Research on the Mechanism of High-Performance Aluminum Alloy Casting of Frozen Sand Mold Coupled with Negative Pressure

Aluminum–copper alloys, typified by ZL205A (AlCu5MnTiCdV, GB/T 1173), pose severe casting challenges due to their wide solidification interval, poor fluidity, and susceptibility to gas porosity and shrinkage defects. This study introduces a negative-pressure frozen sand mold casting process as a solution to these challenges and systematically quantifies its thermal and microstructural advantages over conventional resin sand and atmospheric frozen sand casting. Using inverse heat conduction analysis of multi-point thermocouple data, the interfacial heat transfer coefficient (IHTC) was quantitatively determined for 14 experimental conditions varying in mold type, pressure level, moisture content (2–6 wt.%), and initial freezing temperature (−20 to −40 °C). The results demonstrate that negative pressure combined with frozen sand molds (6 wt.% moisture, −40 °C) produces the highest active-period average IHTC of 236 W/(m2·K), representing a 2.8-fold increase over atmospheric frozen sand casting and a 1.6-fold increase over negative-pressure resin sand casting. This enhanced thermal driving force promotes grain refinement and effective gas removal, yielding superior mechanical properties: tensile strength of 200.6 MPa and elongation of 9.3% in the as-cast state, and 478.5 MPa and 7.4% after T6 heat treatment. Using the optimized process parameters, a thin-walled cabin component (Ø180 mm × 300 mm, minimum wall thickness 3 mm) was successfully fabricated without defects. These findings establish quantitative process–thermal–microstructure–property relationships for negative-pressure frozen sand casting of wide-solidification-interval aluminum alloys.