FR2732911A1 - PROCESS FOR PRODUCING A SILVER ALUMINUM CONDUCTOR - Google Patents

Abstract

A method for making a silver-plated aluminium conductor comprising an at least partially aluminium-based substrate coated with a silver layer. The method comprises firstly forming a cylindrical billet (B) then extruding the billet (B) to give a bimetallic bar with a diameter of 5-20 mm, stretching and drawing the bar (BF) to reduce its diameter and simultaneously performing intermediate heat treatments to produce a fine wire (F) with a diameter of 0.08-0.5 mm and a silver coating 1-2 mu m thick.

Description

 The present invention relates to a method of manufacturing a silver aluminum conductor.

 There are already conductors comprising an at least partially aluminum-based substrate and coated with a silver layer.

 The silver coating improves the surface properties of the conductor such as resistance to oxidation and solderability.

 Until now, these conductors have been manufactured by coating silver electrolytically.

 This is particularly the case for the process described in patent application FR 93 04243.

 However, the rate of electrolytic deposition of silver on aluminum is very low, which limits industrial production capacities.

 In addition, the adhesion of the electrolytic deposition of silver on the aluminum substrate does not result from an intermetallic bond. This results directly in insufficiencies of the mechanical and thermal properties and, in particular, in a low resistance to heat, a bad aptitude for drawing, and a solderability which is not yet high enough for the envisaged applications.

 The present invention aims to solve these technical problems satisfactorily.

 This object is achieved by a method of manufacturing a conductor comprising an at least partially aluminum-based substrate coated with a silver layer, characterized in that a cylindrical billet formed first an aluminum ingot whose diameter is between 50 and 85 mm provided with a silver envelope with a thickness between 0.5 and 1.5 mm, a spinning operation is then carried out on said billet to obtain a bimetallic bar with a diameter varying from 5 to 20 mm, then the section of this bar is reduced by drawing and then drawing by intermediate heat treatments to produce a fine wire whose diameter is between 0.08 mm and 0.5 mm with a silver coating of thickness ranging from 1 to 2 Zm.

 According to a first implementation variant, said billet is prepared by introducing an aluminum ingot with minimum clearance in an envelope made of a silver sheath previously expanded by heating to a temperature between 2000C and 500in for a period ranging from 5 to 30 minutes.

 According to another variant, said billet is prepared by producing the envelope in the form of a silver coating obtained by electrolytic means.

 According to an advantageous characteristic, the spinning operation is carried out at a temperature between 0 and 2000C with a ratio between 5 and 100 and a speed of 0.1 to 2m / min. The spinning ratio is defined by the ratio of the respective sections of the billet to be spun and the bar spun.

 According to a preferred characteristic, the spinning is carried out at ambient temperature.

 According to another characteristic, intermediate heat treatments are carried out before and during drawing and drawing at a temperature ranging from 200in to 350il for a period of between 10 min and 2 hours in a neutral atmosphere.

 According to yet another advantageous characteristic, said spinning is practiced in hydrostatic or semi-hydrostatic mode.

 According to a variant, the front end of said billet is completely or partially enclosed in the silver envelope.

 For a hydrostatic spinning mode, the front end of said billet is produced according to a frustoconical profile with an angle between 30 and 45X.

 For a semi-hydrostatic spinning mode, the front end of the aluminum ingot is produced with a curvilinear profile and the rear end of said billet is closed with an aluminum plug.

 In the case where the envelope is formed of a silver sheath, the latter is previously expanded by heating before introduction of the aluminum ingot and then cooling causes a shrinking of said envelope which tightens on contact with the ingot.

 Billet spinning operations are carried out in hydrostatic or semi-hydrostatic mode because the dimensional ratio between the thickness of the silver envelope and the aluminum ingot is very low (from 1/100 to 1 / 300). The thickness of the silver envelope of the billet in the form of a sheath or a simple coating is determined according to the thickness of the coating and the diameter desired for the final product. This mode is particularly easy to implement and is well suited to a heterogeneous billet in which several different metallic constituents are present insofar as large rheological flows are required.

