3. Results and discussion

## 3.1 Surface characterization of laser-treated samples

Figure 2 illustrates the morphology of hypereutectic Al-2.0 wt.% Fe alloy lasertreated analyzed by OM and FESEM, showing characteristics of the weld fillets formed during laser treatment. OM image in Figure 2(a) shows the surface morphology, while FESEM image in Figure 2(b) shows the morphology in more detail on the weld fillets region and between the weld fillets. As can be seen, on the weld fillet region contains a higher concentration of defects than between the weld fillets region. Zhang et al. [9] and Kalita et al. [1] reported a similar result. In Figure 2(b), the distance between the weld fillets is approximately 300 μm. Note the presence of several nanopores, which may be attributed to volatilization of inclusions or vaporization of the substrate itself, caused by hydrogen and moisture in the atmospheric air, which are absorbed in the laser-treated region, favoring the formation of pores. These results are consistent with reported of Yilbas et al. [10] and Pariona et al. [2]. The micrograph in Figure 2(c) shows on the weld fillets region under higher magnification, showing concentration of defects in more detail. Figure 2(d), also at increased magnification, shows between the weld fillets region, revealing a more uniform morphology with a columnar-like structure. Pariona et al. [2] also observed these structures in Al-1.5 wt.% Fe and Li et al. [11], these last authors stated that Al-Co-Ce alloys contain Al-rich eutectic regions whose structure and was similar to Al-2.0 wt.% Fe alloy. Peculiar characteristics of the microstructure shown in Figure 2(d), so it presented highly improved properties, such as: hardness, corrosion and wear resistance, which is resulted of precipitates dissolution and formation of metastable phases, to respect, several authors have reported similar results, among them, Damborenea [12], Pinto [13], Yue et al. [14], Majumdar et al. [15], Bertelli et al. [16], and Pariona et al. [2].

because, according to Mondolfo [17], formation Al-Fe alloys is impaired, when the material contains coarse Al3Fe particles or intermetallic phase, which tend to produce microcracks and reduce formability, whereas, this does not occur with pres-

(a) OM, and (b) FESEM images of the morphology of hypereutectic Al-2.0 wt.% Fe alloy LSR-treated surface, showing regions on the weld fillet and between the weld fillets, (c) on the weld fillet region at increase

Effect of Microstructure on Microhardness and Electrochemical Behavior in Hypereutectic…

DOI: http://dx.doi.org/10.5772/intechopen.81095

ence of Al6Fe finely dispersed in Al-2.0 wt.% Fe alloy, however, the Al3Fe intermetallic phase does not appear in this alloy, as demonstrated by Pariona and Micene [7] by low-angle X-Ray diffraction analysis. Meanwhile, Gremaud et al. [18] reported, increasing the cooling rate of hypereutectic alloys containing up to 9 wt.% of Fe suppresses formation of stable Al3Fe phase, which is replaced by Al6Fe phase,

magnification, and (d) between weld fillets region under higher magnification.

3.2 Characterization in the cross section of laser-treated and untreated

Figure 3 shows the cross-sectional analysis by OM. In this region can be observed the penetration depth of the treated region was around 250 μm, and the distance between the weld fillets was approximately 300 μm (also was shown in the first micrograph, Figure 2). Note clearly visible difference of the treated region

The laser melted surface micrograph is shown at Figure 3, as can be seen it is free of microcracks and the melted regions are free of precipitates too. Fine microstructure of the melt zone is attributed to high cooling rate. Microstructure obtained in this work is similar to other laser melted aluminum alloys reported in the literature, i.e., Watkins et al. [19] reported that the microstructure of laser melted AA 2014 consists of columnar grains growing epitaxially from the substrate. Although,

which confirms our result.

microstructure and of the substrate.

materials

179

Figure 2.

Pariona et al. [2] analyzed hypoeutectic Al-1.5 wt.% Fe alloy LSR-treated and observed presence of microcracks between the weld fillets. However, this phenomenon in this study was not observed in hypereutectic Al-2.0 wt.% Fe alloy LSRtreated, as can be seen in Figure 2(c) and (d). Absence of microcrack was expected, Effect of Microstructure on Microhardness and Electrochemical Behavior in Hypereutectic… DOI: http://dx.doi.org/10.5772/intechopen.81095

Figure 2.

surface-treated and untreated samples were prepared with epoxy resin to expose a

Schematic diagram of weld fillets on the sample surface and in the cross-sectional area showing the penetration

Figure 2 illustrates the morphology of hypereutectic Al-2.0 wt.% Fe alloy lasertreated analyzed by OM and FESEM, showing characteristics of the weld fillets formed during laser treatment. OM image in Figure 2(a) shows the surface morphology, while FESEM image in Figure 2(b) shows the morphology in more detail on the weld fillets region and between the weld fillets. As can be seen, on the weld fillet region contains a higher concentration of defects than between the weld fillets region. Zhang et al. [9] and Kalita et al. [1] reported a similar result. In Figure 2(b), the distance between the weld fillets is approximately 300 μm. Note the presence of several nanopores, which may be attributed to volatilization of inclusions or vaporization of the substrate itself, caused by hydrogen and moisture in the atmospheric air, which are absorbed in the laser-treated region, favoring the formation of pores. These results are consistent with reported of Yilbas et al. [10] and Pariona et al. [2]. The micrograph in Figure 2(c) shows on the weld fillets region under higher magnification, showing concentration of defects in more detail. Figure 2(d), also at increased magnification, shows between the weld fillets region, revealing a more uniform morphology with a columnar-like structure. Pariona et al. [2] also observed these structures in Al-1.5 wt.% Fe and Li et al. [11], these last authors stated that Al-Co-Ce alloys contain Al-rich eutectic regions whose structure and was similar to Al-2.0 wt.% Fe alloy. Peculiar characteristics of the microstructure shown in Figure 2(d), so it presented highly improved properties, such as: hardness, corrosion and wear resistance, which is resulted of precipitates dissolution and formation of metastable phases, to respect, several authors have reported similar results, among them, Damborenea [12], Pinto [13], Yue et al. [14], Majumdar et al. [15],

Pariona et al. [2] analyzed hypoeutectic Al-1.5 wt.% Fe alloy LSR-treated and observed presence of microcracks between the weld fillets. However, this phenomenon in this study was not observed in hypereutectic Al-2.0 wt.% Fe alloy LSRtreated, as can be seen in Figure 2(c) and (d). Absence of microcrack was expected,

top surface.

Figure 1.

Aerospace Engineering

3. Results and discussion

depth of Vickers indenter in LSR-treated sample.

Bertelli et al. [16], and Pariona et al. [2].

178

3.1 Surface characterization of laser-treated samples

(a) OM, and (b) FESEM images of the morphology of hypereutectic Al-2.0 wt.% Fe alloy LSR-treated surface, showing regions on the weld fillet and between the weld fillets, (c) on the weld fillet region at increase magnification, and (d) between weld fillets region under higher magnification.

because, according to Mondolfo [17], formation Al-Fe alloys is impaired, when the material contains coarse Al3Fe particles or intermetallic phase, which tend to produce microcracks and reduce formability, whereas, this does not occur with presence of Al6Fe finely dispersed in Al-2.0 wt.% Fe alloy, however, the Al3Fe intermetallic phase does not appear in this alloy, as demonstrated by Pariona and Micene [7] by low-angle X-Ray diffraction analysis. Meanwhile, Gremaud et al. [18] reported, increasing the cooling rate of hypereutectic alloys containing up to 9 wt.% of Fe suppresses formation of stable Al3Fe phase, which is replaced by Al6Fe phase, which confirms our result.
