Ablation technology applied to A356 alloys compared with conventional casting processes

Because ablation differs from conventional casting, some conventional metallurgical concepts, such as the relationship among secondary dendrite arm spacing (SDAS), microconstituents and tensile properties, should be revised.

To understand the mechanisms governing ablation technology, the most popular of casting alloys, A356 alloys, were selected, and conventional melt treatments, such as degassing, grain refinement and Si modification with Sr, were applied. All ablated as-cast microstructural characteristics (SDAS, grain size, porosity, Si particle morphology and Fe-bearing phases) and the mechanical properties after T6 were compared with two conventional processes: permanent moulding and sand cast manufacturing with the same metal. SDAS values, which are commonly used to predict mechanical properties in conventional casting processes, are no longer valid for ablation, which presents coarse SDAS microstructures, similar to those obtained with the conventional sand casting process, with some isolated areas of fine SDASs. However, the high freezing rate in the last stage of the solidification process obtained by ablation technology generates fine eutectic Si and iron-bearing particles and low porosity. This makes it possible to obtain quality index values of Q = 480 MPa that are significantly higher than those of sand casting (Q = 426 MPa) and similar to those obtained for permanent moulds (Q = 480 MPa).

Additionally, the potential advantages of ablation for T5 (Q = 419 MPa) and shorter solution time T6 treatments (Q = 479 MPa) were also investigated in terms of mechanical properties and Si particle size and shape.