Conceptual principles of roll casting-rolling of high-strength aluminum alloys

Abstract

This paper presents the results showing the possibility of obtaining thin-sheet billets from a wide range of aluminum alloys by the method of two-roll casting. In the course of the research, an analysis of the technological solutions of the currently known methods of continuous casting and rolling of sheet metal products was performed. At the laboratory installation of two-roll casting of metals, physical and technological parameters (temperature and speed of casting, intensity of heat removal, etc.) have been worked out, which ensure a stable process of obtaining a sheet billet of small thickness (1-5 mm) from the investigated aluminum alloys. For the first time in metallurgical practice, cast sheet billets from wide-interval aluminum alloys EN2024 (Д16) (≥130 °С) and EN7075 (В95) (≥160 °С) were obtained by the roll casting method In the course of research to determine the evolution of the structures of test samples from the studied alloys, their metallographic studies were carried out at all stages of the technological chain "roll casting + hot rolling + heat treatment". Taking into account that there is a hereditary relationship between the primary structure of the cast billets and the quality of the final metal product, it was established that for all studied aluminum alloys, the basis of the structures at the "roll casting" stage is the a-phase. It was established that at the cooling rate characteristic of roll casting, the a-phase in the cast billets has a homogeneous fine-grained structure. At the same time, small inclusions of dispersed intermetallic and eutectic phases, which are present in the structure of cast billets, are evenly distributed along their cross-sections. In order to evaluate the processes occurring in the billets at the "hot rolling" stage, the patterns of changes in the quantitative characteristics of the structures depending on the degree of their deformation were determined, namely: E is the proportion of intermetallic phases; D is the size of intermetallic crystals; A is shape parameter of intermetallics; R is the size of dendritic cells; Ar is a shape parameter of dendritic cells. It was also established that at the stage of "heat treatment" of the test samples after their hot rolling, partial recrystallization of the a-Al solid solution occurs, as well as a decrease in the content of intermetallics and spheroidization of the remaining intermetallic phases. Ultimately, the changes occurring in the structures of the experimental samples had a positive effect on the quality of the final tape, which was confirmed by a relatively higher level of their mechanical characteristics.