Optimization of ZrO2 nanoparticle Content for Superior Mechanical Behavior of 7075 Aluminum Composites

7075 aluminum alloy is widely recognized as one of the most important lightweight structural materials for aerospace, automotive, and defense applications due to its excellent strength-to-weight ratio and favorable mechanical properties. However, its relatively limited wear resistance, moderate hardness, and susceptibility to localized deformation restrict its performance under severe service conditions. In the present study, zirconium dioxide (ZrO₂) nanoparticles were incorporated into a 7075 aluminum matrix to enhance its structural, mechanical, tribological, thermal, and corrosion properties. Four composite systems were fabricated using the powder metallurgy technique: unreinforced 7075 Al (S1), 7075Al + 1 wt.% ZrO₂ (S2), 7075Al + 3 wt.% ZrO₂ (S3), and 7075Al + 5 wt.% ZrO₂ (S4). Structural characterization by XRD confirmed the presence of α-Al and tetragonal ZrO₂ phases without undesirable reaction products. The average crystallite size decreased from 41.56 nm for S1 to 30.04 nm for S3, indicating significant grain refinement. FESEM, EDS, AFM, and TEM analyses revealed improved nanoparticle dispersion, reduced porosity, and enhanced interfacial bonding for the S3 composite. Density measurements showed a maximum density of 2.84 g cm⁻³ and minimum porosity of 1.82% for S3. Mechanical characterization demonstrated that S3 exhibited the highest microhardness (≈182 HV), ultimate tensile strength (486 MPa), compressive strength (684 MPa), impact energy (18.9 J), nanohardness (3.85 GPa), and fatigue endurance limit (248 MPa). Tribological evaluation revealed the lowest wear loss (8.6 mg) and coefficient of friction (0.46) for S3. Furthermore, corrosion and thermal expansion analyses showed improved corrosion resistance and reduced coefficient of thermal expansion. Overall, the results demonstrate that 3 wt.% ZrO₂ is the optimum reinforcement content, providing the best balance between strength, toughness, wear resistance, thermal stability, and corrosion performance for advanced lightweight engineering applications.