EP0408469B1 - Copper-iron-cobalt-titanium alloy featuring high mechanical and electrical properties and process for the manufacture thereof - Google Patents

Description

The present invention relates to a copper-iron-cobalt-titanium alloy, its process for manufacturing it, as well as its field of use.
The electrical interconnection is evolving rapidly. Whether in the field of electronics (component support grids, contacts), or in the field of connectors (clips, lugs, connectors), the size of the parts carrying the electric current is constantly decreasing. On the other hand, the complexity of the form of these contacts is only increasing.
The manufacturer of copper alloys and semi-finished products is therefore subject to the following challenge: increase the electrical and thermal conductivity of traditional alloys to limit the heating of connectors and maintain or improve the level of mechanical properties. The improvement of these mechanical properties must obviously include the ability of the alloy to be deformed in the directions parallel and perpendicular to the rolling direction.

For connectors, bronzes of 4 to 9% tin are generally used which have excellent mechanical properties and a deformability adapted to this type of application. However, their electrical conductivity, which varies from 12 to 20% IACS, is insufficient because it limits the miniaturization of the connectors because of the heating problem.
For electronics, for example in the field of support grids, copper-iron alloys (C19400) are generally used which have a conductivity of 65% IACS. However, the compromise between mechanical properties and softening resistance means that these alloys cannot be used when the encapsulation temperatures are too high and exceed 400 ° C.
Unless otherwise stated, all the alloy compositions of this patent application are in percentage by weight.
A ternary copper alloy with 2% nickel and 0.5% silicon has been known for a long time which has good mechanical properties (mechanical resistance 600 MPa); however, such an alloy has an electrical conductivity limited to 60% IACS because of the solubility of the Ni₂Si precipitate.

Furthermore, US Pat. No. 4,559,200 shows the improvements brought about by small additions of magnesium or nickel to a CuFeTi alloy.
More recently, a copper-iron-cobalt-titanium alloy described in Polish patent No. 115185 has been proposed covering a wide range of compositions. These alloys can reach 85% IACS conductivity for a tensile strength of 440 MPa. However, these properties to be achieved require two heat treatments.

Until now, therefore, it has not been known how to economically manufacture an alloy having both high mechanical characteristics, typically a mechanical resistance greater than 500 MPa and a high conductivity greater than 80% IACS.

• 1) la composition de l'alliage satisfait aux conditions suivantes (composition pondérale):
  • rapport Co/Fe compris entre 0,10 et 0,90
  • rapport Ti/(Fe+Co) compris entre 0,30 et 1
  • teneur en fer comprise entre 0,030 et 2%
  • teneur en cobalt comprise entre 0,025 et 1,8%
  • teneur en titane comprise entre 0,025 et 4%
  • teneur en oxygène inférieure à 50 ppm
  • teneur totale en autres additions éventuelles inférieure à 1,5%
  • teneur en impuretés métalliques inférieure à 0,1% avec chacune d'elle inférieure à 0,015%
  • reste cuivre
• 2) le bain de l'alliage liquide est désoxydé au bore
• 3) le traitement thermique de précipitation est réalisé à une température inférieure, d'au plus 80°C, à la température TM du traitement de précipitation conduisant à la conductivité maximum.

The subject of the invention is a copper alloy with high mechanical resistance, clearly greater than 500 MPa, with conductivity greater than 80% IACS and having, in addition to good resistance to softening, a low manufacturing cost.
According to the invention, obtaining these high performances results from the use of three types of means located at different stages of the process for the production of the alloy and of the semi-products produced from this alloy: these are: means concerning the composition of the alloy, the deoxidation of the bath of the liquid alloy which makes it possible to avoid manufacturing under vacuum and the precipitation temperature during the forming of the alloy.
More specifically, the method according to the invention is characterized in that:

• 1) the composition of the alloy satisfies the following conditions (weight composition):
  • Co / Fe ratio between 0.10 and 0.90
  • Ti / (Fe + Co) ratio between 0.30 and 1
  • iron content between 0.030 and 2%
  • cobalt content between 0.025 and 1.8%
  • titanium content between 0.025 and 4%
  • oxygen content below 50 ppm
  • total content of any other additions less than 1.5%
  • content of metallic impurities less than 0.1% with each of them less than 0.015%
  • rest copper
• 2) the bath of the liquid alloy is deoxidized with boron
• 3) the thermal precipitation treatment is carried out at a temperature lower, at most 80 ° C, than the temperature TM of the precipitation treatment leading to maximum conductivity.

