Electroless nickel-boron plating on magnesium alloy

Abstract

The electroless Ni-B plating has attracted much interest due to its excellent corrosion resistance, solderability, thermal stability and electrical property in recent years. The effects of borohydride, ethylenediamine and sodium hydroxide concentrations on the plating rate and stability of the deposited electroless Ni-B films were systematically investigated in this study. If the molar concentration ratio of Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> to BH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> was below 3:1, the electroless Ni-B bath would decompose; the Ni-B plating rate reached the maximum when the molar concentration ratio was 4:1 and then decreased with the increasing molar concentration ratio up to 7:1. If the molar concentration ratio of ethylenediamine to Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> was around 7, the plating rate would reach the maximum; if the ratio was below 5, nickel was not completely complexing with ethylenediamine. When the sodium hydroxide concentration was below 70 g/L, the Ni-B plating bath would decompose due to the low alkaline; and then the Ni-B plating rate increased with the increasing sodium hydroxide concentration and reached the maximum at 110 g/L; further increase in sodium hydroxide concentration led to the decrease in the plating rate. The optimization of the compositions of the Ni-B plating bath was obtained. The HV hardness of the plated Ni-B film reached 696 HV, which was significantly higher than those of the magnesium substrate (100 HV) and Ni-P film (575 HV). The adhesion strength of Ni-B plating and magnesium substrate was measured by scratch adhesion testing, and the value of the adhesion strength was 6.05 N.