Effect of erbium and hafnium microalloying on the formation of Al3Sc particles in aluminium alloy with a high magnesium content

The paper studies the effect of hafnium and erbium additives on the microstructure formation during heat treatment of aluminium alloys with a high magnesium content additionally alloyed with scandium and zirconium. For the study, ingots of aluminium alloys with a high content of magnesium alloyed with scandium, erbium and hafnium with a content in the ranges of 0.03–0.16 % and 0.05–0.16 %, respectively, were produced by casting in a steel chill mould. After casting, the samples were treated with heat at a temperature of 370 and 440 °C with a holding time of 2 to 96 h. Changes in microhardness depending on the heat treatment were studied. For 1590-3 and 1590-4 alloys in the as-cast condition and after heat treatment at a temperature of 440 °C for 2 and 48 h, the fine microstructure and coarse intermetallic compounds were studied using transmission microscopy. The study found that additions of hafnium and erbium lead to an increase in microhardness due to a decrease in the size and an increase in the number of Al3Sc nanoparticles. After heat treatment at a temperature of 440 °C for 4 h, Al3Sc particles of the same size (8 nm) and density precipitate in all the alloys under study. However, with an increase in the holding time in the alloy with a lower hafnium content and a higher erbium content, the particle size increases by 2 times compared to the particles of the alloy where the hafnium content is higher and the erbium content is low.