Interfacial Behavior and Shear Strength of Al-25Si-4Cu-1Mg Joints by Transient Liquid Phase Bonding with Cu as Interlayer

Kai Qi,Guo Xu,Fengjiang Wang

doi:10.3390/met11101637

Abstract

Spray-formed hypereutectic Al-Si-Cu-Mg alloy is the candidate for automotive and aerospace industries due to its superior wear resistance, lower thermal expansion coefficient and density, and higher thermal conductivity. This paper aims to investigate the bonding properties of hypereutectic Al-25Si-4Cu-1Mg alloys using the transient liquid phase (TLP) method with Cu as an interlayer. To obtain the suitable bonding parameters, the interfacial microstructure and shear strength of Al-25Si-4Cu-1Mg joints were investigated with the effect of different bonding temperatures and holding times. The results showed that TLP bonding between Al-Si-Mg-Cu alloy was mainly realized by large amounts of Al2Cu intermetallic compounds (IMCs), primary Si and α-Al phases. With the brazing temperature increasing, the width of the brazing seam gradually increased, and the voids began to be produced. With the holding time increasing, θ-Al2Cu phases approached into the base metal and Si particles in the brazing seam were obviously coarsened. With the formation of θ-Al2Cu phases into the base metal, more Si particles were segregated at the interface between brazing seam and base metal, and the shear test confirmed that it was the weakest bonding location. Finally, the effect of bonding parameters on the joint strength indicated that the joint brazed at 540 °C for 7.5 min presented the best shear performance with the shear strength reaching 75 MPa because the size of Si particles in the brazing seam was closest to the size of Si particles in base metal under this parameter.

Highlights

The hypereutectic Al-Si alloy is a unique aluminum alloy in which dispersed Si particles are embedded in the surrounding α-Al matrix
Si particles are typically hard and brittle materials, and their thermal expansion coefficient is lower than Al
After spray forming, the alloy was finished with hot extrusion at 440 ◦C with a rate of 0.3–0.5 mm/s to decrease the voids that occurred in spray forming

Summary

Introduction

The hypereutectic Al-Si alloy is a unique aluminum alloy in which dispersed Si particles are embedded in the surrounding α-Al matrix. By changing the ratio of Al and Si, hypereutectic Al-Si alloy can obtain its bias performance, such as lightweight, high strength, high thermal conductivity, controllable thermal expansion coefficient, and good machinability. It serves as an optimal electronic packaging material [2,3] because it meets the requirements of electronic packaging technology in the direction of miniaturization, lightweight, and high-density assembly. These Al-Si alloys have wide application prospects in the fields of electronic packaging and the automobile industry [4,5,6,7]. The research on the joint performance of hypereutectic Al-Si alloy is very important for its industrial application

Objectives

Methods

Findings

Conclusion