# Effect of Ti-B Grain Refiners on Wear and Corrosion of the A332 Alloy with Sr Modification
## 4 Discussion
### Effect of Grain Refiner Addition on Wear Behavior  
After the ball-on-disk test, it could be seen that some debris accumulated in the sample without grain refiner (Figure 10a). These particles probably accumulated in some parts promoting the formation of deeper structures before, where the material was taken from. This mechanism was also visualized and explained by [PERSON] et al. [40], who also noted that a smaller amount of debris observed, may reduce the friction coefficient.  
[PERSON] et al. [41], when analyzing the effect of Al-8B grain refiner and heat treatment conditions in the wear of Al-12 Zn-3 Mg-2.5 Cu aluminum alloys, observed similar results with delamination and adhesion mechanisms. The authors assert that delamination wear is the dominant mechanism in the early stages of sliding, probably due to the microstructural formation. The presence of metal oxides on the surface is also characteristic of this process. [PERSON] et al. [42] observed similar results when studying the effect of Al5 Ti1B grain refiner on the dry sliding wear behavior of an Al-Zn-Mg-Cu alloy. The authors show that regions with a detached layer in the form of craters or cavities could indicate locally adhesive wear, probably because of the formation and breaking of micro-welds during sliding.  
Thus, overall worn-surface study reveals that the A332 alloys tend to exhibit three types of wear mechanisms such as adhesive, abrasive, and oxidative wear. Abrasive wear was mainly observed in the case of as-cast alloy without refiners. Adhesive and oxidative types of wear were mostly observed in the case of the alloy containing grain refiner [43].  
The analysis of wear resistance material showed lower values in the as-cast samples without grain refiners compared to samples with grain refiners (Al5 Ti1B or Al5 Ti2B). This behavior occurs despite the lower friction coefficient (\(\mu\) = 0.48) observed in samples refined with Al5 Ti1B. This previous behavior is related to the incidence of microstructural refinement and Al5 FeSi phase and hardness in the wear mechanisms of the refined A332 alloy. It was proved that the microstructural refinement led to an improvement in wear resistance according to Archard's Law of Wear, that is, the increase in hardness obtained by grain refinement, provided a increase in material wear resistance [43].  
In addition, the smallest grain size from Al5 Ti2B also relate to the higher wear resistance, although the values are very close to Al5 Ti1B. [PERSON] et al. [44], after analyzing commercially pure Al grain refined using Al-Ti and Al-Ti-B grain refiner master alloys in the wear test, found similar results. The authors commented that wear rates decreased with a decrease in grain size, probably due to grain shape transformed from columnar to equiaxed. In their work, the grain size differences were more distinct, which could lead to these observed results.  
However, other microstructural factors such as the presence of Al5 FeSi intermetallic phases, as well as volume fraction, thickness, and size, can influence the wear resistance of the alloy. In this sense, [PERSON] et al. [45] found that similar needle intermetallic phases decreased the wear resistance in Al-Si alloys, due to the higher tendency to form micro-cracking.  
Summarizing the findings, using grain refiners (5 Ti1B and Al5 Ti2B) helped improve the wear resistance of the A332 cast samples. The modifications in intermetallic phases may be the main cause for the observed wear resistance increase.