Brazing Second Edition Mel M. Schwartz

Transcription

1 Brazing Second Edition Mel M. Schwartz ASM International Materials Park, Ohio

2 Copyright 2003 by ASM International All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the written permission of the copyright owner. First printing, September 2003 Great care is taken in the compilation and production of this book, but it should be made clear that NO WAR- RANTIES, EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WARRANTIES OF MER- CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE GIVEN IN CONNECTION WITH THIS PUBLICATION. Although this information is believed to be accurate by ASM, ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. This publication is intended for use by persons having technical skill, at their sole discretion and risk. Since the conditions of product or material use are outside of ASM s control, ASM assumes no liability or obligation in connection with any use of this information. No claim of any kind, whether as to products or information in this publication, and whether or not based on negligence, shall be greater in amount than the purchase price of this product or publication in respect of which damages are claimed. THE REMEDY HEREBY PROVIDED SHALL BE THE EXCLUSIVE AND SOLE REMEDY OF BUYER, AND IN NO EVENT SHALL EITHER PARTY BE LIABLE FOR SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES WHETHER OR NOT CAUSED BY OR RESULTING FROM THE NEGLIGENCE OF SUCH PARTY. As with any material, evaluation of the material under end-use conditions prior to specification is essential. Therefore, specific testing under actual conditions is recommended. Nothing contained in this book shall be construed as a grant of any right of manufacture, sale, use, or reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered by letters patent, copyright, or trademark, and nothing contained in this book shall be construed as a defense against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for such infringement. Comments, criticisms, and suggestions are invited, and should be forwarded to ASM International. Prepared under the direction of the ASM International Technical Book Committee ( ), Charles A. Parker, Chair. ASM International staff who worked on this project include Scott Henry, Assistant Director of Reference Publications; Bonnie Sanders, Manager of Production; and Nancy Hrivnak and Jill Kinson, Production Editors. Schwartz, Mel M. Brazing / Mel M. Schwartz. 2nd ed. p. cm. Includes bibliographical references and index. ISBN Brazing. I. Title. Library of Congress Cataloging-in-Publication Data TT267.S dc ISBN: SAN: ASM International Materials Park, OH Printed in the United States of America

3 Contents Preface vii Chapter 1 Introduction to Brazing Brazing versus Soldering Historical Development of Brazing Advantages and Limitations of Brazing Mechanics of Brazing Brazing versus Other Welding Processes Chapter 2 Brazing Fundamentals Adhesion, Wetting, Spreading, and Capillary Attraction Practical Experience, Work-Related Tips, and Problem-Solving Chapter 3 Elements of the Brazing Process Filler-Metal Flow Base-Metal Characteristics Filler-Metal Characteristics Surface Preparation Joint Design and Clearance Temperature and Time Processes (Heat Sources) Torch Brazing Furnace Brazing Induction Brazing Controlled-Atmosphere Brazing New Induction Brazing Systems Resistance Brazing Carbon Resistance Brazing Direct Resistance Brazing Dip Brazing Infrared (Quartz) Brazing Exothermic Brazing Laser Brazing Braze Welding Diffusion Brazing Microwave Brazing iii

4 The Future of Braze Processing Practical Experience, Work-Related Tips, and Problem-Solving Chapter 4 Base Metals and Base-Metal Family Groups Metallurgical Reactions Base-Metal Family Groups Case Histories and Problem-Solving Examples Chapter 5 Brazing Filler Metals Basic Characteristics Filler-Metal Selection Criteria Filler-Metal Types Specialized Brazing Filler Metals and Materials Filler-Metal Selection Filler-Metal Forms Case Histories and Problem-Solving Examples Chapter 6 Fluxes and Atmospheres Atmospheres Fluxes Case Histories and Problem-Solving Examples Chapter 7 Fixturing, Tooling, Stopoffs, Parting Agents, Surface Preparation, Surface Cleaning, and Repair Fixturing and Tooling Stopoff Materials and Parting Agents Surface Cleaning and Preparation Surface Preparation for Specific Base Metals Clean Rooms Vacuum Brazing Cleaning Postbrazing Treatments Repair Techniques with Cleaning Agents Case Histories and Problem-Solving Examples Chapter 8 Joint Design Types of Joints Joint Clearance Design for Assembly Effects of Brazing Variables on Clearance Strength Joint Design and Ceramics Case Histories and Problem-Solving Examples Chapter 9 Evaluation and Quality Control of Brazed Joints Design and Quality System Quality Standards for Brazing and Brazing Processes Types of Common Defects Brazing Process Planning and Control Nondestructive Inspection Design Testing, Evaluation, and Feedback Destructive Inspection and Testing Methods iv

