## 4 Conclusions  
Magnesium alloy composites (AZ91/x-Si\({}_{3}\)N\({}_{4}\)) were fabricated by stir casting using predefined casting parameters. The physical, mechanical, wear, and metallurgical properties of the fabricated composites were investigated. The following conclusions can be drawn from the study:  
1. Physical properties such as density (experimental and theoretical) and porosity were increased due to the presence of Si\({}_{3}\)N\({}_{4}\) particles. The maximum porosity was depicted to be 2.01%, which is considerable for use in applications.
2. Mechanical properties like hardness and strength (compressive, tensile, impact, flexural, and Young's modulus) were enhanced and found to be 76 HBN (231 MPa, 425 MPa, 29 J/cm\({}^{2}\), 125 MPa, and 98 GPa) consecutively at 9 wt.% of Si\({}_{3}\)N\({}_{4}\), whereas elongation decreased. Further, the forge ability was augmented when increasing the load, while it declined on addition of the reinforcement.
3. Wear characteristic evaluation showed a decrease in wear loss due to the presence of Si\({}_{3}\)N\({}_{4}\) particles, which act as a solid lubricant when first separated from the parent alloy. This property makes the material suitable for biomedical implants having relative motion, as after initial wear it becomes self-lubricating. Mg being biocompatible and biodegradable aids in human bone development; this quality of the AZ91 composite  
Figure 18: SEM micrographs (at different \(\times\)) of AZ91 alloy and Si\({}_{3}\)N\({}_{4}\) (**a**,**b** at 3000\(\times\)), AZ91/x-Si\({}_{3}\)N\({}_{4}\) composites samples highlighting Si\({}_{3}\)N\({}_{4}\) (**c**,**d** at 1000\(\times\)), tensile fractured samples showing fracture mechanism (**e**,**f** at 100\(\times\) and 3000\(\times\), respectively) and worn surface at 100 N load, sliding speed 2 m/s, and 1000 m sliding distance (**g**.**h at 200\(\times\)).  
makes it a strong contestant for biomedical and prosthetic applications. Moreover, magnesium and its alloys are regarded as some of the most important materials for energy storage because they have the ability to store hydrogen gas as magnesium hydride. Among the available materials for renewable energy storage, magnesium has the highest theoretical storage capacity at 7.6 weight percent and an outstanding thermodynamic reversibility.
* Morphological study verified the existence of the reinforced particles in the parent alloy. SEM of the fractured sample showed that the ductile fracture is more dominant over the brittle fracture. Further, various wear mechanisms were predicted on the worn surfaces.  
Conceptualization, M.T.A.; methodology, M.T.A., D.H. and S.A.; data curation, A.M.A. and A.A.; writing--original draft preparation, M.T.A.; writing--review and editing, T.A., A.M.A. and A.A.; funding acquisition, T.A. All authors have read and agreed to the published version of the manuscript.  
The authors extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number ISP-2024.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.