# Effect of Fe and Si Content on Microstructure and Properties of Al-Cu-Li Alloys

## TL;DR

This paper studies how Fe and Si impurities affect the structure and strength of Al-Cu-Li alloys.

## Contribution

It identifies Fe as a major performance limiter and Si as a manageable cost factor in recycled alloy production.

## Key findings

- Fe increases coarse intermetallics and reduces strength and toughness.
- Si causes less severe effects and allows for cost-effective alloy adjustments.
- Controlling Fe is critical for optimal mechanical performance.

## Abstract

This study systematically investigates the effects of Fe and Si impurities on the microstructure and mechanical properties of Al-Cu-Li alloys. Five alloy compositions with controlled Fe (0.03–0.12 wt.%) and Si (0.03–0.12 wt.%) contents were fabricated and processed through homogenization, hot extrusion, solution treatment, and aging. Microstructural characterization demonstrates that Fe promotes the formation of coarse skeletal Al7Cu2Fe intermetallics, while Si facilitates the precipitation of blocky α-AlFeSi phases and eutectic Si particles. An elevated Fe content substantially deteriorates strength, ductility, and fracture toughness, primarily due to two mechanisms: the persistence of thermally stable impurity phases that serve as stress concentrators and preferential crack initiation sites throughout thermomechanical processing, and the consumption of Cu that reduces the volume fraction of primary T1 (Al2CuLi) strengthening precipitates. In contrast, Si exhibits comparatively moderate detrimental effects. The findings establish that stringent Fe control is essential for maintaining mechanical performance, whereas strategic Si adjustment offers a viable approach for cost management in recycled alloy production.