2. Aluminum & Aluminum alloys
Aluminum :
Light in weight
Good ductility at subzero temperatures
High resistance to corrosion and not toxic
Good electrical and thermal conductivity
High reflectivity to both heat and light
Non-sparking and nonmagnetic
N.B. : Some of its alloys have strengths exceeding
mild steel.
3. Designations for Wrought Alloy Groups
Aluminum, 99.0% and greater 1XXX*
Major Alloying Element :
Copper 2XXX
Manganese 3XXX
Silicon 4XXX
Magnesium 5XXX
Magnesium and Silicon 6XXX
Zinc 7XXX
Other elements 8XXX
Unused series 9XXX
•For 1XXX series, the last two digits indicate the minimum
aluminum purity (e.g., 1060 is 99.60% Al minimum).
•The second digit in all groups indicates consecutive
modifications of an original alloy.
4. Series
Major
alloying
element
Non Heat treatable Heat treatable
1000 2000
3000 4000 5000 6000 7000
NONE Mn Si Mg Cu Mg/Si Zn
Elec
/thermal
conduct.
Forming
Ability
Filler
wires
ys
afer
welding
ys
ys
Extrusion
Ability
ys
Advan
tages
1100 3003 4043 5052 2219 6061 7075
E.G
DESIGNATION OF AL. ALLOYS
8. STRENGHTENING MECAHNISMS IN AL
Solid solution strengthening
Grain size control
Strain hardening (cold working)
Second Phase formation
Preipitation or age hardening
9. Strengthening of Non heat-treatable
Aluminum Alloys
• By solid-solution strengthening
• By dispersed phases
• By work hardening
Strengthening of heat-treatable Aluminum
Alloys
• Solution heat-treatment & quenching
followed by either natural or artificial aging
• Cold working for additional strength.
10. Aluminum alloys
Aluminium 1xxx series pure
aluminium
Work hardening
2xxx series ( Cu alloy ) Age hardening, high
strength
3xxx series ( Mn alloy ) Solution & work
hardening
5xxx series ( Mg alloy ) Solution & work
hardening
6xxx series (Mg-Si alloy) Age hardening, medium
strength
7xxx series ( Zn alloy ) Age hardening, high
strength
11. Heat-Treatable Al Alloys
• Alloy Designation
– 2xxx: Al-Cu (2014, 2219, 2090 (contains Li))
– 6xxx: Al-Mg-Si (6061, 6262)
– 7xxx: Al-Zn-Mg (7020, 7075 (contains Cu))
– 8xxx: “Other” alloying elements (Li (8090), Fe, Ni)
• Temper Designation
– O : Annealed
– T : Thermally treated (T1 – T10)
– T3 (ST + CW + NA)
– T4 ( ST + NA)
– T6 ( ST + AG)
– T7 (ST + overaged)
– T8 ( ST + CW + AG)
16. Heat-Treatable Al Alloys – Filler Selection
Base metal Filler wire
Al-Cu (2219, 2014,
2024)
(i) High Cu fillers (2319) (corrosion
problems)
(ii) Al-Si (4043, 4047) and Al-Si-Cu (4145)
Al-Mg-Si (6061) (i) Al-Si (4043) (dilution < 50%)
(ii) Al-Mg (5356) (dilution < 30%)
Al-Zn-Mg (No Cu)
(7005, 7020, 7039)
(i) Al-Mg (5356, 5183)
(ii) Al-Si
(iii) Al-Zn-Mg (less Zn, more Mg)
Al-Zn-Mg (with Cu)
(7075, 7178)
Al-Si and Al-Mg fillers
Avoid welding in critical applications
Considerations: Hot cracking, strength, and corrosion
Some compromise on joint efficiency unavoidable
17. Designation Description
-0 Annealed
-F As fabricated
-W Solution heat treated
-T1 Cooled from an elevated-temperature shaping
process and naturally aged
-T2 Cooled from an elevated-temperature shaping
process, cold worked, and naturally aged
-T3 Solution heat treated, cold worked, and naturally
aged
-T4 Solution heat treated and naturally aged
Basic Temper Designations Application to
Heat-Treatable Aluminium Alloys.
