The adoption of Design for Additive Manufacturing (DfAM) practices brought new industrial components embedding unconventional shapes such as lattice structures or freeform surfaces resulting from topological optimisations. As a drawback of design freedom, designers need to use thermal post-processing to achieve homogeneous properties in metal 3D printing. This contribution analyses the effect of T6-like heat treatment on the hardness of a complex component. Hardness values are reported along with good design practices for effective thermal post-processing to complement the DfAM knowledge base.