Why do you need post-passivation treatment of hot dip galvanizing?

First, let's look at the consequences of passivating screws without hot dip galvanizing. After the screw is galvanized, if it is stored in a humid and non-ventilated environment, the zinc layer will corrode quickly, and it will appear a white substance on the outside. We generally call this substance "white rust". This is the most intuitive way to identify whether the galvanized parts are corroded or not.

Reasons for the formation of white rust: Since metal zinc is an active metal, it is good at reacting zinc hydroxide with moisture in the air. Then the zinc hydroxide further reacts with CO2 to form a dense and adhesive basic zinc carbonate corrosion product, which forms a protective film on the surface of the screw, which can protect the screw to a certain extent. However, a large number of hoarded screws prevent the metal surface from being completely covered with a protective film, and local electrochemical reactions occur, resulting in the formation of white rust.

Passivation and sealing treatment of screws after hot dip galvanizing

Passivation treatment is a kind of chemical conversion coating treatment. The actual passivation process depends on the electrochemical reaction process on the metal surface. It includes an anodic dissolution step, in which the metal surface is oxidized, and the accompanying cathodic process reduces some ions in the passivation solution, producing low-valent ions and metal corrosion products to form a passive film on the surface.

An intact passive film isolates the metal from the ambient medium, interrupting the corrosion reaction. Incomplete or porous passivation films, where the corrosion reaction proceeds but is hindered, which prevents the process of anodic dissolution and renders the metal in a passivated state.

Therefore, in order to improve the process, more protection of the screws. The passivation process should be closed after the passivation process, mainly to prevent the incomplete passivation film from taking remedial measures, and to better protect the screws from corrosion.