Property anisotropy in magnesium containing aluminium alloys

Property anisotropy has been investigated in a range of both model and commercial 5xxx series Al-Mg alloys, in the annealed temper. The term property anisotropy includes the whole range of mechanical tensile properties, but in this paper we are particularly concerned with anisotropy in the tensile elongation to fracture. The tensile elongation in these alloys typically achieves a maximum value in the 45 degrees direction to the rolling direction, and a minimum when the sheet is deformed in a direction parallel to the rolling direction. Both microstructural anisotropy and crystallographic texture have been considered in analysing the results. It is shown that microstructural anisotropy and global parameters, such as the work hardening exponent, n, and the plastic strain ratio, r-value, cannot explain the ductility anisotropy. However, the anisotropy can be understood in terms of the influence of crystallographic texture on the work hardening rate. The behaviour of the work hardening rate with stress and strain controls the onset of plastic instability, and subsequent failure.