterize the compound bonding nature of elements on the EN-P surface. FESEM (EDX) and XRD results showed that the EN-P surface with organic and inorganic passivation were oxidized and composed of nickel oxide, nickel hydroxide, and nickel phosphate, but for organic passivation its exhibits the presence of silicon. It was also shown that the passivation layer thickness was in the range of between 200 to 300 nm. Salt spray test was used to study their corrosion performance for 24, 48, and 72 hours. Most of the specimens were corrode as EN (LP) did not performed corrosion protection to the substrate as EN (HP). However, specimens with organic passivation exhibited more corrosion resistance as indicated from the corrosion rate analysis.