Formability extension of aerospace alloys for tube hydroforming applications

Abstract

Tube hydroforming (THF) is an innovative metal forming process using a pressurized fluid in a closed die to produce complex shapes from tubular starting material. This process has many advantages (weight reduction, reduced tooling and assembly costs, fewer numbers of operations, superior products quality) but remains unconventional in aeronautics because of the limited formability of aerospace alloys. The main objective of the research conducted during this thesis is to study a method for increasing the formability of two designated aerospace alloys by the use of a multi-step forming method that includes cycles of forming followed by intermediate heat treatment steps. An extensive literature review on existing methods to improve the formability of aerospace alloys as well as on the available softening heat treatments has allowed the implementation of an appropriate experimental procedure. This process consists of several sequences of forming followed by successive heat treatments until obtaining the final part. The insertion of intermediate steps of heat treatment as well as the combination "deformation + heat treatment" influences the mechanical and metallurgical behavior of the alloys. Thus, a complete characterization of the materials had to be conducted at each stage of the process. From a mechanical point of view, the effect of heat treatment and more generally the effect of the multi-step forming process itself on the mechanical properties and constitutive laws of the alloys have been studied in detail. At the metallurgical level, the influence of the process on the microstructural characteristics of the alloys such as grain size, phases in presence and texture has been analyzed. These two parallel studies have allowed to understand completely and in details the impact of metallurgical modifications induced by the multistep process on the macroscopic mechanical behavior and final properties of the part.

Date	2 Nov 2016
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Philippe Bocher (Supervisor), Javad Gholipour Baradari (Co-supervisor) & Mohammad Jahazi (Co-supervisor)