Welding Metallurgy of
01 Jan 1987-
About: The article was published on 1987-01-01 and is currently open access. It has received 991 citations till now. The article focuses on the topics: Welding.
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TL;DR: In this article, the results of a study concerned with the surface hardening of nonferrous and ferrous alloys, by integrating the electrospark deposition and plasma nitriding processes, were presented.
22 citations
Cites background from "Welding Metallurgy of"
...For material depositing, several processes exist [1], among hich the following ones are commonly used in industrial appliations: welding [2], thermal spraying [3] and electroplating [4]....
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01 Jan 2012
TL;DR: In this paper, a second pulse current postweld heat treatment was applied to resistence spot welds (RSW) in transformation-induced plasticity (TRIP) steel sheets, and optical and scanning electron microscopy, microhardness, and standardized quasi-static lap-shear tensile testing was investigated for all the pulse current conditions.
Abstract: Resistance spot welds (RSW) in transformation-induced plasticity (TRIP) steel sheets were locally postweld heat treated by applying a second pulse of current in the welding schedule. The evolution of the fusion zone (FZ) microstructure by optical and scanning electron microscopy, microhardness, and standardized quasi-static lap-shear tensile testing was investigated for all the pulse current conditions. The most important result of this study is that improved mechanical properties with desirable pullout failure mode is accomplished when the FZ microstructure consists of a recrystallized structure of martensite, which was achieved in the medium level of the second pulse current postweld heat treatment. Even though a considerable reduction in FZ hardness was observed at the lowest value of the second pulse current due to the presence of plate-like ferrite and tempered martensite structure, the failure mode and load-bearing capacity of the weldment was not improved significantly. At higher current levels of the second pulse condition, remelting occurred with consequent formation of a new weld nugget comprising columnar structure but larger nugget size giving mixed failure modes. The fusion zone microstructures and microhardness results correlated well with the simulated welding thermal history of the postweld local heat treatments.
22 citations
TL;DR: In this paper, a bottom-up strategy that leverages the selective laser melting (SLM) technique to manufacture a three-dimensional (3D) porous copper template was creatively proposed, and Graphene was then in-situ grown via chemical vapor deposition on the obtained porous Cu template, forming 3DG composites.
Abstract: Currently, three-dimensional graphene (3DG) fabrication was restricted by the complicated process, strict chemical reactions as well as structural accuracy. Herein we creatively propose a bottom-up strategy that leverages the selective laser melting (SLM) technique to manufacture a three-dimensional (3D) porous copper template. Graphene was then in-situ grown via chemical vapor deposition (CVD) on the obtained porous Cu template, forming 3DG composites. A combination of conventional graphene growth via CVD technique with SLM fabricated scaffold templates enabled an accurate design and regulation of 3DG from macro-structure (unit type, porosity, aperture) to micro-structure (texture, surface quality) through an elaborately manipulated porous copper scaffold. The 3DG/copper scaffold could achieve around 88% and 27% enhancement in electromagnetic interference (EMI) shielding and thermal diffusion, respectively. Particularly, the highest EMI shielding efficiency (SE) can reach up to 47.8 dB at 2.7 GHz and exhibit an average SE of 32.3 dB at the range of 2–18 GHz. The synergistic shielding mechanisms accounted for the improvement derived from the use of hybrid composite materials and precise architecture of the SLM porous structure.
22 citations
07 Mar 2008
TL;DR: In this paper, the authors present a review of the development of solidification in the 20th century, focusing on the following: 1.2 Descriptive classification vs. "Cases" 28 1.3 Growth modes 28 2.1 Equilibrium solidification; Case 1 29 2.3 Scheil during WWII 30 2.4 Bell Laboratories; Burton, Primm & Slichter, Pfann's Cases 31 2.5 University of Toronto;-1950 32 2.6 MIT; Flemings and Mullins & Sekerka 35 2.7 R
Abstract: 3 FOREWORD 4 CONTENTS 5 LIST OF SYMBOLS 7 ORIGINAL FEATURES OF THIS DISSERTATION 9 INTRODUCTION 11 Chapter 1 GENERAL ASPECTS OF SOLIDIFICATION 14 1.1 Solidification basics 14 1.2 Descriptive classification vs. "Cases" 28 1.3 Growth modes 28 Chapter 2 SOLIDIFICATION RESEARCH IN THE 20 CENTURY 29 2.1 Equilibrium solidification; Case 1 29 2.2 Start of modern solidification theory; Gulliver and Case 2 29 2.3 Scheil during WWII 30 2.4 Bell Laboratories; Burton, Primm & Slichter, Pfann's Cases 31 2.5 University of Toronto;-1950 32 2.6 MIT; Flemings and Mullins & Sekerka 35 2.7 RPI; Savage 36 2.8 Lausanne EPFL; Kurz 39 2.9 David & Vitek 1989; NEGS to EGS transformation 42 2.10 Tokyo University; Koseki 43 2.11 Osaka University; Nishimoto, Mori 44 2.12 St. Petersburg State Polytechnic University 45 2.13 Inverse modeling of temperature field 45 2.14 Paton institute; Demchenkp . 