# Grain Size in Aluminum Alloy 6061 under Hot Ring Compression Test and after T6 Temper
## 3 Results
### Grain Size after Compression Test
It is still hard to observe the influence of individual level of each factor on the grain size from Table 6. Based on Taguchi method, the grain size at each sampling position is regarded as the quality characteristic value \(y\) having the smaller-the-better property. This suggests that the finer the grain, the better the property, so that it can be converted into S/N ratio according to Equation (1). After averaging the S/N ratios for each level of each factor, a response table for each position can be established Table 7. As mentioned above, the larger the effect or the S/N difference among the levels of the same factor, the more significant the influence of the factor on the quality characteristic. From the response listed in the rightmost column of Table 7, which is calculated from the mean grain size in Table 6, it can be observed that the effect of the lubricant on the mean grain size was the most significant (0.86 dB), followed by the working temperature (0.59 dB), and the weakest is then the upsetting speed (only 0.02 dB). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Experiment**}} & \multicolumn{8}{c}{**Position**} & \multirow{2}{*}{**Mean**} & \multirow{2}{*}{**Standard**} \\ \cline{2-2} \cline{5-12} \multicolumn{1}{c}{**No.**} & & & & & & & & & & & \\ \hline
1 & 214 & 226 & 233 & 206 & 219 & 258  & 206 & 219 & 317  & 233 & 35 \\
2 & 233 & 223 & 237 & 207 & 204 & 216 & 230 & 204 & 219 & 219 & 13 \\
3 & 233 & 223 & 223 & 194 & 204 & 201 & 201 & 194 & 194 & 207 & 15 \\
4 & 237 & 199 & 215 & 188 & 188 & 215 & 244  & 193 & 222 & 211 & 21 \\
5 & 251  & 251  & 215  & 215  & 215  & 215  & 215  & 215  & 225  & 229 & 233 & 18 \\
6 & 251  & 244 [1  & 210 & 193 & 215 & 251  & 201 & 222 & 226 & 22 \\
7 & 237 & 229 & 251  & 222 & 215 & 244 [1  & 251  & 215 & 237 & 233 & 14 \\
8 & 251  & 215 & 251  & 215 & 215 & 229 & 215 & 251  & 229 & 17 \\
9 & 261  & 229 & 290 [1 & 222 & 251  & 244 [1  & 251  & 215 & 251  & 246 [1  & 23 \\ \hline mean & 241  & 227 & 244 [1  & 209 & 212 & 225 & 231 & 212 & 238 & 226 & 13 \\ std. deviation & 14 & 15 & 22 & 12 & 18 & 19 & 20 & 18 & 34 & N/A & N/A \\ \hline \hline \end{tabular} \({}^{1}\) Grain size larger than that from the incoming alloy.  
\end{table} 
Table 6: Average grain size measured from each experiment and each sampling position (unit: \(\upmu\)m). Figure 5: Definition of the sampling positions (right) in specimen from the red circle area (left). Comparing the S/N ratios responded from each level of each factor, their largest one has a footer of 2, while their smallest one has a footer of 3, to highlight them. It can be seen that the setting with footer 2 in the rightmost column of Table 7 corresponds a working temperature 400 \({}^{\circ}\)C with a speed of 36 mm/min and a compression amount of 3 mm with lubricant of molybdenum disulfide. This coincides with the setting of experiment 3 (see Table 2), and provides the smallest mean grain size, which is again consistent with the foregoing description of Table 6. The largest mean grain size would be obtained with a setting with footer 3 as a temperature of 500 \({}^{\circ}\)C, a speed of 3.6 mm/min and a compression amount of 1 mm without lubricant. No corresponding set is listed in Table 2, thus experiment 9 with a speed of 36 mm/min and a compression of two millimeters still could be taken as the setting for the largest mean grain size, as the two most significant factor, lubricant (no lubricant) and temperature (500 \({}^{\circ}\)C) are already considered. This again is confirmed by the foregoing description of Table 6. Figure 6 shows the microstructure images taken at each sampling position in experiment 1, in which the grains on the top inner corner are coarser. In addition, it can be seen in Table 7 that the lubricant has a significant effect on the grain size. The setting without lubricant can generate large grains at most (8) positions, while the setting with molybdenum disulfide can generate small grains at most (8) positions.