Exploring the mechanical response of aluminum composites reinforced with SiN and ZrO2: a novel hybrid microwave sintering approach

The present study investigates the mechanical behavior of AA7075-based hybrid metal matrix composites reinforced with silicon nitride (SiN) and zirconium dioxide (ZrO₂), fabricated by a novel hybrid microwave sintering technique. Composites are developed with the constant SiN content of 7 wt.% and the ZrO₂ content varying between 1 and 4 wt.% to understand the influence of dual-phase ceramic reinforcement. The microstructural analysis shows a uniform dispersion of reinforcement at a lower ZrO₂ content, contributing to the improved tensile strength and hardness through such mechanisms as the load transfer, Orowan looping, and grain refinement. The composite reinforced with 7 wt.% SiN and 3 wt.% ZrO₂ demonstrates the best mechanical performance, achieving a 202 MPa tensile strength and 116 HV hardness. However, the impact strength decreases with increasing ZrO₂ content, reaching the maximum of only 10.25 J at 1 wt.% and dropping to 9.72 J at 4 wt.%. The X‑ray diffraction analysis confirms the formation of the brittle Al₄C₃ phase at 4 wt.% ZrO₂, which, despite the presence of thermally stable Al₃Zr, contributes to a decline in mechanical properties. Furthermore, microstructural defects such as agglomeration and pore formation at higher ZrO₂ contents act as crack initiation sites. This study confirms that hybrid microwave sintering, when optimized with suitable reinforcement levels, is a promising technique for fabricating lightweight, high-strength aluminum composites for advanced engineering applications.