Grain Growth in Continuously Recrystallized aluminum with Eine Dispersed Particles

摘要

A 8 mm aluminum slab for the production of capacitor foils which was rolled in the hot mill was subsequently cold rolled to foil thickness in a 320 mm dia. laboratory cold mill. During the thermal mechanical processing, most of the iron (Fe) solute must have precipitated out as Al_3Fe and/or Al_6Fe such that the highly purified matrix underwent continuous recrystallization (CREX) as previously reported for capacitor grade Al. The grain size (d) and texture evolution upon recrystallization and grain growth (GG) were examined by means of electron channeling contrast (ECC) imaging and X-ray orientation distribution function (ODF) from which volume fractions (f_v) of cube texture components (CC) were calculated usign a Gaussian spread of 11 deg. Annealing at 240 deg C for 1 h produced recrystallized grain size of the order of 2 #mu#m and continued times (t) up to 100 h resulted in normal grain growth according to d~2 propor. to t. From such a plot d_0 of 1.49 #mu#m was obtaiend. Isochronal anneals of samples with grain sizes above 20 #mu#m in the 290 to 320 deg C range revealed particle retardation of grai ngrowth (Zener drag) at 35#mu#m. On the other hand, 1 h isochronal anneals of fine grains in 270-300 deg C range produced discontinuous grain growth (DGG) with preferential cube grain growth. Since the initiation of this secondary recrystallization occurred at a grain size value almost an order of magnitude less than that observed for the inception of Zener drag, the cause of this enhanced cube grain growth was concluded to be the increase in Fe solute content of the matrix due to the increased solubility with temperature. These resutls support our previous supposition that selective cube grain growth occurs when the Fe solute levle in the matrix is less than 1 atomic ppm but random or non-selective grain growth takes place when this level becomes less than 0.1 ppm. Cold rolling of the sample annealed for 100 h at 240 deg C resulted in strain induced cube grai ngrowth over the same temperature range as that for discontinuous grain growth except that the conversion to cube texture was an order of magnitude higher with final grain sizes much larger than 100 #mu#m.