Highly Corrosion-Resistant yet Sacrificial Metallic Coatings for High-Strength Aluminum Alloys

High-strength aluminum (Al) alloys offer an excellent strength-to-weight ratio and are widely used in aircraft structures. Traditionally, these alloys are protected by organic and conversion coatings containing corrosion inhibitors, many of which (such as chromates) are carcinogenic. Organic coatings are also susceptible to mechanical damage and have limited use at elevated temperatures. Metallic coatings offer an attractive alternative with improved durability and corrosion resistance. However, because Al is less noble than most corrosion-resistant metals, conventional metallic coatings (such as Cr or stainless steel) can drive severe galvanic attack of the substrate when damaged.

This challenge can be addressed by developing metallic coatings that are both highly corrosion-resistant and sacrificial: two attributes that rarely coexist. We demonstrate such coatings using Al-V alloy powder to produce thin coatings on AA2024-T3 by cold spray. The Al-V alloy powder was produced by high-energy ball milling. The coated structures showed excellent corrosion resistance, with lower corrosion current density and higher breakdown potential in NaCl solution. The corrosion potential of the coating was more negative than that of the substrate, indicating sacrificial behavior. The wear resistance of the coating was about four times higher than that of the substrate. These results highlight the potential of cold-sprayed Al-V coatings to enable corrosion- and wear-resistant Al alloys while eliminating the need for organic coatings.