**4.2 Mechanical properties**

As seen in **Table 2**, the micro-hardness and yield strength data of the fabricated composites reveals that PP900-AE composite experiences hardness or strength enhancement with an increment of 332.0% as compared to that of the base AE44 Mg-alloy. However, there is only marginal increment in the hardness or yield strength of PP900-AZ composite as compared to the unreinforced AZ91 Mg-alloy. The possibility of impeding the movement of dislocation within the primary α-Mg phase seems to be futile as most of the SiCNO particles are entrapped within discontinuous network of β-Mg17Al12 phase (**Figure 8(b)**) [1]. Nevertheless, PP900-AZ composite is expected to offer high temperature creep resistance as unstable β-Mg17Al12 phase is dispersed with thermally stable SiCNO particles. The observed significant improvement in hardness for PP900-AE composites is mainly associated with the contribution of Taylor strengthening and load transfer mechanisms. The contribution of Taylor strengthening is massive in case of PP900-AE specimen as compared to that of PP900-AZ specimen. Notice that all of the fabricated in-situ P-MMCs were subjected to temperature difference (∆T) of about 873 K during solidification processing. Therefore, the probability of achieving highest density of dislocations increases steadily with fabricated composites owing to larger thermal strain induced during solidification. However, thermal mismatch effect loses its importance in first place for the case of PP900-AZ specimen. This can be associated with the entrapment of SiCNO particles by β-Mg17Al12 phase, which in turn generates lesser number of dislocations within the primary α-Mg


**Table 2.** *Mechanical properties of the fabricated In-situ Mg-alloy based composites.* phase which eventually leads to a lowest Taylor strengthening. Next to Taylor strengthening, the load transfer strengthening also plays a major role in enhancing the hardness of the fabricated composites. This can be mainly associated with load bearing capacity of hard ceramic phase due to presence of higher volume fraction of reinforced PDC particles (i.e. *Vf* ≈ 0.28) in PP900-AE specimen [1].
