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Advanced high strength automotive sheet steel (AHSS) is used in body-in-white design to reduce vehicle weight while maintaining high crashworthiness. Surface coatings applied to AHSS to protect it from oxidation and decarburization during its processing and life cycle. Due to the characteristics of AHSS, including alloying content and thermal process requirements, a variation of final surface conditions is possible. The resistance welding process is affected by surface changes as it alters the electrical contact resistance. As a result, a change in resistance spot welding process window occurs. Without proper attention, this variation in the operation window could reduce the joint strength and results in an unpredictable failure by having an undersized nugget. In this study, two surface-related phenomena, internal oxidation, and zinc diffusion, were investigated to characterize their impact on resistance spot welding. Additionally, a heat input based electrical dynamic resistance approach was proposed to determine appropriate welding current given variations in the Zn diffusion layer resulting from heat treating during this hot stamping process for PHS steels. Promotion of internal oxidation is used in Zn galvanizing line to improve the wettability of the steel surface to the Zn pool via the enhancement of the reactive wetting. The presence of these internal oxides has shown to shift the weld lobe to higher currents, increasing the time required to generate an acceptable weld. Study of weld development showed that surface melting is responsible for this shift in the weld process window. The surface melting created a liquid contact surface between the faying surface, which reduced the electric contact resistance and heat generation at the weld faying surface. A smaller nugget was formed due to the reduction of heating. To compensate for this reduced heat generation, a higher welding current was required when RSW of internally oxidized samples. Zinc diffusion from the galvannealed coating to the steel substrate occurs when a galvannealed steel was exposed to elevated temperature during heat treatment in the press-hardening process. This formed a Fe-Zn diffusion layer. The thickness and composition of the diffusion layer were found to be dependent on heat-treatment conditions. With an increase in heat-treatment time, the electrical resistance of the steel sheet was observed to increase as well. With higher electrical resistance, less welding current was needed to weld the material. While a change in nugget size occurred when welding steels made using different heat-treatment conditions with constant welding parameters, the mechanical lap shear strength was not impacted. Martensite tempering in the heat-affected region was more severe in samples with a larger diameter weld nugget, which decreased the required stress for failure to occur, counter-acting the increase in strength gained from the larger nugget size. This work has shown that with a heat-treatment time ranging between 4 to 10 minutes, a robust resistance welding schedule can be determined to generate a mechanically sound weld. Dynamic electrical resistance has been used to monitor the weld quality. Heat input analysis was shown to reflect the weld development as it takes into account the full weld cycle. Heat input has shown to have a linear correlation with nugget size. Undersized nugget can be successfully detected and corrected by changing the welding current based on the heat input value calculated from dynamic resistance measurement.
Welding and Joining of Advanced High Strength Steels (AHSS): The Automotive Industry discusses the ways advanced high strength steels (AHSS) are key to weight reduction in sectors such as automotive engineering. It includes a discussion on how welding can alter the microstructure in the heat affected zone, producing either excessive hardening or softening, and how these local changes create potential weaknesses that can lead to failure. This text reviews the range of welding and other joining technologies for AHSS and how they can be best used to maximize the potential of AHSS. Reviews the properties and manufacturing techniques of advanced high strength steels (AHSS) Examines welding processes, performance, and fatigue in AHSS Focuses on AHSS welding and joining within the automotive industry
Drawing on state-of-the-art research results, Resistance Welding: Fundamentals and Applications, Second Edition systematically presents fundamental aspects of important processes in resistance welding and discusses their implications on real-world welding applications. This updated edition describes progress made in resistance welding research and
In this study, the relationship of welding parameters to fatigue mechanisms is examined in spot welding of advanced high strength steels. Lightweighting efforts in the automotive industry are part of a push for greater fuel economy and improved consumer safety. TBF-1180 is an advanced high strength steel being developed for use in structurally critical components, however its fatigue behavior is not well understood. Electro galvanized TBF-1180 possesses corrosion resistant properties, however the additional zinc layer allows for the possibility of zinc-penetrative liquid metal embrittlement (LME) to occur during resistance spot welding (RSW). Additionally, variations in weld input and correspondingly heat input can affect the performance of welds due to microstructural changes that occur. In this study, the effect of LME and changes in microstructure were assessed in separate experiments for their fatigue impact in TBF-1180. Welds were fabricated in a traditional lap shear geometry in order to investigate the effects of LME, while an hourglass shaped cap geometry was used for welds with microstructural variation. Fatigue testing revealed that for lap-shear coupons containing LME cracks, no deleterious effect was observed. Cap geometry specimens were assessed for performance in a control and a high-current low-time condition, and a significant fatigue knockdown factor was found. Post-mortem fractography on both specimen geometries revealed that fatigue cracks initiated at the inner faying surface, regardless of the presence of LME. Finite element analysis confirmed that the LME cracks in the lap shear weld experience compressive stresses during loading, contributing to the lack of fatigue impact. Experimental conditions used for the cap geometry had lower heat input, which can result in less retained metastable austenite after welding, leading to reduced crack growth resistance. To tests the hypothesis that less retained metastable austenite after welding can cause a reduction in the number of cycles to failure in the spot weld, life prediction were made using fracture mechanics concepts coupled with reported knockdown factors on crack growth rates in relation to the amount of transformed martensite. The life predictions generated with this method strongly matched the observed fatigue behavior for the cap geometry specimens.
