Thermal spray aluminium or zinc coating is a common metal protection technology that is widely used for corrosion protection and high temperature oxidation protection on steel surfaces. Through a high-temperature spraying process, these metal coatings not only improve the corrosion resistance of the substrate, but also enhance its performance in harsh environments.
Performance characteristics
Corrosion resistance
Thermally sprayed aluminum and zinc coatings exhibit excellent resistance to atmospheric and clean water corrosion. Aluminum has a strong affinity with oxygen at room temperature, which can quickly form a dense oxide film (Al₂O₃), which effectively protects aluminum itself from further oxidation. When the coating is applied to a steel substrate, since the electrode potential of aluminum or zinc is lower than that of iron, these metals can act as sacrificial anodes, forming galvanic cells with the substrate, thus providing cathodic protection and extending the life of the steel.
Resistant to high-temperature oxidation
The thermally sprayed aluminium coating, treated by the diffusion aluminizing process, can be used in environments up to 900°C. The aluminium atoms and iron atoms diffuse each other to form an aluminum-iron alloy layer, which makes the coating maintain good oxidation resistance at high temperatures. In addition, if a polymer material is applied to the coating as a sealant, the corrosion resistance can be further improved.
Formation and structure of coatings
Preparation process
There are two main ways to form a thermal spray aluminum or zinc coating: flame spraying of metal wires and arc spraying. In flame spraying, an oxy-acetylene flame heats the metal wire to a molten state, spraying metal particles onto the surface of the workpiece by means of a high-velocity air stream. Arc spraying uses an electric arc to melt a metal wire, which is then sprayed with compressed air to form a coating. The coatings formed by both methods exhibit a typical layered structure with good bonding strength.
Structural features
The porosity of thermal spraying aluminum or zinc coating is generally low, the porosity of flame spraying is 3%~8%, and the arc spraying is usually less than 3%. This layered structure allows the coating to exhibit excellent wear resistance when subjected to external impacts.
Coating preparation process
Substrate pretreatment
Sandblasting the surface of the workpiece is an essential step before spraying to ensure the adhesion of the coating. The abrasive for abrasive blasting should have good cleanliness and angularity in order to effectively roughen the surface.
Spraying process
During the spraying process, the pressure of oxygen and acetylene needs to be controlled, as well as the spray distance and coating thickness. The common coating thickness range is 0.15~0.25mm, and the method of multiple spraying is usually used to ensure the uniformity of the coating.
Closed treatment
After spraying, sealing can significantly improve the corrosion resistance of the metal coating. Good permeability and corrosion resistance of sealants are key to ensuring their effectiveness.
conclusion
Thermally sprayed aluminum or zinc coatings are widely used in various industrial fields due to their excellent corrosion resistance and high temperature resistance. Through reasonable spraying process and post-treatment measures, the service life of the substrate can be effectively extended and maintenance costs can be reduced. In future research, optimizing spraying parameters and developing new sealants will be important directions to improve coating performance.
