With the development of shipbuilding industry technology, the demand for titanium materials in my country’s shipbuilding industry is increasing day by day. At present, the amount of titanium used in Chinese ships is relatively small compared to foreign countries, and the processing technology is immature. Titanium alloy materials are mainly used in submarines and underwater weapons.
What Is TA5-A Titanium Alloy?
TA5-A titanium alloy is a full alpha titanium alloy with medium strength, good welding performance, and seawater corrosion resistance. It is used for stress members, bolts, shafts, and pressure shells under seawater-resistant conditions such as in ships. However, TA5-A titanium alloy material hardens quickly, has a large deformation resistance, and is difficult to form during the hot working process. Cracks are easy to appear on the surface, which affects the yield and surface quality of the material.
In order to solve the problems in sheet forming, the surface of the TA5-A slab is covered with a pure titanium layer before rolling. This process can effectively reduce the surface cracks of the finished product, but the surface of the sheet is easy to form irregularities during the subsequent surface treatment. “Fine patterns” affect the surface quality. Researchers analyzed and studied the “patterns” produced by metallographic, electron microscopy, and energy spectrum analysis methods found out the causes and solutions, and perfected the process route of the TA5-A hot-rolled sheet.
TA5-A Titanium Alloy Sheet
The Experimental Material is 16mm TA5-A Sheets, Chemical Composition (mass fraction, %):
| Al | B | Fe | Si | C | N | H | O | Ti |
|---|---|---|---|---|---|---|---|---|
| 3.7～4.5 | ≤0.005 | ≤0.3 | ≤0.15 | ≤0.1 | ≤0.04 | ≤0.015 | ≤0.15 | margin |
About TA5-A Alloy 16mm Plate Experiment
The TA5-A alloy 16mm plate blank is heated in a roller hearth electric furnace, rolled on a hot rolling mill, and subjected to performance testing after heat treatment and surface treatment. The cold field emission scanning electron microscope, inverted metallographic microscope, and energy spectrometer were used to observe the metallographic structure of the 16mm thick finished sheet. Observation found that there are small patterns on the surface of the board.
PT penetration treatment was performed on the surface of the processed 16mm finished sheet, and no cracks were found on the surface of the pattern. The metallographic structure observation on the surface of the pattern found that the 16mm thick finished sheet structure is equiaxed and completely equiaxed, the grain size is uniform and small, and the pattern does not extend into the matrix. The pattern on the surface of the sheet was observed, and no obvious cracks were observed in the cross-section.
Observing the pattern on the surface of the sample under a scanning electron microscope, it is found that the pattern on the surface of the plate is a number of continuous pits with a size of 10-30 μm. From the results of the energy spectrum analysis, the small pit part is consistent with the composition of the material matrix. It is possible to exclude the segregation of the components of the material.
Comparing the pattern characteristics with the interface bonding characteristics of the explosive stainless steel clad plate, it is found that the characteristics are similar. The pattern on the surface of the TA5-A finished product is a zigzag bonding interface produced by an explosive overlay, and the macroscopic interface of the explosive overlay is a zigzag.
Between the teeth, the base plate and the cover plate are subjected to the strong explosive impact force to form a transition zone several micrometers wide. In this area, the dislocation density increases and there is fine cover plate debris. Research indicates:
(1) The surface pattern of TA5-A alloy is not caused by the segregation of the chemical composition of the material, nor is it the surface cracks produced by rolling, but the bonding interface between the pure titanium layer and the alloy when the surface is coated, and the clad layer is close to the matrix. Combination, different shades.
(2) The surface pattern disappears after multiple surface polishing treatments and then pickling.