<p>In order to reduce energy consumption and simplify experimental operation, an attempt has been made to in situ synthesize ZrB₂/Al composites by Al–K₂ZrF₆–KBF₄ system at the low temperature (665 ± 2&#xa0;°C) that near the melting point of aluminum, accompanied by the mechanical stirring applying at salts/melt interface to inhibit the formation of particle agglomeration. Thermodynamic and mechanic testing were carried to reveal the effect of the process improvements on the structure and properties of the composites. The results showed that Al–K₂TiF₆–KBF₄ can still react violently and quickly at this low temperature. The low temperature did not cause significant loss of reactants, mainly Zr and B elements fully reacted with an atomic ratio of 1:2 and formed ZrB₂ particles, and composites with different particle contents (1, 3, 5, and 7 wt%) could be successfully fabricated. The low-temperature preparation combined with salts/melt interface mechanical stirring did not cause microstructure deterioration, instead could reduce ZrB₂ particle size and enhance the mechanical properties of the composites. As the ZrB₂ content increased from 1 to 7%, nano-ZrB₂ particles distribution was gradually improved, and both the matrix grain size and the average ZrB₂ particle size decreased gradually. The fabricated composites had superior mechanical properties as compared with the matrix and the reference composites fabricated at high temperature. The experimental <i>σ</i>_0.2 and UTS of the fabricated 7 wt% ZrB₂/Al composite were 2.5 and 1.6 times higher than those of the matrix. The concept of effective particles was introduced to explain the discrepancy between the theoretical and experimental values according to the microstructure observation. A parabolic curve function was established to describe the relationship between the effective particle fraction and the nominal particle content, and can be used to predict the mechanical properties of the prepared composites.</p>