Effects of tensile loading direction on the mechanical properties and deformation behavior of columnar-grained HAl77-2 aluminum brass

Abstract

Columnar-grained HAl77-2 aluminum brass ingot was fabricated by directional solidification method, and the tensile samples were then cut from the ingot along the different angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) between the loading direction and the grain growing direction. The effects of the loading direction on the mechanical properties, strain hardening behavior and deformation mechanism of the alloy were investigated. The samples with the angles of 0–30° deformed mainly by dislocation planar slip mechanism during tensile deformation, showing low flow stress, uniform intragranular deformation and excellent plasticity, e.g., their elongations to failure were more than 80.0%. A number of deformation bands or intercrossed low-angle subgrain boundaries formed in the 45–90° samples during deformation, with high strain concentration inside the grains, which caused low plasticity, e.g. the elongations to failure were 62.9–65.2%. High density of dislocations, dense Lomer-Cottrell locks and geometrical hardening mainly contributed to the higher strain hardening rate and tensile strength of the 45° and 60° samples than those of the other samples. In order to obtain columnar-grained HAl77-2 alloy with excellent cold workability, it is supposed to control the angle between columnar grain growing direction and main extension deformation direction in a range of 0–30° by the directional solidification technology.