Metals

Welding and joining technologies remain fundamental enabling processes in modern manufacturing, supporting the production of structures and components across a wide range of industrial sectors [...]

In this study, the high-temperature deformation behavior of TC11 titanium alloy was investigated through hot compression experiments. The relationship between flow stress, strain rate, and deformation temperature was described by analyzing stress–strain curves and establishing a constitutive equation. A hot processing map was constructed based on the Dynamic Materials Model (DMM). The processing map indicated that the optimal processing regions were 1155–1195 K/0.1–8 s⁻¹ and 1265–1273 K/0.1 s⁻¹. EBSD analysis showed that under low-strain-rate conditions, the fraction of high-angle grain boundaries and the proportion of recrystallized grains were relatively high, with dynamic recrystallization primarily governing softening. As the strain rate increased, the proportion of recrystallized grains decreased, the fractions of substructure and deformed grains increased, and dislocation accumulation was significantly enhanced, resulting in a shift in the softening mechanism from dynamic recrystallization to dynamic recovery. Elevated temperatures facilitated dislocation slip and climb, promoting nucleation and growth of dynamic recrystallization, whereas excessively high temperatures caused grain coarsening and localized distortion accumulation, reducing microstructural stability. TEM observations further confirmed that low-strain-rate conditions produced a greater number of recrystallized grains with low dislocation density, while high-strain-rate conditions exhibited pronounced subgrain structures and increased dislocation density. This work constructs the hot processing map of TC11 alloy near β-transus temperature and quantitatively links power-dissipation domains with multi-scale EBSD/TEM microstructure statistics. The obtained hot working window can provide guidance for parameter optimization of high-temperature thermomechanical processing of TC11 aerospace components.

The slow-shot speed phase in high-pressure die casting critically governs molten metal flow within the shot sleeve, directly influencing air entrapment and casting defect formation. Conventional water modeling has been widely used to analyze this stage, but it cannot reproduce the intrinsic characteristics of the actual melt, such as oxide film formation and the appearance of solid-phase crystals that increase the apparent viscosity. In this study, a transparent quartz sleeve apparatus was developed to directly observe the free surface behavior of AlSiCu (ADC12) molten alloy during slow-shot at speeds of 0.10, 0.20 and 0.30 m/s. Water and silicone oil were also tested as conventional modeling fluids; both showed behavior similar to the actual melt in the early shot stage but deviated significantly in the mid-to-late stage owing to the increase in apparent viscosity caused by oxide film formation and solid-phase crystals, confirming the fundamental limitations of water modeling. For the actual ADC12 melt, free surface stability decreased progressively as the slow-shot speed increased, transitioning from laminar-like flow at 0.10 m/s to turbulent flow with surface folding at 0.30 m/s. The gas content of castings increased with slow-shot speed, and the H₂/N₂ ratio decreased from 1.07 to 0.53, confirming that air entrapment becomes the dominant source of blow hole defects at higher speeds. Microstructural analysis revealed that at 0.10 m/s, the extended sleeve residence time promoted coarse externally solidified crystal (ESC) growth, whereas at 0.30 m/s these phenomena were suppressed, but porosity increased owing to greater air entrapment.