2. Material and Methods
3. Results and Discussion
3.3. Hardness Evaluation
3.4. Tensile Properties and Fractography
- Machined sample (the joints were machined from the root side to remove 0.5 mm of thickness).
- The dimension and size of weld zone (including NZ, HAZ and TMAZ) is well related to the welding parameters (welding speed). Increase in welding speed caused less deviation for LHZ, which means decreases in γ and β.
- With increasing welding speed, the grain size of weld nugget zone decreased. In the heat affected zone (HAZ), the grain size was decreased by increasing welding speed, although in all samples, the grain size of HAZ is a bit bigger than base metal.
- Regardless of the process conditions and parameters, all friction stir welded butt joints had a softened region including NZ, TMAZ and HAZs as compared to base metal. This can be influenced by dissolving precipitates in grains and grain boundaries due to mechanical and thermo mechanical works in NZ, TMAZ and thermal effect (heat input) in HAZ. However, the hardness in NZ is higher than TMAZ. The reason should be explained by finer grain size in NZ. The hardness in NZ, TMAZ and HAZ showed an increasing trend by increase in welding speed.
- Kissing bond was introduced in weld at all three different welding speeds, which could be Al2O3. The total length of kissing bond was increased in higher welding speed. However, the appearance of kissing bond in root of joint had destructive effect in tensile test. An improvement was achieved in ultimate tensile strength by removing the kissing bond. This amount was 25% at 110 mm/min welding speed (159 MPa/119 MPa). Fracture location was located in RS-LHZ for all samples after removal of kissing bond from root.
Conflicts of Interest
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|Yield Strength (MPa)||Ultimate Strength (MPa)||Elongation (%)||Hardness (HV)|
|269 ± 2||300 ± 1||15 ± 0||105 ± 3.1|
|Purpose||Lpin (mm)||Dpin (mm)||Dshoulder (mm)||Pitch (mm)||Cone Angle|
|FSW of AA 6061-T6||9.5||10.50||24||1.2||60°|
|Deviation Angle||Welding Speed|
|63 mm/min||89 mm/min||110 mm/min|
|Sample||Welding Speed (mm/min)||Average Grain Size NZ (μm)||Average Grain Size HAZ (μm)||Average Grain Size Base Metal (µm)|
|No.||Welding Speed (mm/min)||Fracture (Location)||Ultimate Tensile Strength (UTS in MPa) RS-LHZ/Kissing Bond||Yield Strength (YS in MPa) RS-LHZ/Kissing Bond||Elongation (%)|
|1||63||RS-LHZ||132 ± 2.1||127 ± 1.4||14 ± 0.4|
|2||89||RS-LHZ/Kissing bond||(141 ± 1.73)/(117 ± 2.2)||(137 ± 1.4)/(97 ± 1.9)||(16 ± 0.3)/(3.6 ± 0.13)|
|3||110||RS-LHZ/Kissing bond||(159 ± 2)/(119 ± 1.6)||(134 ± 1.7)/(95 ± 2)||(16 ± 0.5)/(3.5 ± 0.15)|
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