 According to yet other characteristics, the drawing of the spun bimetallic bar is carried out in at least three passes with a work hardening rate of between 5% and 90% and the wire drawing is done in slip in several passes with a rate of '' pass work hardening between 10% and 20%. The hardening rate is defined by the ratio of the difference between the initial section and the final section over the initial section.

 Preferably, a heat treatment of the spun bar is carried out every three passes in drawing and every twenty passes in drawing.

 The process of the invention makes it possible, for the same final conductor, to produce at a rate of about a thousand times higher than that of the electrolytic process, the only step which limits the speed of manufacture being that of the wire drawing. Under these conditions, it becomes possible to envisage mass industrial production. The spinning step creates a weld between pure silver and aluminum on the spun bar which therefore has intermetallic connections strong enough for the latter to be able to withstand mechanical and thermal treatments during the subsequent stages of drawing and drawing without changing the quality of the silver coating. As a result, the conductive wire of silver aluminum produced has good mechanical and thermal properties and, in particular, good suitability for drawing and drawing as well as good heat resistance.

The invention will be better understood on reading the following examples of implementation, accompanied by the drawings in which:
- Figures 1, 3, 4 show views in longitudinal section of different billets produced according to the method of the invention
- Figures 2a and 2b show micrographs produced from metallographic examination respectively of a spun bar and a drawn wire according to the method of the invention; and,
- Figure 5 is a schematic representation of the method of the invention.

Example 1
A billet B, the geometry of which is shown in Figure 1, is prepared (step I - Fig. 5) by assembling an aluminum ingot 1 of 63 mm in diameter and 168 mm in length and an envelope 2 in the form of a pure silver sheath 1 mm thick with a closed frustoconical end 2a of angle 45-.

 The spinning (II) is carried out in hydrostatic mode at room temperature (26il) using a container C of 75 mm in diameter and a lubricating oil of MOBIL brand reference Vacmul 450. The spinning ratio and the spinning speed are respectively 13.5 and 0.72 m / min.

 The metallographic examination carried out on the spun bar BF, the micrograph of which with a magnification of 50 times is found in FIG. 2a, shows that a) the Ag / Al interface is of perfect adhesion, b) the thickness of the silver coating conforms well and regularly along the periphery of the aluminum substrate, which constitutes an important guarantee for the success of the subsequent operations of drawing III, and of thermal annealing V.

 The 19.5 mm diameter BF spun bar is then drawn on a cold drawing bench E in six passes with a work hardening rate of 30% then in six other passes with a work hardening rate of 28 % per pass to become a 2.5 mm diameter F wire. The lubrication of the stretching is done with an oil of the CONDAT brand, Vicafil reference TF 386. The wire F is then reduced in its turn in 45 passes by conventional wire drawing IV with slip with a work hardening rate of 15% per pass, into a fine wire f of 0.1 mm in diameter.

The micrograph carried out with a magnification of 200 times during the metallographic examination of the intermediate wire of diameter 7 mm is found in Figure 2b and shows the same properties as in Figure 2a. A first heat treatment Va at 300C for 30 minutes under a nitrogen atmosphere was carried out before the stretching III and wire drawing operations IV and another Vb, at the same temperature is carried out for 15 min during these operations, all the 3 passes in drawing and every 20 passes in drawing. The thickness of Ag, which was 1 mm on the starting billet before spinning, fell to 1.5 μm on the fine wire produced by the process.

Ibis example
The same operations as in Example 1 were carried out on a billet B similar to that of Example 1, but the spinning ratio is 52, which leads to a bimetallic bar spun BF 9 mm in diameter, which was then stretched in 12 passes at a work hardening rate of 15% and then drawn in the same way as in Example 1. Metallographic results similar to those of Example 1 were obtained on the spun bar BF and the drawn wire.

Example luter
The same operations as in Example 1 were carried out on a billet B similar to that of Example 1, but the spinning speed is 1.5 m / min. Metallographic results similar to those of Example 1 were obtained on the spun bar BF and the drawn wire.

Example 2
The same operations as in the ibis example were carried out on a billet B produced in the same way as in Example 1 (FIG. 1) but with a frustoconical end angle 2a of 30 instead of 45. Metallographic results similar to those of Example 1 were obtained on the spun bar BF which was then drawn and drawn to the diameter of 0.12 mm with a thickness of final Ag of 1.8 Fm.

