Investigation of microstructural evolution of aluminium alloy 7050 at hot forging conditions
Author(s)
Jiang, Shuai
Type
Thesis
Abstract
Accurately predicting the grain dynamic recrystallisation (DRX) behaviour during hot forging aluminium alloy AA7050 poses a challenge to the aerospace industry, since the final grain structure and distribution in hot forged components determines many vital mechanical properties, such as yield strength, fatigue life and fracture toughness. So far, little research has been devoted to studying the dynamic recrystallisation of AA7050, even aluminium alloys as a whole, during typical hot forging thermal-mechanical processes due to the limited statistically meaningful microstructure characterisation technique and nature of its complexity involving strain, strain rate, temperature as well as microscopic dislocation density, low-angle grain boundaries (subgrain) and high-angle grain boundaries (grain).
Therefore, the aim of this work is to develop a physically-based hot forging material model and associated finite element (FE) simulation to accurately predict the thermomechanical behaviour and microstructural evolution as well as the geometry change in hot forging AA7050 parts. The thermomechanical behaviour is studied using thermal-mechanical simulator Gleeble 3800 under various hot forging conditions, including different strain levels (0 – 0.58), strain rates (0.0005 to 5 s-1) and temperatures (380 - 460 C).
Electron backscatter diffraction (EBSD) reveals the underlying dynamic recrystallisation mechanism. The GND density, LAGB and flow stress exhibit near-linear relationships with the Zener-Hollomon parameter. High dislocation density and more LAGBs are formed at lower temperature and higher strain rate. The dislocations in GND density and the LAGB area are found to be the dominating factor governing the flow stress in the tested ranges of strain rates and temperatures, regardless of the change of HAGBs...
Therefore, the aim of this work is to develop a physically-based hot forging material model and associated finite element (FE) simulation to accurately predict the thermomechanical behaviour and microstructural evolution as well as the geometry change in hot forging AA7050 parts. The thermomechanical behaviour is studied using thermal-mechanical simulator Gleeble 3800 under various hot forging conditions, including different strain levels (0 – 0.58), strain rates (0.0005 to 5 s-1) and temperatures (380 - 460 C).
Electron backscatter diffraction (EBSD) reveals the underlying dynamic recrystallisation mechanism. The GND density, LAGB and flow stress exhibit near-linear relationships with the Zener-Hollomon parameter. High dislocation density and more LAGBs are formed at lower temperature and higher strain rate. The dislocations in GND density and the LAGB area are found to be the dominating factor governing the flow stress in the tested ranges of strain rates and temperatures, regardless of the change of HAGBs...
Version
Open Access
Date Issued
2022-06-27
Date Awarded
01/03/2023
License URL
Advisor
Shi, Zhusheng
Lin, Jianguo
Sponsor
Aviation Industry Corporation of China (Firm)
China Scholarship Council
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)