The practical adhesion of maleic anhydride grafted polyethylene (MAH-PE) to galvanised steel was studied using 3-point flexure tests, before and after hydrothermal ageing. Before bonding, the electro-galvanised steel was treated with gamma-aminopropyltriethoxysilane (gamma-APS). The influence of the silane coating thickness and deposition pH on the practical adhesion of MAH-PE to steel was investigated. FT-IR spectroscopy and microscopy enabled to gain understanding of the interphase formation between the silane and the metal substrate. It was found that, at the natural pH of the gamma-APS, Zn ions dissolved in the silane coating with subsequent formation of crystals. This interphase could be held responsible for the better durability of the bonds than for silane coatings applied at quasi-neutral pH, for which dissolution of Zn ions was not observed.