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

Abstract Synthesis of a (α-Al 2 O 3 + Al 3 Zr)/Al in situ composite via exothermic dispersion synthesis (XD) process in an Al–ZrO 2 system has been investigated. Thermodynamic analysis indicates that the reaction between Al and ZrO 2 can spontaneously occur due to its negative Gibbs free energy of the Al–ZrO 2 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-Al 2 O 3 particles and Al 3 Zr 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–ZrO 2 system have two steps: the first is that the Al atom reacts with ZrO 2 to produce the α-Al 2 O 3 and active Zr atoms, and the second is that the active Zr atoms disperse into the matrix and react with Al to form Al 3 Zr. The values of activation energy of the two reactions are around 315.8 kJ/mol and 191.1 kJ/mol, respectively.