CWB Welding Inspector Level 3 Exam Prep (Latest 2023/ 2024 Update) Questions and Verified Answers| All Modules Covered| 100% Correct| Grade A
CWB Welding Inspector Level 3 Exam Prep
(Latest 2023/ 2024 Update) Questions and
Verified Answers| All Modules Covered|
100% Correct| Grade A
Q: Fluxes that can dissolve the oxides on Al are …………
Answer:
Halide compounds ( Fluorine, chlorine, Bromine etc.)
Q: Chlorine gas from a Chloride flux in presence of an arc can create poisonous gas called
……….
Answer:
Phosgene (COCL2) or Mustard gas produced by the reaction of chlorine and carbon monoxide in
the presence of intense light
Q: Why are Chlorine fluxes removed completely from the weld region?
Answer:
bcz its hygroscopic. The part will be susceptible for corrosion
Q: What is the drawback of the SMAW welding of Al with Chlorine coated electrodes?
Answer:
- Cause Lack of Fusion
- electrodes restricted to Al – Si, Al-Mg-Si and Al- Mg-Si-Cu alloys welding only
- It cannot be applied to a high magnesium-containing alloy such as AA5083.
Q: At what temp does Al melts?
Answer:
660 C
Q: At what temp does Al oxides melts ?
Answer:
2072 C
Q: True / False?
Fluxes are not a viable route to remove the oxides on the surface during welding
Answer:
True
Q: The thermal conductivity of Al is ……… times that of steel
Answer:
4
Q: True / False?
Among Al alloys ,the thermal conductivity can vary by a factor of two and has a pronounced
effect on the welding parameters.
Answer:
True,
Alloying or impurity elements such as titanium , Lithium , magnanese and magnesium can lower
the thermal conductivity
Q: The melting point of the oxides on the Al surface is ……. times greater than the melting point
of the metal
Answer:
3
Q: True / False?
For Al, for the same welding energy input, weld penetration varies by the ratio of the thermal
conductivity of 6061 T6 (167 W/mK) to that of AA-5083-O (117W/mK), which is 1.43
Answer:
True
Q: For the same heat input, AA-5083 will have a …………….. penetration weld than 6061 T6
Answer:
deeper
Q: True / False
3D thermal flow does not extracts more heat necessitating more heat input to get a comparable
weld depth for the two-dimensional heat flow condition
Answer:
False , It does extracts more heat
Q: Which welding processes are not effective on Aluminum ?
Answer:
SMAW, GMAW – Globular or Short circuit… more likely to get inadequate penetration and
excessive weld reinforcement defects
Q: How electrical conductivity varies with Al alloys?
Answer:
by around 50 %
Q: Coefficient of thermal expansion for Al is about _ that of Steel
Answer:
twice.. means for the same temp rise the dimensional change of the Al will be twice that of steel.
Distortion is higher than steel. Also the bright reflective surface of the bare Al causes distortion
to be more visible than is the case with steel.
Q: Distortion is an issue bcs it can :-
Answer:
- Have a deterious effect on the subsequent fit-up of the part to the final assembly.
- Cause the welded component to have an unacceptable appearance
- Cause an un acceptable cosmetic appearance to the finished part.
- Cause the joint line to move.
Q: True / False?
The lower modulus of Al wire means that the wire will buckle more readily than a steel wire
when it is contact with the liner and consequently increases the friction drag forces that inhibit
uniform wire feeding
Answer:
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What is the cause for weld bead cracking in Al ?
Hot shortness of Al
What are the properties of Al ?
- low density
- Corrosion resistance
- High electrical resistance
- High thermal conductivity
- good appearance
- toughness at low temps
True / False ?
Al is covered with a coherent oxide.
True
Thermal conductivity of Al is _ times that of Steel
4
Melting point of Al is about _ of Steel
half
Coefficient of thermal expansion for Al is about _ that of Steel
twice
Modulus of elasticity (stiffness) for Al is about _ that of Steel
one-third
True / False
“Nitrogen is not inert to Al and is not used for sheilding”
True
What is responsible for Al’s excellent corrosion resistance?
