Autocatalytic electroless nickel-boron plating on light alloys

Light alloys are more and more widely used, notably in aeronautics and the car industry. To improve their superficial properties, they can be covered with a hard and wear resistant protective layer. In this article, we examine the possibility of depositing a thick autocatalytic electroless Ni-B plating on aluminium alloys. We propose an alkaline bath containing sodium borohydride as the reducing agent. The deposition rate is held constant by a regular replenishment of the Ni-B bath allowing a rate of about 25 mu m/h. The Knoop microhardness of the Ni-B deposits after the bath reaches about 750 hk(100). Appropriate heat treatment can increase the deposit microhardness up to more than 1000 hk(100) but must be applied with regard to the substrate properties. The study of these heat treatments will be published in a further paper. (C) 2000 Elsevier Science S.A. All rights reserved.