Bauschinger effect in an aluminium alloy designed for laser powder bed fusion

Abstract

Aluminium alloys designed for additive manufacturing often exhibit heterogeneous microstructures. A bimodal grain size distribution is observed with submicron equiaxed grains at the bottom of the melt pool and coarser columnar grains in the melt pool interior. Microstructural heterogeneities also develop at the intragranular scale (a large proportion of intermetallics with differences in size and morphology) down to the atomic scale (solid solution variations and nanoprecipitation) depending on the region of interest. Using uniaxial tensile-compression tests, we evaluate the Bauschinger effect in a new Al-4Mn-3Ni-2Cu-1Zr alloy designed for additive manufacturing. The strong Bauschinger effect is attributed to short-range and long-range back-stresses caused respectively by a high density of interfaces (grain boundaries and intermetallic/matrix interfaces), and strain partitioning between different regions of the microstructure showing different mechanical behaviour. We conclude that the impact of the back-stress should be systematically considered when investigating the mechanical response of this new class of alloys.