5 Chapter 10 Applications and Future Outlook Automation Fluxless Brazing Novel and Emerging Brazing Processes Future Outlook Case Histories and Problem-Solving Examples Abbreviations and Symbols Subject Index Filler Metal Index v

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7 Preface This updated and revised second edition of Brazing is intended to provide the reader with the information needed to braze materials that will be used in the 21st century. My goal has been to fuse experiences, basic understandings, theories, and practical information from the past with guidance about expected brazing applications and problem-solving considerations for the future and what it may hold for materials joining. It will be interesting to observe the continuing development and use of novel types of equipment and how engineers, scientists, and technology innovators will tackle the unknowns of this new millennium. In addition, this revised edition includes lessons learned on tooling, design, materials, atmospheres, processing, and equipment throughout the book. These examples should be helpful to the new brazing initiate as well as to more experienced brazing technologists and engineers. Several new and emerging topics are covered, including nanostructures and materials, microwave and laser brazing, more effective use of vacuum atmospheres, functionally gradient materials (FGM), and intermetallics, to name just a few. Coverage has been increased on beryllium alloys, aluminumlithium alloys, new titanium alloys, various composites (metal, ceramic, intermetallic), ceramic-tometal brazing, and ceramic-to-ceramic brazing. The enforcement of environmental regulations and the rising cost of metals such as copper and silver have forced manufacturers of brazing and soldering products to develop new fluxes and filler metals, while devising more efficient means of applying existing products. These trends have been reflected in the content of this new edition. Residual flux and its disposal have come under the scrutiny of regulatory agencies. To address this concern, a family of concentrated fluxes has come on the market that provides improved fluxing performance with smaller amounts being applied to the part. The quantities used can be reduced even more with automated dispensing, which places a small amount of flux exactly where it is required rather than the more expansive manual brushing of the flux. The increasing use of aluminum for parts has spawned the development of better aluminum filler metals and fluxes for brazing. The elimination of cadmium from braze filler metals is another area that has attracted attention in recent years. Cadmium has for years been used in certain brazing filler metals because of its characteristic as a temperature depressant, which facilitates melting and wetting of the filler metal. OSHA has established stringent regulations on allowable cadmium levels in the air. Some manufacturers have addressed this through the installation of sensitive filtration equipment and closing off the brazing area from other manufacturing operations. Another approach has been to utilize substitute cadmium-free braze filler metals now commercially available. These substitutes are similar in wetting characteristics to the cadmium types, but they do require more heat to produce the wetting. This factor should be taken into consideration when establishing the application of the heat. Other products that are considered are brazing powders and rods pre-coated with flux and equipment that automatically dispenses exact amounts of filler metals in paste form. vii

8 Modeling can be used to increase reliability, repeatability, and efficiency of furnace operations. That is, the optimum cycle for a particular brazing process and workload is determined and a program is designed to allow the influencing parameters to be automatically compensated in real time, thereby achieving optimum operation. The basis for actual in-process control is modern computer methods and more sophisticated knowledge of the brazing process. The thinking and understanding of companies and their management must become global, and engineers must be able to reduce the technology development cycle for new materials and brazing systems from a norm of five to seven years to two to three years. One final area of concentrated development work is ceramic joining. Although the ability to fabricate ceramic materials that are reliably strong and tough is continuously advancing, the successful utilization of these materials will depend on the ability to assemble simple components into structures that will function effectively. While metal joining can be performed by starting at one end of the joint, ceramic joining requires the entire joint region to be brought into a reactive state simultaneously. Preliminary supplemental heating may be needed to prevent thermal shock during joining. A transfer of the experience gained in other material fields could prove helpful. Adaptation of physical and chemical deposition methods, surface engineering by laser beams, ion implantation, and chemical doping to improve surface reactivity and solid state adhesion are just a few of the techniques available for implementation. The development of generic joining technology for ceramic materials is vital and should be pursued in the context of metallurgical and ceramic sciences. Furthermore, it should be paralleled by an engineering effort to design and construct equipment specific to ceramic joining. Extending joining technology to ceramic materials will allow implementation of advanced technologies in circumstances where ceramics are the only materials having the requisite properties. Such a development provides an opportunity for the expertise of joining engineers plus venture capitalists to cash in on solving the underlying basic problems and thus augment the international competitiveness of U.S. products. If one tries to view the future and what it holds, woven through these fanciful visions are items that reflect trends observed in current reality. For instance, with the current pace of technological change, it can take less than six months for a state-of-the-art computer to become old technology. And software viruses can gobble up monthly production reports in seconds. But there is also good news. Within the next few years, micro-robots may crawl through intelligent joining systems, performing preventive maintenance in areas previously inaccessible. Solar power could become the cost-effective, environmentally safe way to fuel many manufacturing processes. Traditional methods of design and manufacture will give way to concurrent engineering (CE) strategies that enable improved communications between design and manufacturing. Automakers, aircraft manufacturers, and even job shops will design for manufacturability. These strategies will strongly influence development and deployment of advanced manufacturing technology well into the new millennium. However, with all the enthusiasm, enhancement, and advancements made by all the above industries, the basics in joining have not been altered. In spite of the move to automation, computer-controlled and monitored processes, and robots, the basic principles for all the various joining processes and fabrication techniques have not changed. You still need a heating media/source, material to be joined, a filler material to be added or preplaced in most cases, and a protective atmosphere/flux or vacuum in many situations. Over the past several years, many organizations have surveyed the changing face of science and engineering within the United States. In each case, the conclusions were the same: Fewer engineering students will be available for industrial employment during the first decade of the 21st century. viii

