Investigation the structure in cast and deformed states of aluminum alloy, economically alloyed with scandium and zirconium

Abstract

The structure and mechanical properties of an alloy of the aluminum-magnesium system with a scandium content of no more than 0.1% (wt.) (experimental alloy) at the stages of obtaining sheet semi-finished products have been investigated. The macro and micro structure of cast, hot, and cold rolled sheet semi-finished products has been studied by the methods of light and diffraction transmission electron microscopy, and their mechanical properties have been tested. Casting of ingots, hot, and cold rolling of the alloy was carried out in the conditions of a metallurgical enterprise. The section of the ingots was a rectangle 300 × 1460 mm in size. Preparation of ingots for rolling included milling of all surfaces and two-stage annealing at temperatures of 350 °C (first stage) and 425 °C (second stage). Rolling was carried out across the casting direction. For hot rolling, the billets were heated to 400–410 °C and carried out on a reversible hot rolling mill of grade quart with a roll barrel length of 2800 mm to a thickness of 8.2–9.2 mm. Then, the strips were rolled into rolls and annealed according to the following regime: temperature 390–400 °С, holding for 1 h, cooling with a furnace to 250–270 °С, and unloading into air. Cold rolling was carried out on a QUARTO mill of the CRM grade with a roll barrel length of 2800 mm to a thickness of 5.9–6.3 mm. Microstructural analysis was performed on a Carl Zeiss Axio Observer A1m light microscope using the AxioVision software package. The fine structure of semi-finished products was studied using Tecnai 30 G2 and JEM-2100 EX transmission electron microscopes. The chemical composition of dispersed particles of the secondary phases was determined using energy dispersive X-ray microanalysis (EDX) of thin foils in transmission using an INCA x-sight attachment. It is shown that alloying the experimental alloy with small additions of scandium, zirconium, and manganese leads to the formation of a supersaturated solid solution in the ingot. And upon annealing of the ingot and subsequent hot and cold rolling, a subgrain structure with inclusions of Al6Mn and Al3(Sc, Zr) phases of distribution density is formed in the alloy structure, explaining dispersion and structural hardening of sheet semi-finished products. It was found that the mechanical properties of cold-rolled sheets from the experimental alloy significantly exceed the properties of alloy 5083 with the same magnesium content. But without scandium and are approximately on the same level with alloy 1570 in which the scandium content in comparison with the experimental alloy is three times higher.