The first process in examining the welds will be to look at the physical aspects of the welds
themselves post welding, post tensile breaking and macrographs. Figure 4.1 shows the tensile
specimens of Weld 1 after they were broken. The advancing side is on the left, while the retreating
side is on the right. The tensiles in the figure are laid in an increasing order with Tensile #2 at the
top, and Tensile #8 at the bottom. Looking at the cracks, the beginning of the weld was more
likely to break on the advancing side, but along the length of the weld, the crack size and location
begins to change. The cracks become more jagged and begin to break along the center of the weld
nugget instead of the TMAZ. This could mean that a proper material mixing was not achieved
along the weld seam over the length of the weld. Examining the fracture break direction, tensiles
7 and 8 are much different than the previous four tensiles. The break type is more in line with a
brittle material as opposed to a ductile material due to the rough jagged edges. It can also be seen
that on tensile 7, there is a hairline crack normal to the applied force during the testing.
38
Figure 4.2 shows the tensile specimens of Weld 2 after they were broken. The advancing side is
on the left, while the retreating side is on the right. The tensiles in the figure are laid in an
increasing order with Tensile #2 at the top, and Tensile #8 at the bottom. Weld 2 shows an increase
in consistent ductility over Weld 1. This can be seen as fractures are cleaner and slight necking is
noticed along the edges. The tensiles are not jagged which is normally seen on brittle material
fractures. The tensiles also consistently broke near the retreating side of the TMAZ. The fracture
type throughout the six tensiles was largely consistent with very little variance in fracture angle
and type. Each tensile broke at a roughly 45° angle and did not show any signs of rough jagged
edges.
Figure 4.2: Weld #2 Post Tensile Break
Figure 4.3 shows the tensile specimens of Weld 3 after they were broken. The advancing side is
on the left, while the retreating side is on the right. The tensiles in the figure are laid in an
39
a decrease in ductility from weld 2 as the breaks are no longer a ta 45° plane. The fracture was
found to be close to the TMAZ on the advancing side of the weld which is counterintuitive as the
metal on the advancing side has higher mechanical properties, making it the stronger side.
Figure 4.3: Weld #3 Post Tensile Break
Figure 4.4 shows the tensile specimens of Weld 4 after they were broken. The advancing side is
on the left, while the retreating side is on the right. The tensiles in the figure are laid in an
increasing order with Tensile #2 at the top, and Tensile #8 at the bottom. Weld 4 had similar input
parameters as Weld 1 and when comparing the two, they are similar in terms of how the tensiles
are experiencing brittle fractures. The last tensile does experience a slight change in the fracture
type as it becomes more brittle then the previous 5 tensiles. This indicates, like weld 2, that
improper mixing must be occurring at the later stages of the weld causing a drop in ductility. The
tensiles also had a tendency to break towards the advancing side along what appears to be the
40
Figure 4.4: Weld #4 Post Tensile Break
Figure 4.5 shows the tensile specimens of Weld 5 after they were broken. The advancing side is
on the left, while the retreating side is on the right. The tensiles in the figure are laid in an
increasing order with Tensile #2 at the top, and Tensile #8 at the bottom. When comparing to the
previous welds, the input parameters are closest to that of weld 2. The fractures do indicate a
decrease in ductility as the lack of a noticeable necking region along with the more jagged edges.
The fractures were close to the advancing side along the weld nugget which is opposite to that of
41
Figure 4.5: Weld #5 Post Tensile Break
Figure 4.6 shows the tensile specimens of Weld 6 after they were broken. The advancing side is
on the left, while the retreating side is on the right. The tensiles in the figure are laid in an
increasing order with Tensile #2 at the top, and Tensile #8 at the bottom. When comparing these
tensiles post break to Weld 3, which had similar welding parameters, a drop-in ductility can be
noticed from the crack propagation and lack of necking on the edges. The fractures were also
42
Figure 4.6: Weld #6 Post Tensile Break
It is noted that Weld 3 and 6 both experience a weld defect known as lack of consolidation. This
can be seen in the Figure 4.7 below, with a red circle identifying the area of concern. There is a
visual indication that the weld was not properly consolidated under these input parameters. The
common similarity between Weld 3 and 6 is that both of them are using the highest RPM setting
at 275. The welds with lower rotations per inch did not show signs of lack of consolidation from
external examination.
