Synthesis and characterization of Mg-AZ91/AlN composites

This work presents the synthesis and characterization of metal matrix composites (MMCs) of magnesium alloy AZ91E reinforced with AlN (49 vol.%). Molten AZ91E magnesium alloy was pressureless infiltrated at 900 °C into AlN preforms sintered at 1450 °C with porosities around 51 vol.%. The composites obtained were microstructurally characterized through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Reinforcement distribution, microstructure, reaction products and some mechanical and thermoelectric properties were evaluated. SEM observations showed a homogeneous microstructure of matrix and reinforcement. AlN, Mg and Mg17Al12 phases were detected through XRD. TEM observations revealed the presence of Mg17Al12, AlN, and MgO precipitates. Results of mechanical characterization indicate average values of elastic modulus of 133 GPa and hardness of 24 HRC (260 HV). The coefficient of thermal expansion (CTE) was 9.53 × 10−6 °C−1 in the temperature range of 27–227 °C (300–500 K). The electrical resistivity was around 45.9 × 106 Ω cm at temperature of 25 °C.