Effects of increased Fe content on local damage in recycled 6xxx aluminium alloy
Yangchao Deng, Zhenjie Cao, Richard Hunt, Wei Sun, Guang Zeng, Sansan Shuai, J.D. Robson, Kun Yan
Abstract
Impurity elements, such as iron (Fe), inevitably form Fe-rich intermetallic compounds (IMCs) in recycled aluminium alloys, some of which adversely affect alloy performance. This study investigates the correlation between microstructure and local damage formation, aiming to elucidate the effect of increasing Fe content in recycling 6xxx series (Al-Mg-Si) alloys. Three-dimensional (3D) in-situ synchrotron radiation X-ray microtomography (SR-μCT) and analytical SEM were employed to identify and track the evolution of particle-involved damages. In the 100% recycled IBA6111 alloy, the number density and volume fraction of Fe-rich IMCs are twice as high as in the baseline AA6111 alloy. The IBA6111 alloy exhibits a high ultimate strength of 328 MPa and uniform elongation of ∼21% under uniaxial tensile loading. However, its post-necking flow stress falls more rapidly, resulting in a reduced elongation to failure of ∼28%. In-situ μCT analysis reveals that local damage predominately originates from particle-cracking voids (PCVs) in both alloys. In IBA6111 alloy, the void volume fraction and number density grow nearly exponentially, reaching significantly higher levels than in AA6111. Void identification and tracking further indicate continuous PCV nucleation, along with individual void growth/coalescence throughout deformation, where IMC particle size and spatial distribution play crucial roles. These findings provide insights into the development of impurity-tolerant aluminium alloys with a balanced combination of strength and ductility.