Optimizing microstructure, shrinkage defects and mechanical performance of ZL205A alloys via coupling travelling magnetic fields with unidirectional solidification

ZL205A alloys tend to form disordered and defective microstructure due to the large solidification intervals and multi-phase. Accordingly, finding ways to effectively optimize the microstructure and mechanical performance is of great significance. In this regard, the coupling of travelling magnetic fields (TMF) with unidirectional solidification was used to continuously regulate the mushy zones of ZL205A alloys. Additionally, experiments are combined with simulations to systematically reveal the mechanisms on the optimizations at each stage of solidification process. Current findings demonstrate that different directional strong melt flows generated by TMF are responsible for these optimizations. Additionally, the effects of TMF on microstructure are different at each stage of solidification process. Specifically, downward TMF coupled with unidirectional solidification can refine and uniform the microstructure, decrease the formation of precipitation, promote the growth consistency of matrix phase α-Al growing along the <001> crystal orientation, reduce the secondary dendrites and overlaps between dendrites, eliminate the shrinkage defects, and increase the ultimate tensile strength, yield strength, elongation and hardness from 198.3 MPa, 102.2 MPa, 7.5 % and 82.3 kg mm⁻² without TMF to 225.5 MPa, 116.1 MPa, 13.6 % and 105.2 kg mm⁻². Contrastively, although upward TMF can reduce Al₃Ti and refine α-Al, it increases the formation of Al₆Mn, Al₂Cu, secondary dendrites, overlaps between dendrites, and shrinkage defects; then it deflects and disorders the growth of α-Al, further to decrease the overall performance of alloys.