In-situ Mg matrix composites are fabricated by combining both liquid-and solid-state processing routes. Firstly, liquid polymer was injected into the molten Mg at a temperature of 800 o C to initiate pyrolysis. In-situ pyrolysis aids in the conversion of liquid polymer into sub-micron sized SiCNO particles (mean particle size in the range of 0.5-1 m) and Mg 2 Si particles. Most of the polymer derived SiCNO particles were pushed by the solidification front and as a result segregated at the grain boundaries of as-cast composites (mean grain size in range of 50-65 m) during subsequent solidification process. Formation of Mg 2 Si phase could be minimized by © 2017. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2reducing the pyrolysis temperature from 800 to 700 o C. Single pass friction stir processing (FSP) of these as-cast composites lead to improved homogeneity in the SiCNO particle distribution, particle refinement (mean particle size of about 200-300 nm) and grain refinement (mean grain size in range of 2.5-3.5 m). Mechanical properties (hardness, compressive yield stress, ultimate compressive stress, strain to failure and strain hardening exponent) of the FS processed composites were enhanced significantly as compared to their as-cast counterparts. Strengthening mechanisms and numerical models are being evoked to explain the observed yield strength in these two stage processed composites.

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In-situ magnesium matrix composites with three different matrix materials (including Mg, AZ91 and AE44 Mg-alloys) were fabricated by injecting cross-linked polymer directly into the molten Mg/Mg-alloys, and having it convert to the 2.5 vol% SiCNO ceramic phase using liquid stir-casting method. In-situ chemical reaction took place within the molten slurry tending to produce 42 and 18 vol% Mg 2 Si crystals in Mg and AE44 matrix composites, respectively but not in AZ91 matrix composite. Microstructural evolution of Mg 2 Si crystals was discussed on the basis of availability of heterogeneous nucleation sites and amount of Al-atoms in the molten slurry. The observed micro-hardness and yield strengths are enhanced by factor of four to three as compared to their unreinforced counterparts, and Taylor strengthening was found to be the predominant strengthening mechanism in magnesium and AE44 matrix composites. Summation model predicted the yield strengths of the fabricated composites more preciously when compared to Zhang and Chen, and modified Clyne models.

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