Fabrication of Copper Clad Aluminum Wire(CCAW) by Indirect Extrusion and Drawing

Transcription

1 Materials Science Forum Online: -3-5 ISSN: , Vols. 9-5, pp 37-3 doi:.8/ Trans Tech Publications, Switzerland Fabrication of Copper Clad Aluminum Wire(CCAW) by Indirect Extrusion and Drawing H. C. Kwon, T. K. Jung, S. C. Lim 3, M. S. Kim,3 Korea Institute of Industrial Technology, 7 Kajwa-dong, Seo-gu, Incheon -5, Korea, School of Materials Science and Engineering, Inha University, 53 Yonghyun-dong, Nam-gu, incheon -75, Korea Keywords : Indirect extrusion, Copper Clad Aluminum Wire(CCAW) Abstract. The optimized extrusion conditions from the present research were the extrusion temperature of 573~63K and the extrusion ratio(a /A) of.39. Above the extrusion temperature of 63K, the fracture of sheath material was observed. It is due to the difference of flow stress between the sheath material and the core material during extrusion process. The bonding strength increased with increasing the extrusion temperature and the extrusion ratio. The bonding strength increased with increasing the annealing temperature. However, over 573K, it decreased abruptly since the thick and brittle intermetallic compounds of larger than 3µm were formed. The electrical conductivity of copper clad aluminum wire was about 7%IACS without annealing. Introduction It has been reported that there are many advantages of copper clad aluminum(cca) for electric and electronic applications. It is 3~% cheaper and 6% lighter than conventional copper products including DHP, DLP, OFHC. Especially, the bus-bar copper alloy used for electric and electrode materials application is difficult to be handled due to its heavy weight. To solve these problems, CCA is used as material of bus-bar. Also, the copper clad aluminum wire can be used for electric wire. Because the copper clad aluminum wire has good mechanical properties and the electric current flows on the surface of conductor. In copper clad aluminum, the fracture phenomenon occurred by the difference of flow stress between the sheath material and the core material during extrusion process[][][3]. Therefore, the extrusion condition such as the extrusion temperature and the extrusion ratio were very important for the CCA manufacturing. Until quite recently, CCA used to be made by using hydrostatic pressure extrusion[]. However, because hydrostatic extruder is costly, CCA was not widely applied. Thus, this study was aimed to find the optimum extrusion conditions such as extrusion temperature and extrusion ratio of the indirect extrusion substituting for the conventional hydrostatic pressure extrusion. Also, the copper clad aluminum wire(ccaw) of mm in diameter was fabricated by using cold drawing, and its electrical conductivity was investigated. Corresponding Author : intennis@lycos.co.kr All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-/3/6,9:5:)

2 38 Designing, Processing and Properties of Advanced Engineering Materials Experimental The extrusion billet of 7mm in diameter and mm in length was produced by using pure aluminum as the core material and copper(tpc) as the sheath material. The thicknesses of sheath material was, 6, 8, and mm. Fig. showed the extrusion billet for CCA and the die for this experiment. The semi angle of the die was 3. The range of extrusion temperature was varied from 73K to 773K and the extrusion ratio(r:a /A) was from 6.9 to.39. Carbon oil was used as lubricant to reduce the friction between billet/sleeve and between billet/die. The CCA rod produced by indirect extrusion was annealed from 73K to 673K for hr. The bonding strength test for the specimens produced under different extrusion condition and at varying annealing temperature was performed. The copper clad aluminum wire(ccaw) of mm in diameter was fabricated by cold drawing without annealing after extrusion. Results and discussion Fig.. The billet with 7mm of diameter and mm of length, and the die having 3 of semi angle for CCA extrusion Fig. showed the variation of extrusion pressure according to the extrusion temperature at a given the extrusion ratio of 6.98 and the initial copper thickness of 6mm. Extrusion pressure decreased with increasing extrusion temperature. It is due to the reduction of the flow stress of materials. However, over 673K, the fracture of copper as the sheath material occurred as fig.3. Extrusion maximum pressure (MPa) Fracture of sheath material Extrusion temperature(k) Fig.. The variation of the extrusion pressure according to the extrusion temperature (a)63k (b)673k Fig. 3. The external view of copper clad aluminum extruded at a) 63K and b) 673K Fig. showed the flow stress of the copper and the pure aluminum. The flow stress was 3 to 65MPa in pure aluminum and to 5MPa in copper below 63K. Therefore, the flow stress of copper was larger than that of the pure aluminum by factor of to 7 below 63K. The flow stress difference became even larger by factor of 7 to 3 at 773K. So, it suggested that the fracture of the copper as the sheath material occurred due to the serious difference of flow stress between the sheath material and the core material.

