Friction Stir Welding and Processing XI: Spot Technologies
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Yuri Hovanski, Brigham Young University; Piyush Upadhyay, Pacific Northwest National Laboratory; Yutaka Sato, Tohoku University; Nilesh Kumar, University of Alabama, Tuscaloosa; Anton Naumov, Peter The Great St. Petersburg Polytechnic University

Thursday 2:00 PM
March 18, 2021
Room: RM 39
Location: TMS2021 Virtual


2:00 PM  
Advances in Refill Spot Welding Productivity: Yuri Hovanski1; Andrew Curtis1; Sarah Michaelis1; Paul Blackhurst1; Brigham Larsen1; 1Brigham Young University
    With more than a decade of research and development documenting both the benefits and the challenges of refill friction stir spot welding (RFSSW), we see remarkedly few industrial applications that have moved to full implementation. Two major challenges have been recognized that are currently impeding further adoption; namely cycle time and tool life. While these two challenges are not mutually exclusive, the focus of the current work will be to contest reported trends that claim reducing cycle time below 2 seconds has a deleterious effect on weld properties. Recently published work challenged this trend for RFSSW of a work-hardenable AA5052-H36, where weld times were reported as low as 800ms. While this study demonstrated that machine capabilities drive reduction in weld cycle time without a commensurate reduction in weld properties, the focus was on demonstrating these changes for a work-hardenable alloy rather than a precipitation hardened alloy. As such, the current work will demonstrate that a similar reduction in cycle time may be realized in AA7075-T6.

2:20 PM  
Finite Element Analysis and Failure Mechanisms of Refill Friction Stir Spot Welding: Enkhsaikhan Boldsaikhan1; Shintaro Fukada2; Mitsuo Fujimoto2; Kenichi Kamimuki2; 1Wichita State University; 2Kawasaki Heavy Industries, Inc.
    Refill Friction Stir Spot Welding (RFSSW) is an emerging solid-state spot-welding methodology for joining workpieces via thermo-mechanical processing without consuming any filler or foreign materials. The conventional pure/poke friction stir spot welding leaves behind a keyhole or exit hole. Unlike the conventional friction stir spot welding, RFSSW produces a spot joint with a near-flush surface finish that is free from a keyhole. This study investigates the stress distributions of refill friction stir spot joints under static remote loading using Finite Element Analysis (FEA). The finite element simulations mimic mechanical testing of single-spot-weld coupons made of aerospace aluminum alloys. The simulation results reveal insights into high-stress weld regions that contribute to the formation of certain mechanical failures that are demonstrated by refill friction stir spot joints. Understanding failure mechanisms of refill friction stir spot joints is crucial for successful applications of RFSSW in the aerospace industry.

2:40 PM  
Characterization of Intermetallics Formation in µFSSW of Dissimilar Al/Cu Alloy Sheets: David Yan1; Logan Vahlstrom1; 1San Jose State University
    Electric vehicle battery packs consist of a large number of battery cells which must be assembled together with robust mechanical and electrical joints. One of the challenges is to join highly conductive and dissimilar multilayer materials such as Al to Cu alloy sheets with 100% reliability. Micro friction stir spot welding (µFSSW) is a spot-like joining process utilizing a non-consumable tool to generate frictional heat and join multilayer materials under the solid-state condition. Which makes the µFSSW a strong candidate for joining dissimilar Al/Cu sheets to manufacture various types of battery interconnects. But investigations to the dissimilar µFSSW of thin (<0.02") Al to Cu alloy sheets are limited. In this paper, experimental studies are performed on µFSSW of 0.016" thick Al 6061 (T6) to Cu (Astm B370) sheets. The effect of µFSSW conditions on the weld zone intermetallics formation is studied in relation to the processing force, torque and temperature.

3:00 PM  
Dissimilar Friction Stir Spot Welding of Low Carbon Steel and Aluminum Alloy by Double Side Adjustable Tools: Xiaopei Wang1; Yoshiaki Morisada1; Hidetoshi Fujii1; 1Osaka University
    The flat friction stir spot welding using double side adjustable tools technique has been developed, which was successfully applied to the magnesium alloy joining and low carbon steel joining in our previous study. In this study, this welding technique was implemented for the dissimilar welding of low carbon steel and an aluminum alloy, whereby sound joints were obtained. The microstructure of the welded joints was investigated in detail, and its effects on the joint properties were discussed. The interlocking effects and uniform intermetallic compounds layer, introduced by the adjustable probes, were considered to significantly improve the joint performance.

3:20 PM  
Microstructural Characterization of Lap-jointed Ti-6Al-4V Plates by Pin-less Friction Stir Spot Welding: Hyojin Park1; Yong Chae Lim2; Scott A Rose3; Zhili Feng2; Hahn Choo1; 1University of Tennessee, Knoxville; 2Oak Ridge National Laboratory; 3Boeing
    During a p-FSSW process, the thermo-mechanical input exerted locally around the welding tool causes drastic microstructural changes and is the key for the joint strength and integrity. In the Ti-6Al-4V alloy, the processing temperature distribution is a critical issue due to the microstructural evolution complicated by phase transformation between α-Ti and β-Ti occurring during/after welding. Especially, friction-stirred Ti-6Al-4V alloys exhibit narrow heat-affected zone and thermo-mechanical zone due to the low thermal conductivity of its alloy. In this talk, we present the microstructural evolutions in a p-FSSWed Ti-6Al-4V alloy. Grain size/morphology and grain boundary characteristics was investigated using SEM/EBSD. TEM analysis was conducted to investigate the degree of thermo-mechanical effects on the Ti-6Al-4V alloy during the p-FSSW process. Finally, the microscopic results will be combined with a high-energy synchrotron XRD analysis of texture and constituent phase fraction to understand the effects of p-FSSW parameters on the microstructure development and joint strength.

3:40 PM  
Temperature Distribution during Friction Stir Spot Welding of Thin AA 6082-T6 and AA 5082-O Sheets: Mikhail Ozhegov1; Fedor Isupov1; Roman Smelianskii1; 1St. Petersburg Polytechnic University of Peter the Great
    Friction stir spot welding (FSSW) is a solid-state joining technique which is widely used in the automotive, aircraft and others industries. The heat treatable aluminum alloy – 6082-T6 and strain hardenable aluminum alloy – 5082-O – were used as a material for the experimental procedure. In the present research the optimization of the FSSW parameters was provided to obtain the joints with the highest mechanical characteristics. After optimization procedure 3 sets of parameters for FSSW of each alloy were taken for the temperature measurements by means of thermocouples.