Study On Corrosion Characteristics Of Aluminum Alloy In Chromium-free Deoxidizing Solution

Anodizing is a commonly used method to improve the corrosion resistance and increase the surface special functions of aluminum alloys.The surface deoxidation process of aluminum alloys is a key process step in the aluminum alloy anodizing process.At present,deoxidizing solutions all use solutions containing higher concentrations of chromic anhydride.It not only generates a lot of chrome-containing wastewater with great toxicity during the production process,which is harmful to the ecological environment and human health,but also has the problem that the corrosion rate cannot be adjusted to the specified value according to the process specifications,which seriously affects the quality of aluminum alloy anodizing.Therefore,it is of great significance to develop an efficient,stable and environmentally friendly chromium-free deoxygenation solution.In this paper,a chromium-free deoxidation solution is studied.Through weightless corrosion experiments,intergranular corrosion experiments,terminal pit corrosion experiments and electrochemical test analysis,combined with scanning electron microscope,metallographic microscope and electrochemical workstation and other analytical characterization methods,the corrosion characteristics and morphology of various aluminum alloys such as 2024 clad aluminum,2024 bare aluminum,6061 bare aluminum and 7050 bare aluminum were systematically studied in this deoxidizing solution,and compared with the commercial deoxidizing solution B.The research contents include the corrosion rate,intergranular corrosion and pitting characteristics,and the effect of temperature on the corrosion rate of different aluminum alloys in two chromium-free deoxidation solutions.Based on the actual production requirements,the analysis and detection methods of the main components of the deoxidized solution were studied.Combined with the comprehensive analysis of indicators such as the specific gravity of the solution and the quality monitoring of dissolved aluminum and the equivalent deoxidized area,the solution adjustment boundaries and adjustment methods were determined.The purpose of this research work is to provide complete technical data and process guidance for the application of the studied chromium-free deoxygenation solution in the aviation industry.The results are as follows:(1)Within the range of possible process parameters(mainly the temperature range used),all basic corrosion data measurements have been completed.It provides a selection basis for the process parameter selection of chromium-free deoxidizing solution in actual production.The experimental results show that the researched chromium-free deoxidation solution A has a faster and more stable corrosion rate for four aluminum alloys than the foreign commercial deoxidation solution B,the possibility of pitting corrosion is small,and the grain boundary corrosion degree within10 minutes is very low,because the deoxidation time is usually less than 10 minutes,so it will not bring adverse effects on the quality of the subsequent anodizing process.(2)In the studied chromium-free deoxidation solution,for the same type of aluminum alloy,the corrosion rate increases with increasing temperature.At the same temperature,the corrosion rate of the four aluminum alloys gradually decreases with the increase of the corrosion time,and decreases rapidly within 0-5 minutes,and the decline rate gradually decreases between 5-30 minutes.After 30 minutes,the corrosion rate tends to a stable value.Corrosion of four aluminum alloys under different temperature conditions,the deoxidation corrosion rate of four aluminum alloys will change with temperature within0-20min,but after 20min,the corrosion resistance of the four aluminum alloys is 7050bare aluminum alloy<2024 bare aluminum alloy<2024 coated aluminum alloy<6061bare aluminum alloy.(3)The results of the method for the determination of nitric acid in the chromium-free deoxygenation solution showed that EDH was selected as a masking agent to mask the interfering metal ions in the solution,bromophenol blue was used as an indicator,and the acid-base neutralization titration method was used to analyze and calculate Nitric acid content,the error completely meets the production requirements.(4)The optimal addition method of tank solution was determined by experiments.When the solution is used up to the lower limit of the corrosion rate(0.0032 mm/single side/h),the maximum corrosion amount M₀ is recorded.The experimental results suggest that:when the corrosion of aluminum alloy reaches half of the maximum corrosion amount,the original solution is added,which is more economical than adding the original solution when the maximum corrosion amount is corroded,which improves the utilization rate of the deoxidizing solution,saves costs,and is more environmentally friendly.