Titanium alloys are widely used in the civil field due to their excellent properties, high specific strength, good medium temperature performance, and no magnetism. The titanium alloy products developed have penetrated into almost every aspect of modern life. In production, we found that the common surface failures of titanium alloy products have been corroded, ash, oxidized skin and stripe spots.
1.Over-corrosion: Over-corrosion refers to the appearance of pits or irregularities on the surface of the titanium alloy after pickling, which is different from the material structure. Generally, the cause of over-corrosion defects is the imbalance of hydrofluoric acid and nitric acid. If the concentration of hydrofluoric acid is too high or the concentration of nitric acid is insufficient, the defect may occur. Another reason is that the pickling time is too long. Generally, the pickling t is 1 mm. ~4min, the process parameters can be adjusted according to the operation site, and the pickling time can be shortened appropriately.
2.Ash hanging: ash hanging refers to the oxides attached to the surface of titanium alloy after pickling. During pickling, the chemical reaction is carried out between dry titanium alloy and acid. The defects of hanging ash are generally caused by excessive deposition of hanging ash during pickling and insufficient washing after pickling. During pickling, the parts should be shaken constantly to make the products fall off from the surface of titanium alloy. After pickling, the ash should be removed by spraying or rinsing. Domestic generally adopt compressed air and tap water mixed high-speed water wash parts, the effect is good.
3. Unremoved scale: there are many reasons leading to the defect, and each process is possible. There may be poor oil removal, insufficient time for molten salt treatment, or failure of pickling solution. When the defect occurs, all possible factors should be eliminated one by one, and if necessary, sand blasting process can be added in the pretreatment.
4. Striped spots: The cause of this defect is generally caused by uneven reaction. It can be removed by shaking the parts during pickling and lowering the temperature of the pickling solution. In addition to the above defects, sometimes products that have passed the inspection after pickling are found, and after a period of time, the surface of the spot appears. For this phenomenon, there are few studies now, which may be due to the presence of residual acid on the surface after pickling or the presence of corrosive media brought into by subsequent production. Under the combined action of stress, under microscopic detection and general corrosion patterns The difference, generally does not affect its performance, can be removed by pickling again, but the force-bearing parts should strengthen the hydrogen removal treatment after the second pickling.