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This article concerns the dynamic transitions of a non‐Newtonian horizontal fluid layer with thermal and solute diffusion and in the presence of vertical magnetic field. First, a linear stability analysis is performed by deriving the principle of exchange of stability condition, which shows the system loses stability when the thermal Rayleigh number exceeds a threshold. Second, we consider the transition induced by real eigenvalues and complex eigenvalues, respectively, and two nonlinear transition theorems along with several transition numbers determining the transition types are obtained via the method of center manifold reduction. Finally, rigorous numerical computations are performed to offer examples of possible transition types. Our results show that both continuous and jump transitions can occur for certain parameters when the diffusivities from big to small are thermal, solute concentration and magnetic diffusion, but only continuous transition induced by real eigenvalues is observed when the diffusivities from big to small is the opposite of the previous case.

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Laser twin-arc GTAW (LTA-GTAW) process has been developed by using the synergic interaction effects of laser and a coupled arc in a weld pool in order to achieve higher energy efficiency. In this study, bead-on-plate welding was conducted on 8-mm-think Q235b workpieces to investigate the variation of hybrid arc profile, Influence of mixed arc profile on weld forming arc, arc pressure distribution during LTA-GTAW process. The influence of Laser-GTAW and LTA-GTAW methods on weld surface appearance, heat input per unit length and weld metal microstructure were also demonstrated systematically. The LTA-GTAW can make the distribution of arc pressure and arc energy more reasonable in welding depth and width. Compared with Laser-GTAW, LTA-GTAW processes has smaller heat input per unit length, significantly finer weld microstructure and the comprehensive mechanical properties of the weld are better when the same penetration depth is achieved.