A Study on the Influence of Zr on the Strengthening of the Al-10% Al2O3 Composite Obtained by Mechanical Alloying

Al2O3 is a traditional strengthening phase in aluminum matrix composites due to its high hardness and melting point. At the same time, zirconium is an important alloying element for heat-resistant aluminum alloys. However, its effect on the structure and properties of Al-Al2O3 composites remains unexplored at present. In this work, the effect of the addition of Zr (5 wt%) on the microstructure and strengthening of the Al-10 vol% Al2O3 composite was investigated for the first time. Composite materials with and without Zr addition were obtained through mechanical alloying as a result of ball milling for 20 h followed by multi-directional forging (MDF) at a temperature of 400 °C. OM, SEM and XRD were used to study the microstructure and its parameters. The work showed that the use of mechanical alloying and MDF contributes to the formation of dense composite samples with a nanocrystalline microstructure and a uniform distribution of alumina particles. The addition of Zr contributes to a 1.4-fold increase in the microhardness and yield strength of a compact sample at room temperature due to the formation of Al3Zr (L12) dispersoids. It was been shown that the largest contribution to the strength of both materials comes from grain boundary strengthening, which is at least 50% of the yield strength. The resulting composites exhibit high heat resistance. For example, their compressive yield strength at 350 °C is approximately 220 MPa.