Abstract
Ultrasound-assisted transient liquid phase bonding (U-TLP) has been regarded as a promising brazing process to join magnesium alloys with a Sn and Zn interlayer; however, the formation of brittle magnesium intermetallic compounds (Mg2Sn, MgZn, and MgZn2) compromises the mechanical properties of the joints. In this study, Mg alloy U-TLP joints with a Ni interlayer were evaluated based on shear strength and hardness measurement. Microstructural evolution along with ultrasonic duration time and intermetallic compound formation were characterized using X-ray diffraction and electron microscopy methods. The results show that incremental ultrasonic durations of up to 30 s lead to the microstructural evolution from the Mg2Ni layer, eutectic compounds (Mg2Ni and α-Mg) to α-Mg (Ni), accompanied by shear strength increases. The maximum value of the shear strength is 107 MPa. The role that ultrasound vibration played in brazing was evaluated, and showed that the MgO film was broken by the acoustic softening effect when the interlayer and base metal were solid. As the MgO and Mg substrate have different stress reduction τ, this plastic mismatch helps to break the oxide film. Additionally, the diffusion between the solid Mg substrate and Ni interlayer is accelerated greatly by the acoustic pressure based on the DICTRA dynamic calculation.
Highlights
Magnesium and its alloys are potential candidates to replace steel and aluminum alloys in manufacturing industries in future, due to some of their unique properties like a low density, high strength-to-weight ratio, good castability, and high damping capacity [1,2]
Various methods have been applied for welding magnesium alloys such as arc welding [3,4], laser welding [5,6], brazing [7], friction stir welding [8,9], and transient liquid phase bonding [10]
Ultrasound-assisted transient liquid phase bonding (U-TLP), which has been developed from the TLP method, is a low-cost, high-efficiency, green, and reliable joining method, which has been applied to join different kinds of alloys [14,15] or dissimilar alloys [16,17,18]
Summary
Magnesium and its alloys are potential candidates to replace steel and aluminum alloys in manufacturing industries in future, due to some of their unique properties like a low density, high strength-to-weight ratio, good castability, and high damping capacity [1,2]. Lai et al had to prolong the ultrasonic treatment time to 120 s in order to Materials 2019, 12, 3732; doi:10.3390/ma12223732 www.mdpi.com/journal/materials in air to get a high mechanical performance and non-defect joints as Mg–Ni intermetallic compounds (IMCs) have lower formation enthalpy and Gibbus energy, and the Ni foil has better oxidation and corrosion resistance compared with Zn, Al, and Sn foil [22,23,24]. The influence of the ultrasonic treatment time on variation of the microstructure of the brazing seam was studied. 2. Experimental heated to 520 °C, the samples were separately treated with ultrasonic vibration for 10 s, 15 s, 20 s, 25 s, 27The s, and. The ultrasonic vibration and heating were shut down and the samples were cooled.
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