Example 3
The same operations as in Example 2 were carried out on a billet produced in the same way as in Example 2 but with a semi-closed frustoconical front end 2b as shown in Figure 3. Metallographic results similar to those presented in Example 1 were obtained on the spun bar BF which was then drawn and drawn to the diameter of 0.12 mm with a final thickness of Ag of 1.8 Zm.

Example 4
The same operations are carried out as in Example 1 except that the spinning II is carried out in semi hydrostatic mode.

B billet B consists of the assembly of an Al ingot 1 of 71.9 mm in diameter and 155 mm in length, of an Ag envelope 2 in the form of a sheath of 71.9 mm of inner diameter and 0.8 mm thick and a 3 Al rear plug 73.5 mm in diameter and 20 mm in height. The assembly being shown in Figure 4 where the front end 10 of the ingot 1 is not sheathed. Metallographic results similar to those presented in Example 1 were obtained on the spun bar BF which was then drawn and drawn to the diameter of 0.1 mm with a final thickness of Ag of 1.1 cru.

Example 5
The same operations as in Example 4 were carried out on a billet B consisting of the assembly of an ingot 1 of Al 71.1 mm in diameter and 155 mm in length, a sheath 2 in Ag internal diameter 71.1 mm and 1.2 mm thick and a rear cap 3 made of aluminum 73.5 mm thick and 20 mm high.

Metallographic results similar to those presented in Example 1 were obtained on the spun bar BF which was then drawn and drawn to the diameter of 0.1 mm with a final thickness of Ag of 1.6 Zm.

Claims (13)

 1. A method of manufacturing a conductor comprising an at least partially aluminum-based substrate and coated with a silver layer, characterized in that a cylindrical billet is first formed, then said billet is practiced a spinning operation to obtain a bimetallic bar of diameter varying from 5 to 20 mm, then the section of this bar is reduced by drawing and then drawing by carrying out intermediate heat treatments to produce a fine wire whose diameter is between 0, 08 mm and 0.5 mm with a silver coating of thickness ranging from 1 to 2 Fm.  2 Method according to claim 1, characterized in that said billet is prepared by introducing an aluminum ingot with minimum clearance in an envelope made of a silver sheath previously expanded by heating to a temperature between 2000C and 5000C for a period ranging from 5 to 30 minutes.  3. Method according to claim 1, characterized in that said billet is prepared by producing the envelope in the form of a silver coating obtained by electrolytic means.  4. Method according to one of the preceding claims, characterized in that the spinning operation is carried out at a temperature between 0 and 200in with a ratio between 5 and 100 and a speed of 0.1 to 2m / min.  5. Method according to one of the preceding claims, characterized in that the intermediate heat treatments are carried out before and during drawing and drawing at a temperature ranging from 2000 ° C. to 350 ° C. for a period of between 10 min and 2 hours under neutral atmosphere.  6. Method according to one of the preceding claims, characterized in that completely or partially encloses the front end of said billet in the silver envelope.  7. Method according to one of the preceding claims, characterized in that said spinning is carried out in hydrostatic or semi-hydrostatic mode.  8. Method according to claim 7, characterized in that for a hydrostatic spinning mode, the front end of said billet is produced according to a frustoconical profile with an angle between 30 and 45W.  9. Method according to claim 7, characterized in that for a semi-hydrostatic spinning mode is carried out the front end of the aluminum ingot with a curvilinear profile and the rear end of said billet is closed with a plug aluminum.  10. Method according to one of the preceding claims, characterized in that the spinning is carried out at room temperature.  11. Method according to one of the preceding claims, characterized in that the drawing of the spun bimetallic bar is carried out in at least three passes with a hardening rate per pass of between 5% and 90%.  12. Method according to one of the preceding claims, characterized in that the drawing is done by sliding in several passes with a work hardening rate per pass of between 10% and 20%.  13. Method according to claims 5, 11 and 12, characterized in that a heat treatment of the spun bar is carried out every three passes in drawing and every twenty passes in drawing.