S. Shirmohammadi - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran
F. Ashrafizadeh - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran
A. Hakimizad - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran

Adhesion of coatings to aluminum components is a critical factor due to the presence of a surface oxide film that prevents intimate contact between coating and the metal. In this research, two different types of interlayers were produced on aluminum alloy specimens prior to electroless nickel coating in an attempt to improve the low adhesion of such coatings to aluminum substrates. The amorphous Ni-P layer of medium phosphorous content was deposited on 3004 aluminum alloy sheet after an interlayer of either a zinc coating (zincate process) or an oxide coating (anodizing process) was applied to the substrate. Formation of electroless coating was evaluated by X-ray Diffraction and microanalysis (EDS). The surface morphology and topography of the coatings were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. Adhesion of the coating to aluminum substrate was evaluated by the bending test according to ASTM B571. It was observed that application of a nano-porous aluminum anodic oxide as interlayer effectively increased the adhesion of electroless Ni-P coating to aluminum surface; the adhesion strength was considerably more than that obtained by the presence of zincate interlayer.

adhesion; interlayer; anodizing; zincate process; electroless Ni-P