Study of kinetics of the supersaturated solid solution decomposition in alloys of the Al – Mg system with transition elements addition

Abstract

The objective of the study is to determine kinetics of L12 structure type particles precipitation in Al – Mg system aluminum alloys, containing scandium and zirconium. The article addresses microstructure evolution of scandium containing alloys, including two-component alloy and Al – Mg system alloys, containing multiple components, i.e., 1565ch alloy (Al – Mg – Mn – Zn – Zr system) and 01570 alloy (Al – Mg – Mn – Sc – Zr system). The samples were produced by casting in water chilled copper permanent mold. Analysis of the samples, representing various alloys, including 99.95% pure aluminum, confirmed quantitative data of solutes effect on electrical resistance. The optimal homogenization modes, enabling max alloying components dissolution in aluminum matrix, were established for the studied alloys. After that the samples were subjected to heterogenization annealing in the temperature range from 250 oC to 450 oC, with soaking time ranging from 1 to 106 s. C-curves of supersaturated solid solution decomposition were plotted based on correlation of samples electrical resistance in max saturated solution and after annealing under different modes; it was demonstrated, that decomposition curves of the alloys, containing 0.2 and more scandium, have two peaks, at 300 oC and at 425 oC. The obtained data are approximated by power functions (min determination coefficient R2 is 0.97), which are helpful for such alloys thermomechanical treatment modelling. It is demonstrated, that during cast samples heat treatment at the temperature above 350 oC decomposition of alloys, containing 0.2% and more scandium, is associated with secondary crystallization, and decomposition product distribution is fan-shaped, confirming the theory of discontinuous decomposition, observed by other researchers in similar alloys. The size of L12 structure particles, generated during discontinuous decomposition, ranged from 50 to 270 nm, which is significantly different from the optimal values of 40–50 nm.The study was supported by a grant from the Russian Science Foundation, project 18-79-10099.