Regulative effect of Mg/Si ratio on microstructure evolution and mechanical properties of cast Al-Li-Mg-Si alloys

• Published in: China foundry 2022, Vol.19 (1), p.81-88
• Main Authors: Zhang, Xue-jian, Wang, Hong-wei, Ye, Feng-bai, Zou, Chun-ming, Wei, Zun-jie
• Format: Article
• Language: English
• Subjects: Alloys; Analysis; Degassing of metals; Engineering; Machines; Manufacturing; Materials Engineering; Mechanical properties; Metallic Materials; Metals; Processes; Research & Development; Specialty metals industry
• ISSN: 1672-6421; 2365-9459
• DOI: 10.1007/s41230-022-1105-3

The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si, Al-2.5Li-1Cu-1.6Mg-0.8Si, and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated. The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio. The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg 2 Si primary phase at the expense of the AlLiSi primary phase. Moreover, a tiny amount of T B -Al 7.5 Cu 4 Li phase transforms into S-Al 2 CuMg phase with the increase of Mg content. In addition, the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase. After ageing treatment, the precipitation sequence as a function of Mg/Si ratio is as follows: δ/δ′+AlLiSi (Mg/Si is ∼1) → δ/δ′+β′-Mg 2 Si+AlLiSi (Mg/Si is ∼2) → δ/δ′+β′-Mg 2 Si (Mg/Si is ∼3). A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing. The rod-like β′-Mg 2 Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.