Papers by Keyword: δ_non-Phase

Abstract: The structure of Al-Li-Mg system alloy 1420, containing a small quantity of Sc, Zr, Ti was investigated in cast, homogenized, hot-pressed, quenched and aged conditions, using the methods of optical metallography, transmission electron microscopy and X-ray examination. An existence of areas, having fine grains (20-30 nm)- "Ultrafine Grain areas"(UFGA) was observed in all the investigated conditions. UFGA are located on the boundaries, sub boundaries and S1(Al2MgLi) phase particles. UFGA can also form near the particles of crystallization origin. These areas have a complex phase composition. Inside the UFGA the particles of S1(Al2MgLi) phase and also δnon-phase, investigated in [1] are always present whereas δ'(Al3Li) precipitations are absent. These areas are formed during crystallization and hot deformation. Their composition changes during the treatment. The nature of these changes is considered.

Abstract: The nonequilibrium δnon-phase was originally investigated in the work[1] when studying the ageing processes of the 1424 alloy ( Al-Li-Mg-system). As shown in the work[2] this phase may also be formed during the cooling from the temperature of SSHT. The δnon-phase precipitates are also present in 1420 alloy of the same system[3]. The basic structure investigations were carried out on the 1424 alloy sheets aged in accordance with the regime: 125°C, 32 hrs. The investigations were performed by TEM using the JEOL JEM 200CX microscope. The diffraction patterns from the δnon-phase on the crystallographic axes of zones close to <110>, <111>, <112> were obtained. It can be seen that the regular reflex networks appeared after the deviation from axes of zones by 3-4˚. It was established that the lattice parameters of δnon-phase and its orientation relation with the matrix can be approximately described by the following way: aδnon≈ aα/2[112] b δnon ≈a α/2[110] cδnon≈ a α [111] where aα- the period of the FCC- lattice of solid solution. The model of the crystallographic structure of the δnon-phase precipitates is proposed. On the basis of this model the mechanism of the δnon-phase formation is discussed. The late ageing stages are analyzed and it was shown that the δnon-phase particles are the nuclei for S1(Al2LiMg)- phase.