These three means will be detailed and located in relation to the prior art.
By studying the properties of Cu Fe Co Ti alloys of the prior art, the applicant observed that the electrical conductivity varied considerably as a function of the Ti / (Fe + Co) ratio and especially erratically as shown in FIG. 1 of l example 1, which therefore does not make it possible to select Cu Fe Co Ti alloys with high electrical performance although the Ti / (Fe + Co) ratio is respected, which translates the stoichiometry of the possible precipitates (FeTi, Fe₂Ti, Co Ti , Co₂Ti).

Continuing the analysis of the performance of these alloys, the Applicant was surprised to note that the Co / Fe ratio had a great influence on the electrical conductivity of these alloys. Figure 2 of Example 1 shows that this ratio is highly significant for expressing the variability of the electrical conductivity. In the field where Co / Fe is between 0.1 and 0.9 and more particularly between 0.15 and 0.45 the electrical conductivity is particularly high. It should be noted that the electrical conductivity values of Example 1 are to be considered in a relative and not absolute manner, these tests being selection tests in the laboratory, which do not necessarily reproduce exactly all the means that can be used industrially, which influences on absolute conductivity values.

Preferably, the compositions of iron, cobalt, titanium are respectively between 0.1 and 1%, between 0.05 and 0.4 and between 0.035 and 0.6%, as for the residual oxygen content it is preferably less than 20 ppm.

It is the precipitation of a well defined compound rich in iron and titanium with cobalt which gives the alloy its exceptional properties: mechanical resistance, conductivity, formability.

Obtaining high-performance alloys requires deoxidation of the bath of the liquid alloy, in particular to have control over the composition of the bath and to prevent the addition elements, titanium in particular, from playing the role of deoxidation and are not eliminated.

The composition is also well controlled by preparation under vacuum, the oxygen content then being very low, generally less than 0.0005%. But due to the high cost, the Applicant preferred a conventional fusion, with deoxidation of the bath.
The Applicant has thus carried out semi-industrial tests with deoxidation of the Cu Fe Co Ti alloy bath of composition according to the invention. She observed that phosphorus, a deoxidizing agent often used in the prior art, did not lead to a very efficient alloy, so she studied and compared several deoxidizing agents (see example 2): phosphorus, magnesium and boron. The Applicant has surprisingly found that boron leads to more efficient alloys than those obtained with phosphorus or magnesium although the latter is, on the basis of thermodynamic data, the most powerful deoxidizing agent of the three. In fact, it can be seen that, on the one hand, boron makes it possible to obtain a bath of low residual oxygen content, and, on the other hand, the boron oxide formed is easily removed from the bath, unlike the other oxides, which, among other consequences, avoids the hard spots of the alloy during cutting at high speed, and finally that the residual boron content in the alloy is very low, generally less than 0.0005%, (but nevertheless detectable); the consequence is a high level of conductivity and a relatively low temperature TM, TM being the temperature of the precipitation treatment which leads to the maximum conductivity (see FIG. 3 of Example 2); finally, note the greater fineness of dispersion of the precipitates in the case of deoxidation with boron.
The precipitation treatment is part of the transformation phase of the alloy which, after the casting of the alloy, includes its homogenization between 800 ° C and 1000 ° C for a time between 0.1 and 10 hours, its hot rolling up to 650 ° C followed by a possible quenching which can vary from 20 ° C / min to 2000 ° C / min , its cold rolling with one or more intermediate anneals; however, the excellent cold deformability of the alloy according to the invention generally allows it to be shaped with only a thermal precipitation treatment, which constitutes an economic range.
The properties of the semi-finished products obtained, whether electrical conductivity or mechanical characteristics, also depend on the transformation phase and in particular on the thermal precipitation treatment.
With regard to the conductivity, FIG. 3 of Example 2 shows that the conductivity passes through a maximum for a precipitation temperature TM (TM = 515 ° C for test C) and that this maximum has a flat shape: conductivity remains high for a wide temperature range, between 475 and 550 ° C for test C and in this area, the slope of the curve giving the conductivity as a function of temperature is low and less than 0.2% IACS / ° C.