18. General consideration for Fusion Welding
• High thermal conductivity (as compared to
steel) necessitates a high rate of heat input
• Aluminium and its alloys rapidly developed
a tenacious refractory oxide film which
should be removed during welding
20. Welding processes for Aluminum and
Aluminum alloys
GTAW – Argon or Ar-He mixtures maybe used.
Back purging recommended to avoid porosity.
GMAW – Argon and Ar -He mixtures (used for
heavier sections )
Other processes - PAW, EBW, Laser and Friction
and resistance welding
23. Typical problem Alloy type Solutions
Solidification
cracking in
fusion zone
High strength alloys
2014, 6061, 7075
Use appropriate filler wires
Use arc oscillation or less susceptible
alloys (2019) In autogenous GTAW
process
Hot cracking
and low ductiity
in PMZ
High strength alloys
Use low heat input
Use proper filler wires
Low frequency arc oscillation
Softening in
HAZ
Work hardened
materials
Heat treatable alloys
Use low heat input
Post weld heat treating
Porosity
Al-Li alloys
Surface scraping or miling
Thermocauum treatment
Variable polarity key hole PAW
Powder
metallurgy
alloys
Thermo vacuuum treatment
Minimize powder oxidation and hydration
during atomization and consolidation
Other types
(less severe)
Clean workpeice and wire surface
Variable polarity key hole PAW
General ISSUES IN Fusion Welding
25. Grain Size Effect IN AL
Loss of strength is often observed in HAZ of Al
weldments due to grain growth during welding
Loss of strength may be observed in weld metal
which is as-cast structure with larger grain size than
parent metal.
In Al alloys strength loss due to grain size effect is
marginal.
Grain size affects hot cracking, smaller size being
more resistant to hot cracking.
Ti, Zr, Scandium may be used to promote fine
grain size.
These elements form dispersed solid particles in
the weld metal.
These particles act as nuclei on which grains form
during solidification
26. Solid solution Effect IN AL
The microstructure is featureless till the limit of solid
solubility is reached.
Up on reaching the limit a second phase becomes visible.
This phase may be secondary solid solution, intermetallic
compound or pure alloying element.
Introduction of second phase increases the strength and
hardness .
Iron carbide in steels Fe3C , Copper Aluminide (CuAl2)in Al-
cu alloys and Si in Al-Si alloys.
The most important Alloying elements are Si that increases
strength. Magnesium that improves strength and ductility and
Zinc in combination with Mg and cu will give increase
strength and will assist in regaining some of the strength lost
when welding.
30. Fig. 3 Effect of natural ageing on Al-Zn-Mg alloy welds
Since the weld metal and the entire HAZ thus respond to aging after
welding, the Al-Zn-M; alloys are considered more easily weldable than the
other types. Natural aging is also possible so that the welded joints regain
their properties by being simply left to age as shown in Fig.3. It is,
however, more common to use artificial aging.
31. Fig. Aluminum-rich portion of the copper-aluminum alloy
system. The alloy aluminium copper containing about 4.5%
copper response aged hardening or specification hardening.
Copper Aluminum alloy system
32. Age Hardening
• Solution treatment
– Heat to dissolve all the
coarse second phase
particles
– Rapidly cool to achieve
super saturation
• Aging treatment
– Heat and soak to form
precipitates with
desired morphology
Prior to ST After ST After Aging
Time
Hardness
Underaged Overaged
Peak aged
Typical aging curve
33. AL-CU SYSTEM
1- SOLUTION TREATMENT
2-QUENCHING THE SOLID SOLUTION
RAPIDLY TO ROOM TEMPERATURE
3-AGEING TO ALLOW THE
STRENGTHENING PRECIPITATE TO
PRECIPITATE FROM THE SUPER
SATURATED SOLID SOLUTION
4-AGEING BY HEATING (160C)
ARTIFICIAL AGEING AND AGEING
WITHOUT HEATING IS CALLED
NATURAL AGEING
34. The GP zones are coherent with the crystal
lattice of the solid solution
They consist of few atoms thick 4-6A and
about 80-100 A in dia formed on the [100]
planes of the solid solution
Since Cu atom is smaller by 11% the GP
zones are richer in Cu the crystal lattice is
strained around GP zones.
