STUDY ON RETROGRESSION DURATION EFFECT ON RETROGRESSION AND REAGING (RRA) HEAT TREATMENT TO MECHANICAL PROPERTIES AND STRESS CORROSION CRACKING (SCC) BEHAVIOR OF ALUMINUM ALLOY 7075

• Main Author: Alfisyahril, Pajero
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/78365
• Institution: Institut Teknologi Bandung

Aluminum alloy 7075 is one of the high-strength aluminum alloys which is used in airplane structures. However, aluminum alloy 7075 is prone to failure due to Stress Corrosion Cracking (SCC). SCC durability on aluminum alloy 7075 is known to be improved by Retrogression and Reaging heat treatment (RRA). Through RRA, SCC durability improvement is obtained without sacrificing strengths. Aluminum alloy 7075 is heat-treated by Retrogression heat treatment with the aim dissolve Grain Boundary Precipitate (GBP). RRA on aluminum alloy 7075 researches have been published by researchers but using limited variation in heating duration. This research will be carried out RRA heat treatment on aluminum alloy 7075 by longer Retrogression duration. On this research, RRA heat treatment began with Solution Heat Treatment at 480°C for a hour, aging treatment at 120°C for 24 hours, retrogression heat treatment at 160°C for 10 until 60 minutes by 10 minute variations, and reaging treatment at 120°C for 24 hours. Strength of RRA specimens was obtained by tensile test. Hardness of RRA specimens was tested by Vickers Hardness Test. Microstructure was observed by optical microscope and Scanning Electron Microscope (SEM). SCC durability of RRA heat-treated aluminum alloy 7075 was tested by constant load method in the 5% NaCl salt solution for 10 days. Fracture surface of SCC tested specimens was observed by SEM. Result of this research shows SCC durability on RRA heat-treated aluminum alloy 7075 is achieved maximum point by Retrogression duration for 20 minutes. Ultimate Tensile Strength increases with the addition of Retrogression duration until reaching maximum point 435,82 MPa at Retrogression for 20 minutes, then decreases with the addition of Retrogression duration. Hardness value increases with the addition of Retrogression duration until reaching maximum point 198,8 HV at Retrogression for 20 minutes, then decreases with the addition of Retrogression duration. Grain Boundary Precipitate (GBP) is sparsely distributed because of RRA heat treatment thus improving SCC durability.