Surface characterization of zincated aluminium and selected alloys at the early stage of the autocatalytic electroless nickel immersion process

Abstract

In this work the changing structure of nickel–phosphorus deposits on aluminium and its alloys at the early stage of electroless nickel phosphorus deposition using hypophosphite ion as reducing agent has been studied. Prior to electroless nickel deposition, zincating is used for pre-treatment of aluminium substrates. The surface morphology and structure of the electroless Ni–P layers were characterized by scanning electron microscopy and X-ray diffraction analysis. Results show that Ni–P deposition is closely related to the dissolution of the zincating layer, followed by progressive nickel nucleation. The nuclei serve as a catalytic surface for further Ni–P deposition which increases with deposition time. The growth and coalescence of the nuclei on the aluminium substrate results in crystalline layers of Ni–P.