43
The results of all testing are organized by the mechanical properties: elongation, the yield strength
and the ultimate strength; the macrograph analysis; and the hardness testing. The results will be
compared to the original abstract of this experiment in where it will be determined if certain
properties will be insensitive to variations of welding parameters and provide consistent results
44
Table 4.1
Elongation for Tensiles
Speed = 13 IPMForce = 2400 lbf, Rotation = 180 RPM Force = 2400 lbf, Rotation = 215 RPM Force = 2400 lbf, Rotation = 275 RPM
Tensile Final Length (inches) ΔL (inches) Elongation (%) Tensile Final Length (inches) ΔL (inches) Elongation (%) Tensile Final Length (inches) ΔL (inches) Elongation (%) W1T2 4.252 0.312 7.92 W2T2 4.271 0.331 8.40 W3T2 4.188 0.248 6.29 W1T3 4.215 0.275 6.98 W2T3 4.2155 0.2755 6.99 W3T3 4.254 0.314 7.97 W1T4 4.19 0.25 6.35 W2T4 4.2385 0.2985 7.58 W3T4 4.129 0.189 4.80 W1T6 4.271 0.331 8.40 W2T6 4.425 0.485 12.31 W3T6 4.182 0.242 6.14 W1T7 4.159 0.219 5.56 W2T7 4.219 0.279 7.08 W3T7 4.152 0.212 5.38 W1T8 4.192 0.252 6.40 W2T8 4.257 0.317 8.05 W3T8 4.2225 0.2825 7.17 Speed = 11 IPM
Force = 2400 lbf, Rotation = 180 RPM Force = 2400 lbf, Rotation = 215 RPM Force = 2400 lbf, Rotation = 275 RPM
Tensile Final Length (inches) ΔL (inches) Elongation (%) Tensile Final Length (inches) ΔL (inches) Elongation (%) Tensile Final Length (inches) ΔL (inches) Elongation (%) W4T2 4.1905 0.2505 6.36 W5T2 4.139 0.199 5.05 W6T2 4.1705 0.2305 5.85 W4T3 4.133 0.193 4.90 W5T3 4.1865 0.2465 6.26 W6T3 4.0765 0.1365 3.46 W4T4 4.1895 0.2495 6.33 W5T4 4.2865 0.3465 8.79 W6T4 4.1575 0.2175 5.52 W4T6 4.144 0.204 5.18 W5T6 4.0855 0.1455 3.69 W6T6 4.165 0.225 5.71 W4T7 4.139 0.199 5.05 W5T7 4.19 0.25 6.35 W6T7 4.0755 0.1355 3.44 W4T8 4.1015 0.1615 4.10 W5T8 4.202 0.262 6.65 W6T8 4.217 0.277 7.03
45
Table 4.2
Yield Stress for Tensiles
Speed = 13 IPMForce = 2400 lbf, Rotation = 180 RPM Force = 2400 lbf, Rotation = 215 RPM Force = 2400 lbf, Rotation = 275 RPM
Tensile 𝜎𝑦 (ksi) Tensile 𝜎𝑦 (ksi) Tensile 𝜎𝑦 (ksi)
W1T2 31.88 W2T2 33.25 W3T2 33.383 W1T3 32.09 W2T3 32.58 W3T3 33.22 W1T4 31.9 W2T4 32.45 W3T4 33.38 W1T6 32.34 W2T6 32.42 W3T6 33.58 W1T7 19.93 W2T7 33.43 W3T7 32.67 W1T8 36.29 W2T8 33.67 W3T8 32.64 Speed = 11 IPM
Force = 2400 lbf, Rotation = 180 RPM Force = 2400 lbf, Rotation = 215 RPM Force = 2400 lbf, Rotation = 275 RPM
Tensile 𝜎𝑦 (ksi) Tensile 𝜎𝑦 (ksi) Tensile 𝜎𝑦 (ksi)
W4T2 31.86 W5T2 31.74 W6T2 29.63 W4T3 31.44 W5T3 31.57 W6T3 28.43 W4T4 31.87 W5T4 31.04 W6T4 28.84 W4T6 31.78 W5T6 32.33 W6T6 30.40 W4T7 32.07 W5T7 31.95 W6T7 29.53 W4T8 32.08 W5T8 31.44 W6T8 29.37
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Table 4.3
Ultimate Strength for Tensiles
Speed = 13 IPMForce = 2400 lbf, Rotation = 180 RPM Force = 2400 lbf, Rotation = 215 RPM Force = 2400 lbf, Rotation = 275 RPM
