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In the present investigation, the numerical code WELDSIM is used to simulate butt welding of 4 mm thick plates of S355 steel and AA6082-T6 by Hybrid Metal Extrusion and Bonding (HYB). This is a new solid state joining process using continuous extrusion as a technique to enable aluminium filler metal additions. In WELDSIM, the finite element heat flow model is coupled to a frictional heating model, an isokinetic diffusion model for the interfacial intermetallic compound (IMC) formation and a nanostructure model for simulating reversion and re-precipitation of hardening phases inside the aluminium part of the joints during welding and subsequent natural ageing. The HYB process model is validated by comparison with experimental data obtained from in-situ thermocouple measurements and hardness testing carried out on three different Al-steel butt welds. Furthermore, scanning electron microscope examinations of the Al-steel interfaces have been conducted to check the predicted power of the IMC diffusion model. It is concluded that the process model is sufficiently relevant and comprehensive to be used in simulations of both the thermal, microstructure, and strength evolutions fields in these dissimilar butt welds. Some practical applications of the process model are described toward the end of the article, where particularly its potential for optimising the load-bearing capacity of the joints, is highlighted.

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