NASACONTRACTOR ~- REPORT w- *o 0 N I e ,v INTEGRATION OF NASA-SPONSORED STUDIES ON ALUMINUM WELDING by Koichi Masubuchi .,, ,'. _... -. .. Prepared by , . .. MASSACHUSETTSINSTITUTE OF TECHNOLOGY Cambridge, Mass. for GeorgeC. Marshall SpaceFlight Center NATIONALAERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. JUNE 1972 - " TECH LIBRARY KAFB, NM TECHNIC . REP 00b1150.. - . .- ¶ REPORT NO. 2. GOVERNMENTACCESSION NO. 3. RECIPIENT'SCATALOG NO. NASA CR-2064 4. TITLE AND SUBTITLE 5. REPORTDATE INTEGRATION OF NASA-SPONSORED STUDES ON June 1972 ALUMINUM WELDING 6. PERFORMINGORGANIZATION COOE ~ ~~ ~~ ~~ 7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT . Koichi Masubuchi 9. PERFORMING ORGANIZATION NAME AND'ADDRESS IO. WORK UNIT NO. Massachusetts Institute of Technology Dept. of Ocean Engineering 11. CONTRACT OR GRANT NO. Cambridge,Massachusetts NAS 8-24364 13. 'TYPE OF REPORT k PERIOD COVEREI 12. SPONSORING AGENCY HAM€ AND ADDRESS Low Series Contractor Report National Aeronautics and Space Administration Washington, D. C. 20546 14. SPONSORINGAGENCY CODE 15. SUPPLEMENTARYNOTES 16. ABSTRACT Gas tungsten-arcand gas metal-arc processes are used extensively in the fabrication of huge fuel and oxidizer tanks of the Saturn V spacecraft used in the Wpollolunar missions. The buildingof these tanks has raised problems related to welding of high-strength, heat-treated aluminum alloysand have revealed a need for basic research leading tothe development of new techniques;both of which will be of benefitto the general industry. This is the secondedition of the report of a study to integrate results obtainedin nineteen individual studies sponsoredby NASA onwelding aluminum. Subjects covered include: Effects of porosity on weld-joint performance Sourcesof porosity Weld thermal effects Residual stresses and distortion Manufacturingprocess system control. 7. KEY WOROS STATEMENTOlSTRlBUTlON 18. Welding Aluminum Alloys Porosity Thermal Effects I 9. SECURITY CLASSIF. (d thb rmport) 20. SECURITYCLASSIF. (of this WE=) 21. NO. OF PAGES 22. PRICE $6.00 Unclassified Unclassified 322 For sale by the National Technical Information Service, Springfield, Virginia 22151 FOREWORD This report is the documentation of the results of a program to analyze and integrate data generated fromNASA-sponsored stud- ies on welding aluminum alloys, especially 2014 and 2219 alloys. Earlier work on this was published as NASA CR-61261, from George C. Marshall Space Flight Center, Marshall Space Flight Center, Alabama 35812. The earlier work was funded under a Department of Army grant, DA-Ol-02I-AMC-14693(Z). The present work was performed under NAS 8-24364 contract. iii -~ ". ". TABLE OF CONTENTS Page CHAPTER 1 Introduction 1-1 CHAPTER 2 Welding Fabricationof Fuel and Oxidizer Tanksof Saturn V 2-1 2.1 Saturn V and It's Fuel and Oxidizer Tanks 2-1 2.2 Selection of Materials for Fuel and Oxidizer Tanks 2-3 BriefHistory Prior toSaturn V 2-3 Al loy 2219 for Saturn2-4S1-CforAlloy 2219 Alloy 2014 for Second and Third Stages 2-6 Characteristics of 2014 and 2219 Alloys 2-6 2.3 Welding Fabrication 2-9 Fabrication Welding 2.3 We lding Techniques 2-9 Techniques Welding R equirement s for Welds 2-11 Welds Requirementsfor Weld Defects,Especially Porosity 2-11 Jigging 2-14 RequirementsJointforMismatch 2-17 CHAPTER 3 WeldingProblems and Research Efforts 3-1 3.1 NASA-Sponsored Studies on Welding Aluminum 3-1 3.2 Welding Problems and Outline of NASA-Sponsored Studies 3-7 Porosity 3-7 T hermal Effects 3-7 Effects Thermal Materials and Welding Processes Studied 3-11 V Page CHAPTER 4 Effects ofPorosity on Weld-Joint Performance 4-1 4.1 GeneralDiscussions on the Effects of Weld Defects on thePerformance of Welded Structures 4-1 Stress Concentrations around Defects 4-2 Ductile Fracture 4-5 Unstable Brittle Fracture 4-0 4.2 PorosityEffects on Weld-Joint Performance underStatic Loading 4-11 Results of Some ExperimentsSimilar to NASA Studies 4-11 ResearchProcedures of the MartinStudy 4-13 ExperimentalResults 4-16 Analysisand Evaluation of the MartinStudy on Porosity Effects on Weld Strength 4-21 4.3Porosity Effects on Fatigue Strength 4-25 4.4 Effectof Repair Welds 4-28 CHAPTER 5Weld Porosity, Its Sourcesand Control 5-1 5.1Mechanisms of Porosity 5-2 Role of Hydrogen 5-2 Effects of Shielding Gas Dewpointand Welding Parameters on Porosity 5-4 Nucleationand Growth of Porosity 5-6 5.2Shielding-Gas Contamination 5-10 The BoeingStudy on Effects of Individual Gas Contaminants 5-11 5.3 SurfaceContamination 5-17 Characteristics of Surfaceof Practical Joints 5-17 Surface Adsorption 5-20 vi Page SurfaceTopography 5-23 Procedures of the IITRI Study 5-27 Results of the IITRI Study 5-32 5.4 Composition of Base Plate and Filler Metal 5-47 5.5 Methods forControlling and Eliminating Porosity 5-50 Surface