Transient Rheological Behavior of Semisolid SEED-Processed 7075 Aluminum Alloys in Rapid Compression

Abstract

The transient rheological behavior and microstructure evolution of semisolid SEED-processed 7075 aluminum alloys were studied using the rapid compression tests. The effects of the TiB 2 grain refinement on the grain morphology and size of semisolid slurries were investigated. Results indicated that the grain refiner could reduce the grain size and improve the globularity of a-Al grains. The grain-refined alloy can be easily deformed at a wide range of solid contents (0.42 to 0.53 Fs), in which the deformation level appears to be independent from the solid content. Under the transient state, the apparent viscosity decreased with increasing shear rate to a minimum value and followed by an increase as the shear rate decreased. The apparent viscosity of the base alloy exhibited a dependency on the solid content, while the apparent viscosity of the grain-refined alloy in the decreasing or increasing shear rate periods was not substantially influenced by the solid content. The viscosity as a function of applied shear rate can be described using the power law viscosity model. The differences in the flow behavior index (n) and the consistency index (k) for two alloys were discussed.

Effects of Heating Rates on Microstructural Evolution of Hot Extruded 7075 Aluminum Alloy in the Semi-Solid State and Thixotropic Deformation Behavior

“…Furthermore, as shown in Figure 10 , the microstructure of the semi-solid billets remains similar at different temperatures. This similarity contributes to the minimal variation in thixotropic behavior during the thixoforming process [ 38 ]. Therefore, the refined microstructure can be readily achieved across a wide range of solid fractions.…”

Effects of Grain Morphology on Flow Behavior of Semi-Solid Slurries

“…Lots of work concluded that fraction solid mainly affects the viscosity of the slurry, and the microstructure also has a significant effect on the rheological behavior. Bolouri and Silva [4,5] found the dendritic structure resulted in higher viscosity, and the viscosity of this kind of slurry is more sensitive to solid fraction compare to a globular structure. For semi-solid forming, the perfect morphology of the solid phase in the slurry is a spherical form, while it's tough to make the ideal slurry.…”

Effect of Temperature Gradient on the Grain Size Homogeneity of SEED Produced Semi-Solid Slurries by Phase-Field Simulation

“…These slurries have a high solid fraction and are free of entrapped oxides, allow for the casting of heat-treatable and weldable components with high mechanical properties, high ductility, and ultra-low porosity. It is high-efficient on a wide variety of aluminium foundry alloys and has been demonstrated on wrought alloys, such as 6061 [4] and 7075 alloys [5]. The weights and dimensions of slurries can be adjusted according to the die casting system, and the process can be applied in both horizontal and vertical die/squeeze casting machines.…”