CHROMIC ACID ANODIZING OF ALUMINIUM ALLOY 2024-T3 AND THE INFLUENCE OF BENDING PROCESS TO THE CORROSION RESISTANCE OF ANODIZE LAYER

• Main Author: GUSMAHARANI (NIM : 22110032); Pembimbing : Dr. Ir. Sunara Purwadaria, M.Met.E., MIA
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/20278
• Institution: Institut Teknologi Bandung

Aluminum and its alloys are light metal and the strength of aluminum alloys after heat treatment (precipitation hardening) is higher than that of carbon steel. Ninety percent of material used for air flight construction consisted of aluminum and aluminum alloys. However, the corrosion resistance of aluminum alloys is not as good as corrosion resistance of pure aluminum. Consequently, the surface of aluminum alloys has to be protected in order to enhance its corrosion resistance and its service life, as well as to reduce the possibility of failure during services. Typical protection method applied on this aluminum alloys are cladding with pure aluminum followed by anodizing process. The later process will prevent the corrosion of the part of alloys which are exposed into the corrosive environment, e.g. on the surface of clad aluminum alloys after machining that causes to localized elimination of pure aluminum clad. <br /> <br /> <br /> A series of anodizing experiment has been conducted to study the influences of prior bending process on the thickness, weight and corrosion resistance of anodize layer formed. The experiment is preceded with preparation to produce test specimens having dimension 10cm x 5 cm x 0.1 cm, followed by bending with different bending angles (0, 45, 90 and 125 degree). Anodizing process is preceded by cleaning of specimen surface with methyl ethyl ketone (MEK) to eliminate any sticky dirt such as oil, grease and finger print. It is followed with further cleaning process by immersing them into 45-60gpl Turco 4215 NCLT alkaline solution at 45-500C for 15 minutes to further eliminate the rest of oil and grease sticking on the surface of specimens. The oxide layer /film on the surface of specimen is then dissolved by pickling process using deoxidizing solution containing 75-150 gpl HNO3 and 5,5-135 gpl Cr6+. The clean specimen is then anodized in chromic acid solution, and then rinsed with distilled water, sealed in a recommended sealing process by immersing into dilute chromate solution for 28 minutes at 93 0C. <br /> <br /> <br /> Salt spray test has been done for 336 hours on each specimen in a salt spray chamber to compare the corrosion resistance of anodized layer produced. Salt spray test results exhibit that anodize layers formed at room temperature is strongly susceptible to degradation due to its limited thickness. The number of pits formed on the surface of specimen is higher than five pits. Same tendency is shown by anodized layer produced by 20 minutes anodizing. The increase of temperature up to 450C, anodizing time up to 60 minutes and bending angle up to 125 degree have reduced the pitting formation on anodize layer. <br /> <br /> <br /> Measurement of the weight of anodize layer formed was carried out by dissolving the layer in a stripping solution containing 20 gpl chromic acid and 35 gpl phosphoric acid at 98-1000C for 10 minutes. While the thickness of specimen anodize layers are measured using eddy current thickness meter. It is revealed that thickness and weight of anodized layer increases with increasing anodizing time even though the thickness and weight increment is not linear. The same tendency has been observed on the increase of anodizing temperature. In contrast, the thickness and weight of anodized layer is relatively not affected by the cell potential varied. In fact, thicker anodize layers were formed on test specimen bent with higher bending angle. <br /> <br /> <br /> Significance influence of anodizing process variables on the thickness and weight of anodize layer formed is tested using ANOVA at &#61537; 0.05. It is obtained by 24 two level factorial design, the most influenced anodizing experimental variables are temperature, anodizing time, bending angle, interaction between temperature and anodizing time, interaction between anodizing time and bending angle, as well as interaction between temperature, anodizing time and bending angle.