Effect of Intermetallic Compound Layer on Peel Strength and Crack Propagation Behavior in Cu/Al/Cu Clad Composites

Sun Ig Hong,Yong Keun Kim

doi:10.3390/met9111155

Abstract

The effects of interfacial modification in tri-layered Cu/Al/Cu composites by heat treatment on interface stability and crack propagation were investigated. In order to investigate the crack path during the peel test, the intermetallic compound layer with the propagating crack was examined using electron backscatter diffraction (EBSD) analyses. The increase of peel strength from 7.8 to 9.1 N/mm in the tri-layered Cu/Al/Cu composite in the presence of thin discontinuous intermetallic compounds with heat treatment at 200–300 °C was accompanied by the increase of electrical conductivity from 65.3% IACS (International Annealed Copper Standard) to 66.8% IACS. Continuous intermetallic layers consisting of Al2Cu, AlCu, and Al4Cu9 were found in Cu/Al/Cu heat-treated at temperatures above 350 °C and its thickness increased rapidly and reached up to 35.2 μm at 500 °C. The peel strength drastically decreased to 5.75 N/mm after heat treatment at 400 °C, and it gradually increased as the heat treatment temperature was increased to 450 °C (5.91 N/mm) and 500 °C (6.16 N/mm). The increased peel strengths after heat treatment at 450 and 500 °C were accompanied by pronounced serrations of the peel strength–displacement curves. The amplitude of serration increased substantially with increasing annealing temperature from 400 to 500 °C. The major crack along the interface propagated, mostly along the Al2Cu/AlCu boundary with some inclined cracks, propagated through the AlCu and Al4Cu9 intermetallic compound layers. The repetition of crack propagation along the interface and crack deflection through the intermetallic layer as an inclined crack induced the serrated surface on the peeled-off Cu plate, enhancing the interface toughening.

Highlights

A large body of research has recently been conducted to develop ways to reduce the vehicle weight in automobile industry [1,2]
The repetitive crack deviation would increase the energy required for crack propagation, resulting in the general increase of the peel strength with increasing intermetallic compounds (IMCs) layer thickness
Interface toughening of Cu/Al/Cu was achieved by forming thin discontinuous intermetallic layers through enhanced the interface diffusion bonding of a weakly roll-bonded region by lower-temperature heat treatment at

Summary

Introduction

A large body of research has recently been conducted to develop ways to reduce the vehicle weight in automobile industry [1,2]. The closely aligned electronics and communications industries share the common goal of weight lightening and are focused on developing light products with high performance. Reducing weight can be accomplished either by replacing conventional materials with new ones or by improving the properties of conventional materials. Many recent studies have been devoted to cladding, which involves joining different materials through mechanical or thermomechanical processing [3,4]. Cladding by joining various metals allows for combination of new properties that may not be possible in monolithic metals and alloys, such as combination of corrosion resistance, specific strength [5], surface properties, and reduced weight.

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