Tensile Maximum Force (lbf) Area (in2) 𝜎𝑢 (ksi) Tensile Maximum Force (lbf) Area (in2) 𝜎𝑢 (ksi) Tensile Maximum Force (lbf) Area (in2) 𝜎𝑢 (ksi) W1T2 17,923 0.36 49.79 W2T2 16,540 0.32 50.99 W3T2 17,731 0.36 49.25 W1T3 18,092 0.36 50.26 W2T3 15,998 0.32 49.43 W3T3 18,115 0.36 50.32 W1T4 18,076 0.36 50.21 W2T4 16,156 0.32 49.92 W3T4 16,933 0.36 47.04 W1T6 18,060 0.36 50.17 W2T6 16,072 0.32 49.66 W3T6 17,556 0.36 48.77 W1T7 9,610 0.36 26.69 W2T7 16,042 0.32 50.64 W3T7 17,123 0.36 47.57 W1T8 14,474 0.31 47.01 W2T8 16,102 0.32 50.83 W3T8 16,867 0.36 46.85 Speed = 11 IPM
Force = 2400 lbf, Rotation = 180 RPM Force = 2400 lbf, Rotation = 215 RPM Force = 2400 lbf, Rotation = 275 RPM
Tensile Maximum Force (lbf) Area (in2) 𝜎𝑢 (ksi) Tensile Maximum Force (lbf) Area (in2) 𝜎𝑢 (ksi) Tensile Maximum Force (lbf) Area (in2) 𝜎𝑢 (ksi) W4T2 13,746 0.36 38.18 W5T2 14,064 0.36 38.87 W6T2 10,992 0.34 32.14 W4T3 14,338 0.36 39.83 W5T3 13,260 0.37 35.94 W6T3 10,960 0.34 32.05 W4T4 14,483 0.36 40.64 W5T4 14,523 0.38 38.42 W6T4 11,116 0.34 32.50 W4T6 13,719 0.36 38.11 W5T6 13,524 0.35 38.53 W6T6 11,543 0.34 34.11 W4T7 14,342 0.36 40.24 W5T7 12,836 0.35 36.57 W6T7 11,187 0.34 32.71 W4T8 13,134 0.36 36.85 W5T8 11,783 0.35 33.57 W6T8 11,224 0.34 33.26
47
All macrographs can be found in Chapter 7. Upon examining the macrographs, it is noted that the
shape of the weld 2195 portion of the weld nugget is changed as the RPM increases. The lower
RPM welds have the nugget looking more like a flame as it is not as compact and waviness is
found throughout. As the RPM increases, the welds begin to consolidate more in the middle and
have a thinner overall layer of material across the latitudinal centerline.
Looking at the shape of the macros it can be deemed that the welding parameters have an effect
on the overall shape of the weld nugget. The higher RPM welds have less waviness overall and a
more concise 2195 material profile. This is because the spindle is able to mix the material more
and cause a more concise weld. When comparing the same RPM values the travel speed also has
an effect on this, as the slower travel speed has less waviness. This is because the spindle is
allowed more contact with a particular location on the weld itself. The voids tend to be more
apparent on the lower RPM welds, also because the spindle is not able to uniformly mix the
material together and instead is leaving voids as it is passing through the area.
Looking at the size of the 2195 material length, or nose, in the weld nugget, the center of the welds,
or M5, possesses the larger weld nuggets when compared to the M1 & M9, the beginning and end
of the weld respectively. This was consistent across all welds, as the beginning of the weld and
end of the weld were normally thinner. Normally in friction stir welding the start point and end
point are completed on raised lips and these cut off post machining to avoid this type of
irregularities in the microstructure.
