**3. Results and discussion**

## **3.1 Intermetallic phases**

**Figure 2** shows microstructures obtained at SEM microscope for specimens of alloy EN AC 51100 with Zn and EN AC 51100 without Zn addition. Different intermetallic phases are noticeable from **Figure 2a**: Al-Fe-Mn-Si phases (spectrums 1 and 4), the eutectic α-Al/Al3Mg2 phase (spectrum 5) and Mg2Si phase (spectrums 2 and 5). Mainly, Al3Mg2 is characterized by the typical acicular shape and the black colour, as in spectrum 2 [16]. Mg2Si can be present inside the eutectic α-Al/ Al3Mg2 phase (grey precipitations). Similar results were noticed in **Figure 2b** for the analysed specimen of alloy EN AC 51100 with Zn addition. In particular, Zn was detected in spectrums 3, 4 and 5, along with Mg and Si. White intermetallic




**Figure 2.** *SEM-EDS analysis of specimen EN AC 51100 (a) and EN AC 51100 + Zn (b).*

**Figure 3.**

*SEM-EDS analysis of specimen EN AC 47000 (a) and EN AC 47000 + Zn (b).*

compounds contain a high amount of Fe and Mn were also noticed in **Figure 2a** spectrum 4 and **Figure 2b** spectrum 2, identifiable as α-Al (Fe, Mn) Si phase.

**Figure 3** shows microstructures obtained at SEM microscope for specimens of alloy EN AC 47000 with Zn and EN AC 47000 without Zn addition. In **Figure 3a**, white intermetallic compounds contain Fe, Mn and Cu, (spectrums 1, 2 and 5) similar to those observed in alloy EN AC 51100 were observed. Spectrum 4 is an intermetallic phase Al-Si-Mg-Cu also known as Q phase [19]. Similarly, intermetallic phases detected in **Figure 3b** highlight the presence of the Q phase in spectrum 2. Spectrum 3 highlights a eutectic silicon polygonal particle. The Zn was noticed in the intermetallic Fe-based, commonly known as Chinese script, α-AlFeSiCuMg.

#### **3.2 FGMs interfaces**

**Figure 4** reports the SEM-EDS maps of the FGMs interfaces obtained. **Figure 4a** highlights the Si diffusion into Mg-based alloy, especially into the eutectic regions α-Al/Al3Mg2.

Iron-based intermetallic compounds are largely diffused into EN AC 47000 alloy, as noticeable from the maps; furthermore, Mg was detected in both the alloys with a slight depletion at the interface. Although Si was detected at the interface

*Development and Characterization of New Functionally Graded Aluminium Alloys DOI: http://dx.doi.org/10.5772/intechopen.101022*

#### **Figure 4.** *EDS maps analysis in FGM without Zn interface.*

into the EN AC 51100 bulk, in the alloy bulk Si was noticed only in a few intermetallic phases. In fact, EDS map analysis conducted into the EN AC 51100 bulk did not evidence appreciable amounts of silicon, as is possible to note in **Figure 5**.

After Zn addition, Zn-based intermetallic compounds are detected. **Figure 6** shows the SEM-EDS maps for FGM with Zn addition in alloy EN AC 47000. Overall, it seems that the Zn amount was not enough to be appreciated in the EDS maps near the interface; on the other hand, Zn was clearly noticed in the bulk alloy of the sample made in single alloy EN AC 47000 + Zn, as is shown in **Figure 7**.

Interface maps for FGM containing Zn in both alloys clearly show the presence of Zn, with a slight depletion into the interface between the compositions (see **Figure 8**). Furthermore, as also noticed in the other FGMs, Mg depletion was observed near the alloy interface. This depletion may be explained considering the alloy mixing that took place during the pouring of the second composition; in fact, near the interface, these were mainly noticed iron-based intermetallic phases (**Figures 4** and **6**).

No defects such as oxide layers or shrinkage were observed in the FGM interfaces.

**Figure 5.** *EDS maps analysis of EN AC 51100 bulk.*

**Figure 6.** *EDS maps analysis in FGM (with Zn addition in alloy EN AC 47000) interface.*

**Figure 7.** *EDS maps analysis of EN AC 47000 bulk.*
