Pre-aged and paint-baked strengthening response on the prolonged natural-aged Al-Mg-Si-Cu aluminum alloys

• Published in: Journal of alloys and compounds 2024-12, Vol.1008, p.176677, Article 176677
• Main Authors: Yeh, Ching-Wen, Chen, Chu-Jen, Tai, Cheng-Ling, Yang, Yo-Lun, Kumar Misra, R. Devesh, Hsiao, Chien-Nan, Chen, Chien-Chun, Tsao, Cheng-Si, Jeng, U.Ser, Lin, Hsin-Chih, Chung, Tsai-Fu
• Format: Article
• Language: English
• Subjects: Co-precipitation strengthening; Paint-baking; Pre-aging; Prolonged natural aged Al-Mg-Si-Cu aluminum alloys
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.176677

This study investigates the response of pre-aging and paint-baking on the microstructure evolution and precipitation kinetics in prolonged natural aged Al-Mg-Si-Cu aluminum alloys using differential scanning calorimetry (DSC), transmission electron microscopy/scanning transmission electron microscopy (TEM/STEM), small-angle X-ray scattering (SAXS), and mechanical tensile testing. The prolonged natural aged samples for 14 days contained a higher fraction of rod-like GP zones with a size of ∼1.1 nm and ∼5.5 nm in diameter and length, respectively. After pre-ageing treatment at 80°C for 1 h, some of the existing GP zones grew, exhibiting an increased aspect ratio from 5.0 to 7.7, while others dissolved, leading to a decrease in UTS strength from 211.3 ± 2.1 MPa to 193.6 ± 2.4 MPa. In the direct paint-baked samples (at 180°C for 30 mins), the partial dissolution and size reduction of GP zones promoted the formation of rod-like Lp-phase precipitates, which grew on (020)Al habit plane, and characterized by Cu-rich layered convex units along the [020]Al direction. In samples subjected to combined pre-aging and paint-baking treatments, the formation of rod-like β" phases within the aluminium matrix as well as disk-like θ' and Q′ phases along the dislocations played an important role in co-precipitation strengthening. Moreover, the presence of co-existing θ'/Q′ along pre-existing dislocations acted as effective barriers, mitigating lattice strain during tensile deformation. This resulted in a higher UTS of 233.0 ± 5.8 MPa and improved elongation of 29.1 ± 3.0 %. [Display omitted] ●After pre-ageing, some GP zones grew with increased aspect ratio while others dissolved, reducing UTS strength.●Paint-baking partially dissolves GP zones but enhances rod-like Lp-phase formation.●Combined pre-ageing and paint-baking treatments form rod-like β", disk-like θ', and Q′ phases, enhancing co-precipitation strengthening.●Co-existing θ'/Q′ phases, grew along dislocations, alleviate lattice strain during deformation, improving elongation.