Investigation of corrosion behaviour and surface properties of aluminium alloys produced by twin roll continuous casting technique

On the occasion of their great characteristics like corrosion resistance, easy processability and weightlessness, aluminium alloys have been mostly preferred in food packaging industry during the recent years. The main reason for the use of aluminium alloy in the food industry is the corrosive property of the chemistry of foods and for this reason, food packaging materials loose their protective features. Aluminium alloys are perfect to the corrosion and pure aluminium exists abundant in the Earth's crust. Today manufacturing and processing to use in food packaging industry of aluminium and alloys are pretty easy and practical. Specifically, 8006 aluminium alloys have been widely used as convenience food packaging and beverage containers. In this master thesis, the corrosion and surface behaviours of 8006 aluminium alloy were investigated which had produced by twin roll casting (TRC) as one of the continuous casting (CC) methods. Firstly melted 8006 aluminium alloy poured into the mould between the twin rolls and 8,5 mm sheet aluminium was obtained. Then 8,5 mm aluminium sheets homogenized between the temperatures 550 °C to 600 °C and cold rolled. After rolling processes the aluminium sheets normalized at the temperatures of 400 °C to 450 °C and the specimens became ready to apply the tests. Before electrochemical corrosion tests, characterization tests applied to the produced specimens. Spectral analyze was applied to detect the elements in the specimens. After that X-ray diffraction (XRD) method used to analyze the phases and elements on the surface of aluminium alloys. With the stereo microscope, the rolling traces and the rolling direction determined. Afterwards, scanning electron microscope (SEM) was applied to examine the surface morphology deeply and the energy dispersive spectroscopy (EDS) was used to found out the percental element weights on the surface. After the before corrosion characterization tests were done, 3,5 % NaCl solution was prepared and used to apply the electrochemical corrosion tests which are open circuit potential (OCP), linear polarization (LP) and electrochemical impedance spectroscopy (EIS) to the aluminium foil alloy specimens. To observe the effects of corrosion tests and the differences on the surfaces of the aluminium foil alloy specimens X-ray diffractometer (XRD), stereo microscope, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods were used after the electrochemical corrosion tests. In addition to these works, to be able to understand the effect or the cold rolling reduction rate to the corrosion behaviour and surface properties, cold rolled aluminium foil alloy specimens were studied which have two different reduction rate 94% and 98% respectively. Same characterization tests were applied before and after corrosion and same electrochemical corrosion tests also were applied. After all these processes, we conclude that when the cold reduction rate increases, depending on the cold rolling route the corrosion rate of the twin-roll cast 8006 aluminium alloys increases and these alloys are suitable for food packaging applications.