Corrosion behavior of aluminum alloy for outdoor air conditioning units in coastal atmosphere

The aluminum-for-copper substitution technology is a critical technical route for the lightweight design and improved environmental adaptability of air conditioning heat exchange tubes. To investigate the corrosion behavior and failure mechanism of aluminum alloys for outdoor air conditioning units under long-term coastal service conditions, this study selected T5-treated AlSi10MnMg aluminum alloy as the research object. An ultra-depth-of-field microscope and scanning electron microscopy were used to observe corrosion morphology, pit depths, and the evolution rules of corrosion products. Weight loss measurement was adopted to analyze the corrosion kinetics of the alloy. Electrochemical impedance spectroscopy and potentiodynamic polarization tests were performed to characterize the evolution characteristics of corrosion resistance and corrosion rate. Tensile tests were also conducted to explore the effect of corrosion damage on the mechanical properties of the alloy. The results show that pitting corrosion is the dominant corrosion form of the aluminum alloys in coastal atmospheres, and the maximum pit depth increases with the extension of exposure time. Corrosion products undergo a dynamic evolution process of cracking, thickening and peeling. This evolution process induced a complex variation trend in corrosion resistance and corrosion rate with an initial decrease, subsequent increase and final decrease. After 12 months of coastal exposure, the tensile fracture strength of the AlSi10MnMg aluminum alloy decreases by 22.5%. This performance degradation is mainly attributed to the stress concentration generated inside pitting pits. The corrosion behavior of the AlSi10MnMg aluminum alloy exhibits distinct stage characteristics. The dynamic evolution of corrosion products dominates the variation of corrosion resistance, and the degradation degree of mechanical performance is highly correlated with the pit depth. In engineering applications, the maximum pit depth can be taken as a core index for service life prediction, and the strengthened anti-corrosion treatment is recommended for welded joints, bending deformation zones and other connecting components. This study only investigates base metal samples with a 12 months coastal exposure period. Further research should focus on longer-term natural exposure experiments, corrosion mechanism analysis of connecting components, and corrosion behavior evaluation under dynamic service environments to further improve the reliability theory of the aluminum-for-copper technology applied to outdoor air conditioner units in coastal areas.