## 4 Discussion
This is in congruence with the studies of the variation of DCP temperatures as function of the alloy composition, in that it has a very similar effect on the solidification path of aluminum alloys. At the DCP there is also an increase in the cooling rate. In general, the regression models demonstrated that when the percentage of an alloying element such as Mg, Fe, Ni, Mn, Ti, and Zn is increased, the RPT values tend to decrease. The increase of percentage of alloying elements in an Al alloy decrease the solidification process related temperature until the minimum solidification temperature, which is reached in the eutectic composition. [PERSON] and his team [20] observed that the coalescence solid fraction is independent of Si content and depends on Mg content for AlSi\({}_{10}\)Mg alloys, because a solid skeleton is developed earlier in the Mg- rich alloys, like \(\pi\)-Al\({}_{8}\)Mg\({}_{3}\)FeSi\({}_{6}\). The Fe and Ni as alloying elements can form \(\beta\)-Al\({}_{5}\)SiFe, Al\({}_{3}\)Ni, and Al\({}_{7}\)Cu\({}_{2}\)Fe needle like structures, that they can reduce the solid particles moving to pass each other, as shown in Figure 9.  
Figure 9: Alloy 7 micrography showing needle like structures of intermetallic containing high Fe concentrations, Ni and Cu. Zn and Mn are normally dissolved in molten aluminum alloy inside the grains, so when combined, an increase of the wt% of Zn and Mn takes place as a more eutectic alloy. Mn also has a direct effect over \(\beta\)-Al\({}_{5}\)SiFe, modifying it to \(\alpha\)-Al\({}_{15}\)Si\({}_{2}\)(Fe, Mn)\({}_{3}\) with a more compact Chinese script morphology, which is normally also precipitated at higher temperatures than the RPT. In we can observe the presence of Chinese script structures and the reduced presence of Al\({}_{5}\)SiFe and Al\({}_{7}\)Cu\({}_{2}\)Fe needle like structures in a high manganese AlSi\({}_{10}\)Mg alloy. In the case of Ti, its effect on the RPT can be explained by the refining effect on the grain size, that promotes smaller grains and increases fluidity. The only elements that increase the RPT values are Cu, Cr, and Si (with a statistical relevance in Method 5). Cu is present in AlSi\({}_{10}\)Mg alloys as Al\({}_{2}\)Cu or as complex intermetallic combined with Fe and Si. Al\({}_{2}\)Cu phase is formed at the final stage of the solidification, at temperatures very close to the solidification point, with an enrichment in Cu in the remaining eutectic liquid. So, Cu precipitates do not decrease the fluidity of solid particles. The combination of Cu with Fe can also modify the beta needle like structure of iron intermetallic to skeleton like structures, as Q-Al\({}_{5}\)MgSCu\({}_{2}\)Si\({}_{6}\), as observed in Figure 10. Cr addition to the alloy changes the beta iron-rich intermetallic into modified alpha phases and therefore it reduces the detrimental effect of iron and the blocking effect on the solid particles moving into the solidifying alloy [21]. An increase of Si moves an alloy from a hypoeutectic to a more eutectic alloy, increasing the RPT in the same way that occurs with the maximum and minimum eutectic nucleation temperature [8]. An increase in high Si levels in the hypoeutectic alloys increase the Al-Si eutectic temperature and therefore the RPT is also increased. Si addition increases volumetric contraction by the formation of a silicon phase, hence reducing shrinkage porosity [22]. Analyzing the data from Table 1 and Figure 7, we can observe that samples from number 6 to 9 have the smallest RPT values, compensating for the increase of RPT values by increasing the Si wt%. These three alloys have the highest wt% values for Mg, Fe, and Mn alloying elements, so they have a minor effect on the RPT obtained values. In the regression equation obtained from the studied methods, allowing both elements, Fe and Mn presents student t coefficient high values but without having a statistical significance in Method 5. The rest of the alloying elements also have an influence on the RPT; however, they are not so relevant.