Effect of Metastable Mg2Si and Dislocations on alpha-Al(MnFe)Si Dispersoid Formation in Al-Mn-Mg 3xxx Alloys

摘要

The effect of metastable Mg2Si and dislocations on the formation of alpha-Al(MnFe)Si dispersoids in Al-Mn-Mg 3xxx alloys were studied by a close examination of the dispersoid precipitation process using the quench technique and TEM observation. Special attention was paid to the nucleation mechanisms. Mg plays an important role in promoting the formation of alpha-Al(MnFe)Si dispersoids. The number density and volume fraction of the dispersoids in the Mg-containing alloy are much higher than those in the control alloy without Mg, resulting in a strong dispersoid strengthening effect. During the heating process in the Mg-containing alloy, metastable Mg2Si precipitated and dissolved, leaving local Si-rich areas on pervious metastable Mg2Si, which provide favorable nucleation sites for alpha-Al(MnFe)Si dispersoids. It was found that beta'-Mg2Si precipitates were more effective at the promotion of the dispersoid nucleation than beta ''-Mg2Si. In the deformed sample, the dislocations become the preferable sites for the alpha-Al(MnFe) Si dispersoid nucleation. By reducing dispersoid-free zones, the dispersoid distribution became more uniform compared to the non-deformed sample. The dispersoid nucleation mechanisms based on both metastable Mg2Si and dislocations are proposed and discussed. (C) The Minerals, Metals & Materials Society and ASM International 2018.