Friction Stir Welding and Processing IX: Lightweight Applications
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Yuri Hovanski, Brigham Young University; Rajiv Mishra, University of North Texas; Yutaka Sato, Tohoku University; Piyush Upadhyay, Pacific Northwest National Laboratory; David Yan, San Josť State University

Wednesday 8:30 AM
March 1, 2017
Room: 9
Location: San Diego Convention Ctr

Session Chair: Christian Widener, South Dakota School of Mines and Technology

8:30 AM Introductory Comments

8:35 AM  Invited
Friction Stir Welding of Thick Section Aluminium Alloys - New Techniques: Jonathan Martin1; 1TWI Technology Centre (Yorkshire)
    There are many applications for which joining of thick section aluminium components is required; these include aircraft wing spars, liquefied natural gas tanks, armour plate, railway headstocks. Using conventional fusion welding techniques can be challenging. Recent innovations at TWI, using the unique twin headed capabilities of the Powerstir FSW machine, have demonstrated several techniques which have the potential to minimise production cycle times, making joining of thick section aluminium alloys both technically and commercially advantageous. This paper describes these techniques and the work undertaken at TWI to develop them. Process benefits and weld properties are discussed highlighting the potential benefits including reduce component processing times through quicker welding and minimal part handling; improve weld quality through use of reduced and uniform heat input and increase tool life leading to reduced tooling costs.

8:55 AM  
Effect of Friction Stir Processing on the Damage Resistance of 6xxx Series Aluminium Alloys: Florent Hannard1; Aude Simar1; Thomas Pardoen1; Eric Maire2; 1UCL; 2INSA-Lyon
    Damage evolution in ductile metals is characterized by the nucleation, growth and coalescence of voids. In aluminium alloys, the void population generally nucleates by the decohesion or fracture of the iron rich intermetallic particles. Previous studies have shown that the nucleation stress increases when the size of the intermetallic particles decreases retarding the final fracture of the material. Furthermore, initial porosities and particle clustering reduce the fracture strain. Hence, friction stir processing (FSP) has been applied to a 6xxx series aluminium alloy in order to eliminate initial porosity, break the intermetallic particles and distribute them more homogeneously to improve the fracture strain. Detailed characterization involving 3D microtomography has confirmed that the size of particles is reduced and that void nucleation is delayed. Furthermore, elimination of initial porosity and homogenization of the intermetallics spatial distribution have been quantified. Tensile tests have confirmed an increase of the fracture strain of the material.

9:15 AM  
Effect of Process Parameters on the Residual Stress Distribution in Stationary Shoulder T-Joints: Tianzhu Sun1; Matt Roy1; Phil Withers1; Phil Prangnell1; 1The University of Manchester
    An advanced variant of the FSW process, stationary shoulder fillet welding has great potential for ‘T’ joint applications in the aerospace industry. In contrast to conventional FSW, the process is facilitated by a profiled stationary shoulder that generates little heat and involves two overlapping weld passes. To date there have been few publications on this technique and little is known about the residual stress distribution created, which is an important consideration of aerospace applications. Of particular interest is the effect of weld sequencing in the production of T-joints with two fillet passes from either side of a flange. In this paper, residual stress distributions in AA7010 T-joints have been studied by neutron diffraction and the contour method, two complementary residual stress measurement techniques, and related to the welding parameters. The corresponding weld distortion, joint mechanical properties, and the evolution of the microstructure across the weld zones are also discussed.

9:35 AM  Invited
Friction Stir Weld Lap Joint Properties in Aeronautic Aluminum Alloys: Egoitz Aldanondo1; Ekaitz Arruti1; Alberto Echeverria1; 1IK4-LORTEK
    A study of properties of FSW lap joints performed with aluminum alloys used in aerostructure manufacturing (2XXX and 7XXX series alloys) are presented in this work. The effects of different tool designs and welding parameters in the microstructural and mechanical properties of the joints were investigated. The microstructural features were analyzed by metallographic examination while the mechanical properties were studied by microhardness measurements. Typical features of FSW lap joints have been identified such as hook features, cold lap defects or joint uplifting. The extension of HAZ regions and mechanical property reduction was evaluated depending on the welding parameters used to perform the FSW joints. The tool design as well as welding conditions that minimize defects such as effective sheet thinning, hardness drops or wide HAZ regions were established.

