The precipitation-hardenable aluminum alloy 6061 (AA 6061) is favored for aerospace components and automotive parts. However, the tenacious oxide layer on the surface greatly limits the quality and applicability of joining AA 6061. In this study, the joining method of solid-state diffusion bonding was implemented for AA 6061 plates, and the effects of post-weld heat treatment (PWHT) on the joint interface were investigated. The bonding temperatures were within the range of 500–530 °C, and the time periods varied from 30 to 240 min under a static pressure of 5 MPa in a vacuum. The diffusion bonded specimens were subjected to T4- and T6-PWHT to improve the bonding quality. The interfacial microstructure of the joints was analyzed by scanning electron microscopy, and the mechanical properties were evaluated with shear tests. The experimental results showed that the shear strength of the diffusion bonded joint could reach around 71.2 MPa, which was highly dependent on bonding temperature and holding time, and T6-PWHT further enhanced it to over 100 MPa. The effects of PWHT on the diffusion bonded AA 6061 joint were investigated, and the fractography on the sheared surfaces indicated that PWHT-T6 played an important role in enhancing joint strength, which was consistent with the measured shear strength. The sequential PWHT for AA 6061 after diffusion bonding was proven to be feasible for bonding of AA 6061 parts, and the joint strength was sufficient for industrial needs.

In this study, AA6061/AA6061 and AA6061/alumina were directly brazed with Al10.8Si10Cu, Al10Si10Cu4Ti and Al10Si10Cu4Ti0.1RE filler alloys at 530 °C for 10 min without the use of flux. The addition of titanium and rare-earth elements into Al10.8Si10Cu alloy effectively improved the bonding shear strengths of AA6061/AA6061 and AA6061/alumina joints. The highest joint shear strengths were 61.1 and 19.2 MPa, respectively. The Al10.8Si10Cu filler alloy without titanium and rare-earth elements could not wet on the alumina and caused failure of the AA6061/alumina joint. The shear strengths of the AA6061/AA6061 and AA6061/alumina joints both strongly depended on the active element addition. Due to the high chemical activity of the rare-earth elements, they formed AlLa between the Al10Si10Cu4Ti0.1RE filler alloy and alumina. The addition of rare-earth elements into Al10Si10Cu4Ti filler alloy resulted in significant enhancement of the average bond strength of AA6061/alumina joints, from 8.0 to 14.8 MPa.

Due to the combined advantages of low cost, good soldering properties, and appropriate melting temperature range, novel Sn₈Zn₃Bi₁Mg active solder was developed for direct soldering of transparent conductive oxide (TCO) ceramic targets with oxygen‐free copper at 200°C in air. The TCO specimens have aluminum‐doped zinc oxide (AZO) and zinc oxide (ZnO) ceramics. The direct soldering process was performed without the need for flux or pre‐metallization of the two transparent conductive oxides. The microstructure, phase constitution, melting characteristics, and soldering properties of the Sn₈Zn₃Bi₁Mg active solder were investigated. The liquidus temperature of the Sn₈Zn₃Bi₁Mg active solder was 198.6°C, which was very close to the binary Sn‐Zn eutectic temperature of 198.5°C. The effect of temperature on the bonding strength of the solder joints was evaluated. The shear strengths of AZO/Cu and ZnO/Cu joints soldered with Sn₈Zn₃Bi₁Mg active solder were 10.3 and 7.5 MPa at room temperature, respectively. Increasing the temperature from room temperature to 180°C reduced the bonding shear strengths of AZO/Cu and ZnO/Cu joints to 3.3 and 3.7 MPa, respectively.

Modular multilevel converter (MMC) submodule capacitor voltage fluctuation causes several technical difficulties. Therefore., this paper establishes a comprehensive mathematical model for capacitor voltage fluctuation under second harmonic circulating current injection. This study proposes an injection approach that accounts for current restrictions on bridge arms., and the ideal amplitude and phase angle of the second harmonic circulating current is identified. The proposed method can significantly reduce the peak-to-peak voltage fluctuation of the submodule capacitor and successfully minimize the required submodule capacitance. Finally., a MATLAB/Simulink model of a three-phase inverter is constructed to confirm the feasibility of the proposed methodology.