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8/6/2019 Final Welding of Ti Alloys and Mg Alloys
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WELDING OF Ti & its alloys
and
WELDING OF Mg & its alloys
Submitted by:
Arjyajyoti Goswami
Shantilal Meena
Rachna Chawla
Submitted to:
Dr. Reeta Wattal
Department of MECHANICAL ENGINEERING
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WELDING OF
TITANIUM & its
ALLOYS
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CHARACTERISTICS OF TITANIUM & its
ALLOY
Silver colored material , which is 45% lighter than steel having
almost same mechanical properties as steel
Some alloys of Ti may have strength up to 925 to 1080 N/mm2
Ti alloys are difficult to machine having a pronounced tendency to
get welded on the tool tip
The higher melting point of Ti makes it relatively difficult to cast, sowelding is a important process in utilization of Ti and its alloys.
Due to its strong affinity towards O2 Ti forms a stable oxide layer
on its surface even at room temperature
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Ti alloys Classification
Classified on the basis of the microstructure, because mechanical
properties depends on the phase ratios in the microstructure.
1. Commercially pure Ti : having 98 99.5% Ti, strengthened by
small amounts of O2. C,N,Fe may be present
2. Alpha and near alpha alloys : single-phase alloys containingup to 7% aluminium and a small amount (< 0.3%) of oxygen,
nitrogen and carbon
3. Alpha-beta alloys : two-phase microstructure formed by the
addition of up to 6% Aluminium and varying amounts of betaforming constituents - V, Cr and Mo
4. Beta alloys : contains a high percentage of phase stabilising
elements, but are not truly single phase.
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WELDING OF Ti & ITS ALLOYS
COMMERCIALLY PURE TITANIUM :
Has moderate strength but good ductility. Main reason for using is
high corrosion resistance, formability and weldability.
Should use filler material with low iron content. They can be
readily fusion welded
All sources of iron contamination must be avoided.
ALPHA ALLOYS :
Has good strength, toughness and weldability. The alloys arefusion welded in the annealed condition.
Has higher strength at elevated temperatures than commercially
pure Ti, so residual stresses are high and suitable stress relieving
must be done
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NEAR ALPHA ALLOYS:
Excellent creep strength at elevated temperatures. Good
weldability but high residual stresses can be a problemStress relieving is highly recommended.
Iron contamination degrades creep strength so it should be
avoided
BETA ALLOYS:
Weldable either in annealed condition or heat treated condition
Weld joints have good ductility but relatively low strength
Few commonly used grades are Ti-13V-11Cr-3Al , Ti-8Mo-8V-3Al-
2Fe
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ALPHA-BETA ALLOYS:
These have a characteristic two-phase microstructure formed bythe addition of up to 6% Al varying amounts of beta forming
constituents - vanadium, chromium and molybdenum.
The alloys are readily welded in the annealed condition
Welding of such alloys may significantly change their strength,
ductility and toughness characteristics
Ti-6Al-4V has the best weldability in this group
Alpha-beta alloys having highly stabilized beta phase tends tocrack when welded under highly stressed conditions
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WELDABILITY RATINGRating is done on the basis of their ability to produce tough and
ductile welds in them
CLASSCLASS COMPOSITIONCOMPOSITION RATINGRATINGCOMMERCIALLY PURECOMMERCIALLY PURE
GRADEGRADE
Ti AA
ALPHA ALLOYSALPHA ALLOYS TiTi--5Al5Al--2.5Sn2.5Sn BB
TiTi--0.2Pd0.2Pd AA
NEAR ALPHA ALLOYSNEAR ALPHA ALLOYS TiTi--8Al8Al--11--MoMo--VV AA
TiTi--6Al6Al--4Zr4Zr--2Mo2Mo--2Sn2Sn BB
ALPHA BETA ALLOYSALPHA BETA ALLOYS TiTi--6Al6Al--4V4V--ELIELI AA
TiTi--6Al6Al--4V4V BB
TiTi--7Al7Al--4Mo4Mo CC
TiTi--8Mn8Mn DD
BETA ALLOYSBETA ALLOYS TiTi--13 V13 V-- 11Cr11Cr--3Al3Al BB
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WELDING PROCESSES EMPLOYED:
GTAW, GMAW, PAW, RESISTANCE WELDING, FRICTION
WELDING, EBW, LBW
STEPS INVOLVED IN ARCWELDING OF Ti
AND ITS ALLOYS:
1. JOINT DESIGN
2. PRE CLEANING
3. SELECTION OF PRE HEAT AND INTER PASS
TEMPERATURE
4. PROTECTION DURINGWELDING
5. WELDING PROCESS SELECTION
6. PWHT
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JOINT DESIGN:
Same as that of steels. Performs the usual functions.
