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For Ti-alloy tri-modal microstructure can be obtained by the near-β forging (water quenching, WQ) + high temperature toughening and low temperature strengthening treatment (HLT) method. However in actual production, it is hard to accomplish water quenching after near-β forging immediately. In this paper a short time of air cooling (AC) after near-β forging was introduced to consider the temperature drop during the forgings transferring in actual production. For TA15 alloy the formation process of tri-modal microstructure in near-β forging (AC + WQ) + HLT was studied. Under the given near-β forging condition, the influences of the subsequent toughening and strengthening treatment on the obtained tri-modal microstructure were revealed as well as on the corresponding mechanical properties. Then the reasonable HLT route for tri-modal microstructure with excellent comprehensive properties was determined.

Hot deformation behavior and microstructure evolution rule of as-extruded 7075 aluminum alloy have been investigated based on the thermal compression experiment and quantitative metallographic test. It was found that the dynamic recovery was the main softening mechanism, along with the dynamic recrystallization in the local area within the deformation temperature range of 300–450 °C and strain rate range of 0.01–10 s− 1. Deforming below 350 °C, only dynamic recovery occurred with a typical subgrain structure, above 350 °C, dynamic recrystallization happened in local area. The dynamic recrystallized grain size increased with the increase of temperature, and decreased as strain rate increasing, showing typical characteristics of continuous dynamic recrystallization. At a higher deformation temperature and a lower strain rate, geometric dynamic recrystallization occurred. A larger strain resulted in more dynamic recrystallization. The second phase particles in the alloy would hinder the slip of grain boundaries, while would promote continuous dynamic recrystallization.

Quantitative characterization of lamellar and equiaxed alpha phases in (α + β) titanium microstructures is needed to investigate how the microstructure affects the mechanical properties. However, the complex touching features between the lamellar and equiaxed alpha of the microstructure make quantitative analysis challenging. To overcome this problem, a four-level procedure for separating touching features, which includes image pre-processing, concave points detection, splitting line determination, and lamellar and equiaxed alpha discrimination, has been proposed to automatically process many microstructures. Moreover, a set of criteria was established for each level to handle various problems caused by the complexity of how lamellar and equiaxed alpha can touch each other. The result on a representative microstructure of a (α + β) titanium alloy, a tri-modal microstructure, shows that the approach works well and is robust. Based on this effort, the phase distributions of the tri-modal microstructure were quantified through two-point and lineal-path correlation functions based on the newly developed, efficient algorithms. Significant heterogeneity and morphological anisotropy in different directions and ranges of the lamellar and equiaxed alpha were quantitatively measured.