The early chapters of this book provide thorough coverage of resistance spot welding fundamentals and principles. Topics covered include lobe and current range curves, contact resistance vs. electrode force, dynamic resistance, heat balance, nugget growth, etc. Equipment issues such as machine types, power supplies, and electrodes are addressed. Subsequent chapters focus on specific spot welding challenges to modern automotive manufacturing. Approaches to welding modern materials including advanced high-strength steels, coated steels, and aluminum alloys are covered in much detail. The final chapters focus on many common production and quality control issues, such as electrode wear, monitoring and testing, computational modeling, and welding codes. The overall goal of the book is to provide a comprehensive resource for automotive engineers and technicians who work with modern spot welding equipment and automotive materials.
The book focuses on multiple areas of manufacturing, including cutting-edge material processing technologies, custom-made materials, metallic and non-metallic materials, new engineering experiments, contemporary machining, joining, surface modification, and process optimization techniques. Readers will find in this volume an extensive exploration of various advanced manufacturing and material engineering topics. It includes a detailed examination of aluminum grades and their applications, an overview of cold spray additive manufacturing, and a discussion on Gas Metal Arc Welding (GMAW) for cladding low-carbon steel plates. The volume also presents innovative approaches to brake pedal design using topology optimization, analysis of resistance-spot welding quality, and the impact of shot peening on the corrosion behavior of SiC Particle Reinforced Aluminum Composite. It highlights crucial factors in 3D printed component strength, reviews 3D milling operations with ABAQUS, and delves into the rare ferroelectric material Fresnoite. The book surveys visual sensing technologies for weld pool analysis, simulates Claus Sulfur Recovery Units with Aspen Plus, and discusses ultrasonic-assisted stir casting for metal matrix nanocomposites. It also covers the joining of dissimilar magnesium alloys, advancements in electrochemical surface coatings, unconventional machining techniques, surface coating processes using pulsed power systems, natural fiber-reinforced composite fabrication, and process parameter optimization in laser beam welding using NSGA-II. Audience The book will interest researchers in academia and industry engineers in advanced manufacturing, materials science, surface science, adhesion and coatings, production engineering, civil engineering, and welding.
"Advanced Steels: The Recent Scenario in Steel Science and Technology" contains more than 50 articles selected from the proceedings of the International Conference on Advanced Steels (ICAS) held during 9-11, Nov, 2010 in Guilin, China. This book covers almost all important aspects of steels from physical metallurgy, steel grades, processing and fabrication, simulation, to properties and applications. The book is intended for researchers and postgraduate students in the field of steels, metallurgy and materials science. Prof. Yuqing Weng is an academician of Chinese Academy of Engineering and the president of The Chinese Society for Metals. Prof. Han Dong is the vice president of Central Iron & Steel Research Institute and the director of National Engineering Research Center of Advanced Steel Technology, China. Prof. Yong Gan is an academician of Chinese Academy of Engineering, the vice president of Chinese Academy of Engineering and the president of Central Iron & Steel Research Institute, China.
The book begins with thorough coverage of Resistance Spot Welding fundamentals and principles, including concepts such as Lobe Curves, contact resistance vs. electrode force, dynamic resistance, heat balance challenges, nugget growth, machine types and power supplies, and electrodes. Subsequent chapters address challenges and approaches to important topics of welding advanced high-strength steels, such as DP, TRIP, TWIP, and Press Hardening Steel, as well as aluminum alloys. Welding issues associated with the various coatings used on these steels are addressed. The final chapters are dedicated to weld quality, monitoring, testing, computational modeling, and common automotive production issues such as the welding of multiple sheet stack-ups and a brief overview of associated codes and standards. The second edition includes updated chapters and additional information, such as expanded information on welding aluminum to steel, a new section on alternative welding and joining methods, and updates on monitoring and control as well as welding issues associated with the latest advanced high-strength steels.
Microstructure and Texture in Steels and Other Materials comprises a collection of articles pertaining to experimental and theoretical aspects of the evolution of crystallographic texture and microstructure during processing of steels and some other materials. Among the topics covered is the processing-microstructure-texture-property relationship in various kinds of steels, including the latest grade. Special emphasis has been given to introduce recent advances in the characterization of texture and microstructure, as well as modeling. The papers included are written by well-known experts from academia and industrial R and D, which will provide the reader with state-of-the-art, in-depth knowledge of the subject. With these attributes, Microstructure and Texture in Steels and Other Materials is expected to serve the cause of creating awareness of current developments in microstructural science and materials engineering among academic and R and D personnel working in the field.