Removal of reactive layer on titanium alloy forgings

The surface reactive layer is the main factor affecting the physical and chemical properties of titanium castings. Before grinding and polishing titanium castings, the surface contaminated layer must be completely removed to achieve satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by the method of pickling after sandblasting.

1. Sandblasting: The sandblasting treatment of titanium castings is generally better with white corundum rough blasting, and the sandblasting pressure is smaller than that of non-precious metals, which is generally controlled below 0.45Mpa. Because when the injection pressure is too large, the sand impact on the titanium surface produces fierce sparks, and the temperature rise can react with the titanium surface, forming secondary pollution and affecting the surface quality. The time is 15 to 30 seconds, and only the sticky sand, surface sintered layer and part and oxidation layer on the surface of the casting can be removed. The remaining surface reactive layer structure should be quickly removed by chemical pickling.

2. Pickling: pickling can quickly and completely remove the surface reaction layer, and the surface will not produce pollution of other elements. Both HF-HCL series and HF-HNO3 series pickling solution can be used for pickling titanium, but HF-HCL series pickling solution has a larger hydrogen absorption capacity, while HF-HNO3 series pickling solution has a small hydrogen absorption capacity, which can control the concentration of HNO3 to reduce hydrogen absorption, and can carry out bright treatment on the surface. Generally, the concentration of HF is about 3%~ 5%. The concentration of HNO3 is about 15% to 30%.