Integrating experimental and computational approaches to unveil processing-microstructure-property relationships in additive friction stir deposited AA6061 alloy

Abstract

Controlling spatial variation in microstructure, texture, and mechanical properties in additive friction stir deposited (AFSD) age-hardenable aluminium alloys is necessary to advance the process for critical applications. The present work addresses this issue through detailed microstructural analysis, mechanical property evaluation, in-situ EBSD tensile testing, and state-of-the-art crystal plasticity simulation of a multilayer AFSD build of AA6061 alloy. A significant decrease (∼68 HV to ∼45 HV) in microhardness, yield strength (201 MPa–98 MPa), and a variation in texture were observed from top to bottom. The DSC and TEM analysis revealed that the top region comprised mainly of needle shape semi-coherent ${\beta }^{″}$ precipitates while the bottom locations consisted of coarse rod shape incoherent ${\beta }^{\prime }$ precipitates. In-situ tensile test with EBSD showed that in the bottom and middle of the build, the strain was uniformly distributed within grains and grain boundaries, while it was preferentially concentrated at grain boundaries in the top region. Higher strength at the top was attributed to a significant contribution from precipitation (∼53 %), while texture and dislocation strengthening dominated (∼57 %) at the bottom of the sample. Crystal plasticity fast Fourier transform (CPFFT) based full-field simulations, using the Düsseldorf Advanced Material Simulation Kit (DAMASK), highlighted the importance of textural heterogeneity along the build direction. Micromechanical Taylor factor and T-parameters calculated from CPFFT simulation captured the in-grain heterogeneity observed experimentally. These findings highlight that in an AFSD build of age-hardenable alloys, strength is primarily controlled by the precipitates and intra- and inter-granular deformation is governed by local texture.