Friction Stir Welding and Processing IX: Derivative Technologies
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 José State University

Tuesday 2:00 PM
February 28, 2017
Room: 9
Location: San Diego Convention Ctr

Session Chair: Glenn Grant, Pacific Northwest National Laboratory; Jorge Dos Santos, Helmholtz-Zentrum Geesthacht GmbH

2:00 PM  Invited
Solid-State Joining of Thick-Section Dissimilar Materials Using a New Friction Stir Dovetailing (FSD) Process: Scott Whalen1; Md. Reza-E-Rabby2; Ken Ross2; Yuri Hovanski2; Martin McDonnell3; 1Pacific Northwest National Laboratory ; 2Pacific Northwest National Laboratory; 3U.S. Army Tank, Automotive, Research, Development, and Engineering Center (TARDEC)
    Solid-state joining of thick section aluminum to steel plate has been achieved using a new process called Friction Stir Dovetailing (FSD). In FSD, a custom designed pin tool is used to flow a lower melting point material (AA6061) into dovetail grooves machined into the surface of an underlying higher melting point material (Rolled Homogeneous Armor – RHA). Repeating dovetails form a mechanical interlocking structure akin to metallic Velcro. In this study, AA6061 sections ranging in thickness from 1.5” to 3.0” are joined to 0.5” thick RHA plates. The effectiveness of FSD is demonstrated through tensile test data which shows specimens failing in the processed aluminum rather than at the joint interface. Numerical simulations are presented which highlight the importance of optimizing dovetail geometry. The effect of process parameters on joint strength, microstructure, and hardness are also discussed.

2:20 PM  Invited
Solid State Additive Manufacturing Using FSW and Low-cost Precursors: Anthony Reynolds1; Ilana Lu1; 1University of South Carolina
    FSW based layer-by-layer additive manufacturing cannot compete with powder bed type processes in terms of build complexity. However, such processes can be used to produce simple structures that might otherwise be manufactured using high speed machining. In such cases, the primary selling point for FSW based AM will be conservation of expensive materials. In the envisioned AM process, structures are built by lap welding and then machining away material not included in the weld nugget. Because the FSW process can transform a cast microstructure into a nominally wrought microstructure with a concomitant increase in properties, it is proposed that homogenized cast aluminum alloy be used as the starting material for AM by FSW, thereby eliminating the cost associated with rolling or extrusion. The paper will elaborate on several process issues critical to making this process viable.

2:40 PM  
Joining Aerospace Aluminum 2024-T4 to Titanium by Friction Stir Extrusion: William Evans1; Alvin Strauss1; George Cook1; 1Vanderbilt University
    The welding of titanium and aluminum is difficult due to differences in their material properties and the formation of intermetallic compounds(IMCs) which can weaken the weld. A new process, Friction Stir Extrusion (FSE), has been used to join dissimilar materials by using Friction Stir Processing to extrude a top sheet of material into a pre-made, concave groove in the bottom sheet of material. FSE has been used to create a strong, mechanically interlocking joint between aluminum 6061 and steel that eliminates IMCs. However, FSE hasn’t been applied to any other material combinations. This current research applies the FSE process to join aluminum 2024-T4 to commercially pure titanium. The process was optimized by adjusting the RPM, traverse rate, and groove geometry. The Al-Ti joints are evaluated based on shear strength and ultimate tensile strength. The groove geometry proved to be the most important parameter as different geometries can enhance the strength by mechanical means and by optimizing the volume and shape of the material extruded. Successful joints were created by the FSE process and can be used as a viable alternative for joining aluminum to titanium.

3:00 PM  
Microscopic Evaluation of Friction Plug Welds– Correlation to a Processing Analysis: Ellen Rabenberg1; Poshou Chen2; Sridhar Gorti1; 1National Aeronautics and Space Administration; 2Jacobs, NASA/MSFC
    Recently an analysis of dynamic forge load data from the friction plug weld (FPW) process and the corresponding tensile test results showed that good plug welds fit well within an analytically determined processing parameter box. There were, however, some outliers that compromised the predictions. Here the microstructure of the plug weld material is presented in view of the load analysis with the intent of further understanding the FPW process and how it is affected by the grain structure and subsequent mechanical properties.