Al oxide but it changes to Magnesium oxide (MgO) or Magnesium spinel ( Mg Al2O4) when the Mg % exceeds 0.05%.
What is the thickness of Al oxide on the surface of Al ?
50-150 angstroms
True/ False ?
The form of magnesium oxide is a function of the magnesium concentration and the thermal history of the alloy
True
True / False ?
The oxide transformation from aluminum oxide to magnesium oxide or magnesium spinel ,has a profound effect on the solid -state bonding b/w any clad and the Al base
True
The solid -state bonding b/w Al and another metal or another Aluminum alloy generally requires a control of the magnesium level to __ %
Less than 0.05%
Why does Mg has the profound influence on the oxide found on Al?
- Mg has a greater affinity than Al for O2.
- Mg behaves as a surface-active element in Al, that is, it tends to diffuse readily to the surface of the metal.
The oxidation rate of Mg containing alloys is _ than for Mg free alloys.
greater
Why is oxide thickness on an Mg- Al alloy surface thicker than one on a Mg free alloy for the same thermal / mechanical history?
The oxidation rate of Mg containing alloys is greater than for Mg free alloys.
Which is the element which reacts with Mg oxide to form its oxides on the Al surface?
Lithium
Which is the surface oxide for lithium bearing Al alloys?
Lithium oxide / spinel
True / False ?
When the Al oxide is transformed to lithium oxide or spinal, then the coherency between the oxide and the metal substrate may change. Instead of the oxide being tenacious it may be a porous scale layer that does not protect the parent metal or that can readily trap moisture or any other air borne contaminant.
True
True / False ?
Oxide is scrapped off the metal prior to welding Al-Li alloys to minimize the weld porosity
True
True / False?
After mechanical milling or chemical treatment for oxide removal prior to welding, the surface will almost instantly re-oxidize in dry air.
True
True / False
Oxide removal prior to welding, the surface will form local electrolytic cells between dry and wet sections and the wet part will corrode preferentially, forming a stain.
True
True / False
Al loses strength with welding
True
Fluxes that can dissolve the oxides on Al are …………
Halide compounds ( Fluorine, chlorine, Bromine etc.)
Chlorine gas from a Chloride flux in presence of an arc can create poisonous gas called ……….
Phosgene (COCL2) or Mustard gas produced by the reaction of chlorine and carbon monoxide in the presence of intense light
Why are Chlorine fluxes removed completely from the weld region?
bcz its hygroscopic. The part will be susceptible for corrosion
What is the drawback of the SMAW welding of Al with Chlorine coated electrodes?
- Cause Lack of Fusion
- electrodes restricted to Al – Si, Al-Mg-Si and Al- Mg-Si-Cu alloys welding only
- It cannot be applied to a high magnesium-containing alloy such as AA5083.
At what temp does Al melts?
660 C
At what temp does Al oxides melts ?
2072 C
True / False?
Fluxes are not a viable route to remove the oxides on the surface during welding
True
The thermal conductivity of Al is ……… times that of steel
4
True / False?
Among Al alloys ,the thermal conductivity can vary by a factor of two and has a pronounced effect on the welding parameters.
True,
Alloying or impurity elements such as titanium , Lithium , magnanese and magnesium can lower the thermal conductivity
The melting point of the oxides on the Al surface is ……. times greater than the melting point of the metal
3
True / False?
For Al, for the same welding energy input, weld penetration varies by the ratio of the thermal conductivity of 6061 T6 (167 W/mK) to that of AA-5083-O (117W/mK), which is 1.43
True
For the same heat input, AA-5083 will have a …………….. penetration weld than 6061 T6
deeper
True / False
3D thermal flow does not extracts more heat necessitating more heat input to get a comparable weld depth for the two-dimensional heat flow condition
False , It does extracts more heat
Which welding processes are not effective on Aluminum ?