The nose length for most of the welds had a trend where it increased over the length of the weld,
where the alternative would be the center of the weld had a decrease in nose length, and the outer
48
average. This could be due to the fact that the higher RPM would produce more heat, allowing
the material to be extruded and flow much more easily.
The length of the nose has an effect on the material properties, with W5M9 being a great example
as it has a very long nose, and the properties are trending downward as they approach this sample
location. When comparing the required forces to break each tensile, as the material had a longer
nose on that particular point of the weld, a lower force was required to break the tensile specimen.
It is expected that this nose length would also be determined by the forge force as a higher forge
force will allow the material to extrude further, but cannot not be confirmed in this study, as all
welds were completed at the same forge force value.
Voids were present in the weld and it can be seen in the macrographs. They appear as white spots
as the silicon used in the grinding/polishing process was lodged into them and filled the void. The
silicon was unable to be removed, but it did make finding the voids much easier. The voids are
present more in the higher travel speed welds when compared to the lower travel speed welds.
Figure 4.9 shows the locations of these voids on a particular weld. The voids are prevalent on both
49
Figure 4.8: Voids in Weld
As noted early in this paper, a lack of consolidation defect was noted on the surface of welds 3 &
6. It appears that this defect is closer to the advancing side. This can be also seen in the
macrographs, displayed in Figure 4.10. On the advancing side, it is seen where the discoloration
is noted as lack of consolidation. This shows that those areas are not a coherent bond.
Voids Present in Weld
50
Figure 4.9: Lack of Consolidation
The hardness testing results can be seen tabulated below in Table 4.5 which shows the total range
of the hardness values on each side of the weld, while the remaining hardness data plots can be
found in Chapter 7. These values are taken from the HAZ to the point of the 2195/2219 material
interface. This is not always in the center of the weld as the interface between the two metals was
Lack of Consolidation
51
not always in a consistent spot. So, reading the below table for W1M1 the 2195 side of the nugget
would be 124.8 HV and the next data point would be on the 2219 material at 101.9 HV.
Table 4.4
Range of Hardness Data
Weld 2195
HAZ & Nugget
2219
HAZ & Nugget Weld
2195 HAZ & Nugget
2219 HAZ & Nugget W1M1 107.6 – 124.8 77.4 – 101.9 W4M1 97.1 – 114.3 78.5 –94.5 W1M5 109.4 – 125.4 77.1 – 116.3 W4M5 101.5 – 115.2 73.4 – 94.4 W1M9 105.4 – 120.2 76.9 – 114.8 W4M9 89.1 – 113.8 75.5 – 108.5 W2M1 111.8 – 128.9 81.4 – 110.4 W5M1 90.8 – 115.2 78.8 – 102.2 W2M5 106.7 – 123.7 80.3 – 93.3 W5M5 88.4 – 115.7 80.8 – 86.1 W2M9 102.4 – 115 81.4 – 96 W5M9 104.9 – 122.6 N/A W3M1 100.3 – 120.4 78.8 – 92.6 W6M1 109.9 – 124.3 81.4 – 115 W3M5 98.3 – 107.6 90.8 – 94.8 W6M5 93.3 – 117.8 78.8 – 91.5 W3M9 103.2 – 130.7 83.9 – 99.5 W6M9 95.6 – 120.4 85.5 – 96.7
This is compared to the parent material hardness of each alloy. Aluminum 2219-T851 has a typical
hardness of 130 HV, while Aluminum 2195-T8 has a typical of value of 180 HV. Typically, the
hardness data for the welds in this experiment experience a drop-in hardness from the parent
material to weld nugget of about 50 HV, while typical drops in friction stir welds of aluminum
alloys have drops of approximately 30HV from the parent material to the weld nugget [36]. This
larger than normal drop in hardness data is expected to stem from the inward mixing material.
This is because the material is being forced into each other causing it to be worked more.
