Influence of heat treatment on interface of Cu/Al bimetal composite fabricated by cold rolling

doi:10.1016/j.compositesb.2011.04.045

Composites Part B: Engineering

Volume 42, Issue 6, September 2011, Pages 1468-1473

https://doi.org/10.1016/j.compositesb.2011.04.045 Get rights and content

Abstract

A copper/aluminum/copper sandwich clad sheet was fabricated by means of cold rolling process and heat treated with different temperature and time. The Al/Cu interface and its bond strength were investigated by SEM, TEM and peeling test. The results reveal that low temperature heat treatment can improve the morphology of Al/Cu interface and increase its bond strength. However high temperature and long time result in the formation of Al₂Cu intermetallic compound layer, which is detrimental to the bond strength, and moreover, small Al₂O₃ particles precipitate along the Al₂Cu and Al interface. When the interlayer along Al/Cu interface grows to a certain thickness, the effect of heat treatment temperature and time become weak. For the present study, the reasonable heat treatment may be 423 K and 20 h.

Introduction

With the development of modern industry, it is difficult to meet the varied demands such as superior electrical and thermal properties for a single material. Therefore, clad metals, consisting of two or more metals, have been developed due to their unique properties [1], [2], [3]. Till now, many kinds of techniques have been developed to fabricate the clad metals, such as explosive welding, rolling bonding, diffusion bonding, extrusion and friction-stir welding [4], [5], [6], [7], [8], [9]. Among these methods, rolling bonding technique has and been extensively investigated, because of its efficiency and economy. Roll bonding is a solid state welding process to join dissimilar metals, which imply that one of the basic parameters is the degree of deformation [10], [11], [12], [13]. There is a certain threshold deformation, and only the deformation exceeding this value could the different metals bond together. In addition, the removal of contamination layers from the surfaces by chemical and mechanical treatments is also very importance [14], [15]. Previous investigations have revealed that the function of scratch-brushing is not only to clean, but also to form a brittle layer on the metal surfaces by work hardening the surface layers [16]. Since the rolling bond is based on the high deformation, there will be great stress in the metals and their interface. Therefore, the clad sheet must be annealed in order to obtain good formability for the next deep drawing process.

In recent years, the roll bonding technique has been widely applied to fabricate many kinds of multi-layer composites, such as aluminum/copper, steel/aluminum/copper, and titanium/steel. [17], [18], [19]. Copper and aluminum clad composites have been widely studied, because of their advantages and widely application. For example, a two-layer clad sheet of aluminum/copper can almost reduce 40% in weight, with the equivalent conductivity and heat conductivity as a copper alloy. But the cost is just the 60% of a copper alloy. For these reasons, Al/Cu clad is frequently used for armored cables, yoke coils in TV sets, air-cooling fin and bus-bar conductor joint. However, the investigations on the Al/Cu composite fabricated by cold rolling are still few, especially its interface. Therefore in the present work, a three-layer clad sheet comprised of copper (TU2), aluminum (1350) and copper (TU2) was fabricated by cold rolling process. The effect of heat treatment on the mechanical properties and interface diffusion of the three-layer clad sheet were investigated.

Section snippets

Experimental

In this research, annealed aluminum plate (1350) and copper strip (TU2) with thickness of 12 mm and 0.6 mm, respectively, were used. The surface of aluminum plate and copper strip were scratch brushed by a 3 cm diameter stainless steel brush with 0.3 mm wire, in order to degrease, remove the oxide film, and form a hard surface. Then the Cu/Al/Cu clad sheet was fabricated by cold rolling on a laboratory rolling mill with a loading capacity of 150 tons. The roll diameter was 400 mm and the rolling

Microstructure

The interface morphology of Cu/Al/Cu clad sheets with different heat treatment temperature is shown in Fig. 1. It is clear that the Al/Cu interface of as fabricated clad sheet is not smooth, and the Al and Cu are squeezed into each other. The low temperature heat treatment causes the Al/Cu interface to become smooth, as shown in Fig. 1b. Such a phenomenon should be attributed to the diffusion between Al and Cu. With the increase of heat treatment temperature, the transition layer appeared along

Conclusions

(1)
The heat treatment can lead to the formation of interlayer, and the temperature has a greater effect on the growth of the interlayer than the heat treatment time.
(2)
When the interlayer grows to a certain thickness, the effect of temperature and time become weak.
(3)
The Al₂Cu intermetallic compound layer forms adjacent to Al layer. In addition, small Al₂O₃ particles precipitate along the Al₂Cu and Al interface at high temperature treatment.
(4)
The relative low temperature and short time heat treatment can

Acknowledgements

The work is financially supported by the National Basic Research Program (973 Program) of China (2009CB930004), the National High Technology Research and Development Program (863 program) of China (2011AA030104) and the Science and Technology Research Foundation of Shenzhen Bureau of Science and Technology & Information (JC200903170498A).

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Influence of heat treatment on interface of Cu/Al bimetal composite fabricated by cold rolling

Abstract

Introduction

Section snippets

Experimental

Microstructure

Conclusions

Acknowledgements

Mater Sci Eng A

J Alloys Compd

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Mater Sci Eng A

J Alloys Compd

Acta Mater

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J Alloys Compd