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Analysis of common faults in surface quality of titanium alloy products

Titanium alloys are widely used in civil applications due to their excellent properties, high specific strength, good medium temperature performance, and no magnetism. The developed titanium alloy products have almost penetrated into all aspects of modern life, including clothing, food, housing, and transportation. In production, we have found that common surface quality faults of titanium alloy products include corrosion, dust accumulation, incomplete removal of oxide skin, and striped spots.

1. Overcorrosion: Overcorrosion refers to the appearance of pits or uneven defects on the surface of titanium alloy after acid washing, which are different from the exposed material structure. The general reason for excessive corrosion defects is the imbalance of the ratio of hydrofluoric acid and nitric acid. Excessive or insufficient concentration of hydrofluoric acid can lead to the appearance of this defect. Another reason is that the pickling time is too long, usually between 1mm and 4mm. The pickling time can be adjusted according to the process parameters on the operation site and shortened appropriately.

2. Hanging ash: Hanging ash refers to the oxide attached to the surface of titanium alloy after acid washing. During acid washing, the dry titanium alloy and acid undergo a chemical reaction, and the generated oxide accumulates on the surface, preventing further reaction from occurring. The defects of hanging ash are generally caused by excessive deposition of hanging ash during pickling and insufficient rinsing after pickling. During acid washing, the parts should be continuously shaken to allow the reaction products to detach from the surface of the titanium alloy. After acid washing, spraying or rinsing should be strengthened to remove hanging dust. In China, high-speed water flow mixed with compressed air and tap water is generally used to wash parts, and the effect is good.

3. The oxide skin has not been completely removed: There are many reasons that can cause this defect, and each process may have the potential. It is possible that the oil removal is poor, the molten salt treatment time is insufficient, or the pickling solution is ineffective. When this defect occurs, various possible factors should be eliminated one by one, and if necessary, sandblasting procedures can be added to the pre-treatment.

4. Striped spots: The cause of this defect is generally due to uneven reactions. It can be eliminated by shaking the parts during pickling and lowering the temperature of the pickling solution. In addition to the above-mentioned defects, sometimes products that pass the inspection after acid washing may also show spots on the surface after a period of time. There is currently relatively little research on this phenomenon, which may be due to the presence of residual acid on the surface after pickling or corrosive media brought in by subsequent production under the combined action of stress. It is different from the general corrosion form under microscopic inspection and generally does not affect its performance. It can be removed by re pickling, but the load-bearing parts need to strengthen the hydrogen removal treatment after secondary pickling.

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