A typical weld joint for Ti has 700 groove angle, 0.5 mm root face,up to 0.25 mm root opening for plate thickness of 3mm
PRE CLEANING:
Cleaning must be done with a suitable inorganic solvent to avoid
contamination.
Light oxide coating may be removed by aqueous solution of HF
acid or nitric acid.Scales formed at temperatures above 600C should be removed
by mechanical methods such as vapor blasting and grit blasting
To control porosity often the edges of the joints are given special
treatment like wire brushing
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PRE HEAT AND INTERPASS TEMPERATURE:
Should be less than 120C otherwise surface oxidation may take
place and the oxides will dissolve in the weld metal and cause
brittleness.
PROTECTION DURING JOINING:
Ti is very sensitive to embrittlement, so any part which is being
heated above 260C must be shielded from atmospheric
contamination, by the use of a high purity shielding gas
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WELDING PROCESS SELECTION: 3 most commonly used
processes.
GTAW-
Maybe done in open atmosphere or in a chamber. DCEN is often
used. Chamber welding yields better results.
GMAW-
Has higher deposition rates than GTAW, but more susceptible to
contamination since the temperature during metal transfer is
higher. Ti filler material is used
PAW-
Welding is done with a transferred arc using DCEN. Can be done
by melt-in technique or keyhole technique. The latter provides
better joint penetration
Has higher welding speeds and joint penetration
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PWHT:
Serves the usual purposes.
The minimum temperature range is 540C to 700C for short timeoperations
Selection of time and temperature depends on mechanical
properties required, since grain size changes may take place
during the PW
HT.Before the PWHT all the contaminants must be removed to avid
stress corrosion cracking.
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PROBLEMS ASSOCIATED WITHWELDING OF
Ti & ITS ALLOYS
POROSITY is the major problem associated with welding of Ti. Itmay be due to improper welding technique, improper surface
preparation, improper shielding
Amongst other sources, the sheared edges of the workpiece is a
source of contamination. The precaution to be taken is removeall the burrs, and shear the metal only a few hours before welding
CONTAMINATION CRACKING is caused due to presence of
contaminants in the weld region
To avoid it, welding of Ti should be done in a specially dedicated
chamber
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WEDLING OF Mg &WEDLING OF Mg &
ITS ALLOYSITS ALLOYS
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Magnesium & Its AlloysMagnesium & Its Alloys
Magnesium is a silvery white metal and has the lowestMagnesium is a silvery white metal and has the lowestdensity of the common structural materials.density of the common structural materials.
Very Light: 1738 kgmVery Light: 1738 kgm--33
Magnesium has a melting point of 650Magnesium has a melting point of 650C.C. Modulus low: E = 44.7 GPaModulus low: E = 44.7 GPa
Crystal structure is fccCrystal structure is fcc
Alloying is for precipitation hardening and (wroughtAlloying is for precipitation hardening and (wroughtalloys) grain refinement.alloys) grain refinement.
Excellent machining propertiesExcellent machining properties
Alloys are weldable (inert gas)Alloys are weldable (inert gas)
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Two main classes of alloys:Two main classes of alloys:
Impact strengths lowImpact strengths low
High damping capacity (useful in machine casings)High damping capacity (useful in machine casings) Corrosion resistance very poor. Can coatCorrosion resistance very poor. Can coat chromate,chromate,
anodise, epoxy resin.anodise, epoxy resin.
alloyed with elements such as Al, Zn, Mn, Zr, etc.alloyed with elements such as Al, Zn, Mn, Zr, etc.
Alloying increases strength and corrosion resistanceAlloying increases strength and corrosion resistance
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ALLOYING ADDITIONSALLOYING ADDITIONS
Alloying:Alloying:
up to 1.25% Mn or 3.5% Mg for solid solutionup to 1.25% Mn or 3.5% Mg for solid solution
strengthening,strengthening,
up to 4.5% Cu, 7% Zn or (3% Mg + 1% Si) forup to 4.5% Cu, 7% Zn or (3% Mg + 1% Si) for
precipitation hardening,precipitation hardening,
up to 0.5% Cr for grain refinement,up to 0.5% Cr for grain refinement,
up to 17% Si, 7% Cu, 10% Mg for castingup to 17% Si, 7% Cu, 10% Mg for castingalloysalloys
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Continue..Continue..
