**6. Microstructure and mechanical behavior of magnesium containing HEAs**

Microstructure of a material has a direct influence on its mechanical behaviors. Equiatomic MgMnAlZnCu HEA produced using induction melting consists of a matrix and a floral pattern where the floral pattern is rich in Al-Mn icosahedral quasicrystals and the matrix consists of an HCP phase comprised of all the alloying elements [31]. The presence of the quasicrystals is responsible for the increased hardness in this alloy, which gradually increases upon increasing the cooling rate. It is worth noting that Al-Mn quasicrystals are thermally stable. The increase in cooling rate also changes the plasticity of the alloy and hence, it increases the elasticity [31]. The microstructures are given in the following **Figure 5(a)**. Increasing the amount of Mg in the alloy reduced the Δ*Hmix* , as a result, there is increase in the amount of SS phases [32]. Along with the HCP and icosahedral quasicrystalline phases, a pure Mg and Mg7Zn3 phases are present in Magnesium

#### **Figure 5.**

*(a) Equiatomic MgMnAlZnCu (Induction melting in Ar atmosphere, cooled using brine in Cu mold), (b)* Mg33ð Þ MnAlZnCu <sup>67</sup> *(Induction melting in Ar atmosphere, Air cooling in Cu mold), (c)* Mg43ð Þ MnAlZnCu <sup>57</sup> *(Induction melting in Ar atmosphere, Air cooling in Cu mold), (d)* Mg45*:*6ð Þ MnAlZnCu <sup>54</sup>*:*<sup>4</sup> *(Induction melting in Ar atmosphere, Air cooling in Cu mold), (e)* Mg50ð Þ MnAlZnCu <sup>50</sup> *(Induction melting in Ar atmosphere, Air cooling in Cu mold) (Reprinted with permission from Refs. [31,32]).*