3 Materials Science Forum Vols Copper Pure Al Fig.. The flow stress between the copper as the sheath material and the pure aluminum as the core material according to temperature Also, the extrusion pressure increased with increasing the extrusion ratio due to the larger flow stress of material. However, over.39 of the extrusion ratio, the fracture of copper as the sheath material occurred. It is thought that the faying surface between the die and the copper as the sheath material increases and the deformation stress increases with increasing the extrusion speed. Also, the extrusion pressure increased with increasing the initial copper thickness. However, the fracture of copper occurred at the initial copper thickness of mm. Therefore, the optimum extrusion conditions were determined as 63K of the extrusion temperature,.39 of the extrusion ratio and 6mm of the initial copper thickness. Fig. 5 showed the variation of bonding strength according to the extrusion conditions at the initial copper thickness of 6mm. The bonding strength increased with increasing the extrusion temperature and the extrusion ratio. Below 53K, the bonding strength was approximately MPa with the extrusion ratio of However, over 63K, the bonding strength increased up to about 6MPa. Also, the bonding strength increased up to 65MPa at a given extrusion ratio of Extrusion temperature (K) 8 6 Extrusion temp. : 63K Extrusion ratio(a /A) Fig. 5. The variation of bonding strength according to extrusion conditions with the initial copper thickness of 6mm Fig. 6 showed the diffusion layer between the copper and the aluminum at extrusion temperature of 63K and the variation of diffusion layer thickness according to the extrusion temperature. The diffusion layer thickness increased with increasing the extrusion temperature and the diffusion layer thickness was about.6µm at 63K. Also, the bonding strength and the diffusion layer thickness increased up to.8µm at a given extrusion ratio of.39. Thickness of diffusion layer (um) 3 Thickness of diffusion layer(um) 3 Extrusion temp. : 63K Extrusion temperature (K) Extrusion ratio (R=A /A) Fig. 6. The diffusion layer of Cu/Al clad at extrusion temperature of 63K and the variation of diffusion layer thickness according to extrusion conditions with the initial copper thickness of 6mm

4 3 Designing, Processing and Properties of Advanced Engineering Materials Fig. 7 showed the variation of the bonding strength and the diffusion layer thickness according to annealing temperature with the extrusion temperature of 63K and the extrusion ratio of.39. The bonding strength increased up to 73MPa at 573K. The diffusion layer thickness increased with increasing an annealing temperature. When the bonding strength was 73MPa, the diffusion layer thickness was about 3µm. However, over 63K, the bonding strength decreased. It is due to the formation the thick and brittle intermetallic compounds. 9 Diffusion layer thickness(um) Annealing temperature(k) Diffusion layer thickness(um) Fig. 7. The variation of the bonding strength and the diffusion layer according to annealing temperature The copper clad aluminum wire(ccaw) of mm in diameter was manufactured from the extruded rod of 6mm by cold drawing. The reduction ratio was 5% for 7mm in diameter, % for 3mm and 5% for mm without annealing. It shows that the copper as the sheath material and the aluminum as the core material have good workability. Fig. 8 showed the external view of CCAW of mm in diameter. The electrical conductivity of CCAW of mm in diameter was about 7%IACS. This has good electrical conductivity rather than wrought aluminum alloy. mm Fig. 8 The copper clad aluminum wire of mm in diameter Summary In this study, the optimum extrusion conditions were determined that the extrusion temperature was 63K, the extrusion ratio.39 and the initial copper thickness 6mm. On this extrusions condition, the bonding strength was 65MPa and the diffusion layer thickness was about.8µm. Also, the diffusion layer thickness was about 3µm at annealing temperature of 573K, the maximum bonding strength increased up to 73MPa. The cold drawn CCAW of mm in diameter has electrical conductivity of 7%IACS. References [] Y. Yamaguchi: J. of the Japan Society for Technology of Plasticity, vol.5, (97) p.73. [] H. J. Park, K. H. Na: J. of the Korean Society for Technology of Plasticity, Vol., (99) p.3. [3] J. H. Kim, B. K. Suh: J. Kor. Inst. Met. & Mater, Vol.38, () [] C. G. Kang, H. C. Kwon: International Journal of Mechanical Sciences Vol. () p.7

5 Designing, Processing and Properties of Advanced Engineering Materials.8/ Fabrication of Copper Clad Aluminum Wire (CCAW) by Indirect Extrusion and Drawing.8/