Al, Zn, ThAl, Zn, Th Produce precipitation hardening very complexProduce precipitation hardening very complex
series of metastable precipitates, depending on alloyseries of metastable precipitates, depending on alloy
compositioncomposition ThTh very stable precipitates, good for creep resistancevery stable precipitates, good for creep resistance
MnMn corrosion resistance (ties up Fe and othercorrosion resistance (ties up Fe and other
impurities)impurities)
ZrZr strong grain refinement, reacts with Al and Mn, Mgstrong grain refinement, reacts with Al and Mn, Mg--ZrZralloys must be Al, Mn free.alloys must be Al, Mn free.
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Magnesium alloys possessMagnesium alloys possess
High strength to weight ratioHigh strength to weight ratio
Good fatigue strength.Good fatigue strength.
Good dimensional stability in service.Good dimensional stability in service.
Good damping capacity.Good damping capacity. High thermal conductivity.High thermal conductivity.
Relatively high electrical conductivity.Relatively high electrical conductivity.
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Welding Characteristics of MagnesiumWelding Characteristics of Magnesium
Most magnesium alloys are readily weldable.Most magnesium alloys are readily weldable.
Weld strengths above 90% are possible when the fillerWeld strengths above 90% are possible when the fillermetal usedmetal used
The weldability of magnesium alloys may be affectedThe weldability of magnesium alloys may be affectedbyby ::
1. Oxidation.1. Oxidation.2. Thermal expansion.2. Thermal expansion.3. Susceptibility to hot cracking (hot shortness).3. Susceptibility to hot cracking (hot shortness).
4. Grain growth and aging effects4. Grain growth and aging effects
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Base Metal Surface PreparationBase Metal Surface Preparation
usually supplied with an oil coating, an acid pickledusually supplied with an oil coating, an acid pickled
surface or a chromate coated surfacesurface or a chromate coated surface
Mechanical cleaningMechanical cleaning
Chemical cleaningChemical cleaning This cleaning solution is kept in a tank made up ofThis cleaning solution is kept in a tank made up of
ceramic or stainless steelceramic or stainless steel
The job is dipped in the bath, which is kept at 22 to 32The job is dipped in the bath, which is kept at 22 to 32C,C,
for about 3 minutesfor about 3 minutes Then is rinsed thoroughly in hot water and dried in air.Then is rinsed thoroughly in hot water and dried in air.
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Welding ProcessesWelding Processes
The various processes employed for welding magnesiumThe various processes employed for welding magnesiumalloys arealloys are
1. Gas Tungsten ArcWelding (TIG or GTAW)1. Gas Tungsten ArcWelding (TIG or GTAW)2. Gas Metal ArcWelding (MIG or GMAW).2. Gas Metal ArcWelding (MIG or GMAW).
3. Resistance (Spot) Welding.3. Resistance (Spot) Welding.4. GasWelding.4. GasWelding.5. Forge welding.5. Forge welding.6. Other processes6. Other processes (PrWelding, Brazing, EB welding,(PrWelding, Brazing, EB welding,TIG spot welding, Stud Welding).TIG spot welding, Stud Welding).
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GTAW for Mg AlloysGTAW for Mg Alloys
Most popular process for welding Mg alloysMost popular process for welding Mg alloys
DC straight or reverse polarity and AC withDC straight or reverse polarity and AC with
superimposed are commonly used.superimposed are commonly used.
Both manual and automatic methods are suitable.Both manual and automatic methods are suitable. On materials over 4.5 mm thick, A.C. is preferred,On materials over 4.5 mm thick, A.C. is preferred,
because it provides deeper penetrationbecause it provides deeper penetration
DCRP is preferred since DCSP is difficult to handleDCRP is preferred since DCSP is difficult to handle
manually and its arc lacks cleaning actionmanually and its arc lacks cleaning action
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Welding techniqueWelding technique for GTAWfor GTAW::
(i)(i) Arc length maintained should be about 0.8 mmArc length maintained should be about 0.8 mm
(ii)(ii) Forehand welding is preferredForehand welding is preferred
(iii)(iii) Weaving should be used only for fillet welds or largeWeaving should be used only for fillet welds or large
corner jointscorner joints
(iv)(iv) Minimize the number of stops during welding. After aMinimize the number of stops during welding. After a
stop, the weld should be restarted on weld metal aboutstop, the weld should be restarted on weld metal about
12 mm from the end of the previous weld12 mm from the end of the previous weld
(v)(v) To prevent weld cracking :To prevent weld cracking :
-- Make use of starting and run off plates (or tabs) toMake use of starting and run off plates (or tabs) to
start and end the weldstart and end the weld
-- Weld from middle of the job towards the endsWeld from middle of the job towards the ends
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GMAW for Mg AlloysGMAW for Mg Alloys
welded using DCRP. Argon shielding is most satisfactory.welded using DCRP. Argon shielding is most satisfactory.
yields welding speeds 2 to 4 times faster than TIG welding.yields welding speeds 2 to 4 times faster than TIG welding.
