What Is The Effect Of The Clad Rolling Process On Gr5 Titanium Alloy Sheets ?

 

As a typical α+β duplex titanium alloy, Gr5 titanium alloy (Ti-6Al-4V) benefits from the cladding and rolling technology. This technology uses a metal cladding layer to improve the uniformity of rolling force, effectively solving the edge cracking problem during large reduction processing of titanium alloy. It provides a feasible path for the high-performance preparation of sheets with different thicknesses. The 0.5mm ultra-thin sheet is often used in precision components and medical implants, while the 3.0mm medium-thick sheet is mostly used in structural load-bearing parts. Under the cladding and rolling process, this study explores the microstructure evolution law and mechanical property differences of 0.5mm and 3.0mm Gr5 titanium alloy sheets, revealing the intrinsic correlation between thickness parameters and process performance.

 

 

Raw Materials and Sample Preparation

Industrial-grade Gr5 titanium alloy ingots were selected for the experiment. Their main chemical compositions (mass fraction) are: Al 5.8%, V 4.2%, Fe 0.15%, O 0.12%, and the balance is Ti, which meets the requirements of ASTM B348 standard. After homogenization annealing at 1050℃ (β region) for 4h, the ingot was forged into a 15mm-thick hot-rolled blank. Q235 steel plate (2mm thick) was used as the cladding material. Argon arc welding was used to assemble and weld the titanium alloy blank and the cladding steel plate into a closed laminated rolling package, ensuring that the titanium alloy does not directly contact the air during the rolling process to avoid oxidation contamination.

Differentiated rolling processes for the two target thicknesses:

 

• 3.0mm sheet: The clad rolling package was heated and insulated at 930℃ (medium temperature section of α+β duplex region) for 2h, hot-rolled to 3.5mm in a single heat, then subjected to recrystallization annealing at 800℃ for 1h to remove rolling stress and refine the structure, and finally cold-rolled to the finished thickness of 3.0mm through 2 passes with a cold rolling reduction rate of about 14%.
• 0.5mm sheet: Using the 3.0mm sheet as the intermediate blank, after surface shot blasting, room temperature cold rolling process was adopted to reach the target thickness through 20 passes of progressive rolling with a total reduction rate of 83%. Low-temperature stress relief annealing at 650℃ for 30min was performed every 5 passes to prevent cracks during rolling.

 

Both thicknesses of sheets were finally subjected to vacuum annealing at 650℃ for 1h to eliminate the final cold working stress and ensure structural stability.

 

Test Methods

Testing Equipments :OM&TEM

 

Microstructure characterization was carried out using OLYMPUS GX71 optical microscope (OM) and FEI Tecnai G2 F20 transmission electron microscope (TEM). After grinding and polishing, the samples were etched with Kroll's reagent (HF:HNO₃:H₂O=1:3:10) for 5-8s to display the metallographic structure. TEM samples were prepared by double spray electrolytic polishing with a working fluid of methanol:nitric acid=3:1 at -20℃.

Mechanical property tests were performed in accordance with ASTM E8/E8M standards on an Instron 5969 universal testing machine for room temperature tensile tests at a tensile rate of 2mm/min. Three parallel samples were taken for each thickness, and the average value was used as the final result. Microhardness was tested using a ZWICK/Roell ZHV30 Vickers hardness tester with a load of 100g and a holding time of 15s. Ten points were tested for each sample, and the average value was taken after removing the maximum and minimum values.

 

 

Macrostructure and Grain Size

Both thicknesses of titanium alloy sheets have an α+β duplex structure, but there are significant differences in grain size, phase distribution and formation mechanism due to thickness (differences in processing technology).

 

micrograph images about 0.5mm&3.0mmTitanium sheet

 

Parameter	3.0mm Medium-Thick Sheet	0.5mm Ultra-Thin Sheet
α Grain Size	8–12μm (Coarse Equiaxed)	2–5μm (Ultra-Fine)
β Phase Distribution	Discontinuous (Strips/Islands)	Continuous (Network + Dispersed Precipitates)
Core Mechanism	Medium-temperature hot rolling + moderate cold rolling	Large reduction cold rolling + low-temperature annealing

 

 

Comparison of Mechanical Properties

Sheet Thickness (mm)	Tensile Strength Rm (MPa)	Yield Strength Rp0.2 (MPa)	Elongation After Fracture A (%)	Microhardness HV
3.0	898	840	17.7	260
0.5	1035	980	16.5	320
Performance Improvement Rate (%)	15.2	16.7	-1.2	23.1

 

 

The clad rolling process can effectively prepare high-performance Gr5 titanium alloy sheets. There are significant differences in the microstructure and mechanical properties of sheets with different thicknesses: the 3.0mm medium-thick sheet presents an equiaxed α+strip β structure with a grain size of 8-12μm, a room temperature tensile strength of 898MPa, and an elongation after fracture of 17.7%; the 0.5mm ultra-thin sheet forms an ultra-fine α+network β structure with a grain size of 2-5μm, the tensile strength is increased to 1035MPa, and the elongation after fracture is maintained at 16.5%, achieving a good combination of high strength and high plasticity.

 

Thickness-dominated rolling deformation and process parameters are the core of microstructure control: the combined process of large reduction cold rolling and segmented annealing is the key to achieving grain ultra-refinement of the 0.5mm sheet, while medium-temperature hot rolling and small reduction cold rolling determine the coarse equiaxed grain structure characteristics of the 3.0mm sheet; the cladding layer plays a role in improving deformation uniformity and inhibiting defect generation in the preparation of both thicknesses of sheets.

 

The 3.0mm medium-thick sheet, with good plasticity and moderate strength, is suitable for load-bearing components such as aerospace structural parts and marine engineering pipelines; the 0.5mm ultra-thin sheet, with its excellent specific strength and dimensional accuracy, can be used in high-end fields such as medical implants (e.g., artificial joint bushings) and lightweight components of aero-engine blades.