With the development of friction stir welding (FSW), there is more and more research content on the optimization of tools. In friction stir lap welding (FSLW), the research about optimizing the tools focused on geometry of pin and shoulder, and few researches about the pin-less tool. In order to eliminate the hook defect and cold lap defect, this paper studied the influence of shoulder geometry with pin-less on FSLW joints with 2024-T4 aluminum alloy. Three kinds of raised pointer shoulder were designed independently in order to explore the basic law of FSLW with pin-less tools on aluminum alloy.
The test focused on the cross-section morphology, microstructure, and lap shear failure load and fracture morphology. The joints with good lap shear failure load were obtained by these three tools, proved to have a successful tool design. The material flow during welding were briefly analyzed. It was found that under the same parameters, increase the number of pointer can improve the flow ability of the lap interface. This paper compares two different rotating speed on the morphology and mechanical properties of the joints. The results show that the increase of pointer quantity, improvement of speed can promote the lap connection and with 6 pointer mixing head, at the rotational speed of 2000r/min and the welding speed of 20mm/min, the highest lap shear failure load was obtained with 78.8N/mm.
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Effect of shoulder geometry on joint morphology and mechanical properties of Friction Stir Lap Welded 2024 Aluminum alloy
1. Effect of Shoulder Geometry on Joint Morphology and
Mechanical Properties of Friction Stir Lap Welded 2024
Aluminum Alloy
Name: Amish Singh
Supervisor: Yue Yu Mei
Shenyang Aerospace University
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3. FSW
Solid State Welding
Thermo-mechanical action
Non-consumable tool
Can be applied on
Magnesium, Copper, Zinc,
steel, Titanium and it’s
alloys.
Best application on
aluminum dude to
thermo-mechanical
properties
Types of joints
Butt
Lap
T-joint
Spot joint
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4. Advantages
• Environment friendly
• Energy efficient
• Great mechanical properties
• Low cost
• Less distortion
Disadvantages
• Welding speeds slower for some welding processes
• Requires a backing bar
• Workpieces must be rigidly clamped
• Keyhole in the end
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5. Friction Stir Lap Welding
• Joint between two overlapping plates
• Tool plunged into the top surface and partially
into the bottom surface
• Widely used in transportation industries like
shipbuilding, train and automobile.
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8. Material and it’s composition
Name of
element Cu Mn Mg Si Zn Ni Cr Pb Bi Al
Compos-
ition
4.3-
4.5
0.5-
0.6
1.3-
1.5
<0.5 <0.5 <0.5 <0.5 <0.5 <0.5 Remainder
Metal: Al2024
Dimensions: 300mm*150mm*1.5mm
Overlap region: 50mm
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10. Experiment Process
Research objectives:
The main objectives of this thesis are:
A) To join two 2024-T4 Al alloy plates using FSLW.
B) To investigate the change occurring within the microstructure of
the welded lap joint during friction stir welding through the use of
experimental welding, constitutive modeling, and physical
simulation.
C) To determine the effect of shoulder geometry on the mechanical
properties of the joint with the use of various kinds of pin-less tools.
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11. Procedure
Plates were cut into respective width, height and length
Used sand paper to remove the oxide layer
Plates were placed in an overlapping position and clamped to the FSW
table to carry out the process
Process repeated with three pin-less tools under two rotational speeds
Serial
number
Type of
tool Rotation speed
Welding
speed
Tilt
angle
Plunge
depth
1 Two-pointer 2000rpm 1500rpm 20mm 2.5° 0.2mm
2 Four-pointer 2000rpm 1500rpm 20mm 2.5° 0.2mm
3 Six-pointer 2000rpm 1500rpm 20mm 2.5° 0.2mm
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12. Obtained welds are taken to Wire Cut Electric Discharge Digital control
machine.
Cut into two different groups of samples- metallographic and lap shear
Lap shear taken to the tensile strength testing machine
Metallographic samples taken to the metallographic microscope to study
microstructures.
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13. Results and Discussion
Grooves work as pins in the case
of a pin-less tool.
The number of grooves on the
shoulder is equally proportional
to the fineness of the weld
material.
The resultant force goes in the
normal direction hence helping
the material to go underneath
the pin-less tool.
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20. Lap Shear Failure Load
Tool Name
Rotational
Speed r/min
Transverse
Speed
mm/min
Average
Tensile
Strength N
Average Lap
Shear Failure
Load N/mm
2-pointer
1500 20 1351 45
2000 20 1746 58.2
4-pointer
1500 20 1964 65.5
2000 20 2136 71.2
6-pointer
1500 20 2245 74.8
2000 20 2364 78.8
Calculated using the tensile strength testing machine
Weld specimen elongated to the point of fracture to calculate the max lap shear failure load
Weld sample cut to 30 mm in diameter
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22. Conclusion
The following conclusions are obtained through this experiment：
(1) The 2024-T4 aluminum alloy FSLW joints have been successful obtained with three
different tools.
(2)By the analysis of the cross section, it is found that with the increase of the number of
pointer, the area of the SZ increases, and the depth of SZ is increased.
(3) There was no traditional Hook defect and cold lap on cross section, but the lap
interface was obviously deformed at high rotational speed.
(4)With the increase of rotational speed when 2, 6 pointer tool was used grain
refinement on SZ or TMAZ, but by 2 pointer tool grains on HAZ did not refinement as
rotational speed increases.
(5) The best lap shear failure load was got when the 6 pointer tool was used and the
rotational speed was 2000r/min, and the value was 78.8N/mm.
(6) The crack propagation along the alcad, all joints showed shear fracture mode;
(7) In the fracture morphology analysis, a large number of dimples were found, which
indicating ductile fracture.
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