3:20 PM  Invited
Friction Stir Welding – A Closer Examination: Tracy Nelson1; Bryan Stringham1; 1Brigham Young University
    There is significant disagreement in the literature regarding relationships between friction stir welding process parameters, process responses, and post-weld microstructure and properties. After reviewing some of the more recent literature, it can appear as if the community is digressing in understanding relative to these relationships. In this presentation, a process map of FSW illustrating the relationships between process inputs, process output, and post-weld material responses will be described. Essential FSW process variables that govern post-weld microstructure and properties will also be discussed, and considerations regarding the selection of essential variables will be presented.

3:50 PM Break

4:10 PM  
Micro-mechanical Testing of Magnesium Based Composites Reinforced by Carbon Fibers Manufactured by Friction Stir Processing: Aude Simar1; Anne Mertens2; Laurence Brassart3; Jacqueline Lecomte-Beckers2; Francis Delannay1; 1Universite Catholique de Louvain; 2University of Liège; 3Monash University, Australia
    Short C fibres–Mg matrix (AZ91D) composites have been produced by friction stir processing sandwiches made of a layer of C fabric stacked between two sheets of Mg alloy. The process parameters have been optimized to ensure a good fiber distribution. 3D X-ray tomography reveals that the fibers orient like onion rings. Thermal treatments have allowed to modify the flow stress level of the matrix material. Tensile testing inside the scanning electron microscope have revealed the decohesion at the fiber/matrix interface if the fibers are preferentially oriented perpendicularly to the loading direction. Modelling allows to estimate the stress needed to initiate this decohesion is about 250 MPa, i.e. appearing early in heat treated samples. To compare with different loading conditions, micro-compression and instrumented micro-indentation testing have also been performed. The consequence of the loading path on the decohesion is discussed.

4:30 PM  
Predicting Friction Pull Plug Welding Results: Justin Littell1; 1NASA
    A method for predicting the quality/strength of a plug weld made using a friction plug weld (FPW) process is defined. The method determines quantitatively the quality of a given plug weld by making use of specific feed back data obtained upon performing a given plug weld using the FPW process. A final static force (forge load) is applied on the plug to complete the FPW process. The magnitudes of both the dynamic and forge loads, as obtained from the feedback data, allow for the determination of the quality of the weld. The analytical method employed to assess feedback data can also be used in the direct development of a plug weld process for numerous materials that can undergo semi-solid formation in an FPW process.

4:50 PM  
Microstructural Analysis and Mechanical Properties of Friction Stir Back Extruded/Aged 7075 Aluminum Alloy: Zeren Xu1; Fadi Abu-Farha1; 1Clemson University
    Friction stir back extrusion (FSBE) was applied to commercial 7075-T6 aluminium alloy rods. Microstructural analysis performed across the tube thickness indicated refined and recrystallized grain structure in the processed region, and elongated-deformed grains in the thermo-mechanically affected zone (TMAZ). Grain size and average aspect ratio were analyzed in different regions in the processed tubes to quantify the microstructural changes and correlate that to microhardness measurements. Grain structure inhomogenities were noted both along the extrusion and the transverse directions of the tubes. Fine grain structure was achieved at locations subject to high accumulated shear deformation; ultrafine grains were noted in highly deformed regions. Microtexture analysis via EBSD indicated shear type texture. Microhardness testing and tensile testing with DIC were used to quantify the effects of FSBE on the as-processed samples as well as post-aged samples. The microstructure and mechanical properties of processed/aged samples are discussed in detail.

5:10 PM  
Dissimilar Metal T-Joint Formed by Friction Stir Extrusion: Adam Jarrell1; Alvin Strauss1; George Cook1; 1Vanderbilt University
    This paper extends the capabilities of the Friction Stir Extrusion process by demonstrating the ability to join aluminum and steel in a T-joint configuration. Friction Stir Welding techniques are used to extrude aluminum into a concave groove cut into the top edge of a steel plate. The Friction Stir Extrusion process forms a mechanical joint avoiding many of the detrimental effects from the formation of intermetallic compounds. Also, eliminating many of the issues of rapid tool wear associated with the Friction Stir Welding of steel. The T-joint configurations would allow joining of dissimilar materials in a variety of applications, such as joining an aluminum skin to a steel/titanium frame. Such construction would allow for a strong, lightweight, and corrosion resistant structures. Strength of the joint was tested in both tension and shear to determine the optimal configuration of the geometry of the joint as a function of the process parameters.