The previous study of the authors has resulted in the development of an Al−10% Mg composition alloyed additionally by zinc, manganese, antimony, and zirconium. The alloy was to be cast into sand molds and had σr=380-400 N/mm2, σ0.2=240-260 N/mm2, and δ=10–12%. The main difficulty in the development and use of the given alloy consisted in attaining stable properties in the operating process. The present paper is devoted to this problem.
Under production conditions articles are not placed in the furnace for aging immediately after hardening. The duration of exposure at room temperature between hardening and tempering has a considerable effect on the properties of aluminum alloys.
The increase in strength and plasticity of an aluminum alloy with additives of REM, zirconium, and hafnium in comparison to alloys containing iron is associated with 1) a more refined grain structure; 2) a full or partial supression of recrystallization; 3) the direct strengthening action of the dispersoid particles.
The basic hardening phase of casting Al-Mg-Zn alloys is the T-phase (Al2Mg3Zn3), which is segregated at temperatures from 160 to 170°C. On heating to 190°C and higher, the β-phase (Al3Mg2) begins to form — along the subgrain boundaries at first, and over the entire body of the grain at temperatures above 200°C.
Cooling with crystallization at high rates makes it possible to obtain a homogeneous highly dispersed dendritic structure in an alloy of the Al−Mg−Li−Zr system.
