Of late, magnesium (density = 1.738g/cc) has been trending in the automobile, aerospace, defense, sports, electronic and biomedical sectors, as it offers a tremendous advantage in light-weighting. In the realm of Mg based materials, magnesium nanocomposites, which are known to have good specific strengths and creep resistance, have not been commercially used as yet. This is because of their industrial unviability due to poor control of dispersion of reinforcement in the matrix, agglomeration of the nanoparticles due to their high surface energy leading to poor properties like ductility, inability to tailor matrix-reinforcement interface and poor ignition resistance of Mg matrix. These are crucial influencing factors in nanocomposites that, ultimately, dictate their properties and performance. Hence, the aims of this thesis are:​ (i) to control the above-mentioned microstructural limitations in nanocomposites and (ii) to synthesize superior nanocomposite, mainly, with a good combination of strength, ductility, weak texture and good ignition resistance.

This thesis proposes a novel controlled approach that combines the benefits of conventional processing routes with those of thermodynamic principles to synthesize in-situ and ex-situ magnesium nanocomposites, thereby enhancing the current state of art processing techniques of high performance nanocomposites. This work is divided into four stages, as discussed below.

In the first stage, identification of matrix is done by selecting Mg-Y alloys as potential matrix materials since they satisfy the thermodynamic, mechanical, chemical and physical properties criteria. Among the studied Mg-Y alloys, Mg-1.8Y alloy was chosen as the matrix owing to its superior combination of properties.

In the second stage, in-situ synthesis of nanocomposites by addition of favorable reinforcement i.e. ZnO nanoparticles to Mg-1.8Y matrix was achieved, through exploitation of the thermodynamic principles. Rod shaped Mg-Zn phase and Y2O3 nanoparticles were observed in the extruded material and a thorough structure and property evaluation was done to understand the mechanisms undergone by the nanocomposite.

In the third stage, conventional/ex-situ synthesis of nanocomposites was done by the addition of Y2O3 nanoparticles to Mg-1.8Y matrix, in order to understand the fundamental disparity between the in-situ and ex-situ nanocomposites. A significant finding was that the in-situ nanocomposites exhibited coherent matrixreinforcement interfaces in contrast to the ex-situ nanocomposites which exhibited incoherent interfaces. Further, the texture, micro-strain, microstructural evolution and properties of the ex-situ composites were significantly different as compared to their in-situ counterparts.

In the last stage, a nanocomposite was tailored by applying the in-situ synthesis technique such that the nanocomposite exhibits the required combination of strength, ductility, weak texture and non-flammable characteristics along with ease in synthesis, controlled distribution and tailored interfaces. For this, CaO reinforcement was chosen such that it promotes weak texture, improves ignition properties along with the mechanical properties. A detailed characterization of the Mg-1.8Y/1CaO nanocomposite demonstrates that it exhibits unparalleled properties. Therefore, it was ascertained that this synthesis technique, resultant of a vigilant choice of alloying element and reinforcement to Mg, is a solution to develop high performance magnesium nanocomposites, thereby enabling nanocomposites industrially realizable.