Monastyrska T. Effect of Sc alloying on the structure stability of Al-Mg-base alloys

The studying of the kinetics and morphology of the precipitation of surplus phases in castable Al-(10-14)wt.%Mg and deformed Al-4,5wt.%Mg alloys in the process of ageing, the effect of Sc alloying on these processes, and also stability of the structure states of Al-Mg-based alloys during the prolonged exploitation are presented in the thesis. The X-ray methods, transmission electron microscopy, resistometry, conventional optic microscopy, hardness and mechanical testing were used in the researches. It has shown that the choice of the optimum regime of the homogenization together with the alloying of castable Al-10wt.%Mg alloy by 0,1-0,15wt.% of scandium removes structural heterogeneity in the spatial distributing of the particles of the phases precipitated during the ageing, reduces the nucleation and growth of these phases in all temperature intervals of the ageing. It has proved, that the correct choice of the regimes of the heat treatment (homogenizations and quenching) of the castable Al-10%Mg-0.1%Sc alloy provides the increase of strength properties and prevents of the deterioration of plasticity caused by the natural ageing process during the prolonged exploitation. It has shown, that the simultaneous alloying of the deformed Al-4.5%Mg alloys by scandium and zirconium or scandium and hafnium provides the formation of composite particles of Al3Sc/Al3Х (Х = Zr, Hf) during the ageing, which promote temperature stability of alloys due to deceleration of the coalescence processes and shift of the temperature interval of the ageing to more high temperatures.