How to judge the quality of aluminized plate process

Aluminized plate is a kind of surface chemical heat treatment method to form aluminum iron alloy coating on steel surface in molten aluminum. The aluminized layer can be divided into immersion type and diffusion type according to its production method. After hot dip plating, the workpiece is directly taken out of the molten aluminum solution and solidified by air cooling. Its surface is not smooth, there are often aluminum adsorption and excessive aluminum solution solidification, and the thickness is uneven. The typical structure of impregnated aluminized plate can be roughly divided into two layers: the outer layer is pure aluminum, and the chemical composition is similar to the original aluminum solution. Below the pure aluminum layer is a composite layer formed by the mutual diffusion of aluminum and iron, which is distributed in the irregular tooth shaped steel matrix. The diffusion type is to put the workpieces after hot dip aluminizing into an air electric furnace, heat them to 850-920 ℃, keep them warm for 3-4 hours, and take them out for air cooling.
In this diffusion annealing process, the aluminum on the surface melts and diffuses into the metal matrix, and the pure aluminum layer disappears without zigzag features, thus forming the aluminum iron compound and solid molten crystal structure on the surface, which has high temperature resistance, oxidation resistance and corrosion resistance. A large number of experiments and practices at home and abroad have proved that as long as the aluminum content on the surface of aluminized layer is not less than 7%, it can protect the metal matrix, slow down or even prevent oxidation and corrosion.
The thickness and concentration of aluminized layer are two main indicators to evaluate the aluminizing quality of aluminized parts, but the more critical is the aluminum concentration on the surface of aluminized parts, not the thickness. The coating with thin aluminized layer and high aluminum concentration is more resistant to high-temperature oxidation and corrosion than the coating with thick aluminized layer and low aluminum concentration.
The corrosion resistance of aluminized plate determines the aluminum content of aluminized layer. When the aluminum content in the aluminized layer reaches 8% (WT%), the corrosion resistance is significantly improved. The current standard generally requires that the aluminum content of the aluminized layer is greater than 15% (WT) and the atomic content of the aluminized layer is greater than 30%. The protective effect on metal materials is reflected in two aspects: first, a dense, strong adhesion and extremely stable Al2O3 protective film is formed on the surface of the infiltrated layer, which has strong self repair and regeneration capabilities. The results show that when the aluminizing amount is more than 8% (WT%), a continuous protective film can be formed. Second, the aluminized layer is a large anode in the liquid medium, and the aluminum in the aluminized layer is consumed for a long time to protect the base metal from corrosion.
What should be paid attention to in the use of aluminized plate furnace lining?
1. Please install the furnace lining in strict accordance with the furnace lining installation manual.
3. Pay close attention to the change of furnace lining in the use process and handle it in time.
2. After the installation of furnace lining, clean up the sundries in the furnace. When opening the new furnace lining, the blanking must be careful. Do not throw large iron blocks into the furnace lining to avoid damage to the furnace lining. When the furnace opens the installed new furnace lining, the medium frequency power supply cannot be pulled too fast, which is conducive to the combination of furnace lining and fixed filler.
4. The lining wall becomes thinner after a certain number of times of use. When the wall thickness of the furnace lining is about to be less than 1 cm, the furnace lining shall be stopped and replaced with a new one.