Effects of Droplet Temperature, Erosion Angle of Attack and Droplet Velocity on the Erosion Behavior of 6061 Aluminum Alloy Droplets

When an aircraft is flying at high speed through a rainy area, the fuselage and wing surfaces are inevitably subjected to strong droplet erosion. This droplet erosion causes significant damage to the aircraft skin material, posing a serious threat to the safety and integrity of the skin material, and thus posing a potential threat to the operational safety of the aircraft. There is a relative lack of research on the droplet erosion behavior of aluminum alloy, a widely used aircraft skin material. In order to explore this issue in depth, this study adopted a high-speed droplet erosion experimental machine to conduct a detailed experimental study on the erosion behavior of 6061 aluminum alloy under different angles of attack, droplet speeds and droplet temperatures. The experimental results showed that the damage amount of 6061 aluminum alloy showed a significant growth trend with the increase of the erosion angle of attack and droplet velocity. At smaller angle of attack, the damage of aluminum alloy mainly originated from the exfoliated particles on the surface of aluminum alloy and the impurity particles in the water, accompanied by the cutting effect of the high-speed lateral jet on the material surface. And when the angle of attack increased, in addition to the cutting effect, the surface plastic deformation generated by the water hammer force also jointly aggravates the damage of the aluminum alloy. In addition, the experiment also found for the first time that the increase of droplet temperature had a significant effect on the droplet erosion damage of 6061 aluminum alloy. As the droplet temperature increased from 10 ℃ to 20 ℃ and then to 40 ℃, the damage of the aluminum alloy increased significantly. This finding suggested that the change of droplet temperature had a non-negligible role in the erosion behavior of aluminum alloys. It was analyzed that the increase in droplet temperature reduced the surface tension of the droplet, which made the shape of the droplet become flatter and the surface rougher. This change enhanced the impact force and cutting effect of the droplets on the surface of aluminum alloy, thus aggravating the erosion damage. In order to gain a deeper understanding of the formation mechanism of droplet erosion damage, the surface and cross-section of the erosion pits were also analyzed in this study for micro-morphological characterization. Through observation and analysis, it was found that the plastic deformation of the material and the emergence and expansion of cracks jointly led to the formation of droplet erosion damage. During the erosion process, the surface of aluminum alloy was subjected to strong impact force and cutting action, which led to plastic deformation and cracks in the material. As the erosion continues, the cracks gradually expand and connect with each other, and eventually form obvious erosion pits.