Effect of microstructure aspects on mechanical properties of nanoparticle-assisted transient liquid phase (NP-TLP) joints for AZ31 alloy

Abstract

To study the effect of nanoparticles on strengthening the transient liquid phase (TLP) joints of AZ31 alloy, different interlayers including pure copper, pure copper+TiO 2 nanoparticles, pure copper+Al 2 O 3 nanoparticles and pure copper+SiC nanoparticles were used. The pure copper was coated on the surfaces to be joined via electroplating. The samples were TLP bonded at 525 °C for 1 and 2 h under the pressure of 1 MPa, in an atmosphere-controlled furnace. After that, the microstructure of the joints were studied using optical and scanning electron microscopy and phase analysis as conducted using Energy-dispersive X-ray spectroscopy. The joints' shear strength was evaluated via a tensile test machine equipped with a special designed fixture and X-Ray Diffraction was utilized to analyze the related fracture surfaces. Microstructural studies showed that athermal solidification induced eutectic compounds at the joints were reduced with increasing bonding time and therefore, the isothermal solidification became more completed. This also increased the homogenity and uniformity of the microstructure and the joint's shear strength. The highest and lowest shear strength was observed for the joints made using pure copper+TiO 2 nanoparticles and pure copper+SiC nanoparticles-containing interlayers, respectively, about 90% and 15% of the base metal's shear strength. Also, the shear strength of the joints made using pure copper+Al 2 O 3 nanoparticles was higher for the 20 nm particles, compared to the 50 nm ones. • Exploring TLP bonding process for AZ31 alloy as an Mg-based one • Using nanoparticles-including interlayers with different materials and sizes • A reverse relationship between the nanoparticle size and joint's shear strength • Obtaining the highest joint's shear strength about 98% of that of the base metal • ASZ size and nanoparticles surface area as the factors of the joint's strength