The Effect of the Pre-treatment of Aluminium Alloy 4045 on the Zincate Immersion Process

Prior to electroplating of aluminium, various pre-treatment steps are required to obtain good adhesion of the deposit. The essential step is the spontaneous deposition of an intermediate zinc layer by immersion in a zincate solution. This paper outlines the influence of the pre-treatment of aluminium alloy 4045 on the zincate immersion process. AA4045 has a low melting range and is for this reason typically used as clad alloy for brazing sheet applications. AA4045 alloy has a specific microstructure due to its high silicon content (9 - 11 wt%). The pre-treatment steps considered in this study include cleaning, etching and desmutting. During the pre-treatment the aluminium substrate undergoes significant chemical and morphological changes that will affect the course of the zincate immersion process. In order to investigate the electrochemical behaviour of AA4045 during the zincate immersion process, the open circuit potential was recorded vs. time. Mass transfer conditions were controlled by the use of a rotating disk electrode. The obtained electrochemical investigations were complemented with surface analysis techniques, like SEM, EDX and XPS measurements, which allowed us to link effects of surface composition, e.g. oxide/hydroxide films, to the deposition of zinc.