The properties of flux-cored Zn-Al filler metals are prone to deteriorating due to corrosion, making filler metals unusable. In this study, flux-cored Zn-2Al-xGe (x = 0, 0.3, 0.5, and 0.8 wt.%) filler metals are prepared to explore the effect of minor Ge on the corrosion resistance of Zn-2Al filler metals. The salt spray test is carried out on filler metals. A scanning transmission electron microscope is used to identify the phases in filler metals. The electrochemical performance of filler metals was tested by a workstation. The findings indicate that the microstructure of the Zn-2Al filler metal is composed of α-Al and η-Zn. Diamond-Ge forms in the microstructure of the Zn-2Al filler metal due to the introduction of Ge. Zn-2Al-xGe filler metals exhibit pitting corrosion characterized by intergranular corrosion (IGC) in the salt spray environment. Ge improves the IGC resistance of filler metals by changing the distribution of α-Al in the filler metal. The Zn-2Al-0.3Ge filler metal demonstrates the most excellent corrosion resistance. It has 16% elongation after 15 d of corrosion, which is higher than that of Zn-2Al by 13.6%.

To address the graphitization of diamond induced by high temperatures during laser cladding of diamond-reinforced composites, this study proposes a laser cladding method utilizing Inconel 718 (IN718) nickel-based alloy as a transition layer which has a lower melting point than the substrate of 45# steel. And then, in order to analyze the detailed characteristics of the samples, scanning electron microscopy (SEM), EDS, Raman spectral analyzer, super-depth-of-field microscope, and friction tests were used. Experimental study and the test results demonstrate that the IN718 transition layer enhances coating performance through dual mechanisms: firstly, its relatively low melting point (1392 °C) reduces the molten pool’s peak temperature, effectively suppressing thermal-induced graphitization of the diamond; on the other hand, simultaneously it acts as a diffusion barrier to inhibit Fe migration from the substrate and weaken Fe–C interfacial catalytic reactions. Microstructural analysis reveals improved diamond encapsulation and reduced interfacial sintering defects in coatings with the transition layer. Tribological tests confirm that samples with the transition layer L exhibit lower friction coefficients and significantly enhanced wear resistance compared to those without. This study elucidates the synergistic mechanism of the transition layer in thermal management optimization and interfacial reaction suppression, providing an innovative solution to overcome the high-temperature damage bottleneck in laser-clad diamond tools.

The performance of flux-cored Zn-Al filler metal is susceptible to corrosion-induced degradation, thereby impairing its brazability. In this study, flux-cored Zn-2Al filler metals are prepared, and the salt spray test is subsequently carried out on the prepared filler metals. Scanning transmission electron microscope is used to identify the phases in filler metals. An electrochemical workstation was employed to test the electrochemical performance of the filler metals. The corrosion pathways and evolution patterns of filler metals are analyzed. The findings demonstrate that the corrosion type of the filler metals is electrochemical corrosion, characterized primarily by the corrosion modes of pitting corrosion and intergranular corrosion. The cathode is the α-Al phase, which undergoes an oxygen-absorption corrosion reaction, while the anode is the η-Zn phase, which experiences corrosion and subsequent dissolution. The continuously distributed α-Al phase bands and discontinuously distributed large-sized rod-like α-Al phases accelerate the corrosion rate, and the corrosion propagation rate along the extrusion direction is higher than that in the radially inward direction. After 15 days of salt spray corrosion, the tensile strength of filler metals decreases by 16.2%, and the elongation rate decreases to 3.73%.

Flux-cored Zn–2Al filler metals were subjected to stress-relief treatment at different temperatures. The salt-spray test was subsequently carried out on the specimens, and the corrosion behavior was analyzed. The findings indicated that Zn–2Al filler metal mainly consisted of α-Al and η-Zn phases. Before stress-relief annealing, α-Al showed a prominent continuous banded distribution. At a stress-relief annealing temperature of 100 °C, recovery and limited recrystallization occurred. This weakened the continuous banded morphology and refined the grain size. Under salt-spray exposure, electrochemical corrosion took place within the filler metal. α-Al acted as the cathode, while η-Zn served as the anode. Stress-relief annealing improved grain-boundary stability and thus enhanced corrosion resistance. In addition, the discontinuous distribution of α-Al impeded corrosion propagation. This further improved the corrosion resistance of the filler metal. After 15 days of salt-spray corrosion, the stress-relieved filler metal retained an elongation of 4.96%. In contrast, elevated stress-relief annealing temperatures promoted Al precipitation at grain boundaries and restored the continuous distribution of α-Al. This created preferential pathways for inward corrosion penetration, which degraded corrosion performance. Accordingly, after 15 days of corrosion, the elongation of filler metal annealed at 250 °C decreased to 2.65%.

Femtosecond laser welding of sapphire to TC4 (Ti–6Al–4V) alloy was conducted under atmospheric conditions, and the interfacial characteristics, metallurgical reaction mechanism, and the effect of laser power on joint strengthening were systematically investigated. The results revealed that the femtosecond laser induced transient high temperatures, elemental intermixing, and interfacial metallurgical reactions at the sapphire/TC4 alloy interface, producing an interfacial compositional transition zone with a maximum measured width of 5.72 μm after rapid cooling. Reaction products including TiO, TiO₂, and Al₃Ti were identified by XRD, while EDS revealed interfacial redistribution of Ti, Al, and O. At a laser power of 8.4 W, the joint exhibited a relatively flat interfacial morphology and a lower apparent shear strength than that at 12.4 W. The highest mean apparent shear strength of 51.55 MPa was obtained at 12.4 W, which was associated with the characteristic wavy interfacial morphology that promoted crack deflection and energy dissipation. At 16.6 W, interconnected microcracks formed near the interface and within the sapphire substrate due to excessive heat input and thermal mismatch, and the apparent shear strength decreased to a level statistically comparable to that at 8.4 W.