SMAW, GMAW – Globular or Short circuit… more likely to get inadequate penetration and excessive weld reinforcement defects
How electrical conductivity varies with Al alloys?
by around 50 %
Coefficient of thermal expansion for Al is about _ that of Steel
twice.. means for the same temp rise the dimensional change of the Al will be twice that of steel. Distortion is higher than steel. Also the bright reflective surface of the bare Al causes distortion to be more visible than is the case with steel.
Distortion is an issue bcs it can :-
- Have a deterious effect on the subsequent fit-up of the part to the final assembly.
- Cause the welded component to have an unacceptable appearance
- Cause an un acceptable cosmetic appearance to the finished part.
- Cause the joint line to move.
True / False?
The lower modulus of Al wire means that the wire will buckle more readily than a steel wire when it is contact with the liner and consequently increases the friction drag forces that inhibit uniform wire feeding
True
True / False
Al changes color like steel as its temp is raised.
False.
Al does not change color like steel as its temp is raised; in the case of steel the color change is an early indicator that the melting point is being approached
Is arc blow a problem in Al welding?
No
What are the safety problems related to the high reflectivity of Al during welding?
The intense arc light can reflect the Al surface and beam up under the welding helmet to the welder’s neck or chest. If these body parts are exposed, then the welder can suffer skin burns. For safety reasons, the welder’s neck and chest should be covered at all times.
What are the process problems related to the high reflectivity of Al during welding?
The high reflectivity of bare Al tends to enhance the effect of thermal or mechanical distortion of fabricated components. Comparing steel and Al sheets, even though they have the same distortion, Al distortion will appear worse bcz of its greater reflectivity.
What is the ore source for Al?
Bauxite
Is Bauxite classified as a mineral ?
No, bcz it is an admixture of Al hydroxide compounds with an aluminum oxide content in the range of 45%-60% that also contains an appreciable amount of iron.
What are the naturally occurring impurities in Bauxite?
3% – 25% iron-oxide,
2.5% – 18% silicon oxide,
2% – 5% – titanium oxide
What is the name of the primary refining process of Bauxite?
Bayer process
Produces commercially pure alumina by leaching bauxite with concentrated sodium hydroxide; this alumina is the feedstock to the reduction cell.
What is the Hall-Heroult process?
The reduction of alumina to aluminum (primary aluminum) in a smelter cell after Bayer process, using large amount of electricity (50,000 – 150,000 amps)
Which element comprises the lion’s share of the alloy elements added in Al?
Magnesium
What are the “master alloys” in Al ?
Silicon, Iron , Chromium or Manganese
What is called secondary al ?
The product of recycling process stream
How is impurities in mixed Al scrap reduced?
By adding pure Al to the melt
Most Al is casted into ingots by ……………….. process
direct-chill (DC) process
What are the forms of ingots produced by DC process ?
large sheets, round log-like, square and T
What represents “T” in T ingot ?
“T” to facilitate its handling by forklift trucks
True / False?
During DC casting, the solidifying metal is under tensile stress and the magnitude of the stress increases as the casting speed increases
True
At critical stress levels, Al alloys will be prone to …
Hot short cracking .. Occurs when Al alloys are partially solidified
What are the grain refiners added to overcome the hot short cracking tendency of the ingots??
Ti, Titanium Carbide (TiC), and Titanium diboride(Tib2)
Which is the most stable among the grain refiners in Al ?
Titanium diboride(TiB2), will not dissolve in molten Al at as low a temperature as the other two agents { ( Ti and Titanium Carbide (TiC) } . Remain effective during welding
What is the drawback for using Titanium diboride in furnace as a grain refiner?
it forms large clusters at the bottom of the furnace which will act as hard inclusions.
What are the temperatures and holding/soak time for homogenization of DC extrusion ingots prior to delivery to the extrusion plant?
530 C to 590 C for a 6-8 hour soak
What are the metallurgical purposes of Homogenization?
- Increased extrusion speeds
- extrusions with superior surface finish
- stronger extrusions
What are the two ways that welded structures like hollow tube sections are extruded?
Either through porthole die or by a die and mandrel process
How is seamless extruded tubes made by?
