Solid State Joining Of Dissimilar Titanium Alloys

Solid state joining of titanium via friction stir welding and diffusion bonding have emerged as enablers of efficient monolithic structural designs by the eliminations fasteners for the aerospace industry. As design complexity and service demands increase, the need for joints of dissimilar alloys has emerged. Complex thermomechanical conditions in friction stir weld joints and high temperature deformation behavior differences between alloys used in dissimilar joints gives rise to a highly variable flow pattern within a stir zone. Experiments performed welding Ti-6Al-4V to ß21S show that mechanical intermixing of the two alloys is the primary mechanism for the generation of the localized chemistry and microstructure, the magnitude of which can be directly related to pin rotation and travel speed weld parameters. Mechanical mixing of the two alloys is heavily influenced by strain rate softening phenomena, and can be used to manipulate weld nugget structure by switching which alloy is subjected to the advancing side of the pin. Turbulent mixing of a weld nugget and a significant reduction in defects and weld forces are observed when the ß21S is put on the advancing side of the weld where higher strain rates are present. Chemical diffusion driven by the heat of weld parameters is characterized using energy dispersive x-ray spectroscopy (EDS) and is shown to be a secondary process responsible for generating short-range chemical gradients that lead to a gradient of alpha particle structures. Diffusion calculations are inconsistent with an assumption of steady-state diffusion and show that material interfaces in the weld nugget evolve through the break-down of turbulent interface features generated by material flows. A high degree of recrystallization is seen throughout the welds, with unique, hybrid chemistry grains that are generated at material interfaces in the weld nugget that help to unify the crystal structure of dissimilar alloys. The degree of recrystallization is tied to the localized thermal profile in the weld nugget as well as the heating rates of a given set of weld parameters. Slow kinetics of alpha dissolution relative to the heating rate and process times of friction stir welding suggest an alpha-particle assisted super-transus recrystallization process contributes to a refined grain size in weld parameters utilizing high travel speed.

This report supplies information on joining processes applicable to titanium and its alloys in sheet metal applications, primarily related directly to airframe construction. Although the material presented here does not cover all titanium joining processes, and omits such processes as plasma-arc, submerged-arc, electroslag, flash, and high-frequency resistance welding, the data presented cover materials up to 2-inches thick in some cases and the report should be useful to anyone seeking titanium joining information. The joining processes covered fall into five categories: welding, brazing, metallurgical bonding (diffusion and deformation bonding), adhesive bonding, and mechanical fastening. The fusion welding processes that are discussed in detail include gas tungsten arc, gas metal arc, arc spot, and electron beam. The resistance processes give extended coverage are spot, roll spot, and seam welding. (Author).

This book presents recent material science-based and mechanical analysis-based advances in joining processes. It includes all related processes, e.g. friction stir welding, joining by plastic deformation, laser welding, clinch joining, and adhesive bonding, as well as hybrid joints. It gathers selected full-length papers from the 1st Conference on Advanced Joining Processes.

Due to the wide application of magnesium alloys in metals manufacturing, it is very important to employ a reliable method of joining these reactive metals together and to other alloys. Welding and joining of magnesium alloys provides a detailed review of both established and new techniques for magnesium alloy welding and their characteristics, limitations and applications. Part one covers general issues in magnesium welding and joining, such as welding materials, metallurgy and the joining of magnesium alloys to other metals such as aluminium and steel. The corrosion and protection of magnesium alloy welds are also discussed. In part two particular welding and joining techniques are reviewed, with chapters covering such topics as inert gas welding, metal inert gas welding and laser welding, as well as soldering, mechanical joining and adhesive bonding. The application of newer techniques to magnesium alloys, such as hybrid laser-arc welding, activating flux tungsten inert gas welding and friction stir, is also discussed. With its distinguished editor and expert team of contributors, Welding and joining of magnesium alloys is a comprehensive reference for producers of primary magnesium and those using magnesium alloys in the welding, automotive and other such industries, as well as academic researchers in metallurgy and materials science.

The continual push for vehicle weight reduction has called for the incorporation of non-conventional automotive alloys, such as advanced high-strength steels, aluminum alloys, and even magnesium alloys and titanium alloys. The advent of these new alloys calls for new joining technologies. Resistance Spot Welding and Arc Welding have served the automotive industry well in joining steel components. However, because these are fusion-based processes involving high heat, they are not suitable for joining combinations of dissimilar metals or high-performance alloys. Thus the search continues for a technique capable of joining the said metals effectively, economically, and flexibly. The work featured in this dissertation aims to explore and develop Vaporizing Foil Actuator Welding (VFAW) as a promising technique for dissimilar-metal joining. VFAW is a form of solid-state impact welding that was developed in the Ohio State University in 2011. In this work, some 20 dissimilar-metal combinations of industrially relevant structural alloys were screened for weldability by VFAW. Successful welds were obtained for some 10 combinations, many of which were Al/Fe pairs, which are a most popular material pair for automotive weight reduction.

This book presents critical information on the principles and operation of friction welding, friction stir welding, and friction stir processing enhanced with many robust illustrations. It explains the application of these technologies and the current research efforts in the field. The authors explain in detail the advantages offered by these welding processes, in particular their ability to join dissimilar materials not possible to weld in the past. Written for graduate students, researchers, and industrial professionals, the book reinforces concepts presented with case studies on the experimental analysis of welding the dissimilar materials of copper and aluminum, and on friction stir processing.

This book will summarize research work carried out so far on dissimilar metallic material welding using friction stir welding (FSW). Joining of dissimilar alloys and materials are needed in many engineering systems and is considered quite challenging. Research in this area has shown significant benefit in terms of ease of processing, material mixing, and superior mechanical properties such as joint efficiencies. A summary of these results will be discussed along with potential guidelines for designers. Explains solid phase process and distortion of work piece Addresses dimensional stability and repeatability Addresses joint strength Covers metallurgical properties in the joint area Covers fine microstructure Introduces improved materials use (e.g., joining different thicknesses) Covers decreased fuel consumption in light weight aircraft Addresses automotive and ship applications

Friction-stir welding (FSW) is a solid-state joining process primarily used on aluminum, and is also widely used for joining dissimilar metals such as aluminum, magnesium, copper and ferrous alloys. Recently, a friction-stir processing (FSP) technique based on FSW has been used for microstructural modifications, the homogenized and refined microstructure along with the reduced porosity resulting in improved mechanical properties. Advances in friction-stir welding and processing deals with the processes involved in different metals and polymers, including their microstructural and mechanical properties, wear and corrosion behavior, heat flow, and simulation. The book is structured into ten chapters, covering applications of the technology; tool and welding design; material and heat flow; microstructural evolution; mechanical properties; corrosion behavior and wear properties. Later chapters cover mechanical alloying and FSP as a welding and casting repair technique; optimization and simulation of artificial neural networks; and FSW and FSP of polymers. Provides studies of the microstructural, mechanical, corrosion and wear properties of friction-stir welded and processed materials Considers heat generation, heat flow and material flow Covers simulation of FSW/FSP and use of artificial neural network in FSW/FSP