Effects of Reinforcement Content and Homogenization Treatment on the Microstructure and Mechanical Properties of in-situ TiB2/2219Al Composites

Abstract

Obtaining an appropriate grain size is crucial for Al alloys or Al matrix composites prior to processing, as it significantly influences the mechanical properties of components and workability during the manufacturing process. TiB₂ particles are exceptional grain refiners in Al and serve as excellent reinforcement particles for particulate-reinforced aluminum matrix composites. However, the optimal particle content for achieving excellent refinement and strengthening effects depends on the matrix composition and requires further investigation. Additionally, homogenization is essential for mitigating the element segregation in the ingot. Although it is anticipated that adding suitable particles can effectively inhibit undesired grain growth during homogenization, comprehensive investigations on this aspect are currently lacking. Therefore, TiB₂/2219Al matrix composites with varying reinforcement contents (0, 1, 3, 5 wt%) were fabricated through traditional casting followed by homogenization treatment to address these research gaps. The effects of reinforcement content and homogenization treatment on the microstructure and mechanical properties of in-situ TiB₂/2219Al composites were investigated. The results demonstrate a gradual strengthening of the refining effect with increasing particle concentration. Moreover, composites containing 3 wt% TiB₂ particles exhibit superior comprehensive mechanical properties in both as-cast and homogenized state. Additionally, potential orientation relationships are observed and calculated between undissolved Al₂Cu eutectic phase and submicron or nanometer-sized TiB₂ particles, resulting in a mixture structure with enhanced bonding strength. This mixture structure is continuously distributed along grain boundaries during solidification, forming a three-dimensional cellular network that acts as primary retarding forces for grain growth during homogenization. Furthermore, the established homogenization kinetic equations were further utilized to analyze the correlation between homogenization time and grain size, as well as the influence of homogenization temperature.