Effect of pre-deformation on quench-induced inhomogeneity of microstructure and hardness in 7050 aluminum alloy

Abstract

7xxx aluminum alloys usually have high quenching sensitivity, which results in the inhomogeneous microstructure and mechanical properties of large-size components. The effect of pre-deformation on the quench-induced inhomogeneity of the microstructure and properties in a high strength 7050 aluminum alloy was investigated by means of the end-quenching technique, transmission electron microscopy (TEM) and three-dimensional electron tomography (3DET). The size of the η′ precipitates and quench-induced precipitates (QP) and the width of the grain boundary (GB) precipitate-free zones (PFZ) increased with the decrease of the quenching rate, leading to a decrease in hardness along the long axial direction of the end-quenching sample. However, after introducing 20% pre-deformation, the PFZ around the GB and QP in the slow-cooled end of the aged samples was significantly reduced, and dispersive η′ precipitates were formed around the GB and QP instead, which greatly improved the strength of the slow-cooled end. Compared with the sample without pre-deformation, the introduction of 20% pre-deformation increased the hardness of the slow-cooled end by 30% without obviously reducing the hardness of the water-quenched end, which means that the 20% pre-deformation effectively reduced the hardness inhomogeneity of the 7050 aluminum alloy. This work provides a new method for reducing the quench-induced inhomogeneity of aluminum alloys.