applied on the degreased sample was the lowest among all sample.All of these observations indicate that the coating adhesion to the aluminium surface was not high enough to resist against applied force during pull-off measurement. The presence of oxide layer on the surface of degreased aluminium caused significant decrease of the work of adhesion and surface wettability by the epoxy coating. However, the adhesion strength was increased after chemical etching. In fact, the oxide layer removal from the aluminium surface caused the increase of wettability resulting in greater adhesion strength of the coating. However, the coating detachment on this sample is still in the form of adhesive failure. According to Table 4,the increase in adhesion strength was most pronounced in the case of the aluminium sample modified with Zr conversion coating than other samples. Moreover, a cohesive failure was observed for the epoxy coating applied on the aluminium sample treated by Zr conversion coating. These all show that the Zr treatment of aluminium could enhance the epoxy coating adhesion significantly. Both the surface free energy and roughness are influential parameters affecting the epoxy coating adhesion to the aluminium surface [35,36].It has been previously shown that chemical etching and chemical treatment of the aluminium surface caused the increase of surface free energy and roughness. The greater surface free energy of the aluminium sample treated by Zr conversion coating than other samples is responsible for the greatest increase in the epoxy coating adhesion to the aluminium surface. The high surface roughness can produce greater surface area to adhere to the epoxy coating.Therefore, the significant increase in pull-off adhesion strength of the epoxy coating to the Zr treated sample is mainly because of the coating solution penetration in to the surface (causing adhesion bonds creation through mechanical interlocking mechanism)[37]. The adhesion of the epoxy coating to the surface of aluminium was affected during exposure to the corrosive electrolyte.In fact, the corrosive electrolyte could diffuse into the coating porosities and reach the coating/aluminium interface. The OH. can be created beneath the coating as a result of oxygen reduction reaction occurring at the cathodic active sites on the aluminium surface (2H2O + O2+ 2e.¨ 4OH.). Therefore, the water molecules can break down the hydrogen bonds between coating and metal surface through the increase of local pH at the coating/metal inter-face [16,38]. This is responsible for the severe coating adhesion loss Fig. 5.