To address the high rejection rate in tilt gravity die casting of A356 aluminum alloy steering knuckles, the work aims to explore effective process improvement solutions to reduce porosity at critical sections of castings and raise the product yield. A closed-loop framework of “defect characterization, mechanism analysis, and process optimization” was constructed. Firstly, X-ray inspection and scanning electron microscopy (SEM) were employed to identify and classify casting defects and the rejection rate distribution at various positions was statistically analyzed. Secondly, multi-physics-field coupled simulation of filling flow field, temperature field and solidification behavior was carried out on the MAGMAsoft platform to analyze the defect formation mechanism. Finally, a multi-factor collaborative optimization strategy was proposed based on the simulation results: adding feeding risers at the hot spot of the central hole, introducing a forced air-cooling system based on solidification sequence control for heavy-section regions, and lowering the mold preheating temperature from 450 ℃ to 400 ℃ to establish a reasonable interfacial temperature gradient. Three typical defects were identified: shrinkage cavity at the center hole, shrinkage porosity at the shock absorber hole, and gas entrapment at the gate, with the center hole exhibiting a rejection rate of 37.3%. Simulation results showed that the “isolated hot spot” effect induced by an excessive local modulus ratio and turbulent gas entrapment caused by abrupt flow velocity variation at the initial filling stage constituted the main defect-forming mechanisms. After process optimization, the porosity at critical sections of the casting decreased significantly from 0.18% to 0.01%, satisfying Grade-I requirements specified in VDG P201 standard. The proposed collaborative optimization measures, including feeding riser arrangement, forced air cooling and mold preheating temperature regulation, can effectively eliminate risks of hot spots and gas entrapment, and substantially improve the forming quality and yield of steering knuckles. This work can provide references for process improvement of similar aluminum-alloy castings.
Key words
gravity casting /
aluminum alloy steering knuckle /
MAGMA simulation /
hot spot /
process optimization /
porosity
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Funding
Scientific Research Project of the Education Department of Jilin Province (JJKH20251882KJ); 2024 Intelligent Vehicle-Mounted Optoelectronic Information Science and Technology Innovation Team and Applied Technology R&D and Service Project of Changchun Vocational Technical University (2024YFP08)
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