Hydrogen Analysis 5-50 TackWelds As a Sourceof SurfaceContamination 5-63 Surface Preparation 5-68 MonitoringShielding Gas Purity 5-75 Other Possible Means 5-88 CHAPTER 6 Weld ThermalEffects 6.1 Time-TemperatureEffect 6-3 Strength vs WeldingEnergy 6- 10 6.2 Welding with High Density Power Sources 6-11 Experimentsto Increase GTA Power Density 6- 11 Electron Beam Welding 6-16 Nonvacuum Electron Beam Welding 6-19 Plasma Electron Beam Welding 6-22 6.3 Time-TemperatureControl by CryogenicCooling 6-26 ExperimentalProcedures 6-26 Experimental Results 6-28 CHAPTER 7 ResidualStresses andDistortion 7-1 7.1 Analysis of Thermal Stresses duringWelding 7-2 TechnicalBackground on Analysisand Control of Weld Distortion 7-2 Developmentof Techniques for Analyzing ThermalStresses and Metal Movement 7 -6 vii Paqe Examples of Analytical Results 7-11 Effects of Welding Parameters 7-15 Effects of Material Propertieson Residual Stress Distributions 7-23 Experimental Investigation 7-27 7.2 Reduction of Warpage and Residual Stresses by Controlling Thermal Pattern during Welding 7-33 Background and Phases of Study 7-33 Analytical Study 7-34 Experimental Work 7-34 Typical Thermal Patterns 7-37 Experimental Results 7-43 Discussion of Results 7-46 7.3 Development of Nondestructive Methods for Determining Residual Stresses 7-48 Ultrasonic Stress Measuring Techniques 7-49 Investigation on Welded Plates 7-54 Application Technique Considerations 7-5 8 Detection of Fatigue Damage 7-61 Summary 7-62 CHAPTER 8 Manufacturing Process System Control 8-1 8.1 Transferability of Welding Parameters 8-2 Phases and Experimental Design 8-3 Welding Test Procedure 8-6 Welding Parameter Control Development 8-7 Statistical Analysisof Effects on Welding Parameterson Weld Qualities 8-11 Analysis and Evaluation of the Lockheed Study on Transferability of Setup Parameters 8-20 viii - " ...... Page 8.2 Developmentof Welding Process Control Sys tems 8-26 Prevention of Porosity by Monitoring Shielding-GasPurity and SurfaceCleanliness 8-26 ComputerSimulation of Welding Processes toThermal EffectsPredict 8-27 CHAPTER 9 Summary andPractical Recommendations 9-1 REFERENCES 10-1 ix CHAPTER 1 Introduction Space exploration is not accomplished by wishful thinkingand intense desire alone. Artifacts, tools, and transportation vehicles are brought about by scientific and technologicalactivity. As inother escapades of curiosity, man derivesby-products of knowledge in technology that are beneficial in respect to peacefulcoexistence and biosocial well-being. The weldingtechniques and equipment that are used to producespace vehicles of high structural reliability can also beused to make better and more economicalproducts, necessary in our moremundane existence. During the fabrication of the Saturn V space vehicles used for theApollo lunar missions, an extensive research programon aluminum welding was conductedby the Welding DevelopmentBranch in the ManufacturingEngineering Laboratory ofthe G. C. MarshallSpace Flight Center, NASA. As a part of theprogram, a study was conducted at theMassachusetts Institute of Technologyunder Contract No. NAS 8-24364 to integrate NASA-sponsored studies onaluminum welding. Results discussed in these reports are associated with weldingfabrication of the Saturn V. However, theyshould beapplicable to thewelding of aluminum alloys used in futurespace vehicles and aerospace structures. Basic prin- ciples described here can be also applicable to structures in non-spaceindustries. Although this report is concernedwith the welding of aluminum structures, it is important to understand that this is onlyone phase of the fabrication of a complex structure such as the Saturn V space vehicle, and must eventually be related to a much greaterwhole. The Saturn V requires a very complexsystem of design and fabrication composed of many phases.These phases include design, material selection, stress analysis,cutting, machining, forming, joining, and inspection.Each phase is closelyrelated to anddependent upon theothers. For example, the material selectionmust be made not only on the basis of mechanical properties but also withregard to forming and joining the material. The designmust be made so that a structure with sufficient re- liability can be fabricated with a tolerable dimensional accuracy.There are also many factorswithin each phase of designand fabrication. For example, the quality of a weld depends upon such factors as the cleanliness of the metal surface, purity of theshielding gas, and the welding condi- tions. To improvethe structural reliability of a space vehicle, we must know more about each phase, the relation- ship of factors within it, the relationship of anyone phase toother phases, and ultimately, the importance of eachphase tothe final product. With this knowledge,