The Applicant has observed that, contrary to what one might suppose, it is advantageous to subject the alloy according to the invention to a precipitation treatment at a temperature below TM: in this case there, for a minimal loss in conductivity electrical mechanical characteristics increase very significantly.
Thus, the comparison of examples 2 and 3 (tests C and C ') shows that the conductivity goes from 83.5 to 83% IACS (-1%) while the mechanical resistance goes from 488 MPa to 525 MPa (+ 7, 6%).
By temperature below TM, we mean any temperature corresponding to the desired conductivity level (> 80% IACS); the graphical determination (see Figure 3) is immediate: the intersection of the 80% IACS ordinate line with curve C determines the minimum temperature Tm.
According to the invention, the precipitation treatment takes place at a temperature between TM and Tm and preferably close to Tm to obtain "balanced" properties according to the invention:% IACS> 80 and Rm> 500 MPa. In general, Tm will be, at most, 80 ° C lower than TM; another method to define Tm is to consider the slope of the% IACS curve as a function of the temperature: Tm corresponds to the temperature where the slope begins to increase appreciably and reaches for example the value of 0.3% IACS / ° C. The slope change area is preferred.

Example 3 clearly shows that only the alloy according to the invention (test C ′) exhibits high properties both in conductivity and mechanical properties, but it is however necessary to note the advantage of this type of treatment for greatly increasing the characteristics. mechanics of other alloys (tests A 'and B') when average conductivities (around 70% IACS) are sufficient.

More generally, a precipitation treatment "at low temperature", between 350 ° and 550 ° C will give maximum mechanical resistance (tests A 'and B') while a treatment at "high temperature" between 450 ° and 650 ° C will rather lead to maximum conductivity, the common domain between 450 ° and 550 ° being that in which the mechanical and conductivity properties are "balanced".

précis, le choix particulier d'un agent de désoxydation et d'une plage de température pour le traitement de précipitation, permet d'obtenir à la fois une conductivité électrique et une résistance mécanique élevées. L'exemple 4 illustre bien les propriétés "classiques" des alliages de l'art antérieur : quand ils ont une conductivité électrique élevée leur résistance mécanique est faible et réciproquement. Il montre clairement les performances avantageuses du produit obtenu selon l'invention.
Comme déjà mentionné, la gamme d'élaboration des alliages selon l'invention est particulièrement économique car des taux d'écrouissage élevés peuvent être atteints avec un seul traitement thermique: le traitement thermique de précipitation.The duration of the precipitation treatments varies according to the technology used: from 1 hour to 10 hours in a static oven and from 10 seconds to 30 minutes in a passing oven.
From the alloy according to the invention, it is possible to reinforce the mechanical properties by adding elements such as aluminum, tin, zinc, nickel, silver, chromium to the basic composition. , beryllium, rare earths. The total sum of these elements must be less than 1.5% if one wants to keep sufficient conductivity: these additions of elements generally reducing the electrical conductivity constitute only a secondary form of the invention.
The invention shows that only the combination of particular means that are the composition of the alloy with a ratio $$\frac{\text{Co}}{\text{Fe}}$$

precise, the particular choice of a deoxidizing agent and a temperature range for the precipitation treatment, makes it possible to obtain both a high electrical conductivity and a high mechanical resistance. Example 4 illustrates well the "classic" properties of alloys of the prior art: when they have a high electrical conductivity their mechanical resistance is low and vice versa. It clearly shows the advantageous performances of the product obtained according to the invention.
As already mentioned, the range of production of the alloys according to the invention is particularly economical since high work hardening rates can be achieved with a single heat treatment: the precipitation heat treatment.