Die and mandrel technique
What are the 5 categories of Al products?
- Plate
- Sheet and coil
- Rod, bar, and wire
- Pipe and tubing
- Extruded shapes
What are the two groups of Al alloys?
Wrought and casting alloys
How is Al alloys designated?
by Aluminum Assiciation’s (AA) alloy and temper designation systems are used
What happens when an Al alloy is pounded with hammer?
Its strength increases (Work hardening or strain hardening)
What happens when an Al alloy is heated up and then rapidly cooled ?
Its strength increases (Heat treating)
How are strengthening mechanisms divide Wrought Al Alloys?
- Non-heat treatable / work hardening alloys ( 1XXX, 3XXX, 4XXX and 5XXX alloy series)
- Heat treatable alloys (2XXX, 6XXX, 7XXX)
What is the major alloying element of AA 1XXX alloy series?
99.00 % Al and greater (Pure aluminum series)
What is the major alloying element of AA 2XXX alloy series?
Copper
What is the major alloying element of AA 3XXX alloy series?
Manganese
What is the major alloying element of AA 4XXX alloy series?
Silicon
What is the major alloying element of AA 5XXX alloy series?
Magnesium
What is the major alloying element of AA 6XXX alloy series?
Magnesium and Silicon
What is the major alloying element of AA 7XXX alloy series?
Zinc
What are the key characteristics of 1XXX series ?
Excellent electrical conductivity and corrosion resistance
True / False ?
In the work-hardened state, alloy AA-1350 is excellent for overhead Al overhead electrical cables
True
What are the characteristics of 2XXX series Al?
- Heat treatable
- Contains copper that imparts very high strength and machinability to the alloys, though with some loss of corrosion resistance
What is the principle alloying addition for 3XXX series?
Manganese .. it imparts greater strength to Al while maintaining excellent ductility or foamability
What is the application for AA3304 and AA3014 ?
Best used for beverage cans
Where is AA 4XXX series used for ?
For welding and brazing filler alloys
What is the principle alloying addition for 4XXX series?
Silicon, lowers the melting point of the alloys making them suitable for brazing
What is the principle alloying addition for 5XXX series?
Magnesium… Work hardening alloys… Alloys with less than 3% Mg have good corrosion resistance whereas alloys having more than 3% Mg can be susceptible for exfoliation and stress corrosion
What is the principle alloying addition for 6XXX series?
Mg and Si
Where is AA 6XXX series used for ?
Fabrication of general structures (extrusions welded to the dump body truck sides as stiffeners) and in rolled form for automotive outer panels
What is the alloying addition for 7XXX series?
- Zinc and Magnesium for high strength
- Cu is also added for high strength but alloys are susceptible for stress corrosion cracking. High Cu content deems the alloy unweldable
What is the application for 7XXX series?
- Used for aircraft structures where the product can be clad to prevent corrosion or the components are continually inspected for signs of stress corrosion cracking.
- AA 7004 & AA 7005 are used for welded ground transportation vehicles
What does the last 2 digits of AA 1050 indicates?
99.50 % min Al
What does the last 2 digits of AA 1065 indicates?
99.65 % min Al
Which are the non-heat treatable alloys?
1XXX,3XXX,4XXX & 5XXX
How does the non-heat treatable alloys reach full potential of their strength?
By work hardening. (cold rolling or drawing)
How is the final temper obtained in the non-heat treatable alloys ?
Work hardening alone, work hardening followed by partial annealing or work hardening followed by stabilizing
What is stabilizing treatment after work hardening of the non-heat treatable alloys ?
thermal treatment ,at low temperature that may be given to alloys such as AA-5052 and AA-5454 that otherwise would tend to “age-soften” after production. The stabilization treatment usually improves ductility.
How does the letter “H” specification (1st digit) of work hardening/ tempering applies to the non-heat treatable alloys ?
H1 – The material has been work-hardened
H2 – The material has been work-hardened and partially annealed
H3 – The material has been work-hardened and Stabilized
How does the 2nd digit applies to the non-heat treatable alloys ?
