Superplasticity of friction stirred processed al 7075

• Main Author: Teo, Elizabeth Shu Hui
• Other Authors: Tan Ming Jen
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/61397
• Institution: Nanyang Technological University

Superplastic forming has posed a strong industrial attraction due to its forming ability of large intricate shapes with sheet metal in one operation. This phenomenon is assisted by the fine grain size possessed by the material placed in an environment with an elevated temperature. The first objective for this experiment was to determine the optimal conditions (i.e. Temperature and strain rate) for which a post Friction Stir Process (FSP) Al 7075 would exhibit the greatest deformation. Samples were first cut into a dog-bone shape and subsequently an air sevo endurance testing system and thermostat were used to ensure temperature and initial strain rate constancy during the experiment period. The results showed a maximum deformation of 800% when placed in 425°C and 3x10-2 s-1 strain rate. The second objective for the experiment was to analyse the variation of microstructure in the material as it undergoes deformation. 5 samples were prepared for the Electron Backscattering Diffraction analysis: Pre-FSP, Post-FSP, after 5 minutes of preheating, at 50% of maximum elongation, at maximum elongation. Results indicated recrystallization as the dominant mechanism during the initial phases. However, upon the onset of strain, Grain Boudary Sliding became an active mechanism.