The alloys of the invention are suitable for applications requiring simultaneously high conductivity and mechanical resistance, they are recommended for the manufacture of conductive elements for electronics and in connection and in particular for applications such as leadframes, springs contact, connections.

DESCRIPTION OF FIGURES AND EXAMPLES

FIG. 1 illustrates, on a diagram having the ratio Ti / (Fe + Co) on the abscissa and the electrical conductivity in% IACS on the ordinate, the results obtained for the 7 tests denoted R1 to R7, described in Example 1.

FIG. 2 illustrates, on a diagram having the Co / Fe ratio on the abscissa and the electrical conductivity in% IACS on the ordinate, the results obtained for the 7 tests, denoted R1 to R7, described in Example 1, which allow the plotting of a curve.

FIG. 3 illustrates, on a diagram having the temperature in ° C on the abscissa and the electrical conductivity in% IACS on the ordinate, the variations in electrical conductivity as a function of the precipitation treatment temperature for each of the three deoxidizing agents studied in Example 2 magnesium (curve A), phosphorus (curve B), boron (curve C).

FIG. 4 illustrates, on a diagram having on the abscissa the mechanical resistance in MPa, and on the order of the electrical conductivity in% IACS, the performances of the alloy obtained according to the invention (C '), according to Polish patent n ° 115185 , (D and F) and according to American patent n ° 4559200 (E), as indicated in example 4. The zone (III) where the alloy obtained according to the invention is found is that of the alloys having at the same time mechanical characteristics and electrical conductivity high.

EXAMPLE 1

In this example, we study the influence of the composition of the alloy on the electrical conductivity.

Seven Cu Fe Co Ti alloys, referenced from R1 to R7, were developed in the laboratory, by fusion of pure elements (Cu C2, electrolytic Fe, electrolytic Co, Ti 140 supplied by CEZUS), in a boron nitride crucible heated to induction oven. The fusion was carried out under argon, at atmospheric pressure. These laboratory conditions make it possible to develop Cu Fe Co Ti alloys without it being necessary to deoxidize the bath, so as to obtain results essentially dependent on the composition of the alloy.

Table 1 shows the composition of these alloys

• a) d'homogénéisation: les échantillons bruts de coulée, enveloppés dans une feuille de molybdène, sont enfermés dans une ampoule à quartz sous vide. L'ampoule est ensuite placée au coeur d'un bloc d'acier chauffé par un four à résistance à la température de traitement, à 920°C. Après deux heures de maintien à cette température, l'ampoule est brisée dans une cuve d'eau.
• b) d'écrouissage: les alliages sont laminés à froid après le traitement d'homogénéisation. Ce taux d'écrouissage appliqué est d'environ 80%, soit une épaisseur finale de bande de 0,5 mm, obtenue en une dizaine de passes successives.
• c) de précipitation: les échantillons sont chauffés dans un four à résistance sous pression atmosphérique d'argon dans les conditions suivantes: chauffage depuis la température ambiante jusqu'à 200°C, palier d'une heure à cette température, montée de 200° à la température de précipitation à 200°C/heure, maintien pendant 1 heure à la température de précipitation, puis refroidissement à 400°C/heure.

The liquid metal is poured into a water-cooled copper ingot mold. The ingot mold allows the casting of billets of approximately 16 mm in diameter for 100 mm in height, approximately a load of 180 g.
Parallelepipedic samples of 3 x 3 x 50 mm are then cut from the ingots. It is on these bars that the various thermal and mechanical treatments are carried out:

• a) homogenization: the raw casting samples, wrapped in a molybdenum sheet, are enclosed in a quartz vacuum interrupter. The bulb is then placed in the heart of a block of steel heated by an oven with resistance to the processing temperature, at 920 ° C. After two hours of maintaining at this temperature, the bulb is broken in a tank of water.
• b) work hardening: the alloys are cold rolled after the homogenization treatment. This applied work hardening rate is around 80%, ie a final strip thickness of 0.5 mm, obtained in ten successive passes.
• c) precipitation: the samples are heated in a resistance furnace under atmospheric pressure of argon under the following conditions: heating from ambient temperature to 200 ° C., one hour plateau at this temperature, rise by 200 ° at the precipitation temperature at 200 ° C / hour, holding for 1 hour at the precipitation temperature, then cooling to 400 ° C / hour.

