Influence of Zirconium and Processing Modes on Microstructure and Properties of Mechanically Alloyed Al-10%Al2O3 Composite

The effects of milling time and sintering temperature on the microstructure and properties of Al-10 vol.%Al₂O₃ composites with and without adding 5 wt.%Zr were investigated. Composite granules milled for 30 h were hot pressed at temperatures of 400°C and 500°C followed by annealing for 1 h. With increasing milling time, the microhardness of Al-10%Al₂O₃-5%Zr and Al-10%Al₂O₃ composite granules increased smoothly to ~ 230 HV and ~ 180 HV, respectively. Increasing the subsequent sintering temperature from 400°C to 500°C resulted in a decrease in porosity for both materials but also a decrease in strength properties with an increase in crystallite size. For the Zr-containing composite, the Al₃Zr-L1₂ phase was precipitated at 400 °C, and the tetragonal D0₂₃ phase was precipitated at 500°C. Due to the strengthening effect of Al₃Zr precipitates and oxide particles, the Al-10%Al₂O₃-5%Zr composite sintered at both temperatures exhibited a high compressive yield strength (290 and 230 MPa for 400°C and 500°C, respectively) at a test temperature of 300°C.