46 2.15 Phase-Field simulation 47 2.16 Bimetallic surfaces: Special phase diagrams and anomalous nano-particles 48 Chapter 3 THE FOUR CASES OF SOLIDIFICATION 49 3.1 Case 1: Equilibrium solidification' ( 49 3.2 Case 2: No diffusion in solid, total mixing in liquid 49 3.3 Case 3: No diffusion in solid, partial diffusion in liquid 50 3.4 Case 4: Splat cooling ' 50 Chapter 4 INTERMEDIATE SUB-CASES v 51 4.1 Sub-Cases below Case 3 51 4.2 Sub-Cases above Case 3: Mullins & Sekerka / Lausanne / Solute Trapping 53 Chapter 5 WELD SOLIDIFICATION CONTINUUM AND ITS MODELING 55 5.1 Rate-Gradient analyses ._, 55 5.2 Geometric morphology-model 55 5.3 Solid solute profile-model: One Case 56 5.4 Weld Solidification Continuum Model Frame a tool for modeling 56 5.5 Discussion of the proposed Model Frame 60 5.6 The melting stage and Melting/ Solidification(M/S-) model 62 5.7 About the Model Frame, Cases, Sub-Cases, Sub-Case Variables and the Lausanne and RPI approaches 65 Chapter 6 EXPERIMENTS ON PURE AND DOPED Cu 67 6.1 Materials and tests 67 6.2 Metallographic observations 71 6.3 Hot cracking 74 6.4 About the experimental method 75 Chapter 7 DISCUSSION 76 Chapter 8 SUMMARY OF THE DISSERTATION 77 REFERENCES 79 APPENDIXES 84 Appendixes 1... 10: No dope, Cu 85 Appendixes 11... 22: B i-dope 98 Appendixes 23...27: La-dope 110 Appendixes 28...31: Li-dope 115 Appendixes 32...33: P-dope 118 Appendixes 34...35 Pb-dope 121 Appendix 36. Ambiguities in the definitions of some central concepts 125 Appendix 37. The dismissal of the cellular dendritic growth 126 Appendix 38. The Melting/Solidification(M/S-) model 127 Appendix 39. Pool Shape 139 Appendix 40. Joining Case 2 to Case 1 with added solid diffusion, Sub-Case 2(-)Ds 141 Appendix 41. Visualization of the Cases, Sub-Cases and operation paths of Cases 2 and 3 from solidification start to its end 142 Appendix 42. The Stagnant Layer and the Concentration Gradient Width 144 Appendix 43. The Lausanneand RPI-approaches at cell centerline 147
22 citations
01 Dec 2015
TL;DR: In this paper, the weldability of high strength aluminium alloys, principally the 7xxx series, is discussed in addition to consideration of joint types, weld defects and recommendations for minimizing or preventing weld defects.
Abstract: Muyiwa Olabode Weldability of high strength aluminium alloys Lappeenranta 2015 59 pages Acta Universitatis Lappeenrantaensis 666 Diss. Lappeenranta University of Technology ISBN 978-952-265-865-4, ISBN 978-952-265-866-1 (PDF), ISSN-L 1456-4491, ISSN 1456-4491 The need for reduced intrinsic weight of structures and vehicles in the transportation industry has made aluminium research of interest. Aluminium has properties that are favourable for structural engineering, including good strength-to-weight ratio, corrosion resistance and machinability. It can be easily recycled saving energy used in smelting as compared to steel. Its alloys can have ultimate tensile strength of up to 750 MPa, which is comparable to steel. Aluminium alloys are generally weldable, however welding of high strength alloys like the 7xxx series pose considerable challenges. This paper presents research on the weldability of high strength aluminium alloys, principally the 7xxx series. The weldability with various weld processes including MIG, TIG, and FSW, is discussed in addition to consideration of joint types, weld defects and recommendations for minimizing or preventing weld defects. Experimental research was carried out on 7025-T6 and AW-7020 alloys. Samples were welded, and weld cross sections utilized in weld metallurgy studies. Mechanical tests were carried out including hardness tests and tensile tests. In addition, testing was done for the presence of Al2O3 on exposed aluminium alloy. It was observed that at constant weld heat input using a pulsed MIG system, the welding speed had little or no effect on the weld hardness. However, the grain size increased as the filler wire feed rate, welding current and welding speed increased. High heat input resulted in lower hardness of the weld profile. Weld preheating was detrimental to AW7020 welds; however, artificial aging was beneficial. Acceptable welds were attained with pulsed MIG without the removal of the Al2O3 layer prior to welding. The Al2O3 oxide layer was found to have different compositions in different aluminium alloys. These findings contribute useful additional information to the knowledge base of aluminium welding. The application of the findings of this study in welding will help reduce weld cost and improve high strength aluminium structure productivity by removing the need for pre-weld cleaning. Better understanding of aluminium weld metallurgy equips weld engineers with information for better aluminium weld design.
22 citations
References
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TL;DR: In this article, the state of the art in selective laser sintering/melting (SLS/SLM) processing of aluminium powders is reviewed from different perspectives, including powder metallurgy (P/M), pulsed electric current (PECS), and laser welding of aluminium alloys.
1,172 citations
TL;DR: In this article, the authors show that the pre-existing dislocation network, which maintains its configuration during the entire plastic deformation, is an ideal modulator that is able to slow down but not entirely block the dislocation motion.
557 citations
TL;DR: In this article, the fundamental understanding of structure-properties relationship in automotive steels resistance spot welds is discussed. And a brief review of friction stir spot welding, as an alternative to RSW, is also included.
Abstract: Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.
369 citations
TL;DR: In this article, a unified equation to compute the energy density is proposed to compare works performed with distinct equipment and experimental conditions, covering the major process parameters: power, travel speed, heat source dimension, hatch distance, deposited layer thickness and material grain size.
369 citations
TL;DR: This study attempted to predict solidification defects by DNN regression with a small dataset that contains 487 data points and found that a pre-trained and fine-tuned DNN shows better generalization performance over shallow neural network, support vector machine, and DNN trained by conventional methods.
314 citations