Table 2 which follows indicates the conductivity of each alloy expressed in% IACS measured at room temperature, as a function of the precipitation temperature:

) permet, comme le montre la figure 2, de sélectionner les alliages à conductivité élevée quand ce rapport $$\frac{\text{Co}}{\text{Fe}}$$

est compris entre 0,1 et 0,9 et de préférence quand il est compris entre 0,15 et 0,45.Table 2 shows that the maximum conductivity values, expressed in% IACS and underlined in this table, are obtained for a precipitation temperature close to 560 ° C and that these maximum values are very dispersed.
The analysis of these results according to the criterion of the prior art (Ti / (Fe + Co) ratio of Polish patent n ° 115185) shows that, on the one hand in the range 0.25 - 1 for Ti / (Fe + Co) claimed for this report, the conductivity varies a lot for similar values (comparison of tests R1, R2, R3, R4 between them and tests R5, R6, R7 between them) and that, on the other hand this ratio Ti / (Fe + Co) does not make it possible to determine the favorable domain of high conductivities since the 7 representative points do not make it possible to draw a curve having an indisputable maximum (see FIG. 1).
However, the analysis of these results according to the criterion found by the applicant (the report $$\frac{\text{Co}}{\text{Fe}}$$

) allows, as shown in Figure 2, to select alloys with high conductivity when this ratio $$\frac{\text{Co}}{\text{Fe}}$$

is between 0.1 and 0.9 and preferably when it is between 0.15 and 0.45.

EXAMPLE 2

voisin et différent par le choix de l'agent de désoxydation: le magnésium (essais A), le phosphore (essais B), le bore (essais C).
Ces trois agents de désoxydation sont introduits dans le bain liquide de façon à neutraliser la même quantité d'oxygène. $$\text{Mg + 1/2 O₂ → Mg O}$$

$$\text{2/3 B + 1/2 O₂ → 1/3B₂O₃}$$

$$\text{2/5P + 1/2 O₂ → 1/5 P₂O₅}$$

Compte tenu des masses atomiques du magnésium, du phosphore et du bore et si l'on se base sur une quantité de 0,06% de Mg alors il faut 0,03% de P et 0,018% de B pour neutraliser la même quantité d'oxygène. Dans un four à induction de 10 kg de capacité utile, on fait fondre à 1250°C dans un creuset en graphite, le cuivre, le fer, le cobalt, ces deux derniers étant sous forme d'alliages mère. On ajoute ensuite le bore ou le phosphore ou le magnésium et le titane également sous forme d'alliage mère puis on procède à un dégazage. Le tableau 3 indique la composition de la charge pour chaque essai:

In this example, we study, under conditions close to industrial conditions, the influence of the deoxidation mode of the bath by realizing three related trials $$\frac{\text{Co}}{\text{Fe}}$$

neighboring and different by the choice of the deoxidizing agent: magnesium (tests A), phosphorus (tests B), boron (tests C).
These three deoxidizing agents are introduced into the liquid bath so as to neutralize the same amount of oxygen. $$\text{Mg + 1/2 O₂ → <figure-callout id="2" label="Mg O" filenames="imgf0001.png" state="{{state}}">Mg O</figure-callout>}$$

$$\text{2/3 B + 1/2 O₂ → 1 / <figure-callout id="2" label="3B2O3" filenames="imgf0001.png" state="{{state}}">3B₂O₃</figure-callout>}$$

