Structural die casting application of a heat treated free aluminum-silicon alloy

The advancement of integrated die-casting technology calls for high-strength, high-ductility heat-treatment-free Al alloys. This study investigates the use of a new AlSiFeMnVTiSrZr heat-treatment-free die-casting alloy for shock tower manufacturing. Results show the alloy has excellent overall mechanical properties, but significant regional differences in microstructure and performance are found in the shock tower casting: Far-gate Position 6 has almost no externally solidified crystals (ESCs), whereas dense coarse dendritic ESCs exist in the center of near-gate Position 5. The fracture surface of Position 6 shows a steeper slope, while Position 5 has a rough crack propagation platform. Far-gate Position 6 also has higher porosity (nearly triple that of near-gate Region 5) and larger average pore size. Analysis reveals microstructural heterogeneity between near- and far-gate regions strongly influences mechanical performance. Notably, coarse dendritic ESCs in the near-gate region restrict grain boundary strengthening, leading to lower yield strength despite low porosity. Conversely, while fine grains in the far-gate region could enhance grain boundary strengthening, abundant porosity acts as crack initiation sites, severely reducing ductility. These findings provide theoretical guidance for evaluating integrated die-cast component performance.