Titanium alloys are widely used in civil fields because of their excellent properties, high specific strength, good medium temperature properties and no magnetism. Titanium alloy products developed have almost penetrated into all aspects of modern life. In production, we found that the common surface quality faults of titanium alloy products were corrosion, ash hanging, oxide scale not removed and stripe pattern.
1. Over-corrosion: Over-corrosion refers to pitting or unequal pitting defects on the surface of titanium alloy after pickling, which are different from the appearance of material structure. Generally, the cause of over-corrosion defect is the imbalance of the ratio of hydrofluoric acid to nitric acid. Excessive concentration of hydrofluoric acid or insufficient concentration of nitric acid can lead to the occurrence of the defect. Another reason is that the acid pickling time is too long. Generally, the acid pickling time is 1mm-4min. The process parameters can be adjusted according to the operation site, and the acid pickling time can be shortened appropriately.
2. hanging ash: hanging ash refers to the oxides attached to the surface of titanium alloy after pickling. During pickling, the oxides produced by dry titanium alloy and acid solution are accumulated on the surface, which prevents further reaction. The defects of hanging ash are generally caused by excessive deposition of hanging ash during pickling and insufficient washing after pickling. During pickling, parts should be shaken constantly to make the products fall off the surface of titanium alloy. After pickling, spraying or washing should be strengthened to remove hanging ash. In China, high-speed water flow with compressed air and tap water is usually used to wash parts, and the effect is good.
3. The oxide scale has not been removed: there are many reasons for this defect, and each process is possible. There may be poor oil removal, or insufficient molten salt treatment time, or acid pickling solution failure. When this defect occurs, all possible factors should be eliminated one by one. Sandblasting process can be added in the pretreatment when necessary.
4. Stripe pattern: The cause of the defect is usually due to uneven reaction. It can be eliminated by shaking parts during pickling and lowering the temperature of pickling solution. In addition to the above several defects, sometimes found after pickling qualified products, after a period of time, the surface of the phenomenon of spots. For this phenomenon, there is little research now. It may be due to the presence of residual acid solution on the surface after pickling or corrosive medium brought in by subsequent production. Under the joint action of stress, it is different from the general corrosion form under microscopic examination. Generally speaking, it does not affect its performance. It can be removed by re-pickling, but the stressed parts need to be strengthened after re-pickling. Dehydrogenation treatment.
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