Semi-Solid Slurries for Rheocasting of Hypoeutectic Al-Si-X Alloys Produced by Self-Stirring in Serpentine Channels

Abstract

Nowadays it is common to see the production of complex and critical automotive and aeronautical components reduced in weight for energy efficiency using light alloys with improved microstructural and mechanical properties. The casting processes involved in this trend are strong; in this study, an optimized design of a vertical serpentine channel and a novel design of a horizontal serpentine channel to produce semi-solid slurry (S2S) with thixotropic behavior by self-stirring for rheocasting of A380 and A356 alloys are tested. Simultaneously, chilling during solidification, flow development, and shearing on the alloys to improve the performance of solid fractions and self-stirring at high shear rate are applied. The effects of these conditions on the modification of the morphology transition of the α(Al) phase from dendrite to equiaxed grain are discussed. The results suggest the ability of the mentioned processes to promote the morphological transition of the primary solid due to the produced equiaxed grains of α(Al) phase having sizes between 25–50 µm from A380 alloy processed by vertical self-stirring. On the other hand, the treatment of the A356 alloy using the new horizontal serpentine channel produces equiaxed grains with an average size of 39 µm. Unexpected Si crystals, trapped in the α(Al) phase using both methods with both alloys, are detected. The applied operation parameters were aided by gravity-pouring close to the liquidus temperature, and the obtained microstructural results show the ability for S2S to form alongside thixotropic behavior and non-dendritic solidification by mean of self-stirring in the serpentine channels, suggesting the potential for further experiments under die-casting conditions.

Keywords

• casting
• rheocasting
• solidification
• microstructure
• characterization