Friction Stir Welding of 2XXX Aluminum Alloys including Al-Li Alloys

By Rajiv S. Mishra and Harpreet Sidhar

Friction Stir Processing of 2XXX Aluminum Alloys including Al-Li Alloys is the latest edition in the Friction Stir Welding and Processing series and examines the application of friction stir welding to high strength 2XXX series alloys, exploring the past and current developments in the field. The book features recent research showing significant benefit in terms of joint efficiency and fatigue performance as a result of friction stir welding.

Friction stir welding has demonstrated significant benefits in terms of its potential to reduce cost and increase manufacturing efficiency of industrial products including transportation, particularly the aerospace sector. The 2XXX series aluminum alloys are the premium aluminum alloys used in aerospace.

The book includes discussion of the potential future directions for further optimization, and is designed for both practicing engineers and materials scientists, as well as researchers in the field.

• Provides comprehensive coverage of friction stir welding of 2XXX series alloys
• Discusses the physical metallurgy of the alloys
• Includes physical metallurgy-based guidelines for obtaining high joint efficiency
• Features illustrated examples of the application of FSW in the aerospace industry

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 1, 2016
• ISBN: 9780128092927

Rajiv S. Mishra

Rajiv S. Mishra is a professor in the Department of Materials Science and Engineering, and Site Director, NSF IUCRC for Friction Stir Processing, at the University of North Texas. Dr. Mishra’s publication record includes 255 papers. Out of these, 10 of his papers have more than 100 citations. He has many ‘firsts’ in the field of friction stir welding and processing. He co-authored the first review paper (2005), co-edited the first book on the subject (2007), edited/co-edited seven TMS symposium proceedings, and served as guest editor for Viewpoint Set in Scripta Materialia (2008). He also has three patents in this field. He published the first paper on friction stir processing (2000) as a microstructural modification tool.

Book preview

India

Preface to This Volume of Friction Stir Welding and Processing Book Series

Rajiv S. Mishra, University of North Texas

This is the seventh 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 welding was invented more than 20 years back as a solid-state joining technique. In this period, friction stir welding has found a wide range of applications in joining of aluminum alloys. Although the fundamentals have not kept pace in all aspects, there is a tremendous wealth of information in the large volume of papers published in journals and proceedings. Recent publications of several books and review articles have furthered the dissemination of information.

This book is focused on friction stir welding of 2XXX alloys, a topic of great interest for practitioners of this technology in aerospace sector. 2XXX series alloys are among highest specific strength aluminum alloys and achieving high joint efficiency is a desired goal. The basic research towards this has reached a level that warrants compilation of the scientific knowledge. This volume provides a good summary of the current understanding and provides brief guideline for future research directions. It is intended to serve as a resource for both researchers and engineers dealing with the development of high efficiency structures. As stated in the previous volumes, this short book series on friction stir welding and processing will include books that advance both the science and technology.

August 25, 2016

Chapter 1

Friction Stir Welding

Abstract

In this chapter the basic working principles and applicability of the friction stir welding (FSW) process in aerospace and automobile industries are discussed. FSW results in the formation of three microstructural zones, namely weld nugget, thermomechanical-affected zone, and heat-affected zone. An overview of these zones has been provided. Process variables such as tool geometry, joint configurations, and the effect of process parameters have also been discussed in this chapter.

Keywords

Friction stir welding; joint configurations; FSW tools; FSW of aluminum alloys; weld nugget; thermomechanical affected zone; heat-affected zone

Before the invention of friction stir welding, shortcomings of fusion welding of precipitation strengthened 2XXX aluminum alloys in creating structurally viable joints could not be eliminated. This led to mechanical fastener based joining as the key process for joining aluminum in aerospace applications.

Friction stir welding is a solid-state joining process that was invented by Thomas et al. [1] at The Welding Institute (TWI, UK) in 1991. FSW quickly gained research and industrial attention around the world and has been most widely studied on aluminum alloys during its first decade of evolution. The ability of FSW to join two separate parts without melting is the most significant feature. FSW has been most successful in aluminum-related industries as it can join any similar and dissimilar aluminum alloys with workpiece thickness ranging from 1-mm thin sheets to as thick as 75-mm thick blocks. More recently, other alloy systems, such as magnesium-, ferrous-, titanium-, copper-, nickel-based alloys, have also been subjected to FSW or its derivative processes [2–5]. Also, the ability of FSW to join dissimilar metals (alloys of different metals) in various configurations has been demonstrated successfully [6,7].

The basic principle of FSW is fairly simple. In this process, a nonconsumable rotating tool, made of material stronger than workpiece, with a larger diameter shoulder and a pin, plunges into the workpiece to a preprogrammed depth. Plunging of rotating tool into the workpiece produces frictional heat due to the interaction of tool shoulder and workpiece. Another contribution to the heat input comes from adiabatic heat produced during plastic deformation of workpiece material around the rotating tool pin. Plastic deformation at high temperature leads to the softening of material around the pin. The softened material moves around with the rotation of tool pin which then traverses along a joint line and completes the weld. The larger diameter of tool shoulder helps in containing the hot material which can otherwise flow out easily to form flash and may lead to loss of material and defective weld. Schematic shown in Fig. 1.1 illustrates the process for welding of a workpiece in the butt configuration. During FSW, a solid-state joining process, melting does not take place. Thus, this process has inherent advantages and avoids the possibility of common defects like segregation, dendritic structure, and hot cracking, porosity formation associated with fusion-based welding techniques [3–5,8,9]. Dissimilar material can also be efficiently joined by using this process [3,5,6]. FSW has been used for many structural applications in aerospace and automobile industries [3]. Key benefits of FSW process over fusion welding techniques are listed in Table 1.1. FSW is also a green process as the energy consumption during this process is usually between 2% and 5% of energy consumption in arc-based welding [3,5]. Another benefit of this process is that the tool is nonconsumable and thus the requirement of filler material is completely avoided.

Figure 1.1 Schematic showing operational details of FSW process [10]. Source: (© 2012 Published in J.T. Khairuddin, I.P. Almanar, J. Abdullah, Z. Hussain, Principles and Thermo-Mechanical Model of Friction Stir Welding, INTECH Open Access Publisher, Croatia, 2012 under CC BY 3.0 license. Available from: http://dx.doi.org/10.5772/50156).

Table 1.1

Key Benefits of FSW Process Over Conventional Fusion Welding Techniques [5]