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GR5 Titanium Alloy Surface Scale Removal
May 27, 2016

 

GR5 titanium alloy has excellent corrosion resistance, small density, high strength and good toughness and weldability and a series of advantages, have successful applications in field, like the aerospace, petrochemical industry, shipbuilding, automobile and medical and so on. GR5 titanium alloy, during hot forming, its surface can form a layer of oxide skin, hot forming temperature is different, the oxide skin color is different also. Among them, the temperature about 600 ℃ in hot forming, surface scale is blue. When the temperature is about 850 ℃, the surface scale will be reddish gray. And when the hot forming temperature at 900 ℃, the surface scale will be gray. With the increase of temperature, oxide skin removing will be more and more difficult. In domestic and abroad, titanium oxide coating removal mostly adopts two-step method, namely first molten caustic washing, then pickling; But, molten caustic washing medium temperature is higher, can reach about 450 ℃, and easy to cause α+β and β titanium alloy semi-finished products of untimely age-hardening, bring difficulties to further processing. In addition, the hot caustic washing and then clean with nitric acid and hydrofluoric acid may also cause hydrogen embrittlement corrosion of titanium alloy.

Aimed at the surface scale under 590, 850 and 920 ℃ these three kinds of temperature, first take the low temperature alkali wash, and then acid pickling to remove the oxide layer on the surface, the researchers have studied the process. The surface scale morphology were characterized by optical microscope, studies the influence of time to oxide skin removal, and through international advanced RH-404 Hydrogen determination apparatus of LECO companies in the United States to determine the hydrogen mass of titanium alloy after removing the oxide skin.

Through analysis shows that using hot caustic wash before pickling process of GR5 titanium alloy on the surface of the oxide coating can be removed completely. The conclusion is as follows:

(1) The thickness of the surface scale of GR5 titanium alloy after hot forming is less than 2μm.

(2) through the hot caustic washing, pickling process, the surface scale of GR5 titanium alloy can be removed completely, alkali ratio is 700g/L NaOH+250g/L NaNO2, boiling temperature is about 160 ℃, supersaturated hot alkali soak 6h can achieve removal efficiency.

(3) GR5 titanium alloy with a surface scale, its hydrogen mass change little by thermal alkaline cleaning, acid pickling process, so it can meet production needs.

 




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