The influence of in-situ alloying of electro-spark deposited coatings on the multiscale morphological and mechanical properties of laser welded Al–Si coated 22MnB5

During laser welding of Al–Si coated 22MnB5 steel, the melted Al–Si coating alloys with the molten weld pool promoting α-ferrite phase formation during the heat-treatment stage of hot-stamping, which results in a fusion-zone (FZ) microstructure consisting of α-ferrite islands disbursed through a martensitic matrix. The presence of the softer ferrite phase is the main cause for premature failure of laser-welded 22MnB5 joints in the hot-stamped condition. This work showed that surface modification of the Al–Si coating using an additive manufacturing technique called electro-spark deposition (ESD) prior to laser welding prevented α-ferrite formation in the FZ post-welding and hot-stamping. This was achieved by the in-situ alloying of ferrite-suppressing carbides and austenite-stabilizing elements. These alloying agents were added to the FZ by applying different ESD-modified coatings to the material surface, which melted into the molten weld pool during laser welding, leading to the simultaneous dispersion and solid-solution strengthening of the FZ after hot-stamping, respectively. The modification of the Al–Si coating prior to welding using tungsten-carbide (WC) and Inconel 625 (In625) resulted in drastically improved mechanical properties of the welded joint in the hot-stamped condition. In fact, this study showed that by carefully modifying the as-received Al–Si coating using ESD prior to laser welding could be used as an effective method to shift failure from the FZ, where it normally occurs, to the base material (BM). This work is highly relevant to the on-going discussion in the advanced manufacturing and materials science communities regarding the production of functionally-graded components as it proposes the implementation of an advanced processing technique to achieve the production of novel materials with highly optimized properties.