# Effect of Selectively Etched Al-Rich and Si-Rich Microstructures on the Adhesion of Polyimide Coatings to SLM AlSi10Mg

## TL;DR

This study improves the adhesion of polyimide coatings on aluminum parts by selectively etching microstructures, significantly increasing bonding strength.

## Contribution

A novel method using selective etching of Al-rich and Si-rich microstructures to enhance adhesion of polyimide coatings on SLM AlSi10Mg is introduced.

## Key findings

- Selective etching increased shear strength from 2.6 MPa to 43.2 MPa.
- Pull-off strength reached up to 29.0 MPa with cohesive failure in polyimide on Al-rich surfaces.
- Si-rich microstructures showed mixed failure modes including microcracks and PI tearing.

## Abstract

Interfacial adhesion between selective laser-melted (SLM) AlSi10Mg and polyimide (PI) insulating coatings is often limited by mismatched physicochemical properties. To improve adhesion, Al-rich and Si-rich microstructured surfaces were fabricated on the XY plane (perpendicular to the build direction) and the Z plane (parallel to the build direction) by acidic and alkaline etching, exploiting the characteristic microstructure of SLM AlSi10Mg. Surface topography, chemical composition, and wettability were characterized, and interfacial mechanical performance was evaluated by shear and pull-off tests. The microstructures increased surface roughness and improved wettability. The shear strength rose from 2.6 ± 1.5 MPa for the polished surface to 43.2 ± 8.6 MPa. The polished surface showed a pull-off strength of 2.2 ± 0.25 MPa. In pull-off tests, failure mainly occurred within the dolly/adhesive/PI system, indicating that the interfacial tensile strength exceeded the strength of the adhesive system; the maximum measured pull-off strength was 29.0 ± 1.3 MPa. Fractography predominantly showed cohesive failure in PI on Al-rich microstructures. Si-rich microstructures exhibited mixed failure, including fracture of the Si skeleton and tearing of PI, together with interfacial microcracks.