0-8
denotes the degree of work hardening.
8 – tempers having a UTS eqv to that achieved by a cold reduction of approx 75% of the metal from its softest stage.
0 is Fully annealed – the softest temper
F – As fabricated
True / False
Materials having the F temper should not be used for structural welding
True
What is the annealing temp for 1XXX & 5XXX series ?
345 C
What are the thermal processes which increase the strength of heat-treatable alloys?
Solution heat treatment and aging
What is the aging temp and solution treatment emp for 2024 ?
aging temp = 160 C
solution treatment temp = 500 C
What is the aging temp and solution treatment emp for 6061 ?
aging temp = 175 C
solution treatment temp = 530 C
What is the aging temp and solution treatment emp for 6063 ?
aging temp = 175 C
solution treatment temp = 520 C
What is the annealing temp for 2024,6061 and 6063 ?
415 C
What is the annealing temp for 7005 ?
345 C- 400 C
How is Solution heat-treatment done for heat treatable Al alloys?
by heating the alloy to a temp below the melting point for a specific period of time and rapidly cooling from this temp.
Eg -For AA-6061, the solution heat treatment temp is 530 C
How is aging done for heat-treatable Al alloys?
relatively low temp heat treatment that results in additional hardening of the solution heat-treated material.
Eg – For AA6061 it is 170C
The aging process strengthens these alloys by the precipitation of constituents that are too fine to observe with an optical microscope.
What is the pre requisite for aging?
alloying constituents are in a solid solution as a result of rapid cooling from the solution heat treatment temp.
What is over-aging?
The precipitated constituents have a stress field around them to accommodate the precipitates in the solid phase. This accommodation of a solid particle in a solid matrix accounts for the strengthening by aging.
If aging is conducted for an excessive amount of time, or at an excessive temperature then the precipitates no longer have the stress field about them and there is a loss of strength. that can range from little to a great deal. This process is called over-aging
What are naturally aged alloys?
Heat treatable alloys ,such as alloy AA-7005, age at the room temp. These are called naturally aged alloys.
Does age strengthening of AA-7004 & AA-7005 require rapid cooling/water quenching to retain constituents in the solid solution?
No
True / False?
Water quenching does not causes distortion of the extrusions
False
How is heat temper designation given for heat treatable alloys?
by the prefix letter “T” followed up by four number.
The first and second numbers indicate the basic sequence of the operations that has been carried out.
What is the major alloying element in cast alloy 1xx.x ?
99.00 % min Al and greater
What is the major alloying element in cast alloy 2xx.x ?
Cu
What is the major alloying element in cast alloy 3xx.x ?
Silicon, with added Cu and/or magneisum
What is the major alloying element in cast alloy 4xx.x ?
Silicon
What is the major alloying element in cast alloy 5xx.x?
Magnesium
What is the major alloying element in cast alloy 7xx.x ?
Zinc
What is the major alloying element in cast alloy 8xx.x ?
Tin
What does the alloy name AA-150.0 indicates?
unalloyed Al casting having Al purity of 99.50%
What does first and second digits in 2xx.x to 9xx.x indicates?
The first digit indicates the Al alloy group. The second two digits only serve to identigy different alloys in the group.
What does the fourth digit in 2xx.x to 9xx.x indicates?
The fourth digit, which is separated from the first three by a decimal point, identifies the product form, ie, casting or ingot.
A zero in the fourth place , xxx.o ,refers to the final casting; and a 1 or 2 in the fourth place , xxx.1 or xxx.2 refers to ingot.
True / False ?
It is highly unlikely that casting would be work-hardened to achieve a final shape. Therefore the “H” temper designation is not applied to castings.
True
True / False ?
Heat treatments increases the strength ,hardness, toughness and impact resistance of castings. The same processing terms that applied to the heat-treatable wrought alloys also apply to the heat-treatable castings
True
How is strengthening done for heat treatable casting alloys?
