Natural-ageing-enhanced precipitation near grain boundaries in high-strength aluminum alloy

• DOI: 10.1016/j.jmst.2019.11.035
• Publication Date: 2020-02-04T10:53:39Z
• Authors: Peipei Ma; Chunhui Liu; Qiuyu Chen; Qing Wang; Lihua Zhan; Jianjun Li
• Keywords: 0205 materials engineering; 02 engineering and technology

Abstract Artificial ageing above 165 °C directly after quenching induces the formation of ∼50 nm wide precipitate-free zone (PFZ) and ∼100 nm wide precipitate-sparse zone (PSZ) consisting of coarse precipitates with a gradient in size and density toward the grain center in a commercial Al-Zn-Mg-Cu alloy. With the grain size decreasing, the fraction of PFZ and PSZ in a grain becomes larger and could even occupy the entire volume of the grain. This undesirable microstructure near the grain boundary is mitigated substantially by natural pre-ageing, leading to an exceptional enhancement of the age hardening potential at elevated temperatures. Natural ageing could fundamentally alter the precipitation near grain boundary, and is a promising method to optimize the precipitation hardening in high strength aluminum alloys with unconventionally small grains.