Effects of TiO2/ZrO2 Ratio on Microstructure, Mechanical Properties and Metallization Performance of 95 Al2O3 Ceramics

Alumina (Al2O3) ceramic sealing rings have attracted considerable attention in power battery packaging applications due to their excellent chemical stability, electrical insulation, and mechanical properties. In this study, 95% Al2O3 ceramics were fabricated using a CaO–SiO2–TiO2–ZrO2 quaternary sintering aid system, and the effects of the TiO2/ZrO2 ratio on densification behavior, microstructural evolution, mechanical properties, and Mo–Mn metallization bonding performance were systematically investigated. As the TiO2/ZrO2 ratio decreases, the grain size first increases and then decreases, which is attributed to the pinning effect of the Al2TiO5 phase formed by excessive TiO2 at grain boundaries that inhibits grain growth, whereas an appropriate TiO2/ZrO2 ratio promotes grain growth. After sintering at 1600 °C and 1625 °C, the density first increases and then decreases with decreasing TiO2/ZrO2 ratio; at 1650 °C, accelerated grain boundary migration engulfs residual pores into grain interiors, reversing the density trend. The flexural strength exhibits a rise–and–fall pattern with decreasing TiO2/ZrO2 ratio at all sintering temperatures, governed by the synergistic interplay among densification, grain size, and grain boundary characteristics. The metallization tensile strength first decreases and then increases with decreasing TiO2/ZrO2 ratio for ceramics sintered at 1600 °C and 1625 °C, but shows the opposite trend for those sintered at 1650 °C, governed by the glass–phase diffusion capability and surface roughness, respectively. The Al–2–2 sample (TiO2/ZrO2 = 1/1) sintered at 1650 °C exhibits the optimal overall performance, achieving a flexural strength of 351 ± 46 MPa and a metallization tensile strength of 153 ± 2 MPa.