9 As a result of the aging work force and benefits of early retirement programs, the demands for qualified joining (brazing) engineers will increase especially with the retirement in of the baby boomers. The changing face of industry will result in the need for more technically trained individuals. Department of Labor statistics predict an increased need in the engineering work force of 165% for the ten-year period from 1999 to As indicated in a recent National Science Foundation report, the educational system in the United states has always been hierarchical. For this reason, the progression (and attrition) of students from primary education through graduate programs is conceptualized as a pipeline. The feeder to engineering education resides in middle school (grades 6 to 8). It is here that students begin to take an interest in career opportunities and the educational requirements needed to enter these professional careers. This is where they begin planning their high school curriculum, which will either prepare them for a college education or vocational endeavors. The real solution will take the cooperative effort from each portion of industry, i.e., professional societies, industry and educational organizations. Professional societies and educational foundations can assist in image-building and career planning. Finally, the secondary schools and universities must begin to view themselves as equal partners with industry and societies in course requirement development and articulation agreements. A knowledge of metallurgy is basic to an understanding of the brazing process. This does not mean that the brazing engineer, brazer, and the brazing inspector must become a metallurgist. But it does mean that engineering schools of the world increasingly must face up to the fact that in the future engineers must play a key part in management s strategic planning group. The university system recognizes that tomorrow s engineers will have to have enhanced capabilities due to three significant factors: increased product sophistication and variation; a global manufacturing environment; and a multitude of social and economic changes. The 21st century engineer or technologist will require a radically different education from that of his predecessors. The workplace of the future will need systems integrators, not individuals classified as metallurgists, brazing technologists, manufacturing engineers, quality engineers, or industrial engineers; individuals will need knowledge and talent in each of these fields. The engineer of the future must be fully conversant with modern materials applications. Those who are involved in developing industrial computer networks must also be familiar with the manufacturing processes themselves. Improvements in joining science and technology must keep pace with advances in materials science and technology, or else the benefits of these new materials will not be achieved in the marketplace. Mel Schwartz ix

10 ASM International is the society for materials engineers and scientists, a worldwide network dedicated to advancing industry, technology, and applications of metals and materials. ASM International, Materials Park, Ohio, USA This publication is copyright ASM International. All rights reserved. Publication title Product code Brazing #06955G To order products from ASM International: Online Visit /bookstore Telephone (US) or (Outside US) Fax Mail Customer Service, ASM International 9639 Kinsman Rd, Materials Park, Ohio , USA CustomerService@asminternational.org In Europe In Japan American Technical Publishers Ltd Knowl Piece, Wilbury Way, Hitchin Hertfordshire SG4 0SX, United Kingdom Telephone: (account holders), (credit card) Neutrino Inc. Takahashi Bldg., 44-3 Fuda 1-chome, Chofu-Shi, Tokyo 182 Japan Telephone: 81 (0) Terms of Use. This publication is being made available in PDF format as a benefit to members and customers of ASM International. You may download and print a copy of this publication for your personal use only. Other use and distribution is prohibited without the express written permission of ASM International. No warranties, express or implied, including, without limitation, warranties of merchantability or fitness for a particular purpose, are given in connection with this publication. Although this information is believed to be accurate by ASM, ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. This publication is intended for use by persons having technical skill, at their sole discretion and risk. Since the conditions of product or material use are outside of ASM's control, ASM assumes no liability or obligation in connection with any use of this information. As with any material, evaluation of the material under end-use conditions prior to specification is essential. Therefore, specific testing under actual conditions is recommended. Nothing contained in this publication shall be construed as a grant of any right of manufacture, sale, use, or reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered by letters patent, copyright, or trademark, and nothing contained in this publication shall be construed as a defense against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for such infringement.