Investigation On Surface Wetting Behavior And Mechanical Durability Of Aluminum Alloy

Due to low density,oxidation resistance,high electrical conductivity,sufficient mechanical strength and low price,aluminum alloy has been widely used in many fields,such as automobile,construction,mechanical equipment,ship and aerospace.It plays an irreplaceable role in human life and industrial production.Due to the large-scale use of aluminum,its application scenarios vary greatly.For many aluminum products and equipment that work in dirty,high humidity and low temperature environments,the accumulation of dirt,water and ice on their surfaces may hinder the operation of the equipment or even cause damage to it.The total amount of aluminum and its alloys used in China is a world leader all year round.Improving the surface properties of aluminum and its alloys will further expand its application areas and has high scientific significance and application value.Therefore,there is an urgent need to improve the dirt,water and ice resistance of aluminum surfaces.Nowadays,the construction of superhydrophobic surfaces on aluminum alloys is a popular way to solve the above problems.Chemical etching is a fast method to prepare superhydrophobic surfaces because of its simplicity,high efficiency and low cost.Meanwhile,aluminum,as a reactive metal,easily reacts with strong acids and bases to etch rough surface microstructures.Therefore,hydrophobicity is usually imparted to aluminum surfaces by chemical etching,and many related studies have been reported.However,most reports focus only on the method rather than the substrate material.They usually consider etching time,etchant concentration,and etchant type as variables and ignore the effect of substrate material.However,due to the differences in chemical composition,manufacturing process and heat treatment process,aluminum alloys will form different microstructures and intermetallic phases,which will exhibit different corrosion behaviors during the chemical etching process,resulting in different etched surface morphologies.Based on this,this paper aims to investigate the influence of intermetallic phases or non-intermetallic phases on the surface properties of superhydrophobic aluminum alloys by comparing the differences in wettability,self-cleaning property and mechanical durability of aluminum alloys with different elemental compositions through a simple chemical etching method.The main studies in this paper are:(1)The surface microstructural differences of five different series(1060,2024,5052,6061,7075)of deformed aluminum alloys after etching were investigated by chemical etching.After modification with 2 wt.% perfluorodecyltrimethoxysilane(FAS-17),superhydrophobic(or hydrophobic)aluminum alloy surfaces were prepared and their differences in wettability,ice resistance,self-cleaning properties and mechanical durability were investigated.The results show that the superhydrophobic surfaces of 1060 pure aluminum possess the best hydrophobicity and ice resistance among the five aluminum alloys due to the stepped micro-and nanostructures.The superhydrophobic surface of 6061 aluminum alloy has the second best hydrophobicity and ice resistance after the superhydrophobic surface of 1060 pure aluminum,but its mechanical durability is relatively much stronger.Therefore,after a comprehensive comparison,it was determined that 6061 aluminum alloy could obtain the relatively best surface properties after etching.(2)Due to the small content of other elements in different series of deformed aluminum alloys,the impact of the formed phases on the surface structure after etching is not significant enough.At the same time,considering that Si does not react with hydrochloric acid,it can be more completely retained on the surface after etching to form surface micro-nano structure.Therefore,A390 hypereutectic Al-Si alloy with Si content of 17.4wt.% was further selected as the experimental object,and the superhydrophobic surface was prepared by chemical etching method and modified by FAS-17.The etched surface is mainly composed of primary Si phase,eutectic Si phase and intermetallic phase(IMPs),and shows different morphological structures with different etching time.The surface of the sample etched for 5min has the best hydrophobicity,and its surface microstructure is mainly composed of regular octahedral primary Si phase and rod-like eutectic Si phase.The surface structure was modeled and the theoretical contact Angle was calculated by Cassie-Baxter equation.Finally,through friction and wear experiments,it is proved that the mechanical durability of the A390 super hydrophobic aluminum surface is stronger than that of the previous 5 different series of aluminum alloys.(3)COMSOL Multiphysics 6.0 simulation software was used to simulate the wetting wall of the sample surface etched for 0.5min and 5min,and the theoretical contact Angle was calculated and compared with the actual contact Angle.The results showed that the droplet wetting state was more inclined to the Cassie-Baxter wetting state after 0.5min and 5min etching.(4)Inspired by the relatively regular geometric structure of A390 etched aluminum alloy surface,the theoretical contact angles of seven common geometric microstructure arrays were calculated by Cassie-Baxter model,and the limitations of Cassie-Baxter model were analyzed.The Cassie-Baxter model is modified and the theoretical contact Angle of the surface of common geometric microstructure arrays is calculated repeatedly.The results show that the modified Cassie-Baxter model is more reasonable.At the same time,the modified CassieBaxter model can describe other wetting models except Wenzel model by changing the parameters.In addition,the modified Cassie-Baxter model can also be used to calculate the theoretical contact angles of heterogeneous geometric microstructures.In summary,by comparing the etched and modified surface properties of different series of deformed aluminum alloys,it is found that different element composition will affect the etched morphology of the surface,and then affect the surface properties.It is further found that the primary Si phase and eutectic Si formed by the addition of a large number of Si elements have decisive effects on the surface etch morphology,wettability and mechanical durability of A390 aluminum alloy.