Solute Sn-induced formation of composite β′/β″ precipitates in Al-Mg-Si alloy

• DOI: 10.1016/j.scriptamat.2018.06.028
• Publication Date: 2018-06-19T15:55:06Z
• Authors: Chunhui Liu; Peipei Ma; Lihua Zhan; Minghui Huang; Jianjun Li
• Keywords: Substructure

Abstract The composite β′/β″ precipitates rather than well-defined β′ phase form in trace-Sn containing Al-Mg-Si alloy peak-aged at 250 °C, leading to considerable morphological refinement. The preferential occupation of 2~6 adjacent Si sites of the tiny β′ phase by Sn and typical β″ substructure units covering the precipitates are frequently observed. The substructures grow upon further ageing into differently oriented β″ with 2~3 complete structural unit cells. It is inferred that the β′ (Mg9Si5-xSnx) forms initially on the Sn/vacancy complexes and then acts as heterogeneous nucleus for β″. These findings demonstrate Sn could fundamentally alter the pre−/precipitation behaviors in Al-Mg-Si alloys.