In the case of aluminium structures, welding may introduce weak zones, so-called heat-affected zones (HAZ), close to the weld. Such zones should be accounted for when predicting the overall behaviour of the structure since the deformation tends to localise within such weak zones, leading to failure initiation. In an early design stage, the structural capacity is usually assessed based on numerical simulations using the finite-element (FE) method and shell elements rather than carrying out extensive test campaigns. A literature review reveals that numerical tools could predict the spatial variation of material properties within a HAZ when using a fine discretisation of solid elements. No unified approach, however, exists for large-scale analyses of thin-walled structures where only a few shell elements represent the HAZ. To address this challenge, this work presents a virtual calibration procedure establishing the mechanical behaviour of a welded aluminium connection relevant to an early design stage. A modelling framework that captures the overall weld and HAZ behaviour in large-scale analyses is calibrated using a multi-scale approach. The input is the chemical composition and the through-process history of the material, where welding simulations are used to account for the welding process. A nanostructure model predicts the material flow stress by considering the intrinsic resistance to dislocation motion and classical dislocation theory. The spatial variation of flow stress is introduced into a detailed FE model of an idealised HAZ, and the model parameters for the shell elements are based on this HAZ. To this end, numerical simulations using the proposed calibration procedure are compared against experiments. Figure 1 gives a summary of the methods used herein.