Factors Affecting the Alkali Corrosion Rate of Aluminum Profiles and Control Methods

In order to accelerate the alkali etching rate of aluminum profiles, sodium nitrate or sodium nitrite can be added to the alkali etching solution based on sodium hydroxide, along with additives such as sodium gluconate. In addition, factors such as the concentration of the bath, temperature, and etching time will also affect the alkali etching rate of industrial aluminum profiles, as well as how to control these factors.

Tank Solution Concentration

Dissolving sodium hydroxide in water creates an alkaline solution, which is commonly used as a chemical cleaning tank solution for aluminum profiles, also known as an alkaline etching solution. The sodium hydroxide in the alkaline etching solution exists in a free ion state. As the concentration of sodium hydroxide increases to 250 g/L, the etching rate of industrial aluminum profiles also increases. This shows that the higher the concentration of sodium hydroxide in the tank solution, the faster the etching rate. However, nowadays, many people control the sodium hydroxide content within the range of 50-100 g/L to save costs. To control the sodium hydroxide content, a method of adding a stabilizer can be used by adding gluconates into the tank solution, keeping the free sodium hydroxide content within the range of 70 g/L.

Aluminum Dissolution Amount

Place the aluminum profile in a sodium hydroxide alkaline solution. Aluminum reacts chemically with sodium hydroxide to produce aluminum hydroxide. Affected by the reaction products, the corrosion rate of aluminum decreases. Experiments have shown that when the aluminum dissolution amount is 26 g/L and the sodium hydroxide concentration is 50 g/L, the higher the temperature, the slower the aluminum corrosion rate. This indicates that, with the electrolytic solution concentration remaining constant, the higher the aluminum dissolution amount, the slower the corrosion rate, meaning that the aluminum dissolution amount is inversely proportional to the corrosion rate. The appropriate aluminum dissolution amount should be obtained through calculation. Observe changes in the electrolytic solution and, according to the situation, control the aluminum dissolution amount within the specified range.

Bath Solution Temperature

Through experiments on 6063 aluminum profiles, we concluded that as the temperature of the bath solution rises, the rate of alkaline corrosion of aluminum also increases rapidly. For every 10°C increase in temperature, the rate of aluminum corrosion reaction doubles. Therefore, the higher the temperature, the faster the alkaline corrosion of aluminum profiles, meaning that the bath solution temperature is directly proportional to the corrosion rate. This is because the corrosion of aluminum profiles in the alkaline solution is an exothermic reaction, which can release 20 kW/m² of heat. Usually, a cooling system with sufficient capacity needs to be installed to maintain the bath solution temperature within the range of 50-60°C. In winter, this system can also serve as a heating device.

Etching Time

In the alkaline etching reaction, the longer the etching time of industrial aluminum profiles, the greater the weight loss due to aluminum dissolution. However, etching time is not directly related to etching speed. Shortening the etching time can only reduce the weight loss from aluminum dissolution and decrease the consumption of alkaline etching agents, which is not proportional to the etching speed. If a smooth aluminum profile surface is desired, mechanical brushing or sandblasting can be used for processing, or the desired shiny and smooth effect can be achieved by improving the quality of the molds and the extrusion process.