Processability and Structure Formation of the Al–Zn–Mg–Ca–Fe–Zr–Sc Alloy upon Hot Rolling and TIG Welding

Technological regimes for producing wrought products (2 and 1 mm) from the Al–4.5%Zn–2.5%Mg–2.5%Ca–0.5%Fe–0.2%Zr–0.1%Sc experimental alloy, including thermomechanical processing at temperatures of 400–450°C and a reduction ratio up to 98%, as well as softening annealing of the sheet metal at 350–400°C for 1–2 h, are presented. It is found that the as-cast structure consists of eutectic phases (Al, Zn) 4 Ca, Al 10 CaFe 2 , and a nonequilibrium T-phase Al 2 Mg 3 Zn 3 with a size from 5 to 25 μm located along the boundaries of dendritic cells (Al). Zirconium and scandium in solid solution out of solidification are observed. After hot rolling, the structure of 2-mm sheets consists of oriented discrete intermetallic particles and their conglomerates up to 40 μm in scale in the (Al) matrix. The structure of 1-mm sheets is characterized by greater fineness and uniformity of structure. An analysis of the fine structure of deformed semifinished products using transmission electron microscopy (TEM) shows that the size of nanoparticles of the Al 3 (Zr,Sc) phase of the L1 2 structural type does not exceed 20 nm in cross section. In wrought semifinished products, the following level of mechanical properties is achieved: ultimate strength σ u ~ 310–330 MPa and yield strength σ 0.2 ~ 250–280 MPa with a relative elongation δ ~ 4.5–7.0%. The possibility of using argon-arc welding with standard AMg5 wire as an additive material is studied. It is shown that the new alloy does not show a tendency to form hot cracks. According to the results of X-ray tomography, the percentage of porosity in the weld is 1.27 vol %. The prevalent pore diameter does not exceed 0.2 mm. In general, the resulting structural and qualitative parameters of welded joints contribute to obtaining a strength of 75% of the strength index of the initial deformed semifinished products (sheets), which is achieved by stabilizing annealing at a temperature of 350°C for 3 h.