Reducing the loose-layer-to-dense-layer ratio in PEO coatings on aluminum and its alloys is the key to improving their corrosion resistance and expanding their applications in the aerospace industry and other fields. In this paper, we describe the discharge evolution during the PEO process in exhaustive detail and report the appearance of a novel “chain-like” discharge for the first time. We investigated the microstructure and composition of PEO coatings using a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The results reflected that the coating composition changed from amorphous Al₂O₃ to crystalline γ-Al₂O₃ and α-Al₂O₃ phases with the evolution of the plasma spark discharge state. We evaluated the electrochemical behavior of the coatings using a potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. Under “chain-like” discharge, the icorr of the coating on Al was 8.564 × 10^–9 A∙cm⁻², which was five orders of magnitude lower than that of the sample without the PEO coating. Moreover, we evaluated the adhesion strength of the coatings at different stages using a pull-off test. The adhesion strength of the PEO coatings at stage V reached 70 MPa. Furthermore, the high content of α-Al₂O₃ increased the hardness of the coating to 2000 HV. Therefore, the “chain-like” discharge promoted the formation of a single dense layer with 2.8% porosity and that demonstrated excellent properties. We also propose a mechanism to explain the influence of the plasma spark discharge state on the microstructure and composition of the PEO coatings.

To improve the corrosion resistance of TiNi alloy fabricated by laser powder bed fusion (LPBF), a porous oxidation layer was synthesized by micro-arc oxidation in a sodium aluminate and sodium silicate electrolyte. The influences of the applied voltage and the processing time on the morphology of oxidation layer were investigated, and the corrosion behavior of the oxidation layer in artificial saliva was evaluated and compared with that of the as-fabricated LPBF alloy. The results indicate that, as increasing the applied voltage and the processing time, the oxidation layer becomes uniform and integrated. The optimum parameters are with an applied voltage of 450 V and processing time of 40 min. The oxidation layer primarily contains α-Al₂O₃ and consists of two layers, i.e., a thin, compact and uniform inner layer and a porous outer layer. The formation of stable α-Al₂O₃ phase in the coating and its almost non-porous dense structure reduce the channels for corrosion ions to penetrate into the substrate through coating, thereby improving the corrosion resistance of TiNi alloy.

As the demand for high-performance dissimilar material joining continues to increase in fields such as aerospace, biomedical engineering, and electronics, the welding technology of dissimilar materials has become a focus of research. However, due to the differences in material properties, particularly in the welding between metals and non-metals, numerous challenges arise. The formation and quality of the weld seam are strongly influenced by laser process parameters. In this study, successful welding of high-borosilicate glass to a TC4 titanium alloy, which was treated with high-temperature oxidation, was achieved using a millisecond pulsed laser. A series of process parameter comparison experiments were designed, and the laser welding behavior of the titanium alloy and glass under different process parameters was investigated using scanning electron microscopy (SEM) and a universal testing machine as the primary analysis and testing equipment. The results revealed that changes in process parameters significantly affect the energy input and accumulation during the welding process. The maximum joint strength of 60.67 N was obtained at a laser power of 180 W, a welding speed of 3 mm/s, a defocus distance of 0 mm, and a frequency of 10 Hz. Under the action of the laser, the two materials mixed and penetrated into the molten pool, thus achieving a connection. A phase, Ti₅Si₃, was detected at the fracture site, indicating that both mechanical bonding and chemical bonding reactions occurred between the high-borosilicate glass and the TC4 titanium alloy during the laser welding process.

Hermetic glass-to-metal sealing (GMTS) technology combines metal and glass and can be used to construct vacuum tubes; electric discharge tubes; semiconductor diodes; reed switches; and pressure-tight glass-to-metal windows, optical windows, and lenses in electronics or electronic systems. The hermetic and mechanically strong seals engineered using GTMS are highly reliable, making them suitable for deployment in harsh environments and for applications requiring high performance. However, it has always been challenging to precisely and robustly join glass and metal due to the significant disparities in their properties. In this study, the laser transmission welding of borosilicate glass and aluminum alloy using a pulsed Nd:YAG laser to achieve hermetic glass–metal seals was experimentally investigated. This research focused on various processing parameters and the influence of surface conditions on bonding quality. Three different types of surfaces—a polished surface, a surface subjected to preoxidation, and a laser-modified surface—were compared. To evaluate the weld strength, shear-tensile separation forces were measured. The analysis of fracture and separation encompassed detailed examinations of the weld morphology, microstructure, and elemental composition. The results revealed that increasing the laser welding energy initially enhanced the weld strength until a saturation point was reached. Among the three different surface treatments tested, the laser surface modification of aluminum alloy yielded the highest weld strength. The maximum achieved bond force exceeded 35.38 N, demonstrating the feasibility of using cost-effective pulsed laser welding for glass-to-metal sealing. The results were significantly better than those from previous research in which aluminum alloy surfaces were pretreated using microarc oxidation.

This study adopts a new surface pretreatment method, Laser Surface Remelting (LSR). This experiment aims to establish a set of laser welding process parameters suitable for aluminum alloy and glass under this specific pretreatment. This experiment explores the impact of laser welding parameters on the welding strength between high borosilicate glass and aluminum alloy. The study specifically investigates the effects of four process parameters: defocus amount, laser power, frequency, and pulse width on the welding outcome. The results indicate that the welding quality between the aluminum alloy and glass reaches its optimum when the defocus amount is zero (i.e., when the laser converges at the interface between the glass and the metal) and the laser welding parameters are set to a power of 250 W, a welding speed of 1 mm/s, a welding frequency of 10 Hz, and a pulse width of 2.5 ms. The experiment also analyzes the fracture morphology under different parameters, summarizing the locations and causes of fractures, and establishing the relationship between the fracture location and the welding strength.