# Grain Size in Aluminum Alloy 6061 under Hot Ring Compression Test and after T6 Temper
## 3 Results
### Grain Size after Compression Test  
The grain sizes measured from the ring compression test are shown in Table 6. The positions shown in Table 6 are defined in Figure 5. The sampling positions 1 to 3 are assigned to the region where the specimen contacts to the lower die, while positions 7 to 9 are assigned to the upper die. The sampling positions 4 to 6 are located in the middle part of the specimen without any contact to either to the upper die or to the lower die. The grain sizes shown in Table 6 are the average from the readings of five specimens tested under the same setting. The grain sizes shown with a footer 1 in Table 6 are larger than that measured from the incoming alloy. Although Figure 5 shows that the positions where the specimen contacts the upper and lower die should be vertically symmetrical and their grain sizes should be comparably similar, the results shown in Table 6, however, are quite different. The reason for this is that the specimen is placed on the lower die first and then contacts to the upper die, so that positions 1 to 3 are early brought into contact with die and therefore cooled. Thus their grain size is different to that on the upper boundary. Among the mean grain sizes for each experiment setup, it can be observed that the mean grain size was obtained from experiment 3, which reaches the minimum as 207 \(\upmu\)m, while experiment 9 can cause the maximum one in 246 \(\upmu\)m. Furthermore, only experiment 9 can cause a mean grain size larger than that obtained from the incoming alloy. The remaining experiments only have smaller mean grain sizes. Among those experiments, the grain size in experiment 2 and 3 becomes smaller at all sampling positions. In view of the standard deviation, it can be further seen that experiment 1 has the largest standard deviation, 35 \(\upmu\)m, which means that the sampling position in this case might significantly influence grain size. On the other hand, the standard deviation in experiment 2 is the smallest, only \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Factor** & **DF** & **SS** & **MS** & **\% C** & **\% C\({}^{\prime}\)** & **F** \\ \hline temperature & 2 & 1.42 & 0.71 & 8.25\% & 7.54\% & 8.1 \\ speed & 2 & 0.02 & 0.01 & 0.11\% & - & (0.11) \\ compression & 2 & 0.33 & 0.17 & 1.92\% & - & (1.89) \\ lubricant & 2 & 15.53 & 7.77 & 89.72\% & 92.46\% & 88.1 \\ error & 0 & - & - & - & - & - \\ (error) & (4) & (0.35) & (0.09) & - & - & - \\ sum & 8 & 17.31 & 8.66 & 100\% & 100\% & - \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Analysis of variance in friction coefficient. 13 \(\upmu\)m, suggesting that this experiment setup might cause a relatively homogeneous distribution of grain size. If the grain size is observed at individual position, the grains at position 9 from experiment 1 are the coarsest, 317 \(\upmu\)m in average, while position 4 and 5 from experiment 4 have the smallest grain size, 188 \(\upmu\)m in average. Furthermore, position 4 has the smallest mean grain size as well, 209 \(\upmu\)m, while position 3 has the largest one, 244 \(\upmu\)m. In addition to position 3, position 1 has a mean grain size larger than that from the incoming alloy as well. The remaining positions have grains smaller than that of the incoming alloy. Position 4 of the specimen under all 9 experiment setups has a smaller grain size than that from the incoming alloy. In view of standard deviation of grain size at a certain position obtained under different experiment setups, position 9 has the largest standard deviation of grain sizes, 34 \(\upmu\)m, which means that this position might demonstrate the influence of setups designed by Taguchi method, while position 4 shows the smallest one, only 12 \(\upmu\)m, which means that at this position the grain size is less sensitive to the settings designed by Taguchi method.