Eliminating shrinkage defects and improving mechanical performance of large thin-walled ZL205A alloy castings by coupling travelling magnetic fields with sequential solidification
(National Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China)
Abstract: ZL205A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields (TMF) with sequential solidification, to eliminate the shrinkage defects and optimize the mechanical performance. Through experiments and simulations, the parameter optimization of TMF and the influence on feeding behavior, microstructure and properties were systematically studied. The results indicate that the magnetic force maximizes at the excitation current of 20 A and frequency of 200 Hz under the experimental conditions of this study, and increases from center to side-walls, which is more convenient to process thin-walled castings. TMF can break secondary dendritic arm and dendrites overlaps, widen feeding channels, prolong the feeding time, optimize the feeding paths, eliminate shrinkage defects and improve properties. Specifically, for as-cast state, TMF with excitation current of 20 A increases ultimate tensile strength, elongation and micro-hardness from 186 MPa, 7.3% and 82.1 kg/mm2 to 221 MPa, 11.7% and 100.5 kg/mm2, decreases porosity from 1.71% to 0.22%, and alters brittle fracture to ductile fracture.
Key words: ZL205A alloys; large thin-walled alloy castings; travelling magnetic fields; sequential solidification; shrinkage defects; mechanical performance