For max strength, the castings have first to be solution heat treated to place the soluble constituents into the solution and then the casting has to be cooled rapidly from that elevated temperature.
The cooling techniques include forced air and boiling water immersion. Less severe quenching practices are followed to minimize distortion.
True / false?
Distortion of castings is a concern during heat treatment of casting Al alloys.
True.
Distortion of castings is a concern during heat treatment of casting Al alloys since distorted parts require rectification to ensure dimensional compliance to drawings.
Ductility of Al casting is very low in ………………. castings
Sand
True / False?
The amount of rectification (ie, cold working) to compensate for distortion has to be minimalized to avoid fracture that would otherwise occur when the ductility was exceeded.
True
What is the solution heat-treatment temps employed for cast Al alloys?
432 C to 540 C depending upon the alloy
What is the temp to anneal castings to 0 temper ?
heat treated to 316 C – 343 C.
What are the heat-treatable cast Al alloys?
2xx.0, 3xx.0, 5xx.0 and 7xx.0 series
What is “F” temper for castings?
As cast, cooled naturally form the mould in room temp air.
no further heat treatment done
What is “0” temper for castings?
Annealed
Most dimensionally stable condition, softest and most ductile
What is “T4” temper for castings?
Solution heat treated and naturally aged to substantially stable condition
Mechanical properties and stability may change over a long period of time bcz aging will continue for a considerable period of time.
What is “T5” temper for castings?
Naturally cooled from the mould and then artificially aged
Attains improved mechanical properties and dimensional stability
What is “T6” temper for castings?
Solution heat treated and artificially aged
Attains optimum mechanical properties and generally good dimensional stability
What is “T7” temper for castings?
Solution heat treated and overaged
Improved dimensional stability, but usually with some reduction from the optimum mechanical properties
What are the different casting methods employed for cast Al alloys?
- Die casting
- Permanent mould casting
- Sand casting
Describe die casting of casting Al alloys?
molten Al alloy forced into a steel mould under pressure
produces near-net-shape
economical process for high volume production and is tolerant of lower purity Al alloys.
recycled (secondary) Al can be the feed stock
Describe permanent casting
moulds and cores are made of steel
Al fed into the mould by gravity, vacuum or pressure
moulds represent substantial investment and therefore relatively high volume production is required
Describe sand casting
any pattern can be pressed from sand to form a mould
sand extracts heat more slowly than metal moulds
Productivity is not as great as with the other two processes
used for low production runs
True / False
With respect to structural uses of castings, the mechanical properties of the rapidly solidified permanent mould casting are higher than the strength values of comparable sand castings.
True
Properties of castings are a function of :-
- Solidification rate
- Quality ( porosity and inclusions)
- chemical composition or alloying components
True / False
Weld beads are also cast structures and weld bead strengths will be a function of the same parameters as the castings { solidification rate (welding speed), quality and composition }
True
What is the spacing of the constituents of a Al weld ?
10 microns
What is the size of a grain in Al casting / weld ?
25 microns or greater
True / False
Poorest casting to fusion weld is an injection die casting
True.
this is due to the large amount of entrained gas and lubricant in this pressure casting that is liberated by fusion welding.
The oxide on the cast surface will be _ than on a wrought product
thicker, it is important that the casting surface is wire brushed thoroughly prior to welding
What is the min scrape depth for sand castings prior to welding?
1.5 mm.
In the case of sand castings, it is likely that the surface will have entrained sand particles.
what is the max amount of “other elements” in wrought and cast Al alloys?
0.05 %
What is the total content of “other elements” in wrought and cast Al alloys?
0.15 %
Is a certificate of analysis of Al alloys represent the actual analysis of heat or lot of metal received?
No, It represents the limits of the composition of the alloy designation and is not an actual analysis of heat or lot of metals received.
When is the actual analysis of heat required ?
if problems in fabrication , joining or performance arise.
Actual analysis of heat is required for Weldments which are expected to require high-service performance
Is weave welding allowed in Aluminum?