It is noted that due to the shape of the weld nugget, sample W5M9 had all data points collected on
2195 portion of the weld nugget. This is why the hardness range is not available for the 2219
section. These shapes effect the total hardness distribution along the face of the macro, as the
length of the nose of 2195 dictates when the drop-in hardness will be. This is because the material
52
from the last data point on the 2195 and the first data point of the 2219, although both being in the
weld nugget. For This is unusual as it is expected to have a proper mix of the two material types,
but since it is a bi-alloy friction stir weld, the properties of the 2195 are still dominant and present.
Looking at the difference between a Left-Hand Right-Hand threaded pin tool and compare it to a
typical Right Hand threaded pin tool, the microstructure of the weld is different. In the next two
figures, there are two macrographs of welds with similar conditions. Both welds used self-reacting
pin tools. The weld input parameters were also similar as the forge force was 2400 lbf, and the
travel speed was also 13 IPM. The only different factors would be that the LHRH weld had 215
RPM, while the RH weld had 200 RPM, and the retreating side material is different aluminum
alloys, 2195 vs 2050. This difference is approximately 0.5% more copper in 2050 and another
<0.5% of other alloying materials, so there is not a larger difference between the two materials. If
anything, the Al 2050 would be less resistant to material flow.
When examining the differences in microstructure between the two welds, it can be clearly seen
that the LHRH weld has the material consolidated in the center as opposed to being spread out like
the RH. This is an expected result as the LHRH pin tool pushes the material to the center of the
weld. It is hypothesized that the larger drop in hardness values than expected is due to the LHRH
53
Figure 4.10: Left-Hand Right-Hand Threaded Pin Tool
Figure 4.11: Right-Hand Threaded Pin Tool
Once the final results from the experiment were completed and recorded, the data from the tensile
testing was input into a linear regression model using the methods described in Chapter 2. The
54
the yield strength and the ultimate strength, which resulted in three separate final formulas as
dictated below and the following equations were derived from the data collected in this experiment.
∆𝑳
𝑳 = −𝟒. 𝟕𝟏𝟏𝟑𝟖+ . 𝟖𝟑𝟒𝟑𝟗𝟏 ∗ 𝑻𝒓𝒂𝒗𝒆𝒍 𝑺𝒑𝒆𝒆𝒅 + . 𝟎𝟗𝟔𝟗𝟎𝟏 ∗ 𝑭𝒐𝒓𝒄𝒆/𝑹𝑷𝑴 Eq 4.1
𝝈𝒚= 𝟐𝟑. 𝟓𝟐𝟕𝟓𝟕+ . 𝟔𝟓𝟖𝟖𝟔𝟏 ∗ 𝑻𝒓𝒂𝒗𝒆𝒍 𝑺𝒑𝒆𝒆𝒅 + . 𝟎𝟏𝟕𝟏𝟔𝟓 ∗ 𝑭𝒐𝒓𝒄𝒆/𝑹𝑷𝑴 Eq 4.2
𝝈𝒖 = −𝟑𝟑. 𝟐𝟕𝟓𝟔𝟐 + 𝟓. 𝟗𝟏𝟐𝟗𝟕 ∗ 𝑻𝒓𝒂𝒗𝒆𝒍 𝑺𝒑𝒆𝒆𝒅 + . 𝟒𝟎𝟒𝟗𝟖𝟓 ∗ 𝑭𝒐𝒓𝒄𝒆/𝑹𝑷𝑴 Eq 4.3 These equations were then used to calculated a value (dependent value) that the regression model
would output with the input parameters (independent variables) used for each trial run. Looking
at the above three equations, it can be seen that the effects of the Travel Speed are much greater
than that of the Force/RPM. It was noted that multiplying constant of the Travel Speed is several
orders of magnitude higher than the secondary constant for the Force/RPM, meaning that the final
mechanical property is much more dependent on the travel speed than the Force/RPM.
Comparing the results of a linear regression to the measured data, it can be seen from the next
three figures that a linear regression model fits the dataset of the ultimate tensile strength but not
for the yield strength and the elongation based on the R2 values.
Before looking at the three regression models, it must be noted that each weld on the model is