Process-related Changes in Polyetherimide Joined by Friction-based Injection Clinching Joining (F-ICJ)

Area of Science:

• Materials Science
• Mechanical Engineering
• Polymer Science

Background:

• Hybrid joints combining polymers and metals offer unique advantages.
• Friction-based joining processes are increasingly used for dissimilar material assembly.
• Understanding the impact of processing on material properties is crucial for joint performance.

Purpose of the Study:

• To investigate the effects of the Friction-based Injection Clinching Joining (F-ICJ) process on the microstructure and local properties of polyetherimide (PEI) in hybrid joints.
• To evaluate the quasi-static mechanical performance of F-ICJ joints made from amorphous PEI and aluminum AA6082.
• To correlate microstructural changes with local property variations and assess their impact on global joint strength.

Main Methods:

• Microhardness mapping combined with cross-polarized transmitted-light optical microscopy (CP-TLOM) to analyze the stake head.
• Mechanical testing including lap shear and cross tensile tests to evaluate global performance.
• Size exclusion chromatography (SEC) to analyze potential polymer chain degradation.

Main Results:

• Two distinct lower-strength zones, plastically-deformed zone (PDZ) and thermo-mechanically-affected zone (PTMAZ), were identified in the PEI stake head.
• PDZ and PTMAZ showed reduced local mechanical properties (12%-16% and 8%-12% respectively) due to loosely packed PEI chains and larger free volume.
• Despite local property reduction, F-ICJ joints exhibited robust global mechanical performance in lap shear (1419 ± 43 N) and cross tensile (430 ± 44 N) tests.
• Mechanical strength reduction was reversible through thermal annealing, and process-induced chain scission did not significantly affect local strength.

Conclusions:

• The F-ICJ process induces localized microstructural changes in PEI, leading to reduced local mechanical properties.
• These localized changes do not compromise the overall mechanical integrity of hybrid PEI-aluminum joints.
• The findings support the optimization of F-ICJ for manufacturing reliable hybrid joints.