No,
C/S area withstanding the shrinkage strain is reduced when a weave pattern weld is applied which will result in weld bead cracking
True / False
During Al welding the cross -sectional area withstanding the shrinkage strain is reduced when a weave pattern weld is applied or a weld termination is made without a “crater fill”
True
True / False
GMA welding equipment with crater fill capability is recommended to avoid getting a small C/S area to withstand the shrinkage strain, thus avoiding weld bead cracking
True
Hoe does the use of filler alloys avoids cracking?
Use GMAW and GTAW process.
Filler alloys like AA 5356 has the potential to move the weld bead composition of an AA-5052 joint to a less crack-sensitive region by increasing the magnesium in the weld pool
What happens where when the filler alloy barely fuses to the walls of the parent metal without any penetration occurring ?
Weld bead composition will be at its max crack-resistance composition
What happens when AA 5353 filler alloy mixes with an equal or greater amount of parent AA 5052 ?
Then the chemistry can only be altered very little from the composition of AA-5052 and it follows that the crack resistance of the weld bead will be enhances only by a small amount.
The greater the parent metal dilution, the ……….. effective the filler alloy addition for the composition adjustment to avoid weld bead crack
less
What is % parent metal dilution in the case of a zero root opening butt joint?
85 % , moving the elements of interest in the crack sensitive curves a very small amount
What is % parent metal dilution for a butt joint with V groove ?
Dilution of parent metal will have much less effect and the weld bead composition will be moved significantly out of the crack sensitive region.
What is the dilution for T-joint fillet welds ?
10 %, the weld bead composition will approach the filler alloy composition.
To allow a filler alloy to minimize cracking, the actual weld bead composition should be as close to the filler alloy composition as possible.
Why is for high temp applications, the Mg is kept below 3% ?
To avoid exfoliation corrosion and stress corrosion cracking
Which is the highest strength structural alloy ?
AA-2219
Which is the highest welded strength alloy ?
AA-7005
True/False
The welded strength of medium to high Mg bearing alloys of the non-heat treatable alloys have higher strengths than the heat-treatable alloys
Treu
What is the allowed limit for Be (Beryllium) ?
3 ppm max , Be is controlled to a low level bcz in welding fume it can pose a health hazard to welders
The cracking of Al is primarily due to …………….. of the alloy
Hot shortness
What is hot shortness?
Chara of a metal that results in complete loss of plasticity while alloy is between the liquidus and solidus temps.
What are the two criteria for a weld to become weld crack?
- The alloy composition is in the range that during solidification nucleated grains have been surrounded by liquid phase
- A tensile stress has to be applied to the solidifying weld bead to cause the separation of regions that have been largely solidified.
How is stresses generated in welding ?
Stresses are generated by the dimensional changes caused by the differential expansion and contraction of the weld region during the weld’s heating and cooling cycles.
Since this tensile stress exists during welding, then cracking occurs with alloy systems that are prone to cracking unless it is possible to apply a compressive stress on the solidifying weld bead.
True / False
The rate of applied strain increases so does the probability of cracking
True
How is cracking related to mechanical forces i weld metal?
Cracking occurs when the material’s ability to resist cracking, by supplying liquid metal to the regions that otherwise would separate , is exceeded by the mechanical forces towards cracking.. ie the strain rate
True / False,
” One critical factor to avoid weld bead cracking is that the solidifying metal must be able to with stand the tensile strain causes by thermal distortion. One methos for structures to withstand strain is to increase their cross sectional area normal to the strain direction “
True
True / False
During Al welding the C/S area withstanding the shrinkage strain is reduced when a weave pattern weld is applied or a weld termination is amde without crater fill.
True.
Weave welding is not recommended for Al welding.
GMA welding equipment with crater fill capability is recommended to avoid getting a small C/S area to withstand shrinkage strain.
True / False
The degree of difficulty to weld an alloy free of cracks is related to the degree of difficulty to cast the alloy crack-free either as a DC ingot or a shape casting
True.
The peak crack sensitivity of Al-Mg2Si system is about __ %
1 %
How is addition of Silicon influences Aluminum ?
