Influence of cold-rolling deformation and annealing temperature on the grain growth of al-4%mg-mn alloy

Abstract

The propensity of an alloy toward an abnormal grain growth (AGG) severely limits the annealing temperature range, capability for hot forming, and deteriorates mechanical properties. In this work, the results of a study of the effect of thermo-mechanical processing (TMP) of Al-Mg alloy AA5182 on the AGG are reported. TMP included cold rolling with a reduction range of 40-85 % followed by isochronal annealing (1 h) in a temperature range of 350-520 degrees C or isothermal treatment at 480 degrees C for different periods of time. The microstructure was characterized using optical microscopy in polarized light and an FEG SEM. The results showed that an increase in the degree of reduction lowers the annealing temperature for the onset of the AGG, while an increase in the annealing temperature increases the extent of the AGG for a given cold reduction. The abnormal grains tended to form in the region close to the surface of the plates, and with extended annealing bands. develope parallel to the surfaces in the rolling direction. However, no appreciable grain growth occurred in the plate center. The AGG and grain-boundary mobility showed a strong anisotropy with a much faster lateral growth than the motion of the growth front normal to the plate surface. Such anisotropy was attributed to the rod-like shape and alignment of Al6Mn dispersoids through Zener pinning.