Effect of Scandium Addition on Mechanical Properties and Microstructural Evolution in Al-Zn-Mg Alloys Processed through the Friction Stir Processing

Abstract

In the present work, the different alloys belong to 7xxx series of aluminium were prepared by varying the Scandium content, i.e. 0 wt.%, 0.20 wt.% and 0.45 wt.%, respectively. The cast alloys further underwent the friction stir processing (FSP) for the microstructural refinement. The addition of 0.45 wt.% of Scandium content provided the significant grain refinements. Further, Scandium (0.45 wt.%) containing alloy followed by the FSP provided the highest hardness and strength, compared to all investigated alloys. The enhancement in mechanical properties of Scandium (0.45 wt.%) containing alloy attributed to the grain size refinement and uniform distribution of the Al3Sc intermetallic particles. The intermetallic particles (Al3Sc) increased the particle–matrix interface characteristics and further help in removing the porosity during FSP. The artificial ageing at 120°C was performed in all investigated cast alloys and found that Scandium addition up to 0.45 wt.% provided the highest peak hardness of 350 HV after 12-h ageing time. It was because high Scandium addition led to formation of Al3Sc particles, and these Al3Sc particles might be providing the additional site for the nucleation of main matrix precipitates. Further, Al3Sc particles and main matrix precipitates increased the hardness significantly due to more pinning effect produced during their interaction with the grain boundaries and dislocations. © 2022, ASM International.