The effect of Fe content and thermo-mechanical processes on corrosion properties of the EN AW 8006 alloy
Aluminium foil in food industry has been primarily used as a construction material for flexible packaging because of its rare mechanical properties as well as corrosion resistance. Economical significance and increasing application of foil made out of EN AW 8006 alloy in food industry encouraged the research of its behaviour in working conditions. According to the European norm EN 573-3 the content of Fe in EN AW 8006 alloy may vary from 1.2 do 2.0%. Increasing the Fe content improves alloy mechanical properties and as well, it effects its electrochemical behaviour. In this phase of the study, large aluminium slabs of EN AW 8006 with four different levels of Fe content (1.20, 1.50, 1.70 i 1.91% Fe) were cast and industrial processed into 0.030 mm thick foil. The corrosion properties of EN AW 8006 alloy with different contents of Fe were studied in a 0.5 M NaCl solution at 25oC, by the means of potentiodynamic polarization and cyclic voltammetry. Electrochemical measurements were performed using a PAR Model 273A Potentiostat and PAR Model 5210 Lock-In Amplifier, remotely controlled by computer. The potentiodynamic measurements were carried out in the potential range from -0.25 to +0.15 V versus open circuit potential (OCP) with the scan rate of 2 mVs-1, while cyclic measurements were preformatted in the potential range from -1.2 to -0.6 V with the scan rate of 10 mVs-1. The tested electrodes have been made of samples taken after each production phase (casting, homogenization and hot rolling). The dissolution (corrosion) of the cast sample electrode takes place mostly on the border of dendrites right on the position of alloying elements high concentration and impurities. Comparing to the cast sample the homogenizated sample electrode shows improved corrosion resistance. The process of homogenization eliminates segregation inside of the crystal grain and followed by high temperature atoms are given enough time to change the place and establish equilibrium state. The recrystallized structure of material that results at hot rolling process represents undirected crystal grains structure and electrodes with that type of structure show uniform dissolution. The study shows those thermo-mechanical industrial processes, casting, homogenization and hot rolling, increase alloy stability as well as the corrosion resistance.