# Effect of Ti-B Grain Refiners on Wear and Corrosion of the A332 Alloy with Sr Modification
## 4 Discussion  
### Microstructure Characterization  
From OM and SEM images, the EDS analyses both alloys with and without different grain refiners presented the phases of primary aluminum, Al15(FeMn)3 Si2, Al5 FeSi, and Al2 Cu. The use of Sr modifier and grain refiners (Al5 Ti2B and Al5 Ti1B) promoted microstructural changes in the samples.  
Cu-based intermetallic phases are commonly obtained in the Al-Si alloys. Moreover, the existence of this phase is well observed in the work [PERSON] et al. [6], where the Al2 Cu phase appeared as a predominant Cu-rich one within the microstructure, in comparison with other small phases with Cu.  
Figure 16: Optical micrographs of cross-section from (**a**) as-cast condition without grain refiner; (**b**) grain refiner Al5 Ti2B; (**c**) grain refiner Al5 Ti1B 500\(\times\).  
Figure 15: Tafel plots for the analyzed samples from as-cast condition without grain refiner; grain refiner Al5 Ti2B; grain refiner Al5 Ti1B.  
The Al\({}_{5}\)FeSi intermetallic phase is not desirable in aluminum alloys, as it increases the material's brittleness. This is commonly found in the A332 aluminum alloy, as confirmed by [PERSON] et al. [26], who also reported this phase, characterized as Fe-bearing particles present in the microstructure, mainly in the form of Al\({}_{5}\)FeSi in the form of needles, even if some particles in the form of Al\({}_{15}\)(FeMn)\({}_{3}\)Si\({}_{2}\) (Chinese-script) were detected.  
In the A332 alloy, the dimensions of the Al\({}_{5}\)FeSi intermetallic phase needles are influenced by the addition of Sr, as also concluded by [PERSON], et al. [35]. These authors observed that Sr, besides being effective in modifying eutectic silicon, also reduces the size of needle-shaped Al\({}_{5}\)FeSi intermetallic compounds.  
In addition, different thicknesses and sizes of needles were observed and this geometry has a relationship with the zone of the microstructure where they appear. In this sense, it can be seen that the thinner Al\({}_{5}\)FeSi intermetallic were in the eutectic region and the thickest ones in the inside of the primary aluminum phase. These thicker intermetallic Al\({}_{5}\)FeSi phase, probably served as nucleation sites of primary aluminum denoting its proeutectoid nature in these phases, as explained by [PERSON] and [PERSON] [29]. The authors also comment that during the growth of primary aluminum dendrites, Fe is rejected in the residual liquid and the formation of the Al\({}_{5}\)FeSi phase occurs in the eutectic phase controlled by the higher nucleation rate and lower growth compared to the Al\({}_{5}\)FeSi intermetallic that form in the primary aluminum phase. As a result, this fraction of Al\({}_{5}\)FeSi intermetallic formed at low temperatures is finer, as shown in the SEM images shown in Figure 5.  
In spite of the dimensional changes of the Al\({}_{5}\)FeSi phase, variations in the amounts of this intermetallic phase were not proven as a function of the type of refiner used, as found by [PERSON] [27]. This author also explains that the entry of hydrogen, which causes submerged oxide films, is the cause of hydrogen porosity and acts as a nucleation site for Fe-rich intermetallic. This Al\({}_{5}\)FeSi phase nucleation phenomenon, which favors the proeutectoid formation of the phase, was not the main mechanism proven in the alloy processing conditions used in this work, where the intermetallic phase formed in the form of fine needles is mainly observed in the eutectic phase.