The strain field associated with GP zones
allow them to be detected in the electron
microscope.
The ” phase is also coherent with the
crystal lattice with its size 10 to 40 A and dia
100 t0 1000A.
The ’ phase is semi coherent. It is not
related to GP zones or ” phase .
The size of the ’ phase ranges from 100 to
150A and dia 1000 to 6000A. The figure
shows ’ phase in 2219. Finally the phase
is coherent with the crystal lattice
AL-CU SYSTEM
35. Age Hardening
• Conditions
– Sloping solvus
– Coherency strains
• Strengthening
depends on
– Coherency strains
– Precipitate Vol.%
– Size and
distribution
Al-Cu phase diagram
Strengthening precipitates in Al 2219
36. AL-CU SYSTEM
Max hardness occurs when the amount of GP2 (” phase ) is at maximum. As
grows the cocherent strain decrease and alloy becomes overaged. As it
gets further overaged the phase forms and the alloy is softened far
beyond max strength condition.
39. SOLIDIFICATION CRACKING IN AL ALLOYS
SOLIDIFICATION CRACKING:
Often seen at the solid –liquid interface near the FZ.
It occurs during the last step of solidification where the dendrites have
grown alomost fully in to grains.
The cellular dendrites are separated from each other by small amount of
liquid in the form of GB films.
At this moment the material is weak and susceptible to cracks due to
tensile strains or stress induced in the weld or if the metal is not free to
move due high restraint
41. Hot cracking in Non-Heat-Treatable Al Alloys
Base Filler
1xxx 1xxx (1100, 1188) and 4xxx (4043, 4047)
3xxx 1xxx, 3xxx, and 4xxx
4xxx 1xxx and 4xxx
5xxx
(Low Mg)
5xxx (5183, 5356, 5556) and 4xxx
Caution: Mg2Si formation
5xxx
(High Mg)
5xxx
Caution: Mg3Al2 network
Special considerations
Dissimilar welding or welding with dissimilar fillers: Dilution can result in a
susceptible weld composition
EBW or LBW: Loss of Mg can result in a susceptible weld composition
42. SOLIDIFICATION CRACKING IN AL ALLOYS
Occurs when high levels of thermal stress and
solidification shrinkage are present when the weld undergoes
various degrees of solidification.
A combination of mechanical, thermal and metallurgical
factors influence the hot cracking sensitivity of Al alloys.
By combining various alloying elements many high
performance heat treatable al alloys have been developed
with improved mechanical Properties.
In some cases the combination of the required alloying
elements has produced materials with high hot cracking
sensitivity.
43. Factors Influencing SOLIDIFICATION CRACKING:
Solidification temp range influences the formation
of micro- segregations.
The amount and distribution of liquid in the last
step of solidification which also influences
micro segregation.
The pirimary solidification phase.
The surface tension of the GB liquid.
The grain structure
The ductility of the solidifying weld material.
The tendency of the weld meateial contraction
and degree of restraint.
Welding at high speeds and high cooling rates.
SOLIDIFICATION CRACKING IN AL ALLOYS
44. SOLIDIFICATION CRACKING IN AL ALLOYS
COHERENCE RANGE:
The most important factor is the temperature range of
dendrite coherence and the type and amount of liquid
available during the freezing process.
Coherence occurs when the dendrites begin to inter-lock
with one another so that the melted material begins to form a
mushy range.
Coherence range is the temp difference between the
formation of coherent interlocking dendrites and the solidus
temperature.
Wider the coherence range the more likely hot cracking will
occur due to the accumulating strain of solidification
between the interlocking dendrites.
45. SOLIDIFICATION CRACKING IN AL ALLOYS
7XXX series ( Al-Zn):
Al-Zn-Mg alloys: [7005]
Resists hot cracking better than Al-Zn-Mg-Cu alloys (7075).
The Mg content in this group increases crack sensitivity.
But Zn which is added to refine the grain size reduces the
cracking tendency.
