In April 2016 Manchester eScholar was replaced by the University of Manchester’s new Research Information Management System, Pure. In the autumn the University’s research outputs will be available to search and browse via a new Research Portal. Until then the University’s full publication record can be accessed via a temporary portal and the old eScholar content is available to search and browse via this archive.

Systematic Analysis of the Advantages of Stationary Shoulder Friction Stir Welding in Joining High Strength Aluminium Alloy AA7050-T7651

Wu, Hao

[Thesis]. Manchester, UK: The University of Manchester; 2017.

Access to files

Abstract

Stationary (static) shoulder friction stir welding (SSFSW) is a variant of conventional friction stir welding (FSW) that was originally invented to improve the quality of welds produced with titanium alloys. Its predominant advantage is a reduction of the severe through thickness temperature gradients seen in conventional FSW, when welding low thermal conductivity alloy. However, SSFSW has rarely been utilised as a method to weld aluminium alloys because it is generally thought that in conventional FSW the rotating shoulder plays an essential role in the heat generation and, due to the high thermal conductivity of aluminium alloys, a rotating shoulder is beneficial for the welding process.In the work presented, the advantages of SSFSW have been examined when welding a typical high strength aluminium alloy AA7050-T7651. The process window for each approach has first been determined, and the optimum welding conditions were systematically evaluated, using power-rotation rate curves. Direct comparison of the two processes was subsequently carried out under these optimum conditions. It has been demonstrated that SSFSW can dramatically improve the quality of a weld’s surface finish. Under optimum conditions it has also been shown that SSFSW was able to weld with approximately a 30% lower heat input than FSW and the stationary shoulder led to a narrower heat affected zone (HAZ). As a result, the through thickness properties of SSFSW were much better and more homogeneous than that for FSW, in terms of grain sizes, hardness and cross-weld mechanical properties. Uniaxial tensile tests proved that the average tensile strength of SSFSW samples was around 500 MPa, which was about 100 MPa larger than that of the FSW sample. Also, it was shown that during tensile testing the deformation zones, which correspond to minima in the hardness distribution of SSFSW welds, were about half the size of those found in FSW welds under the same traverse speed.The mechanisms that give rise to these advantages have been investigated systematically, focusing on directly comparing the SSFSW and FSW processes, and are discussed aided by finite element modelling (FEM) of the heat distribution in welds produced by each process and microstructural investigations.

Bibliographic metadata

Type of resource:
Content type:
Form of thesis:
Type of submission:
Degree type:
Doctor of Philosophy
Degree programme:
PhD Advanced Metallics DTC
Publication date:
Location:
Manchester, UK
Total pages:
275
Abstract:
Stationary (static) shoulder friction stir welding (SSFSW) is a variant of conventional friction stir welding (FSW) that was originally invented to improve the quality of welds produced with titanium alloys. Its predominant advantage is a reduction of the severe through thickness temperature gradients seen in conventional FSW, when welding low thermal conductivity alloy. However, SSFSW has rarely been utilised as a method to weld aluminium alloys because it is generally thought that in conventional FSW the rotating shoulder plays an essential role in the heat generation and, due to the high thermal conductivity of aluminium alloys, a rotating shoulder is beneficial for the welding process.In the work presented, the advantages of SSFSW have been examined when welding a typical high strength aluminium alloy AA7050-T7651. The process window for each approach has first been determined, and the optimum welding conditions were systematically evaluated, using power-rotation rate curves. Direct comparison of the two processes was subsequently carried out under these optimum conditions. It has been demonstrated that SSFSW can dramatically improve the quality of a weld’s surface finish. Under optimum conditions it has also been shown that SSFSW was able to weld with approximately a 30% lower heat input than FSW and the stationary shoulder led to a narrower heat affected zone (HAZ). As a result, the through thickness properties of SSFSW were much better and more homogeneous than that for FSW, in terms of grain sizes, hardness and cross-weld mechanical properties. Uniaxial tensile tests proved that the average tensile strength of SSFSW samples was around 500 MPa, which was about 100 MPa larger than that of the FSW sample. Also, it was shown that during tensile testing the deformation zones, which correspond to minima in the hardness distribution of SSFSW welds, were about half the size of those found in FSW welds under the same traverse speed.The mechanisms that give rise to these advantages have been investigated systematically, focusing on directly comparing the SSFSW and FSW processes, and are discussed aided by finite element modelling (FEM) of the heat distribution in welds produced by each process and microstructural investigations.
Thesis main supervisor(s):
Language:
en

Institutional metadata

University researcher(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:308791
Created by:
Wu, Hao
Created:
24th April, 2017, 15:30:59
Last modified by:
Wu, Hao
Last modified:
3rd November, 2017, 11:30:59

Can we help?

The library chat service will be available from 11am-3pm Monday to Friday (excluding Bank Holidays). You can also email your enquiry to us.