Friction stir welding (FSW) was employed to achieve a reliable joining of 2 mm thick dissimilar metals, 6061 aluminum alloy and AZ31B magnesium alloy. This study revealed the evolution of interfacial interlocking features and their impact on the mechanical properties of the joints under different welding speeds (25–35 mm/min). The results indicate that the Al/Mg FSW joint interface exhibits a strip-like interlaced structure, the morphological characteristics of which are closely related to the welding speed. For quantitative analysis, the ratio of interlocking length to plate thickness (embedding ratio) was used as a quantitative indicator of the structural interlocking feature. As the welding speed increased from 25 mm/min to 35 mm/min, the embedding ratio decreased from 13.2 to 7.9, and the average thickness of the intermetallic compound (IMC) layer decreased from 2.71 μm to 2.19 μm. Transmission Electron Microscopy (TEM) results confirmed that the Al/Mg FSW joint interface consists of a bilayer of IMCs, specifically Al₃Mg₂ and Al₁₂Mg₁₇, with thicknesses of 220 nm and 470 nm, respectively. Tensile testing of joints with different embedding ratios demonstrated that the tensile strength of the welded joint exhibits a positive correlation with the embedding ratio, reaching a maximum of 178 MPa.

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.

Lubricant additive plays an important role in reducing the friction and wear for base oil. MAX phase ceramics may have superior advantages for additive application due to their unique nanolayered structure. In this paper, Ti₂SnC ceramic is prepared by sintering the elemental mixtures at 1250 °C. In addition, Cu-coated Ti₂SnC ceramic is successfully prepared using a chemical plating method for the first time. It is confirmed that the Ti₂SnC ceramic has good self-catalytic activity, and a layer of stacking Cu nano-particles can be deposited on the Ti₂SnC surface without pretreatment. When the Cu-coated Ti₂SnC ceramic powder is doped into PAO10 base oil, the oil can exhibit excellent lubrication properties, where the friction coefficient is as low as 0.095. A layer of tribo-film can be formed during the sliding process when the Cu-coated Ti₂SnC ceramic is incorporated into PAO10 base oil, which can reduce the friction coefficient. The superior lubrication properties can be attributed to the synergistic lubrication effect of Ti₂SnC ceramic and Cu nano-particles.