Composite Materials

Resistance Welding

Lesson ObjectivesWhen you finish this lesson you will understand:•

Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line workbook

Keywords

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 (SiC)• Aluminum Oxide (Al2O3)• Titanium Carbide (TiC)• Boron Carbide (B4C)

Other• Graphite (C)• Titanium Diboride (TiB2)

Metal Filaments• Boron• Steel• Tungsten

Choice of matrix and reinforcement depends on:• Desired properties of composite• Compatibility between matrix and reinforcement• MMC Processing route

orcementinfrer

matrixm

compositec

fractionvolumeV

consideredpropertyX

Where

VXVXX rrmmc

Rule of Mixtures

Designation for MMC

Matrix + Reinforcement / Volume % Form

Matrix = metal or alloy designation of matrixReinforcement = chemical formula of reinforcementVolume % = Volume percent without the % signForm = Form of the reinforcement

• f, fiber or filament• c, chopped fiber• w, whisker• p, particulate

Example: 6061 + SiC/20w

Welding Handbook, AWS

Particulate Composite

Short-Fiber Composite

Long-Fiber Composite Laminated Composite

Manufacturing ProcessesWelding Handbook, AWS

Processing Methods

Solid StateSemi-solidLiquid

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/B4C; Al/SiC

Semi-Solid Processing

Spray Deposition

Chilled Plate

MMC Build UpMMC Build Up

Flame Spray MatrixFlame Spray Matrix

Flame Spray Reinforcement

………..

Rheocasting• Mix reinforcement into matrix held between solidus and liquidus

TEMP

COMP

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[Al2]s[OMgAl3]s[OAl4]Al[Mg3

)TiAlAlTi](l[Al]Al[Si]s[TiC]s[SiC]l[Al3]Al[Ti5

]Al[Si3]s[CAl]s[SiC3]l[Al4

4232l

3ll

l34

[l] indicates liquid phase[s] indicates solid phase[All] indicates in solution with liquid aluminum

ResistanceWelding

ArcWelding

Time-Temp Effect of Chem Reaction

Welding Handbook, AWS

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

Capacitor Discharge Stud Welding

MMC Materials Welded• 6061, 2024, 6061/SiC/40p, 6061/SiC/48f, 6061/B4C/30p,

AZ61/B4C/40p• Studs = 0.25 in; Sheet=0.13 in• Time = 0.4 ms• Solidification rate = 106 C/s

Welding Handbook, AWS

Stud Welding

Welding Handbook, AWS

Welding Handbook, AWS

Capacitor Discharge - Solid State Welding• Ti-6Al-4V/SiC Sheets• Ti-6Al-4V/SCS-6

Diffusion (solid state) BondNo Melting

Failure Occurred Upon Loading Remote from Weld Interface

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

SCS-6 is a complex fiber with SiC vapor deposited onto a graphite carbon core

Increase in Welding Current (Voltage) Causes ChangeFrom Solid State to Fusion Weld

Cox et al, Capacitor Discharge RSW of SiC Fiber…Welding Journal, Oct 1993

Capacitor Discharge Solid State WeldNo liquid - Weld Strength 80% of Monolithic

SCS-6 Fiber

Cox et al, Capacitor Discharge RSW of SiC Fiber…Welding Journal, Oct 1993

Solid State Weld with no Fiber degradation

Cox et al, Capacitor Discharge RSW of SiC Fiber…Welding Journal, Oct 1993

Capacitor Discharge - Fusion Welding

Partial Melting Fusion Weld

Cox et al, Capacitor Discharge RSW of SiC Fiber…Welding Journal, Oct 1993

Solidified Liquid around fiber, Property degradation

Cox et al, Capacitor Discharge RSW of SiC Fiber…Welding Journal, Oct 1993

Al-7Zn/CBAlSi-4BrazingFoil

Low force = expulsion> 400 lb = fiber packing at weld center (see next slide)

Spot Brazing Continuous C Fiber MMC

Welding Handbook, AWSBrazing

Spot Brazing Continuous SiC Fiber MMC

Ti-22Al-23Nb/SiC

Ti-Cu-NiBraze Foil

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

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

ResistanceWelding

ArcWelding

Time-Temp Effect of Chem Reaction

Welding Handbook, AWS

Resistance Spot Welding• Solid State• With Melting/Solidification

Spot Welding

Welding Handbook, AWS

Adjusting Welding ForceWelding TimeTo Avoid FiberCrushing inAl/B MMC

Welding Handbook, AWS

(Continuous Fiber)

Aluminum/Boron Continuous Fiber

Hersh, Resistance Spot Weld MMC,Welding Journal, June 1970

Aluminum/Boron Continuous Fiber

Hersh, Resistance Spot Weld MMC,Welding Journal, June 1970

Aluminum/Boron Continuous Fiber

Hersh, Resistance Spot Weld MMC,Welding Journal, June 1970

Aluminum/Boron Continuous Fiber

Hersh, Resistance Spot Weld MMC,Welding Journal, June 1970

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