Fabrication and properties of Al/AlN composites by a pressureless infiltration process

Al/AlN composites with different Al content were prepared by infiltrating AlN preforms with molten AlSi7Mg alloy. Phase composition of the composites was characterized by XRD. Microstructure of the composites was observed by optical microscope and SEM. Mechanical and thermal properties of the composites with different Al content were also tested. The results show that Al/AlN composites with relative density of more than 98.5% can be obtained by infiltrating the AlN preforms with different porosity at 900℃ in N₂ atmosphere. There is nearly no shape and dimension change of AlN preforms during the infiltration process. The mechanical and thermal properties of the composites vary with Al content. As Al volume fraction varies from 38% to 62%, the Vickers hardness of the composites decreases from HV 715 to HV 203, the bending strength decreases from 492 MPa to 388 MPa, the room temperature thermal conductivity of the composites increases from 73 W/(m·K) to 120 W/(m·K), and the mean linear thermal expansion coefficient (TEC) between room temperature and 200 ℃ varies from 8.60×10^-6 K^-1 to 1.11×10^-5 K^-1. The results also show that the relation between the TEC and Al volume fraction of the composites agrees with the Kerner model.