Optimization of Homogenization Treatment Parameters and Microstructural Evolution of Large Size DC AA2014 Aluminum Alloy

抄録

The microstructural evolution of the as-cast large size AA2014 aluminum alloy ingot prepared by direct chill (DC) casting during homogenization was investigated by OM, SEM, EDS, DSC, EBSD, TEM and tensile tests. The results showed that serious dendrite segregation and numerous coarse nonequilibrium eutectics existed in the as-cast alloy were dramatically eliminated, while a small amount of Fe-rich phase was still present along the grain boundaries when the alloys were subjected to the optimized two-step homogenization. Compared with the nonhomogenized alloys, homogenization treatment can effectively reduce grain and second phase particles size, and increase the fraction of precipitates and high angle grain boundaries (HAGBs) during the hot deformation and T6 treatment. Besides, recrystallized grains with random orientation are formed due to dynamic recrystallization (DRX) for the alloys with hot deformation and T6 treatment. Additionally, the strength and elongation of the alloys were simultaneously improved with the application of optimum two-step homogenization because of the more homogeneous structures, finer grain and particles size, higher fraction of HAGBs and fine and uniformly distributed precipitates. The suitable homogenization schedule of the AA2014 aluminum alloy is 490°C × 10 h + 530°C × 8 h.

Fig. 12 Microstructure characteristics of the alloys after hot deforming and T6 treatment under different homogenized conditions: (a, a′) as-cast; (b, b′) OTH; (c, c′) THT30