ã€China Aluminum Industry Network】1. Spot Corrosion Corrosion, also known as hole erosion, is a type of localized corrosion pattern that produces needle-point, dot, and hole-like patterns on metals. Pit corrosion is a unique form of anodic reaction. It is an autocatalytic process in which the conditions caused by the corrosion process within the pitted pits both promote and sustain corrosion. 2. Uniform corrosion of aluminum in the phosphoric acid and sodium hydroxide solution, the oxide film on it will dissolve, resulting in uniform corrosion, dissolution rate is uniform. As the temperature of the solution increases, the solute concentration increases, which promotes the corrosion of aluminum.
3. Crevice Corrosion Crevice corrosion is a type of localized corrosion. Metal components in the electrolyte solution, due to the formation of gaps between the metal and the metal or metal and non-metal, its width is enough to make the medium immersed and the medium is in a stagnant state, making the phenomenon of increased corrosion within the gap is called crevice corrosion.
4. Stress Corrosion Cracking (SCC) The SCC of aluminum alloys was discovered in the early 1930s. A type of damage that occurs under the combined action of stress (tension or internal stress) and corrosive media is known as SCC. SCC is characterized by the formation of corrosion-mechanical cracks that can either grow along grain boundaries or extend through grains. Since the crack propagation is inside the metal, the strength of the metal structure will be greatly reduced, and sudden damage will occur in severe cases. SCC will only happen under certain conditions. They are:
- Certain tensile stresses or residual stresses in the metal; Types of waste materials in the process of sheet metal strips and causes 1. Throughout the blow hole casting quality is not good.
2. The surface of the bubble ingot has a high hydrogen content and loose structure; the surface of the ingot surface is uneven and dirty; there is no rubbing before the furnace is installed; after the etching, the surface of the ingot and the coated aluminum plate has traces of etching residue; the heating time is too long. Or the temperature is too high, the surface of the ingot is oxidized; when the former is welded and rolled, the emulsion nozzle is not closed and the emulsion flows under the aluminum plate.
3. When the ingot is cracked and hot-rolled, the amount of reduction is too large to crack from the end of the ingot; the temperature of the ingot heating is too high or too low.
4. Unqualified mechanical properties Failure to properly implement heat treatment system or abnormal heat treatment equipment, poor air circulation; Quenching material quantity is large, salt bath temperature is not enough Furnace furnace, the holding time is insufficient, and the temperature is not reached when the temperature is reached; the heat treatment system used in the laboratory Or the test method is incorrect; the sample size is not correct and the surface of the sample is destroyed.
5. Ingot casting slag casting quality is not good, there are metal or non-metal residues in the plate.
6. Tear lubricant composition is not qualified or the emulsion is too thick, slip between the plate and the roller, the metal deformation is not uniform; did not control the rolling rate, the amount of reduction is too large; rolling speed is too large; spool tension adjustment is not Correct, unstable tension; poor quality of annealing; insufficient plasticity of metal; incorrect control of roller type, excessive internal stress of metal; cracking of hot rolled reels; poor lubrication during rolling, excessive friction between plate and roller; The coil is not fed properly, and the plate has tensile stress on one side, compressive stress is generated on the plate side, and small cracks occur on the edges. After repeated rolling, the expansion continues from the crack and tearing occurs; the clamp of the stretching machine is not properly clamped during finishing. Or uneven, or the plate has cracked edge, it will cause tearing when stretching; when quenching, the pocket chain is not well or too tight, so that the plate piece is cracked, causing tearing when stretched and straightened.
7. Over-thin-thickness adjustment is not correct; thickness gauge is faulty or improperly used; roller type control is incorrect.
8. Crimp (fold) Roll type is not correct, such as calender bearing heat, so that both ends of the roll swell, resulting in the pressure of the middle of the plate thickness is thin on both sides; light before the plate wave is too large, so that the amount of light is too large, As a result, there are creases; when the sheet is calendered, it is easy to produce a crease when it is fed incorrectly; the thickness difference between the two sides of the sheet is large, and it is easy to produce a crease.
9. Non-metals are not cleaned by the rollers, roller tables, shears, etc., which are pressed into the hot rolling mill. During the processing, the dirt is dropped on the trolley belt and formed by rolling; the rolls, guide rollers, three rollers of the cold rolling machine are straightened. The parts of the contact strips, such as the machine and the coiler, are not clean and the dirt is pressed in; the rolling oil nozzles are blocked or the pressure is low, and the non-metallic dirt adhered to the surface of the strip can not be washed out; the emulsion replacement is not timely, The aluminum powder is not flushed and the emulsion tank is not washed clean.
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