Interface characteristics and mechanical behavior of Cu/Al clad plate produced by the corrugated rolling technique

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Abstract

Corrugated Cu/Al clad plates are prepared by the corrugated roller with a reduction ratio of 50 % at room temperature. The effects of this rolling technique on the interfacial characteristics and mechanical properties have been evaluated. Microstructure results show that the Cu/Al interface is excellent combination and the grains near the interface are significantly refined, especially at the trough position. The reason for grain refinement at the interface can be attributed to the inhomogeneous strain induced by the corrugated roller, which can improve the bonding strength of the clad plate. Gauss texture appears at the Cu and Al substrates both at peak and trough positions, but the texture intensity is low. The peeling curve of the corrugated sample shows a trend of rising first and then decreasing quickly and the average peeling strength value reaches 135 N/cm. The tensile-shear strength at trough position reaches 80 MPa. The ultimate tensile strength of the sample at trough position reaches 237 MPa, which is 18 % higher than that the peak position. Excellent mechanical properties can be obtained for the corrugated Cu/Al clad plate mainly due to the grain refinement and corrugated-shape interface under the action of inhomogeneous stress distribution.

Introduction

Cu/Al clad plates have attracted much interest owing to the excellent properties associated with light quality, high thermal and electrical conductivity in recent years [1]. They are frequently used for transfer pipes, conductor wires, power cables and armor protection [[2], [3], [4], [5], [6]]. Now, many methods have been introduced to prepare Cu/Al clad plates, such as roll bonding [2,7,8], diffusion bonding [9], and explosive-welded [10,11]. Among all these methods mentioned above, the roll bonding method is commonly employed because of stable product quality, low-cost and mass production [[12], [13], [14], [15]].

The influence factors of Cu/Al plates by cold rolling under large reduction ratio and the interface structure and fracture mechanism had been analyzed, showing that the intermetallic compounds (CuAl2, CuAl, Cu9Al4, and Cu4Al3) promoted creaks propagation and weakened the bond strength and the fracture mechanism transformed from ductile to brittle cleavage [16]. The deformation characteristic of Cu/Al plate during the rolling process under different parameters was researched, obtaining the plastic deformation characteristics under various technological parameters (including initial thickness ratio, reduction ratio, deformation rate, etc.) [17]. The superiority of asymmetric roll bonding was qualitatively expressed by the stress state of the deformation zone [18]. Their researches showed that the asymmetric roll can lead to severe shear deformation for clad plates, which provided a good interface during annealing process. In comparison with the traditional rolled plates, the strengthening of asymmetrical rolled plates resulted from the improved interfacial microstructure. Although the preparation of Cu/Al clad plate by roll bonding has become very common, low bonding strength is also the problem in Cu/Al plates.

In recent years, inhomogeneous plastic deformation was introduced to improve the mechanical properties of light alloys. AA5083 alloy forming process was introduced by using different corrugation dies profile (V groove, flat groove and semi-circular) and the effect of repetitive corrugation and straightening (RCS) on grain refinement was analyzed, showing that an average grain size of ∼20 μm was observed in both the flat groove and the semi-circular dies [19]. The influence of the RCS process on the grain size of Al-3Mg-0.25Sc alloy was discussed through 8 passes at room temperature [20]. Their results displayed that this procedure introduced significant grain refinement with an average grain size of ∼0.6−0.7 μm.

Up to now, the deformation process of the corrugated sheets is still limited to single metal alloy, however, there are a few studies on rolling clad plates with corrugated rollers. Based on the corrugated technique, the corrugated + flat rolling (CFR) process was put forward to produce bimetal composite plates. In the prior article [21], flat Cu/Al clad plates had been produced by this process under a low reduction ratio of 20 % at room temperature. It was concluded that the corrugated interface was formed without intermetallic compounds and the interfacial grain refinement occurred. Meanwhile, Mg/Al clad plates were manufactured by CFR process and the microstructure characterization and mechanical property were measured [22]. It was concluded that spatial distribution was observed for the grain along both the normal and rolling directions for AZ31B Mg alloy and the transverse tensile strength was much higher than the rolling tensile strength.

The contents of the previous paper mentioned above are about the interface characteristics and tensile properties of the flat clad plate after the second flat pass, and the microstructure and mechanical behavior of the corrugated clad plate only after the first corrugated pass process are not studied in detail. During the CFR process, corrugated Cu/Al clad plate made by the corrugated rolling can be used as an intermediate product, or as a final product in aircraft seatback, armor protection, and other aspects to meet the needs of customers. Previous corrugated plates were mostly extruded by abrasive tools [20,23]. While the purpose of this study is to manufacture the corrugated Cu/Al clad plates by a simple and efficient rolling method for the extensive application.

Section snippets

Experimental

T2 copper (99.98 wt.% Cu + Ag, 0.001 wt.% Bi, 0.005 wt.% Fe, 0.002 wt.% As, 0.002 wt.% Sb, 0.005 wt.% Pb, 0.005 wt.% S) and 1060 aluminum (99.62 wt.% Al, 0.05 wt.% Si, 0.22 wt.% Fe, 0.03 wt.% Mg, 0.05 wt.% Zn, 0.03 wt.% Mn) were obtained as starting materials in this study. The dimensions of Cu and Al were 100 × 50 × 3 mm3 and 100 × 50 × 7 mm3, respectively. Before rolling, the initial materials were ground with wire brush until fresh metals leak out. And then, the surfaces were repeatedly

SEM analysis

Fig. 3 displays the SEM images and EDS line scan results of near-interface regions at various interfacial positions on the RD-ND plane. For the corrugated sample, the interfaces both peak and trough positions are tightly bonded. Furthermore, it can be seen that the Cu/Al bonding interface appears to be wavy, rather than a straight line. At the same time, the concentration of the Al element rapid declines from Al side to Cu side while the concentration distribution of the Cu element presents the

Interface microstructure

Fig. 3, Fig. 4 show that the well-bonded interfaces of the corrugated clad plate are obtained. Meanwhile, Fig. 4 presents that the grains near the interface are finer than that far away from the interface, especially at the trough position. The higher grain refinement efficiency in Cu side and Al side during plastic deformation is attributed to large local deformation induced by the corrugated roller. Such finer grains can contribute to a higher bonding strength owing to the fine grain

Conclusions

  • (1)

    Corrugated Cu/Al clad plate was obtained by the corrugated rolling process at the 50 % reduction ratio. The grain size at the Cu/Al interface was refined significantly, especially the trough position, because of the asymmetrical shear strain induced by the corrugated roller.

  • (2)

    Due to the plastic deformation during the rolling process, relatively low intensity gauss texture appears in the Cu and Al matrixes both at peak and trough positions. Furthermore, for metal Cu, the proportion of LAGBs at the

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

This project is supported by Major Program of National Natural Science Foundation of China (U1710254), National Natural Science Foundation of China(51975398, 51904205, 51804215), Shanxi Province Science and Technology major projects (MC2016-01,20181101008), Natural Science Foundation of Shanxi Province (201801D221221), Key Projects of Shanxi Province Key Research and Development Plan(201703D111003), and the China Postdoctoral Science Foundation(2018M641680, 2018M641681).

References (41)

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