Bands of interdendritic porosity and positive macrosegregation are commonly observed in pressure die castings, with previous studies demonstrating their close relation to dilatant shear bands in granular materials. Despite recent technological developments, the micromechanism governing dilatancy in the high-pressure die casting (HPDC) process for alloys between liquid and solid temperature regions is still not fully understood. To investigate the influence of fluid flow and the size of externally solidified crystals (ESCs) on the evolution of dilatant shear bands in HPDC, various filling velocities were trialled to produce HPDC samples of Al8SiMnMg alloys. This study demonstrates that crystal fragmentation is accompanied by a decrease in dilatational concentration, producing an indistinct shear band. Once crystal fragmentation stagnates, the enhanced deformation rate associated with a further increase in filling velocity (from 2.2 ms⁻¹ to 4.6 ms⁻¹) localizes dilatancy into a highly concentrated shear band. The optimal piston velocity is 3.6 ms⁻¹, under which the average ESC size reaches the minimum, and the average yield stress and overall product of strength and elongation reach the maximum values of 144.6 MPa and 3.664 GPa%, respectively. By adopting the concept of force chain buckling in granular media, the evolution of dilatant shear bands in equiaxed solidifying alloys can be adequately explained based on further verification with DEM-type modeling in OpenFOAM. Three mechanisms for ESC-enhanced dilation are presented, elucidating previous reports relating the presence of ESCs to the subsequent shear band characteristics. By applying the physics of granular materials to equiaxed solidifying alloys, unique opportunities are presented for process optimization and microstructural modeling in HPDC.

Steel products typically undergo intricate manufacturing processes, commencing from the liquid phase, with casting, hot rolling, and laminar cooling being among the most crucial processes. In the background of carbon neutrality, thin-slab casting and direct rolling (TSCR) technology has attracted significant attention, which integrates the above three processes into a simpler and more energy-efficient sequence compared to conventional methods. Multi-scale computational modeling and simulation play a crucial role in steel design and optimization, enabling the prediction of properties and microstructure in final steel products. This approach significantly reduces the time and cost of production compared to traditional trial-and-error methodologies. This study provides a review of cross-scale simulations focusing on the casting, hot-rolling, and laminar cooling processes, aiming at presenting the key techniques for realizing cross-scale simulation of the TSCR process.

The production of AISI 304 stainless steel (a corrosion-resistant alloy prone to solidification defects from high alloy content) particularly benefits from twin-roll strip casting—a short-process green technology enabling sub-rapid solidification (the maximum cooling rate exceeds 1000 °C/s) control for high-performance steels. However, the internal phenomena within its molten pool remain exceptionally challenging to monitor. This study developed a multiscale numerical model to simulate coupled fluid flow, heat transfer, and solidification in AISI 304 stainless steel twin-roll strip casting. A quarter-symmetry 3D model captured macroscopic transport phenomena, while a slice model resolved mesoscopic solidification structure. Laboratory experiments had verified that the deviation between the predicted temperature field and the measured average value (1384.3 °C) was less than 5%, and the error between the solidification structure simulation and the electron backscatter diffraction (EBSD) data was within 5%. The flow field and flow trajectory showed obvious recirculation zones: the center area was mainly composed of large recirculation zones, and many small recirculation zones appeared at the edges. Parameter studies showed that, compared with the high superheat (110 °C), the low superheat (30 °C) increased the total solid fraction by 63% (from 8.3% to 13.6%) and increased the distance between the kiss point and the bottom of the molten pool by 154% (from 6.2 to 15.8 mm). The location of the kiss point is a key industrial indicator for assessing solidification integrity and the risk of strip fracture. In terms of mesoscopic solidification structure, low superheat promoted the formation of coarse columnar crystals (equiaxed crystals accounted for 8.9%), while high superheat promoted the formation of equiaxed nucleation (26.5%). The model can be used to assist in the setting of process parameters and process optimization for twin-roll strip casting.

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of overheated aluminum alloy melt into the shot sleeve would lead to evaporation and burning of the lubricants once in contact with the piston tip. The burning products, however, would form gas and non-metallic inclusions in the melt which would be transported and injected into the die area and finally trapped in the castings, all of which would affect the mechanical properties of the as-cast samples and deteriorate the product quality. To further investigate this issue, a pilot scale HPDC machine is used and the lubricant burning issue is studied based on material characterization and numerical modelling. The chemical composition, size, and morphology of the burned products are observed using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). In order to better explore the issue of lubricant combustion discovered in the experiment, a finite element model describing the entire HPDC process is established and the burning, motion, and trapping of the lubricant are calculated. The final distribution of the burned products such as gas and non-metallic inclusions are predicted and their influence on final solidification quality of the as-cast products under various process parameters are analyzed qualitatively. Finally, a slow shot velocity range of 0.4–0.6 m/s and an acceleration profile that ramps up to 0.3 m/s over 0–370 mm of the shot sleeve proved to be the most effective in reducing air entrainment and oxide inclusions to alleviate the burning of lubricant on final product quality.

Bands of interdendritic porosity and positive macrosegregation are commonly observed in pressure die castings, with previous studies demonstrating their close relation to dilatant shear bands in granular materials. Despite recent technological developments, the micromechanism governing dilatancy in the high pressure die casting (HPDC) process for alloys between liquidus and solidus temperature region is still not fully understood. To investigate the influence of fluid flow and the size of externally solidified crystals (ESCs) on the evolution of dilatant shear bands in HPDC, various filling velocities were trialled to produce HPDC samples of Al8SiMnMg alloy. This study demonstrates that crystal fragmentation is accompanied by a decrease in dilatational concentration, thus producing an indistinct shear band. Once crystal fragmentation stagnates, the enhanced deformation rate associated with a further increase in filling velocity (from 2.2 ms^-1 to 4.6 ms^-1) localises dilatancy into a highly concentrated shear band. The optimal piston velocity is 3.6 ms-1, under which the average ESC size reaches the minimum and the average yield stress and overall product of strength and elongation reaches the maximum value of 144.6 MPa and 3.664 GPa%, respectively. By adopting the concept of force chain buckling in granular media, the evolution of dilatant shear bands in equiaxed solidifying alloys can be adequately explained based on further verification with DEM-type modelling in OpenFOAM. Three mechanisms for ESC enhanced dilation are presented, elucidating previous reports relating the presence of ESCs to the subsequent shear band characteristics. By applying the physics of granular materials to equiaxed solidifying alloys, unique opportunities are presented for process optimization and microstructural modelling in HPDC.

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of overheated melt into the shot sleeve would lead to evaporation and burning of the lubricants once in contact with the piston tip. The burning products, however, would form gas and non-metallic inclusions in the melt which would be transported and injected into the die area and finally trapped in the castings, all of which would affect the mechanical properties of the as-cast samples and deteriorate the product quality. To further investigate this issue, a pilot scale HPDC machine is used and the lubricant burning issue is studied based on material characterization and numerical modelling. The chemical composition, size and morphology of the burned products are observed using scanning electron microscope and energy dispersive spectrometer. Based on this, a finite element model describing the entire HPDC process is established and the burning, motion, trapping of the lubricant are calculated. The final distribution of the burned products such as gas and non-metallic inclusions are predicted and their influence on final solidification quality of the as-cast products under various process parameters are analyzed qualitatively. Finally, the optimal process parameters such as piston shot profile, slow/fast shot speed are obtained to alleviate the burning of lubricant on final product quality.