samples by an OCA 15 plus type contact angle measuring system using distilled water as the probe liquid at temperature and humidity of 25 } 2.C and 30 } 5%, respectively. In this regard, a small drop of distilled water (2-3 l) was applied on the surface of samples.The shape of droplet was recorded by a Canon type digital camera after 10 s. The images were transmitted to a personal computer for evaluation. Using an image analysis system (G2/G40), the contact angle values were calculated.
2.5.2. Pull-off adhesion test
Posi pull off adhesion tester (DEFELSKO) was used to evaluate the adhesion strength values of the epoxy coating applied on different substrates (ASTM D 4541). The measurements were conducted before (dry pull-off strength) and after (recovery pull-off strength) 30 days immersion in 3.5% w/w NaCl solution. To measure adhesion strength values, the aluminium dollies were glued on the surface of the epoxy coating using a two-part Araldite 2015(Huntsman advanced materials, Germany) adhesive. Samples were ten kept at ambient temperature for 24 h to insure that the glue fully cured. Finally, a slot was made around dollies and they were pulled at a speed of 10 mm/min normal to the coating surface until the epoxy coating was detached from the aluminium substrate. All tests were carried out using three replicates to ensure the measurements repeatability.
2.5.3. Anticorrosion performance measurement
The corrosion protection properties of the epoxy coatings applied on the aluminium substrates with and without Zr conver-sion coating were studied by salt spray test and electrochemical impedance spectroscopy (EIS). The salt spray test was performed according to ASTM B117 for 1000 h. The EIS was performed by AUTOLAB G1. The test was carried out at amplitude and frequency range of }10 mV and 10 kHz.10 mHz, respectively. The measurements were done in a conventional three electrode cell including aluminium specimen as working electrode, Platinum as counter electrode and Ag/AgCl (KCl 3 M) as reference electrode. The impedance data were evaluated at open circuit potential (OCP) on 1 cm2 area of each sample after different immersion times in 3.5%w/w NaCl solution