Effect of Hafnium on the Microstructure Formation during High-Temperature Treatment of High-Magnesium Aluminum Alloys Microalloyed with Scandium and Zirconium

The paper studies the effect of hafnium additives on the microstructure and mechanical properties during high-temperature annealing of high-magnesium aluminum alloys microalloyed with scandium and zirconium. The objects of investigation are two cast aluminum alloys alloyed and unalloyed with hafnium. The alloys are heat treated at 440°C for 48 h. The cast and heat-treated material is studied in mechanical tests, as well as under optical scanning and transmission microscopes. The structural-phase composition of these alloys is examined, and the effect of hafnium on the mechanical properties is analyzed. Atom probe tomography is used for a more detailed investigation of the internal structure of Al3Sc nanoparticles. It is shown that both alloys lack discontinuous precipitation of the supersaturated solid solution. The addition of hafnium decreases the size of Al3Sc nanoparticles. Like zirconium, hafnium forms a thermostabilizing shell around Al3Sc particles, thus preventing the growth of particles and contributing to their fine dispersion.