Friction Stir Processing for Enhanced Low Temperature Formability: A volume in the Friction Stir Welding and Processing Book Series

By Christopher B. Smith and Rajiv S. Mishra

The use of friction stir processing to locally modify the microstructure to enhanced formability has the potential to alter the manufacturing of structural shapes. There is enough research to put together a short monograph detailing the fundamentals and key findings. One example of conventional manufacturing technique for aluminum alloys involves fusion welding of 5XXX series alloys. This can be replaced by friction stir welding, friction stir processing and forming. A major advantage of this switch is the enhanced properties. However qualification of any new process involves a series of tests to prove that material properties of interest in the friction stir welded or processed regions meet or exceed those of the fusion welded region (conventional approach). This book will provide a case study of Al5083 alloy with some additional examples of high strength aluminum alloys.

• Demonstrates how friction stir processing enabled forming can expand the design space by using thick sheet/plate for applications where pieces are joined because of lack of formability
• Opens up new method for manufacturing of structural shapes
• Shows how the process has the potential to lower the cost of a finished structure and enhance the design allowables

• Language: English
• Publisher: Elsevier Science
• Release date: Mar 21, 2014
• ISBN: 9780124201835

Christopher B. Smith

Mr. Smith is a Project Manager at Wolf Robotics in Fort Collins, Colorado, specializing in projects advancing the state of the capability automatic robotic solutions and has been with Wolf Robotics since early 2013. Prior to that, Chris was Co-Founder and Vice President of Engineering of Friction Stir Link, Inc. (FSL) in Brookfield, WI which was founded in 2001. At FSL, Chris led efforts in the commercialization of friction stir welding and the related technologies. Prior to FSL, Chris began his career at A.O. Smith Automotive Products Company, where he was responsible for the development of new robotic processing technologies. Throughout his career, Mr. Smith has lead the development and integration of new automated technologies and has been involved with friction stir welding, arc welding, machining and material handling technologies. He developed the first production capable industrial robotic system for friction stir welding. Chris has managed projects leading to significant advancements in robotic material handling, friction stir welding and its related technologies, as well as robotic machining and drilling. At FSL he managed projects leading to many of North America’s first and/or most significant friction stir welding applications. Mr. Smith has a Bachelor of Science Degree from the University of Colorado-Boulder and Master of Science degree from the University of Wisconsin-Madison in Mechanical Engineering. He was awarded the American Welding Society’s A.F. Davis Silver Medal Award in 2001. Chris has authored over 30 papers and chapters on FSW in two engineering books and has two patents. Chris also is co-chair of the American Welding Society’s C6 Committee on Recommended Practices for Friction Stir Welding.

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Preface

Rajiv S. Mishra

University of North Texas

This is the second volume in the recently launched short book series on friction stir welding and processing. As highlighted in the preface of the first book, the intention of this book series is to serve engineers and researchers engaged in advanced and innovative manufacturing techniques. Friction stir processing was started as a generic microstructural modification technique almost 15 years back. In that period, friction stir processing-related research has shown wide promise as a versatile microstructural modification technique and solid-state manufacturing technology. Yet, broader implementations have been sorely missing. Disruptive technologies face greater barrier to implementation as designers do not have these in their traditional design tool box! Part of the inhibition is due to lack of maturity and availability of large data set.

This book has primarily a technological flavor. It contains significant volume of data generated as a part of technology approval document for the US Navy. The intention behind this book is to share an example that can boost the confidence with engineers and designers as they consider friction stir processing as a viable technology for advanced manufacturing. This short book series on friction stir welding and processing will include books that advance both the science and technology.

March 8, 2014

Chapter 1

Concept of Friction Stir Processing for Enhanced Formability

Since its invention in 1991 and then first production implementation in 1995, friction stir welding (FSW) has experienced a continual increase in use throughout the world (Thomas et al., 1991; Dawes and Thomas, 1995). Its increase in implementation has occurred because of FSW’s benefits over traditional fusion welding processes, such as improved static strength, improved fatigue properties, less sensitivity to disturbances (e.g., contamination), and significantly less distortion. The benefits of FSW are arguably the most prominent when comparing with fusion welding of aluminum. As such, most of the implementation of FSW has occurred in the aluminum fabrication industry, especially for applications that have been specifically designed for FSW.

Keywords

friction stir welding; enhanced formability; friction stir processing; gas metal arc welding; structural angles, aluminum; 5083-H111; forming; bending

1.1 Background

Since its invention in 1991 and then first production implementation in 1995, friction stir welding (FSW) has experienced a continual increase in use throughout the world (Thomas et al., 1991; Dawes and Thomas, 1995). Its increase in implementation has occurred because of FSW’s benefits over traditional fusion welding processes, such as improved static strength, improved fatigue properties, less sensitivity to disturbances (e.g., contamination), and significantly less distortion. The benefits of FSW are arguably the most prominent when comparing with fusion welding of aluminum. As such, most of the implementation of FSW has occurred in the aluminum fabrication industry, especially for applications that have been specifically designed for FSW.

The FSW process is fairly simple in concept and is illustrated in Figure 1.1 (Mishra and Ma, 2005). The FSW process first involves a machine initiating rotation of a friction stir tool. The friction stir tool has a probe and a shoulder, both with specially designed features. The FSW machine then plunges the rotating friction stir tool into the workpiece, creating heat locally via friction and plastic deformation of the material, softening the material to be welded. Once the probe is completely plunged into the workpiece and the shoulder contacts the face surface, the FSW machine initiates the traverse of the friction stir tool along the weld path or joint. While the FSW machine traverses the tool along the path, the rotation of the tool is maintained, with geometric features on the shoulder and probe displacing and mixing (i.e., stirring) material along the weld joint. Then, when the friction stir tool reaches the end of the path, the friction stir tool is retracted from the joint and finally rotation of the friction stir tool is ceased.

Figure 1.1 Schematic illustration of friction stir welding.

During the initial years of research and implementation, it was observed that FSW would locally modify the material properties in and around the weld area. As FSW is an autogenous process (no filler material), the area of the weld has chemistry identical to the base material. With these two considerations, a variant of the FSW process was developed and is referred to as friction stir processing (FSP) (Mishra et al., 1999; Mishra and Mahoney, 2001). The FSP basically involves the same concept as FSW, but it is generally performed on base material, without a weld joint and is shown in Figure 1.2. FSP has been demonstrated to be capable of locally modifying various material properties, including but not limited to ductility/elongation, fatigue properties, static mechanical properties, corrosion properties, hardness, etc. (Mishra and Mahoney, 2007). The ability to modify material properties is material dependent. As such, FSP can be used to locally improve material properties to enhance product capability or to enable different fabrication methods. While there are numerous potential applications, a few such applications