Composite Materials Resistance Welding Lesson Objectives When you

Composite Materials

Resistance Welding Lesson Objectives When you finish this lesson you will understand: • Keywords Learning Activities 1. View Slides; 2. Read Notes, 3. Listen to lecture 4. Do on-line workbook

Matrix Materials Magnesium • Lowest density (37% lighter than aluminum) • Aerospace applications • Creeps at low temp • Relatively low strength • Prone to variety of corrosion problems Aluminum • Easy to process, inexpensive • Density only 35% of Steel • Can be alloyed to fairly high strengths • 57% stiffer than Magnesium • Excellent corrosion resistance • Most widely used material

Matrix Materials Titanium • Twice as strong as aerospace aluminum • 65% heavier than aluminum, but 65% stiffer • Temp & corrosion resistant = use in demanding environments Copper, Iron, Nickel, Tungsten • Special use alloys • Electronic Circuits • Metal forming dies • Jet engines • Military applications

Reinforcements Ceramics • Silicon Carbide (Si. C) • Aluminum Oxide (Al 2 O 3) • Titanium Carbide (Ti. C) • Boron Carbide (B 4 C) Other • Graphite (C) • Titanium Diboride (Ti. B 2) Metal Filaments • Boron • Steel • Tungsten Choice of matrix and reinforcement depends on: • Desired properties of composite • Compatibility between matrix and reinforcement • MMC Processing route

Rule of Mixtures

Designation for MMC Matrix + Reinforcement / Volume % Form Matrix = metal or alloy designation of matrix Reinforcement = chemical formula of reinforcement Volume % = Volume percent without the % sign Form = Form of the reinforcement • f, fiber or filament • c, chopped fiber • w, whisker • p, particulate Example: 6061 + Si. C/20 w

Welding Handbook, AWS

Particulate Composite Short-Fiber Composite Long-Fiber Composite Laminated Composite Manufacturing Processes Welding Handbook, AWS

Processing Methods Solid State Semi-solid Liquid

Solid State Processing Bonding of continuous fibers between metal foils to make panels • Aerospace Applications • Ti/Sic; Al/B Laminated Composite Powder Metallurgy • Mix particles of matrix with reinforcement • Vacuum hot press (near solidus) • Extrude or roll • Al/B 4 C; Al/Si. C

Semi-Solid Processing Spray Deposition Chilled Plate MMC Build Up ………. . Flame Spray Matrix Flame Spray Reinforcement Rheocasting • Mix reinforcement into matrix held between solidus and liquidus x

Liquid Processing Infiltration • Interfacial reactions can be a problem

Applications - From Ukraine Krivov, Optimization of design-production…, Welding in the World, Nov-Dec 1994

Applications Krivov, Optimization of design-production…, Welding in the World, Nov-Dec 1994

Krivov, Optimization of design-production…, Welding in the World, Nov-Dec 1994

Welding Handbook, AWS

Detrimental Weld Pool Chemical Reactions [l] indicates liquid phase [s] indicates solid phase [All] indicates in solution with liquid aluminum

Time-Temp Effect of Chem Reaction Resistance Welding Arc Welding Handbook, AWS

Capacitor Discharge • Stud Welding • Solid State • Fusion Weld • Brazing

Capacitor Discharge Stud Welding MMC Materials Welded • 6061, 2024, 6061/Si. C/40 p, 6061/Si. C/48 f, 6061/B 4 C/30 p, AZ 61/B 4 C/40 p • Studs = 0. 25 in; Sheet=0. 13 in • Time = 0. 4 ms • Solidification rate = 106 C/s

Stud Welding Handbook, AWS

Welding Handbook, AWS

Capacitor Discharge - Solid State Welding • Ti-6 Al-4 V/Si. C Sheets • Ti-6 Al-4 V/SCS-6 is a complex fiber with Si. C vapor deposited onto a graphite carbon core Diffusion (solid state) Bond No Melting Failure Occurred Upon Loading Remote from Weld Interface Baeslack & Froes, Joining Similar & Dissimilar……, JOM March 1995

Increase in Welding Current (Voltage) Causes Change From Solid State to Fusion Weld Cox et al, Capacitor Discharge RSW of Si. C Fiber… Welding Journal, Oct 1993

SCS-6 Fiber Capacitor Discharge Solid State Weld No liquid - Weld Strength 80% of Monolithic Cox et al, Capacitor Discharge RSW of Si. C Fiber… Welding Journal, Oct 1993

Solid State Weld with no Fiber degradation Cox et al, Capacitor Discharge RSW of Si. C Fiber… Welding Journal, Oct 1993

Capacitor Discharge - Fusion Welding

Partial Melting Fusion Weld Cox et al, Capacitor Discharge RSW of Si. C Fiber… Welding Journal, Oct 1993

Solidified Liquid around fiber, Property degradation Cox et al, Capacitor Discharge RSW of Si. C Fiber… Welding Journal, Oct 1993

Spot Brazing Continuous C Fiber MMC BAl. Si-4 Brazing Foil Al-7 Zn/C Low force = expulsion > 400 lb = fiber packing at weld center (see next slide)

Brazing Welding Handbook, AWS

Spot Brazing Continuous Si. C Fiber MMC Ti-22 Al-23 Nb/Si. C Ti-Cu-Ni Braze Foil Baeslack & Froes, Joining Similar & Dissimilar……, JOM March 1995

Baeslack & Froes, Joining Similar & Dissimilar……, JOM March 1995

Time-Temp Effect of Chem Reaction Resistance Welding Arc Welding Handbook, AWS

Resistance Spot Welding • Solid State • With Melting/Solidification

Spot Welding Handbook, AWS

Adjusting Welding Force Welding Time To Avoid Fiber Crushing in Al/B MMC (Continuous Fiber) Welding Handbook, AWS

Aluminum/Boron Continuous Fiber Hersh, Resistance Spot Weld MMC, Welding Journal, June 1970

Spot Welding Discontinuous Fibers Segregation of reinforcement (see next slide)

Welding Handbook, AWS