The role of transition metal solutes in the deformation texture, recrystallization and grain growth in aluminum and its alloys.

摘要

The thermo-mechanically induced dynamic recrystallization (DyReX) and continuous recrystallization (CReX) in aluminum and its alloys have been systematically studied. The materials used included the nominally pure aluminum, electrical conductor grade aluminum, and the commercial alloys AA5182 and AA5754. The thermo-mechanical processing which was designed to reduce the concentration of specific solute elements in the aluminum matrix to atomic ppb levels consists of a pre-strain, a low temperature intermediate aging (230–320°C) and final deformation. The deformation is carried out at room temperature, and the total strain is within the range of industrial processing (90% reduction in thickness upon rolling). The evolution of microstructure, texture and microtexture during recovery, recrystallization and subsequent grain growth was systematically investigated, using the scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back scatter diffraction technique in SEM, orientation distribution function (ODF) from X-ray pole figures, qualitative X-ray peak broadening and micro-hardness testing.; The uniform ultra-fine grain structure after DyReX/CReX and the very dilute solid solution provided great opportunities for fundamental grain growth studies. Two sets of grain growth experiments were performed using the ultra-fine grained nominally pure aluminum sheets, one in the sheet surface at very low temperatures (60–160°C), and the other at the 1/3 thickness from the sheet surface at relatively higher temperatures (240–275°C). In the first set of experiments the absolute grain boundary migration rates were measured and the grain growth kinetics was investigated. In the second set of experiments, the parabolic grain growth relation between grain size and time was observed. The growth kinetics and the solute drag effect on the grain boundary migration were studied in the nominally pure aluminum sheets, in which the solute Fe content was varied to different atomic ppb levels. The integrated analyses of these results predict a quantitative way in which the effect of solute drag during grain growth can be represented.; The success in producing fine grain size by DyReX/CReX without severe deformation also offers a new concept for improving the strength and formability of aluminum alloy sheets. When specific transition metal solute (Fe and Mn) atoms in aluminum matrix are reduced to atomic ppb level, the mode of slip upon deformation is dramatically different from that of less pure case. (Abstract shortened by UMI.)