Speeds range from 60 to 150 cm per minute and even higher.Speeds range from 60 to 150 cm per minute and even higher.
Increased welding speeds result in reduced distortion.Increased welding speeds result in reduced distortion. Involves high metal deposition ratesInvolves high metal deposition rates
limited to flat, horizontal and vertical down welding positions.limited to flat, horizontal and vertical down welding positions.
MIG welding are equal to TIG welds in strength andMIG welding are equal to TIG welds in strength and
soundness.soundness.
constant voltage power supply must be used with shortconstant voltage power supply must be used with short--
circuiting type metal transfercircuiting type metal transfer
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ResistanceWelding for Mg AlloysResistanceWelding for Mg Alloys
Either AC or DC used to join Mg alloys.Either AC or DC used to join Mg alloys.
Can be welded as spot, seam and flash welding.Can be welded as spot, seam and flash welding.
In Spot welding thicknesses up to about 4.5 mmIn Spot welding thicknesses up to about 4.5 mm
Spot weld penetration in Mg should not be less thanSpot weld penetration in Mg should not be less than20%, nor more than 80%, into each of the parts being20%, nor more than 80%, into each of the parts being
joinedjoined
To prevent corrosion, the spot welded joints should beTo prevent corrosion, the spot welded joints should be
wire brushed and chemically treatedwire brushed and chemically treated
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GasWelding for Mg AlloysGasWelding for Mg Alloys
Gas welding is generally restricted to pure Mg and toGas welding is generally restricted to pure Mg and toMnMn--Mg alloys, and limited to groove weldsMg alloys, and limited to groove welds
OxyOxy--acetylene, oxyacetylene, oxy--hydrogen and oxyhydrogen and oxy--carbon hydrogencarbon hydrogengases may be employed.gases may be employed.
OxyOxy--acetylene is preferred for welding heavier gauges.acetylene is preferred for welding heavier gauges.
The filler rod should be either of the same compositionThe filler rod should be either of the same compositionas the BM or have a lower melting point than BMas the BM or have a lower melting point than BM
Flux ( KCl, NaCl ) applications to both sides of theFlux ( KCl, NaCl ) applications to both sides of the
groove and on to the rod are importantgroove and on to the rod are important
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ForgeWelding for Mg AlloysForgeWelding for Mg Alloys
Developed to join high strength Mg alloys.Developed to join high strength Mg alloys.
Joint efficiencies as high as 95Joint efficiencies as high as 95--100% (Mg100% (Mg--AlAl--Zn)Zn)
Upset pressures of 35 tonnes with a total upset of 50Upset pressures of 35 tonnes with a total upset of 50
mmmm are used to weld 19 mm diameter rod.are used to weld 19 mm diameter rod. Heating and welding times of less than 30 seconds atHeating and welding times of less than 30 seconds at
temperatures between 280 to 316temperatures between 280 to 316C are used for MgC are used for Mg--3%3%
AlAl--l % Zn alloy.l % Zn alloy.
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PROBLEMS ASSOCIATED WITH WELDING OF MgAND ITS ALLOYS
SOLIDIFICATION CRACKING:Solidification cracking or hot cracking, consists offractures at the weld metal boundaries in the solidificationprocess, during which the liquid phase of the mushy meltbecomes rich in impurities, mainly S and P
This tendency is augmented by addition of Zn and Ca to Mgand its alloys
Al, Mn and Zr have little or no effect on this tendency whileThorium inhibits solidification cracking
The most high strength high alloying types of Mg alloys arethe most prone to such cracking
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STRESSCO
RROSIONCRAC
KING
:Al bearing Mg alloys are susceptible to such type of cracking.To avoid this, the weld must be heat treated to 250C torelieve the stresses.
Zr and Th inhibits this type of cracking tendency
During joining of Mg foils, through arc welding or resistance
welding, there is a risk of catching fire.So precautionsmust be taken to avoid any fatalities
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