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TC4 titanium alloy surface oxide removal

Author : Date : 7/17/2016 11:40:04 PM
 TC4 titanium alloy with excellent corrosion resistance, low density, high strength and good toughness and weldability series of advantages in the aerospace, petrochemical, shipbuilding, automobile and pharmaceutical sectors have been successfully applied. TC4 titanium alloy in the thermoforming process, the surface will form a layer of oxide, thermoforming temperature difference, the resulting color is not the same scale. Wherein the heat forming temperature at about 600 ℃, the blue scale; thermoforming temperature at about 850 ℃, the reddish gray scale; and thermoforming temperature of 900 ℃, the gray scale. As the temperature increases, the difficulty of removing the oxide scale is gradually increased. Titanium oxide removal at home and abroad are mostly two-step method, that is, first molten caustic and acid; however, high temperature molten caustic media, can reach about 450 ℃, and could easily lead α + β and β titanium alloy semi-finished products premature aging strengthening, for further processing difficult. In addition, hot caustic and then with hydrofluoric acid and nitric acid cleaning may also cause hydrogen embrittlement of titanium alloy surface corrosion.

For researchers at 590,850 and 920 ℃ three temperatures resulting scale, the first low temperature alkaline solution and then pickling process to remove the oxide layer on its surface were studied. By optical microscopy to characterize the morphology of the oxide scale, the effects of time on descaling, and by the more advanced international companies in the United States LECO RH-404 analyzer for a given hydrogen mass fraction of hydrogen after descaling titanium were Determination.
Industrial tests with lye NaOH and pure industrial pure supersaturated solution of NaNO2 mixed, a mixed solution of hydrofluoric acid and nitric acid (volume ratio HF:HNO3:H2O = 1:1:3). The hot-water rinse caustic and TC4 Alloy after completely immersed in the acid taken out after 20s, and then rinsed with tap water. Finally, the sample after the ultrasonic cleaning with acetone or ethanol after drying weighed using an electronic balance of thermal mass alkaline wash, the sample is measured before and after pickling, accuracy of 0.001g. Through the analysis showed that the first use hot caustic pickling process, TC4 titanium oxide surface can be completely removed. conclusion as below:
(1) TC4 titanium hot forming surface oxide thickness of less than 2μm.
(2) by hot caustic washing, pickling process, TC4 titanium oxide surface can be completely removed, lye ratio of 700g / L NaOH + 250g / L NaNO2, when the boiling temperature of about 160 ℃, supersaturated hot lye removal can be achieved by soaking 6h.
(3) TC4 titanium alloy with oxide by thermal alkaline cleaning, the mass fraction of hydrogen changes the pickling process is unlikely to meet production needs.

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