Impacts of Microalloying Elements on the Hardening β"-Phase in Automotive AlMgSi Alloys

Microalloying elements play a crucial role in mechanical properties and phase stability of metallic alloys. In this work, we employ first-principles calculations and atomic-scale high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to find promising microalloying elements that will improve the stability and properties of β"/Al interface and β" phase in Al-Mg-Si alloys. First, we define a substitution energy for evaluating the stability of β" phase and β"/Al interface with microalloying elements doped. Then, experiments of HAADF-STEM imaging are carried out to verify the calculational results. Next, using the most stable structures doped with microalloying elements, the mechanical properties of the β" bulk and the β"/Al interface were calculated and analyzed. At last, we have figured out the effects of all considered microalloying elements and obtained a rule that the stable occupancy of solute atoms is related to their own radius and the radius of Mg, Si, and Al. These findings will provide some theoretical basis for future microalloying strategies of Al-Mg-Si alloys.