Optimization of 75 mm Ultra-Thick Ti-6Al-4V Alloy Plates for Aerospace Applications: Microstructure and Mechanical Properties Analysis

Abstract

The production of ultra-thick Ti-6Al-4V (Ti-64) alloy plates is critical for aerospace applications, however, meeting the demanding mechanical and microstructural standards presents significant challenges. This study focuses on optimizing the manufacturing process of 75 mm ultra-thick Ti-64 plates to meet the stringent requirements of the AMS4905E specification. Initial attempts revealed that the presence of the primary hcp-α phase, even after β-annealing, severely limited ductility and work-hardening capacity. The mechanical performance, particularly elongation, failed to meet the standard despite achieving adequate yield strength (YS) and ultimate tensile strength (UTS). To overcome these limitations, an optimized process was developed, incorporating a homogenization step prior to hot forging and a globularization step after hot rolling. This approach was aimed at achieving a more uniform microstructure and enhancing the α-to-β phase transformation during heat treatment. Microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) confirmed the elimination of the primary hcp-α phase, with the formation of a refined and homogenous Widmanstatten structure. These changes resulted in a significant improvement in mechanical properties, particularly elongation, which increased from 4–7.5% in the preliminary trials to 10–11.5%, fully meeting the AMS4905E requirements. In addition to mechanical properties, the size of the prior β grains was carefully controlled to remain within the specified limits of the standard, ensuring full compliance with both microstructural and performance criteria. This optimized process not only enhances the mechanical performance of 75 mm ultra-thick plates but also establishes a reliable foundation for the future production of 100 mm thick Ti-64 plates, which are currently under development. The advancements demonstrated in this study contribute significantly to the field of high-performance titanium alloys for aerospace applications.