Zinc is a silver-white metal with metallic luster. Melting point 419 degrees, density 7.14g/cm3, standard electrode potential is -0.76V, is one of the more active metals. The crystal structure of zinc is hexagonal close-packed, and with the increase of temperature, it shows allotropic conversion.
The appearance of the zinc coating is dark white, and the coating density is generally 6.27g/cm3. It is the earliest and most commonly used coating material in thermal spray anti-corrosion construction. However, zinc coatings do not have corrosion resistance in sulfur or oxide-contaminated air. Although the passivation of zinc is very small, it can be significantly passivated in the chromate solution to form a zinc chromate protective film.
The zinc raw material used for thermal spraying requires high purity, and the purity required for corrosion protection is Zn99.995% or more, and iron content is less than 0.001%. As a wire, the purity of the wire is at least 99.9% of zinc and 0.05% or less of Cu. In order to prevent the interruption of spraying, it is required to have a tensile strength of more than 150 MPa and an elongation of more than 40%. The purity is high, the finer the sprayed particles, the denser the coating surface. .
1) The zinc-aluminum alloy used for thermal spraying is mainly a zinc-aluminum binary alloy containing 5% to 25% of AI. When the aluminum content in the alloy is more than 28%, many of the chemical and electrochemical properties of the alloy are similar to those of pure aluminum. If it is used for thermal spray preservation, the cathodic protection effect cannot be exerted well. On the other hand, due to the increase in the amount of aluminum contained in the alloy, it is difficult to process the alloy wire. Therefore, the binary zinc aluminum alloy containing 85% of zinc and 15% of aluminum is currently used. The general grade of this alloy is Zn-AI15.
2) Zn-AI15 alloy
The Zn-Al15 alloy has a melting point of 440 deg. and a coating density of about 5.0 g/cm3. The Zn-Al15 Zn-Al alloy is a two-phase structural coating that is superior to pure zinc or pure aluminum in many respects. The alloy coating has good corrosion resistance in many environments and can provide effective protection of steel substrates. At present, there is a commercial Zn-Al15 alloy thermal spray wire supply in China.
The mechanical properties of the Zn-Al15 alloy coating are good, its strength and hardness are better than pure zinc coating and pure aluminum coating; the electrochemical properties are between the zinc and aluminum coating, and both have some advantage. The application of corrosion protection in steel structures is similar to that of zinc or aluminum. Therefore, the overall performance of Zn-AI alloy coating is superior to that of zinc coating and tantalum coating, and it is a highly efficient electrochemical cathodic protection corrosion resistant coating at room temperature.