Traditionally, lead-based bearing overlays dominate the commercial automotive
market and it has been proven that an excellent combination of properties can be
attained through their use. However, lead is a toxic metal and a cumulative poison in
humans. According to the European Union End-of-Life Vehicle (ELV) Directive
proposed in 1997, vehicles that registered in'all the member states after 1st July 2003
should contain no lead, mercury, cadmium and hexavalent chromium. In this study, a
new sulphate-gluconate electrolyte was used to produce multilayer SnCo coatings,
aimed at a lead-free overlay for future market use.
Tin-cobalt compositionally modulated alloy (CMA) coatings produced from sulphategluconate
electrolytes have been previously examined as a potential replacement for
lead-free bearing overlays [1]. However, some obstacles may exist which limit their
potential use on an industrial scale. For example, long electroplating times are
required to produce a thick coating which is very undesirable from an industrial
viewpoint, and also the possible elemental interdiffusion occurring in the coating
system under engine operating temperatures could rapidly deteriorate the coating
properties. In addition, there is an increasing demand from automotive industry to
further improve bearing overlay properties, for example for high performance and
high compression ratio engines... cont'd