Microstructure evolution during the homogenization heat treatment of an Al-Zn-Cu-Mg (AA7475, which is typically used for the manufacture of aircraft design) alloy, was investigated using a combination of light microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ingots after different types (one-or two-steps treatments) of temperatures (from 380 to 510 °C) of homogenization and cooling conditions (cooling with an air or quenching to water) were investigated. The results show that the microstructure of ingot presents a typical microstructure with some isolated Al7Cu2Fe particles, which after homogenization almost remains in both the size and morphology. The structure ingot after homogenization below 400 °C contains secondary phases, based on η (MgZn2), S (Al2CuMg) and T (Al2Mg3Zn3) are distributed along the grain boundary. In the T (Al2Mg3Zn3) phase copper dissolves up to 30 wt.%. Then the increase in temperature and the complication of heat treatment of homogenization, which led to the complication of the kinetics of the evolution of inter-dendritic phases, were found. The two-steps homogenization has a better effect than a single homogenization, as its completely dissolution of non-equilibrium phases was established.

The study of the processes occurring in the surface layer of the MgO coated commercial alloy Fe-3 %Si-0.5 %Cu (grain oriented electrical steel) demonstrated that the amorphous phase in the form of a Fe-based solid solution is formed during continuous heating in the 95 %N 2 + 5 %H 2 atmosphere. For the purposes of this study, the following methods were used: nonambient XRD at 20 -1060°C with heating and cooling at a rate of 0.5 dps, layer-by-layer chemical analysis performed by a glow discharge analyzer, scanning electron microscopy and energy dispersive X-ray spectroscopy. ThermoCalc software was used to calculate the potential phase equilibrium states. The amorphous phase was formed in the α → γ transformation temperature range, when the heating rates were altered in the surface layer of 1 µm initially consisted of a solid α-Fe-based solution with ~1-2 wt.% Si with (MgFe) 2 SiO 4 , (MgFe)O, SiO 2 oxide inclusions. We suppose that (MgFe) 2 SiO 4 oxides are partly reduced by H 2 to Mg 2 Si molecular complexes, which become solid solutions in the temperature range of the metastability of the α-Fe crystal lattice with subsequent amorphization as an alternative to the α → γ transition. The amorphous state is obtained at 920 -960°C and is retained both at subsequent heating (to 1060°C) and cooling (to 20°С), which is super-stable compared to the established metallic glasses. The composition of the amorphous phase can be described by the formula Fe 89.5 Si 6 Mg 4 Cu 0.5 .

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