EFFECT OF PRE-STRAIN DEFORMATION ON MECHANICAL PROPERTIES AND STRESS CORROSION CRACKING BEHAVIOR OF 2024-T72 ALUMINUM ALLOY

• Main Author: Grahish Vidhi, Shuantdifa
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69126
• Institution: Institut Teknologi Bandung

Aluminum alloy is one of the materials that is widely used today in various sector, such as aircraft manufacturing. One of the most common types of aluminum alloys used in aircraft structures is the 2024 aluminum alloy. This alloy has comprehensive properties, such as excellent specific strength, formability, and good fatigue resistance. However, it is susceptible to stress corrosion cracking (SCC). The demand for aluminum alloys applied to commercial structural components is reducing weight with increasing strength. In general, high-performance mechanical properties are achieved by thermomechanical treatment (TMT), i.e. deformation strengthening by applying plastic deformation and transformation strengthening by heat treatment. The properties of aluminum alloys that undergo forming tend to be unstable, so overaging heat treatment is fundamental to soften aluminum alloys with the aim of avoiding cracking. In this study, the effect of pre-strain deformation on the mechanical properties and stress corrosion cracking of 2024 aluminum alloy by overaging heat treatment (T72) was examined. Pre-strain was given to samples with variations of 0%, 1%, 3%, 6%, and 12%. The automatic setting of Universal Testing Machine is used at a strain rate of 2 mm/min. The heat treatment used is T72 temper design. The mechanical properties studied were strength, elongation, toughness, and hardness. Microstructure observations and hardness tests were carried out on the specimens after tensile tests. The stress corrosion cracking (SCC) tests were carried out with a constant load of 10 kgf. The corrosive environment used was NaCl solution with a concentration of 5% (weight percent). The test is carried out until the sample fails or is stopped after 10 days if it is not failed. SCC test samples that are failed will be subjected to fractographic observations with Scanning Electron Microscope (SEM). The highest strength and hardness properties were obtained in the pre-strain sample of 12%, with yield strength, ultimate tensile strength, and hardness values of 289.76 MPa, 361.86 MPa, and 147.65 HV, respectively. Strength and hardness values tend to be directly proportional to the increase in pre-strain. The toughness tends to increase with increasing pre-strain up to 6%, then decreases. SCC samples with 0%, 1%, 3%, and 6% pre-strain did not fail after 10 days of experimentation, while 12% pre-strain sample failed on the 8th day. The best stress corrosion cracking resistance was obtained in the pre-strained samples of 6%, 3%, 1%, 0%, 12%, respectively. The most optimal combination of mechanical properties and resistance to SCC in this experiment is considered to be at 6% pre-strain, with the highest toughness value of 22.18 MJ/m3 and did not experience SCC failure after 10 days of experimentation.