Increases Al’s fluidity making the alloy ideal for casting where it can completely fill any intricate mould cavity.
This high fluidity also causes the Al-Si filler alloy to wet out on the parent metal surface leaving a low weld reinforcement angle.
What is reinforcement angle?
Angle between the weld bead and the plate of the welded specimen.
Low reinforcement angle will also improve the fatigue performance of a weld.
True / False
1XXX series filler alloys, eg AA-1100 and AA-1188 has a tendency to form “wormhole” defects.
True..
They have a very limited solidification temperature range. This means that they will solidify quickly and not fill any cavity completely. This leads to a tendency to form “wormholes”. Therefore, if possible, welders will select a 4XXX filler alloy to avoid wormholes.
Which filler alloy is appropriate for dynamic loading applications ?
Al-Si filler alloys
Which filler alloy is used for heat treatable Al and why is it used?
AA-4643 is used when PWHT is required.
Heat treatable Al alloys gains their strength by thermal treatment (resolution heat-treated, quenched and then aged) . However this may cause the parent metal to overmatch the strength of the weld bead if AA-4043 filler alloy was used. Use of AA-4643 ensures that there is the potential to have Mg2Si precipitation in the weld bead . The Mg2Si will go into solution during heat-treatment and then be precipitated by artificial aging to strengthen the weld.
What is Smut formation of weld region?
Magnesium vapor deposit (Mg oxide or Mg spinel) which runs as two symmetrical black ands along the weld bead.
Can be easily wiped off immediately following welding.
Smut is a cost factor if the fabricated product is expected to have cosmetic appeal.
Magnesium free filler alloy will be selected to avoid smut.
Which filler wire is used for GMAW when wire feeding is an issue?
AA-5356
where is AA-5454 used?
The plate alloy AA-5454 (Max Mg = 3%) was developed for applications involving the storage or transportation of chemicals at temp exceeding 65C.
What happens if an Al alloy that has more than 3% Mg and it is exposed to temps between 120 C and 205 C?
It becomes susceptible to stress corrosion cracking
To avoid stress corrosion cracking. the filler alloy used for elevated temp application is …………..
AA-5554, which has 3% max Mg.
Which welding process generates the greatest amount of smoke?
GMAW with 5XXX filler alloys
What happens when Mg free filler alloys are used ?
Much less smoke but much more ozone (O3) is generated with both GMAW and GTAW.
Ozone generated most during GMAW with Mg-free 443 or AA-1100.
How is ozone produced?
The electrical arc and an ultraviolet photochemical reaction form Ozone(O3).
Ozone is a …………. irritant
respiratory
Why is less ozone generated while using AC GTA welding with Mg- free alloys?
bcz there is more nitric oxide generated that will in turn convert much of the ozone that forms to nitrogen dioxide and oxygen.
Which filler alloy would you use when strong consideration is given to avoid ozone generation ?
AA 5356 rather than AA 4043
What are the problems with 1XXX filler alloys?
- Poor GMAW wire feedability
- Tendency to form wormholes due to poor fluidity
- Ozone fume generation
How is the filler wire manufacturers ensure less friction resistance for filler wires in GMAW ?
By shaving / scraping of 15% of the wire C/S area to remove fines and surface drawing damage and reduction of the surface oxidation ensuring smoother wire feeding during GMA welding.
What is “cast” of filler wire ?
the diameter of single loop of wire
What is the min cast of 6.8 Kg spool ?
30 – 41 cm
What if the cast is much less than 30 cm ?
there will be more resistance to wire feeding in push wire feed system . The reason for that is as the cast is reduced the number of points where the wire contacts the liner increases and the friction resistance increases.
What happens if the cast is too great?
Installation of spool on the feeder and the subsequent threading of wire through the drive rolls may be more difficult bcz the wire will tend to spring off the spool. Also, too straight a wire can lead to a problem bcz there is an increased risk of the wire “floating” through the contact tip and subsequent loss of current pick-up.
What is Helix of filler wire?
The space between two unrestrained wire.