Synergistic enhancement of in-situ (Al2O3+ZrB2) nanoparticles and Er on microstructure and stress corrosion resistance of 7075Al matrix composites

Abstract

This study explores the influence of in-situ (Al2O3+ZrB2) nanoparticles and erbium (Er) synergistic strengthening on the microstructure and stress corrosion resistance of 7075 aluminum (7075Al) composites. The Al2O3 and ZrB2 nanoparticles were successfully synthesized via in-situ reactions by mixing K2ZrF6 and B2O3 salts in a stoichiometric ratio, though the resulting nanoparticles exhibited severe clustering. The introduction of Er significantly refined the grain structure of the composites, transforming coarse dendritic grains into fine equiaxed grains at 0.2 wt% Er, with an average grain size of 26.45 μm. Additionally, Er addition enhanced the wettability between the matrix and nanoparticles, promoting a more homogeneous distribution of reinforcement particles and mitigating particles agglomeration. The formation of dispersed nanoparticles and Al3Er phases suppressed recrystallization during heat treatment, preserving a high fraction of low-energy small-angle grain boundaries in the deformed structure. This microstructural stabilization inhibited η (MgZn2) phase precipitation, facilitating a more uniform distribution of η-phase particles that obstruct stress corrosion cracks propagation. Slow strain rate test analysis indicated that the ultimate tensile strength (UTS) and elongation of 7075Al composites increased to 652.28 MPa and 18.79 %, respectively, with 3 vol% (Al2O3+ZrB2) nanoparticles and 0.2 wt% Er addition, while the stress corrosion susceptibility index decreased to 13.4. These findings demonstrate that in-situ (Al2O3+ZrB2) nanoparticles and Er synergistic strengthening plays a critical role in enhancing both the mechanical performance and stress corrosion resistance of 7075Al composites, offering promising potential for advanced structural materials in aerospace.

Keywords

• In-situ nanoparticles
• Precipitates
• Grain refinement
• Uniform distribution
• Inhibition of recrystallization
• Stress corrosion resistance