This welds easily with 5356 which ensures the wld contains
sufficient Mg to percent cracking.
The use of 4043 alloys with high silicon is not
recommended for this alloy as it can result in the formation of
brittle Mg2Si in the weld.
46. SOLIDIFICATION CRACKING IN AL ALLOYS
7XXX series ( Al-Zn-Mg-Cu):
Al-Zn-Mg-Cu alloys: [7075]
The small amounts of copper along with Mg extend the
coherence range and therefore increases the crack
sensitivity.
A similar situation arises with 2024 alloys.
The stress of solidification may cause cracking at the grain
boundaries and establish a the condition within the material
conducive to stress corrossion cracking later
47. SOLIDIFICATION CRACKING IN AL ALLOYS
2XXX series ( Al-Cu): [2219,2024]
The hot cracking sensitivity increase in Al-Cu alloys when
adding approx 3% of Cu. However it then decreases to a
relatively low level at 4.5%Cu and above.
Alloy 2219 with 6% Cu shows good resistance to hot
cracking because of its relatively narrow coherence range.
Alloy 2024 contains 4.5% Cu causing the perception of low
cracking sensitivity. The small amount of Mg in this alloy
depresses the solidus temperature but it does not affect the
coherence temperature and therefore the coherence range
extends increasing the hot cracking tendency.
Welding will allow segregation of the alloying elements at
the grain boundaries in 2024. Higher heat inputs repeated
weld passes and large weld sizes can increase the grain
boundary segregation problem and subsequent cracking
tendency.
48. SOLIDIFICATION CRACKING IN AL ALLOYS
The crack sensitivity substantially increases when welding
incompatible dissimilar base alloys ( which are normally
easily welded to themselves) and/or through the selection of
incompatible filler alloy.
By joining 2xxx series base alloy to a weldable 5xxx series
base alloy /or/ by using 5xxx series filler alloy to weld a 2xxx
series base alloy /or/ a 2xxx series filler alloy on a 5xxx series
base alloy, we can may create higher susceptibility to hot
cracking by increasing the coherence range.
If we mix high cu and high Mg during welding operation we
may increase the coherence range and therefore the crack
sensitivity.
49. AVOIDING CRACKING IN AL ALLOYS
The crack sensitivity curves
illustrates why Al welds crack
and how the choice of filler alloy
can affect crack sensitivity.
The curves reveal with the
addition of small amounts of
alloying elements the crack
sensitivity becomes severe and
reaches a max and then falls off
to a relatively low levels.
It can be seen that most of the
Al base alloys considered
unweldable autogenously have
chemistries at or near the peaks
of crack sensitivity.
The figures also show alloys
that have low cracking
characteristics that have
chemistries away from the crack
sensitivity peaks.
It is clear that crack sensitivity of an
al base alloy is primarily dependent
on chemistry.
50. AVOIDING CRACKING IN AL ALLOYS
It can be concluded that
crack sensitivity of an Al
alloy weld which is
comprised of base alloy
and filler alloy is also
dependent on chemistry.
When welding base
alloys tht have low crack
sensitivity always use a
filler alloy of similar
chemistry.
When welding more commonly used 5xxx series (Al-Mg)
and 6xxx series (Al-Mg-Si) alloys these principles are clearly
illustrated.
When welding base alloys that have high crack sensitivity
use filler alloy with a different chemistry than base alloy to
create a weld metal that has low crack sensitivity.
56. Cracking
• In general the non-heat treatable aluminum alloys can be
welded with a filler metal of the same basic composition as
the base alloy.
• The heat-treatable alloys which are most sensible to ‘hot
short’ cracking during welding.
• A dissimilar filler metal having a lower melting temperature
and similar or lower strength than the base metal is used.
57. Filler Metal Selection
• Freedom from cracks
• Tensile strength of the weld metal
• Weld ductility
• Service temperature
• Corrosion resistance
• Colour match after anodizing
68. Fig. Solubility of Hydrogen in liquid metals.
Note : Aluminium has a very low solubility for hydrogen at the
freezing point but a substantial solubility at higher
temperature.
Thus hydrogen is prime cause of porosity in aluminium
welds.
