Deciphering and Mitigating Failure Mechanisms in Poly(ether Imide) Corrosion Protection Coatings for Automotive...

Area of Science:

• Materials Science
• Electrochemistry
• Corrosion Engineering

Background:

• Corrosion hinders the use of light metal alloys as steel alternatives in vehicles.
• Aluminum alloys require specialized protection due to limited conventional mechanisms.
• Nanocomposite coatings offer potential for aluminum alloy corrosion resistance.

Purpose of the Study:

• To investigate the thickness-dependent corrosion protection of AA 7075 aluminum alloy using poly-(ether imide) (PEI) coatings.
• To evaluate the impact of incorporating unfunctionalized exfoliated graphite (UFG) and siloxane co-polymerization on PEI coating performance.
• To understand the role of polymer secondary structure and interphasic domains in corrosion protection.

Main Methods:

• Electrochemical impedance spectroscopy (EIS) to monitor ion transport and coating performance.
• Systematic variation of PEI coating thickness.
• Incorporation of UFG platelets and siloxane co-polymerization into the PEI matrix.
• Accelerated corrosion testing under aggressive conditions.

Main Results:

• Increasing PEI coating thickness enhances ion sequestration and permeation selectivity, improving corrosion protection.
• Incorporation of UFG platelets can initially degrade protection but enhances it in thicker coatings due to improved matrix rigidity and tortuosity.
• Siloxane co-polymerization aids in sequestering corrosion products but may weaken adhesion.
• Thicker PEI coatings with UFG platelets demonstrate superior corrosion resistance under aggressive testing.

Conclusions:

• Coating thickness is a critical factor for effective corrosion protection of aluminum alloys with PEI.
• Polymer secondary structure and interphasic domains significantly influence permeation selectivity and barrier properties.
• PEI-based nanocomposite coatings, particularly thicker ones with UFG, offer a viable strategy for protecting light metal alloys against corrosion.