2. Objectives:
Analyze the heat affected zone (HAZ)
created by 3 types of welding and 2
different cooling rates
Identify any changes in the properties of
the material characteristic of each type
of welding
Identify any changes in the properties of
the material based on the method of
cooling used after welding
3. Parent metal:
Low carbon steel ASTM 569
Easy to form and weld
Max carbon content of 0.15 wt%
0.30 – 0.60 wt% Mg
Max phosphorous content of 0.04 wt%
55,000 psi tensile strength
30,000 psi yield strength
30% elongation
4. TIG welding:
Non-consumable tungsten electrode is used to
create an arc
Inert gas used to shield the weld zone from
contaminants
Temperature of electric arc exceeds 6500º F
The intense heat is focused on a very small area
The process is quick, clean, and free of slag and
sputter
6. MIG welding:
A consumable wire is used to establish an
arc and as a filler material in the weld
zone
Can be used with inert gas or flux cored
filler wire to shield the weld zone from
contaminates
As with TIG welding, an intensely hot
electric arc is created with the filler wire
As with TIG welding, a minimum amount
of material is necessary to produce a weld
of maximum strength
9. Gas welding:
Brazing is a process of gas welding
Oxygen and acetylene are burned at correct
proportions to create a flame ranging from 5800º
to 6300º F
An alloy of a lower melting temperature is used to
join the parts of the base metal
Brazing typically takes longer to weld than either
TIG or MIG
The flame is not as intense or focused as an
electric arc
Because of the inherently lower tensile strength of
brass, a proportionately larger amount of brass
must be used in the weld to provide sufficient
strength
13. Procedure:
Weld 2 sets of metal samples with TIG, MIG
and BRAZING
One set is to be AIR COOLED at room
temperature
The other set is to be WATER QUENCHED
Conduct laboratory experimentation:
Rockwell hardness measurements at 2mm
increments.
Fatigue testing by bending the sample at
the joint 60º in both directions
Collect and analyze data
Discussion of results
16. 70
75
80
85
90
0 10 20 30 40
Distance from the weld (mm)
Hardness(HRC)
Hardness plot of the TIG welded sample
Water quenched sample
97 cycles to failure, crack at 10mm
Air cooled sample
116 cycles to failure, crack at 18mm
18. 50
60
70
80
90
0 10 20 30
Distance from the weld (mm)
Hardness(HRC)
Water quenched sample
72 cycles to failure, crack at 6mm
Air cooled sample
85 cycles to failure, crack at 16mm
Hardness plot of the MIG welded sample
20. Air cooled sample
6 cycles to failure, crack at welded joint
Water cooled sample
4 cycles to failure, crack at welded joint
Inconclusive Results !!
21. 60
65
70
75
80
85
0 5 10 15 20 25 30 35 40
Distance from the weld
Hardness(HRC)
TIG water quenched
TIG air cooled
MIG air cooled
MIG water cooled
Hardness comparison of TIG and MIG welding…
22. Effects of different types of welding:
TIG welding created a very strong weld with
good hardness and ductility
MIG welding created a similarly strong weld
with slightly greater hardness values, less
ductility, and a smaller heat affected zone
than TIG
Gas welding with brass created a weld of
insufficient strength hence its strength and
ductility could not be compared to the two
types of arc welding
23. Effects of different methods of
cooling:
Typically the grain structure adjacent to the weld
has relatively lower hardness and greater ductility
associated with a coarse grain size. Water
quenching decreases the size of the grain
structure, thus raising the hardness.
The next zone consists of a band of finer grains at
the critical temperature. This zone is relatively
harder and less ductile than the first zone and is
more prone to cracking. Water quenching tends
to harden this zone and causes cracks to occur
closer to the weld than air cooled samples.
The third zone consists of a normal grain structure
resembling those of the parent metal and is
furthest from the weld.