变质处理对挤压态Al-20Mg_(2)Si-4.5Cu合金初生及共晶Mg_(2)Si变质形貌的影响机制

Influence Mechanism of Modification Treatment on Morphology of Primary and Eutectic Mg_(2)Si Modification in Extruded Al-20Mg_(2)Si-4.5Cu Alloy

目的研究微量元素复合变质下挤压态Al-20Mg_(2)Si-4.5Cu合金初生Mg_(2)Si和共晶Mg_(2)Si的形貌演化规律,揭示Mg_(2)Si相的变质和球化机制。方法采用形貌调控元素Be和异质形核元素Sb协同变质调控初生及共晶Mg_(2)Si相的形貌,然后结合挤压工艺对初生及共晶Mg_(2)Si形貌进行进一步调控。结果经0.5%(质量分数)Be-Sb复合变质与挤压工艺处理后,初生Mg_(2)Si转变为近球形,尺寸约为10μm,共晶Mg_(2)Si转变约1μm的球形。结论挤压变形可以使Be-Sb复合变质后的合金中的初生及共晶Mg_(2)Si相发生明显球化。其中,Sb元素生成的Mg_(3)Sb_(2)相作为初生Mg_(2)Si的异质核心,有效细化了初生Mg_(2)Si相;Be元素选择性吸附在初生Mg_(2)Si及共晶Mg_(2)Si的择优生长晶面上。

The work aims to investigate the morphological changes in primary Mg_(2)Si and eutectic Mg_(2)Si within extruded Al-20Mg_(2)Si-4.5Cu alloy under combined trace element modification,and reveal the mechanism behind the modification and spheroidization of Mg_(2)Si phases.The morphology-controlling element Be and the heterogeneous nucleation element Sb were used to modify both primary and eutectic Mg_(2)Si phases.Extrusion heat treatment was subsequently employed to further fine-tune the morphology of these phases.The application of 0.5wt.%Be-Sb composite modification combined with extrusion heat treatment resulted in the transformation of primary Mg_(2)Si crystals into nearly spherical shapes,approximately 10μm in size.Simultaneously,eutectic Mg_(2)Si transformed into spherical shapes around 1μm.The extrusion deformation significantly ad-vances the spheroidization of primary and eutectic Mg_(2)Si phases in the Be-Sb composite-modified alloy.Notably,Sb element triggers the formation of Mg_(3)Sb_(2) phases as heterogeneous nucleation centers for primary Mg_(2)Si,which effectively refines the primary Mg_(2)Si phase.Moreover,the Be element selectively adheres to preferred crystal growth planes of both primary and eutectic Mg_(2)Si.