**7.1 Microstructural characterisation**

Microstructural studies conducted on the casted hybrid composites sample revealed the equiaxial grain morphology and monolithic showed coarse grain structure. The unreinforced AZ91 showed coarse dendrites and SEM observation indicated the presence of the α-Mg matrix which was surrounded by inter dendrite and β phase (Mg17Al12). Further SEM image with EDS analysis was used to verify the microcomposition of the unreinforced AZ91 magnesium alloy. The EDS analysis shows the presence of magnesium, aluminium and zinc peaks but manganese cannot be detected due to low content of addition (0.3%) as shown in **Figure 4**.

Addition of titanium and graphene to AZ91 magnesium has positively refined the grain size. The AZ91 magnesium alloy, AZ91 + 1% Ti + 0.5%Gr and AZ91 + 2% Ti + 0.5%Gr showed the intermetallic compounds appeared brighter surrounding the grains. The titanium combines with aluminium during initial stage of solidification. Hence at eutectic temperature there is less content of aluminium available to form β phase (Mg17Al12) [23]. The EDS analysis proves the presence of graphene of the

**Figure 4.** *AZ91/1% Ti/0.5% Gr (a) optical micrograph (b) SEM image (c) EDS spectrum.*

**Figure 5.**

hybrid composites [24] depicted in **Figure 4**. The other combination of hybrid composite AZ91 magnesium alloy was with titanium dioxide and graphene also shows the discontinuous β precipitates are found around the grains. The EDS spectrum clearly signifies in the **Figures 4**–**7** and reveals the presence of magnesium, aluminium, zinc, graphene and titanium dioxide. The titanium dioxide as overlapped with Ti and oxygen. It was observed that the reinforcements are uniformly distributed in the AZ91 magnesium matrix for all the hybrid composites. It was also observed no voids or cracks from the micrographs which is assisted by density measurement.
