Under the long-term action of the complex outdoor environment, the aging of the zinc layer of galvanized welded wire mesh directly affects its protective performance and service life. As a key barrier to protect the steel wire substrate, the aging process of the zinc layer is affected by the synergistic effect of multiple environmental factors. Exploring its aging mechanism and establishing a scientific life prediction model are of great significance to extending the service life of galvanized welded wire mesh and reducing maintenance costs.
The aging of the zinc layer of galvanized welded wire mesh is essentially the result of physical and chemical reactions between zinc and the external environment. Oxygen and moisture in the atmosphere react with zinc to form zinc oxide (ZnO). In the early stage, zinc oxide forms a relatively dense film on the surface of the zinc layer, which plays a certain protective role on the internal zinc layer. However, when there are pollutants in the outdoor environment, such as sulfur dioxide emitted by industry and chloride ions in coastal areas, the zinc oxide film will be destroyed. Sulfur dioxide combines with water to form sulfurous acid, which accelerates the corrosion of zinc; chloride ions have extremely strong penetrability and can quickly destroy the passivation film on the surface of the zinc layer, exposing the zinc layer to the corrosive medium and accelerating the aging process.
Rainwater erosion and alternating wet and dry conditions are important factors that accelerate the aging of the zinc layer. In a humid environment, an electrolyte solution is formed on the surface of the zinc layer, forming a microbattery with impurities or the iron substrate, causing electrochemical corrosion. Zinc loses electrons as the anode, undergoes an oxidation reaction to generate zinc ions, and the electrons flow to the iron substrate. At the cathode, oxygen and water obtain electrons to generate hydroxide ions, which combine to form zinc hydroxide, which further decomposes into zinc oxide. When the environment is dry, the residual salt crystals will produce stress on the surface of the zinc layer, causing cracks in the passivation film, creating conditions for subsequent corrosion. Long-term dry-wet cycles continuously destroy and rebuild the protective film on the surface of the zinc layer, causing the zinc layer thickness to gradually decrease.
The effect of temperature changes on the aging of the zinc layer should not be ignored. A high temperature environment will accelerate the chemical reaction rate of the zinc layer and increase the corrosion rate; in a low temperature environment, although the chemical reaction slows down, the presence of condensed water will still cause electrochemical corrosion. In addition, the thermal expansion and contraction effect caused by the temperature difference between day and night will generate stress at the interface between the zinc layer and the steel wire substrate. When the stress accumulates to a certain extent, it will cause the zinc layer and the substrate to peel off, exposing the steel wire directly to the corrosive environment, accelerating the overall failure of the galvanized welded wire mesh.
When pollutants are deposited on the surface of the zinc layer, a local corrosive environment will be formed. For example, metal oxide particles in dust will form a galvanic pair with the zinc layer, accelerating the corrosion of zinc; if the particulate matter emitted by industry contains acidic substances, it will directly react chemically with zinc. Organic acids secreted during the growth of vegetation and corrosive components in biological excrement such as bird droppings will also cause erosion of the zinc layer. The long-term accumulation of these pollutants will cause local pitting of the zinc layer. As the pitting depth increases, it will eventually penetrate the zinc layer and threaten the steel wire substrate.
Based on the aging mechanism of the zinc layer, establishing a life prediction model combined with environmental factors is the key to ensuring the reliability of galvanized welded wire mesh. The commonly used method is to collect corrosion data of galvanized welded wire mesh in different regions and under different environmental conditions, analyze the relationship between the change of zinc layer thickness and environmental parameters (humidity, pH, pollutant concentration, etc.), and use mathematical statistics or machine learning algorithms to build a prediction model. For example, regression analysis is used to establish the functional relationship between zinc layer thickness and time and environmental factors; or artificial neural network is used to simulate the nonlinear process of zinc layer corrosion in a complex environment, so as to predict the remaining life of galvanized welded wire mesh in a specific environment.
In practical applications, the establishment of a life prediction model also needs to consider the differences in galvanizing processes. The hot-dip galvanized layer is thicker and denser in structure, with strong corrosion resistance, and its aging rate is relatively slow; while the electroplated zinc layer is thinner and ages faster under the same environment. Therefore, the model needs to set corresponding parameters for different galvanizing processes. At the same time, combined with on-site monitoring data, the model is corrected and optimized in real time to improve the prediction accuracy and provide a scientific basis for the replacement and maintenance of galvanized welded wire mesh.
With the development of science and technology, new detection technologies and analysis methods have provided new directions for zinc layer aging research and life prediction. Spectral analysis, scanning electron microscopy and other technologies can more accurately observe the microstructural changes of the zinc layer and the composition of corrosion products; IoT sensors can monitor the temperature, humidity, pH and other parameters of the environment in which the galvanized welded wire mesh is located in real time. These technologies combined with the life prediction model will promote the maintenance of galvanized welded wire mesh from passive repair to active prevention, and realize its more efficient and lasting application in outdoor environments.
