EFFECT OF AGING TREATMENT ON STRESS CORROSION CRACKING (SCC) AND MECHANICAL PROPERTIES IN ALUMINUM 2024 ALLOYS

• Main Author: Varisal Amir, Roys
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69184
• Institution: Institut Teknologi Bandung

Indonesia is a country in Southeast Asia with the fastest growing aviation market in Southeast Asia. One of the alloys that is often used in aircraft structures is aluminum alloy 2024 (AA2024). AA 2024 has good mechanical properties but has a susceptibility to stress corrosion cracking (SCC). This is due to the presence of chloride ion deposits from seawater in the structure of the aircraft which can cause failures in the structure of the aircraft. One method that can be used to increase resistance to SCC is by conducting heat treatment in the form of aging treatment. Aging treatments carried out in this experiment include natural aging and artificial aging. This study was conducted to study the effect of aging treatment on mechanical properties and resistance to SCCs in AA 2024. Heat treatment was carried out starting with a solution treatment to all samples for two hours, then a variation of aging was carried out, one sample was carried out natural aging for 55 days at room temperature (T4) while the rest were carried out artificial aging with variations in aging time, those are: 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 8 hours, 12 hours, 16 hours, and 20 hours. SCC experiment was carried out by providing a constant load of 75% of the AA2024 yield strength value of 250 MPa. The solution used in the SCC test was a NaCl solution with a concentration of 5% (percent by weight). Experiment was carried out until the sample was broken or stopped after 168 hours of immersion. Resistance to SCC was determined based on the duration for which the sample has fractured and the rate of length gain. The mechanical properties studied were hardness and strength with variations in aging treatment carried out. In this study, observations were made using an optical microscope to determine the state of the sample microstructure. SCC experiment samples that experienced a fracture were observed using scanning microscope electron (SEM) to analyze the crack mechanism. The highest SCC resistance was obtained in samples with an aging time of 16 hours that experienced the smallest length gain and did not break until 168 hours. The lowest SCC resistance was obtained in samples with an aging time of 5 hours which broke at the 48 hours of experiment. The highest strength and hardness values were obtained in samples with a 3-hour aging time of 414.36 MPa and 159.7 HV while the lowest strength and hardness values were successively obtained in samples with aging time of 20 hours and 12 hours of 116.1 HV and 274.34 MPa. Sample Values that have the best combination of mechanical properties of strength, hardness and resistance of SCC are T4 samples.