9:55 AM  
Flow Features in Shoulder Zone during Scroll Tool Friction Stir Welding Thick 6061 Aluminum Plates: David Yan1; Xiaoming Wang2; Guy Littlefair3; 1University of Wisconsin-Green Bay; 2Purdue University; 3Deakin University
    The objective of this present study was to reveal the material flow interaction between the shoulder zone and nugget zone in a thick 6061 aluminum plate during scroll tool friction stir welding. It was observed via microstructural examinations that the scroll tool induces the bulk plasticized material to flow into the advancing side from the retreating side in the shoulder flow zone. This results in a unique flow pattern in the shoulder zone, including, among others, a near-half-onion ring pattern in the transverse section of the weld center. Moreover, a semi-circular pattern accumulated in the longitudinal direction of the bottom portion of the weld zone, but featureless in the top portion of the same weld zone. The obtained flow patterns have also been quantified in relation to the welding parameters to build a database for further and more detailed numerical investigation.

10:15 AM Break

10:30 AM  
Corrosion Fatigue Performance of Friction Stir Processed Magnesium Alloy AZ31B-H24: A Comparative Evaluation: Daniel Tapp1; Joseph McDermid1; Joseph Kish1; 1McMaster University
    Load-controlled fatigue experiments were conducted in both laboratory air and in a near-neutral salt fog environment to delineate the effect of friction stir processing on the atmospheric corrosion fatigue performance of magnesium alloy AZ31B-H24 sheet product. Compact tensile (CT) specimens were utilized to restrict the crack initiation to the metallurgical weld zone of interest. The CT samples were oriented such that the loading axis was perpendicular to the friction stir weld direction yet parallel to the rolling direction of the sheet product. The fatigue performance of non-stir processed CT samples in both environments was included as the comparative basis. Results have revealed a significance reduction in the number of cycles to failure at each stress level tested in the near-neutral salt fog (0.05 wt.% NaCl) relative to laboratory air for both stir processed and non-stir processed specimens.

10:50 AM  
High-speed FSW Aluminum Alloy 7075 Microstructure and Corrosion Properties: Jingyi Zhang1; Piyush Upadhyay2; Yuri Hovanski2; David Field1; 1Washington State University; 2Pacific Northwest National Laboratory
    Friction stir weld technique offers great industrial potential with advantages such as superior joint properties and low energy consumption rate. High welding speeds on the order of meters per minutes enable FSW process to be applied on high-volume production lines. This study is the first microstructural characterization of high-speed FSWed heat–treatable aluminum alloys butt joints. Micro-hardness measurement shows that the higher welding speed results in narrower HAZ with higher hardness values. The material flow is analyzed with a shear texture approach using EBSD data collected from the cross section of welds. The results show strong gradient throughout the nugget zone and the welds with higher welding speeds have shear directions flattened towards top (WD-TD) plane, giving less relative through thickness flow. This is associated with the fact that high traverse speed contributes to a larger in-plane component of material flow.

11:10 AM  
Round Material Flow in Friction Stir Welding of Aluminum Alloy: Xiaochao Liu1; Yufeng Sun1; Yoshiaki Morisada1; Hidetoshi Fujii1; 1Osaka University
    Round material flow during the friction stir welding of an aluminum alloy was fully observed by an ingenious experimental design, in which two different aluminum alloys were configured side-by-side and the tool traversed from one to the other. After welding, observation of the keyhole from the transverse cross-section, horizontal cross-section and longitudinal cross-section was performed. Under various weld lengths, the distributions of the first material around the keyhole clearly showed the round flow and the dynamic evolution of the material in the stir zone. These results revealed that the round flow mainly occurred in the shoulder-affected zone. The material beneath the shoulder travelled with the tool for a long distance and gradually deposited on the weld top surface.

11:30 AM  
Friction Stir Welding of Thick Aluminium Welds – Challenges and Perspectives: Murshid Imam1; Yufeng Sun1; Hidetoshi Fujii1; Yasuhiro Aoki1; Nishu Ma2; Seiichiro Tsutsumi1; Hidekazu Murakawa1; 1Joining and Welding Research Institute, Osaka University; 2JSOL Corporation, Engineering Technology Division
    There has been growing interest in the heavy metal industries with the recent progress in the friction stir welding (FSW) of thick aluminium welds. However, despite the recent progress in this area, many challenges still need to be overcome before it comes to full scale industrial use. With an increased thickness, the requirements of a higher power, load bearing ability of the tool, axial load, and welding and clamping forces make the task more challenging in terms of the selection of the process control parameters, FSW machine, tool material technology and design and the weld thermal management. Therefore, this paper describes the main challenges related to the FSW of thick aluminium plates as well as provide the perspectives to the researchers and industries to evaluate the changes to the welding tool design and operating parameters, extension of process window and suggest new improvements to the process.