In situ fabrication of (α-Al2O3 + Al3Zr)/Al composites in an Al–ZrO2 system

Synthesis of a (α-Al2O3 + Al3Zr)/Al in situ composite via exothermic dispersion synthesis (XD) process in an Al–ZrO2 system has been investigated. Thermodynamic analysis indicates that the reaction between Al and ZrO2 can spontaneously occur due to its negative Gibbs free energy of the Al–ZrO2 system. When the reinforcement volume fraction is 30 vol.%, there is only one exothermic peak observed in the DSC curve. The final combustion products are α-Al2O3 particles and Al3Zr blocks, which distribute uniformly in the aluminum matrix. The tensile strength, elongation rate and micro-hardness are 215.2 MPa, 3.0% and 304 MPa, respectively. However, if the reinforcement volume fraction increases to 100 vol.%, two exothermic peaks are observed in its corresponding DSC curve and the peak intensities are significantly increased. When the heating rates are 10 °C/min, 20 °C/min and 30 °C/min, the initiation temperatures are 744 °C, 776 °C and 782 °C, respectively. The reactions occurred in the Al–ZrO2 system have two steps: the first is that the Al atom reacts with ZrO2 to produce the α-Al2O3 and active Zr atoms, and the second is that the active Zr atoms disperse into the matrix and react with Al to form Al3Zr. The values of activation energy of the two reactions are around 315.8 kJ/mol and 191.1 kJ/mol, respectively.