Removal method of oxide skin on the surface of TC4 titanium alloy rod

Release time：2022-06-14 23:43:03 丨 Number of visits：

TC4 titanium alloy rod has a series of advantages such as excellent corrosion resistance, small density, high specific strength, good toughness and weldability, etc., which have been successfully applied in aerospace, petrochemical, shipbuilding, automobile and pharmaceutical sectors. TC4 titanium alloy in the process of hot forming, its surface will form a layer of oxide, hot forming temperature is different, the color of oxide is not the same. When the hot forming temperature is about 600℃, the oxide scale is blue. When the hot forming temperature is about 850℃, the oxide scale is gray and reddish. When the forming temperature is 900℃, the oxide scale is gray. With the increase of temperature, the removal of oxide scale becomes more and more difficult. At home and abroad, the removal of titanium alloy oxide skin mostly adopts a two-step process, that is, first molten alkaline washing, then pickling; However, the temperature of molten alkaline washing medium is high, which can reach about 450℃, and it is easy to cause premature aging strengthening of α+β and β titanium alloy semi-finished products, which brings difficulties to further processing. In addition, hot alkaline cleaning followed by nitric acid and hydrofluoric acid cleaning may lead to hydrogen embrittlement of titanium alloy surface.

The researchers studied the process of removing the oxide layer on the surface of the oxide layer obtained at 590, 850 and 920℃ by washing it with a low temperature alkaline solution and then pickling it. The morphology of the oxide was characterized by optical microscope, and the effect of time on the removal of the oxide was studied. The hydrogen mass fraction of titanium alloy after the removal of the oxide was determined by the advanced hydrogen determination instrument OF LECO Company RH-404 in the world.

The alkaline solution used in the test was a mixed supersaturated solution of industrial pure NaOH and industrial pure NaNO2, and a mixed solution of hydrofluoric acid and nitric acid was used for pickling (HF∶HNO3∶H2O=1∶1∶3). The TC4 titanium alloy after hot alkali washing and washing with water was completely soaked in acid for 20 seconds, and then washed with running water. Finally, the samples were cleaned by ultrasonic wave with acetone or alcohol and then dried and weighed. The quality of the samples before and after hot alkaline washing and pickling was measured by electronic balance with a precision of 0.001g. The results show that the surface of TC4 titanium alloy can be completely removed by the process of hot alkaline washing and then pickling. The conclusions are as follows:

(1) The oxide thickness of TC4 titanium alloy hot-formed surface is less than 2μm.

(2) Through hot alkaline washing, pickling process, TC4 titanium alloy surface oxide can be completely removed, alkali ratio of 700g/L NaOH+250g/L NaNO2, boiling temperature is about 160℃, supersaturated hot alkaline soaking for 6h can achieve the removal effect.

(3) The mass fraction of hydrogen of TC4 titanium alloy with oxide skin changes little in the process of hot alkaline washing and pickling, which meets the production needs.