As an important strengthening phase in Al-Mg-Fe alloy, the elastic and ductile–brittle characteristics of Al₁₃Fe₄ intermetallics hold prime significance in ascertaining the mechanical properties and potential application of Al-Mg-Fe alloys. In this study, multialloying of Co, Cu, Cr, Mn, and Ni has been adopted for tuning the mechanical characteristics of the Al₁₃Fe₄ phase; their effects on mechanical features and electronic structure of the Al₁₃Fe₄ phase have been scrutinized systematically by first-principles calculations employing the density functional theory. The replacement of Fe with M (M = Co, Cu, Cr, Mn, and Ni) is energetically advantageous at 0 K, as evidenced by the negative cohesive energy and mixing enthalpy of all Al₁₃(Fe,M)₄ phases. Cu and Ni, on the contrary, have a detrimental impact on Al₁₃Fe_4′s modulus and hardness due to the evolution of chemical bonding strength. Co, Cr, and Mn are thus, interesting candidate elements. In the light of B/G and Poisson’s ratio (σ) criteria, Al₁₃Fe₄, Al₁₃(Fe,Cu)₄, and Al₁₃(Fe,Ni)₄ have superior ductility; however, Al₁₃(Fe,Co), Al₁₃(Fe,Mn), and Al₁₃(Fe,Cr)₄ tend to be brittle materials. Calculation-based findings show that Co, Cr, and Mn are appropriate alloying elements for enhancing fracture toughness, whereas Mn reduces Al₁₃Fe_4′s elastic anisotropy. The electronic structure assessment found that the mechanical properties of the intermetallics are predominantly influenced by the Al-M bonds when the alloying element M replaced Fe.

In this study, a three-dimensional transient multi-physics coupled numerical model of narrow-gap tungsten inert gas (TIG) welding of TC4 alloy is established, and the heat transfer, flow behavior of the liquid metal in the molten pool, and the formation mechanism of sidewall lack-of-fusion defects are quantitatively investigated. The results show that, along the groove width direction, the temperature and flow velocity of the liquid metal gradually decrease from the center toward the sidewall. Along the welding direction, the fluid velocity presents multi-peak fluctuation characteristics. As the weld pass increases, the maximum velocity of the liquid metal significantly increases, enhancing the overall fluidity of the molten pool, and the temperature distribution becomes more uniform due to the weakened geometric constraints of the sidewall and the inter-pass heat accumulation effect. Furthermore, excessively high welding speeds (0.2 m/min) or insufficient welding currents (150 A) drastically reduce the per-unit-length heat input, resulting in diminished molten pool volume and decreased maximum liquid metal velocities of 0.075 m/s and 0.1 m/s, respectively. Under these conditions, lateral driving forces generated by the Marangoni effect are insufficient to overcome the viscous resistance of the molten metal. Consequently, the liquid metal solidifies prior to reaching the sidewall, inducing pronounced sidewall lack-of-fusion defects and localized humping on the weld top surface.