EFFECT OF ANODISATION AND SEALING TO FATIGUE BEHAVIOUR OF ALUMINUM ALLOY 2024-T351

• Main Author: TAUFIK HYA (NIM : 12513024), NANDA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/29538
• Institution: Institut Teknologi Bandung

Al alloy 2024-T351 has been used as a structural material in aircraft. This alloy is used because of its high strength and lightweight. However, this alloy has a lower corrosion resistance than pure aluminum. Anodization was carried out on Al alloy 2024-T351 to improve corrosion resistance through the Chromic Acid Anodization (CAA) method. In the latest development, the sealing process was also carried out to improve the corrosion resistance after anodizing. The application of anodizing treatment creates a protective layer on the alloy surface. The protective layer can change the mechanical properties of the alloy. The important mechanical property for aircraft structure material are strength against repetitive loads (fatigue strength). Therefore, it is necessary to study the effect of anodizing and sealing on the fatigue strength of Al alloy 2024-T351. <br /> <br /> This research was conducted to compare the fatigue behaviour between anodized 2024-T351 and sealed 2024-T351. Comparison can be seen from the S-N (Stress-cycle) curve. This curve was formed from the fatigue test results of the five standard EN6072 samples for both anodized 2024-T351 and sealed 2024-T351. Electrolyte solution of anodizing process was chromic acid with concentration was maintained in the range of 30 – 100 gpl. The CAA was carried out at a voltage of 38 – 42 Volts with detention of 30 – 35 minutes. While the sealing process using dichromic anions in the form of sodium dichromate with concentration was maintained in the range of 47.5 – 52.5 gpl. Dichromate seal was carried out at a temperature of 90.5 – 96.1°C for 23 – 28 minutes. Fatigue tests were performed on five anodized samples and five sealing samples. The cyclic load of fatigue tests were set at 280, 260, 240, 220, and 200 MPa with 0.1 stress ratio and 20 Hz frequency. Fatigue testing data were presented in the form of S – N curves. <br /> <br /> The results of this research based on the S – N curves showed that the anodisation treatment has slightly lowered fatigue life of bare aluminum alloy 2024-T351. While the sealing treatment after anodisation has increased fatigue life of Al alloy. The sealing samples were able to pass through 105 cycles. While the anodizing samples were only able to be in the range of 104 to 105 cycles. This occurs because of the porous surface morphology resulting from anodization process. Sealing treatment covers this defect so that alloy surface is smooth. The results of SEM showed that the crack initiation of anodized sample was started from the defect of anodic oxide surface layer in the form of pore. While the crack initiation of sealing sample was started from subsurface defect. Energy Dispersive Spectroscopy (EDS) analysis showed the presence of alumina at the crack initiation area of the anodized sample. While the EDS analysis at crack initiation area of the sealing sample showed the presence of Cu element.