$$\text{2 / 5P + 1/2 O₂ → 1/5 P₂O₅}$$

Taking into account the atomic masses of magnesium, phosphorus and boron and if one bases oneself on an amount of 0.06% of Mg then one needs 0.03% of P and 0.018% of B to neutralize the same amount of 'oxygen. In an induction furnace with a useful capacity of 10 kg, copper, iron, cobalt are melted at 1250 ° C in a graphite crucible, the latter two being in the form of master alloys. Next, boron or phosphorus or magnesium and titanium are also added in the form of a parent alloy, followed by degassing. Table 3 shows the composition of the load for each test:

essai A

575°C

essai B

535°C

essai C

515°C

Ce traitement thermique est suivi d'un laminage final avec réduction d'épaisseur de 44%.
On obtient des alliages présentant les caractéristiques suivantes:

et les propriétés mécaniques et propriétés de conductivité suivantes:

During all these operations, the bath is covered with charcoal. We pour at around 1200 ° C. The plates are then homogenized at 920 ° C for two hours and then hot rolled in several passes. After the last pass, they are soaked in water at around 700 ° C. After milling to 9 mm, the plates are cold rolled without intermediate annealing until strips of 0.8 mm thick are obtained. The alloys are then subjected to a precipitation treatment for 4 hours at the temperature TM below, between 500 ° C and 600 ° C, leading to the optimum conductivity (see Figure 3):

test A

575 ° C

test B

535 ° C

test C

515 ° C

This heat treatment is followed by a final rolling with thickness reduction of 44%.
Alloys are obtained having the following characteristics:

and the following mechanical properties and conductivity properties:

EXAMPLE 3

This example illustrates a modality of the shaping of alloys produced in all points as in example 2 (test A 'of example 3 corresponds to test A of example 2, likewise for B 'and C')), except that the precipitation treatment takes place at a lower temperature (505 ° C for A ', 485 ° C for B', 475 ° C for C ') for 4 hours and the final rolling corresponds at a thickness reduction of 29%:
The following properties are obtained:

These alloys exhibit a hardness greater than 130 HV after 30 minutes at 450 ° C., which illustrates their excellent resistance to softening.

EXAMPLE 4

essai C'

: exemple 3

essai D

: selon brevet polonais n° 115185

essai E

: selon brevet américain n° 4 559 200

This example compares the invention to the prior art for a transformation range comprising only one heat treatment (precipitation annealing):

test C '

: example 3

test D

: according to Polish patent n ° 115185

test E

: according to US Patent No. 4,559,200

FIG. 4 situates these tests in a plane having the mechanical resistance on the abscissa and the electrical conductivity on the ordinate and clearly illustrates the advantage of the invention.
The non-comparative test F is given for information: it corresponds to test D but with a transformation range comprising two heat treatments instead of one.

Claims (11)

1. Process for the production of a Cu-Fe-Co-Ti alloy incorporating a phase of producing the alloy and an alloy transformation phase with a precipitation heat treatment, characterized in that:

   a) an alloy is prepared, whose composition satisfies the following conditions (weight compositions):
   Co/Fe ratio between 0.10 and 0.90
   Ti/(Fe+Co) ratio between 0.30 and 1
   iron content between 0.030 and 2%
   cobalt content between 0.025 and 1.8%
   titanium content between 0.025 and 4%
   oxygen content below 50 ppm
   total content of other optional additions below 1.5%
   content of metallic impurities below 0.1% with each of them below 0.015%, the residue being copper;

   b) the molten alloy bath is deoxidized by introducing boron into it and eliminating the boron oxide formed;

   c) the cold drawn alloy undergoes a precipitation heat treatment at a temperature lower, by at the most 80°C, than the temperature TM leading to the maximum electrical conductivity.
2. Process according to claim 1, wherein the $$\frac{\text{Co}}{\text{Fe}}$$

   

   ratio is between 0.15 and 0.45.
3. Process according to claim 2, wherein the oxygen content is below 20 ppm.
4. Process according to claim 2, wherein the iron content is between 0.1 and 1%.
5. Process according to claim 2, wherein the cobalt content is between 0.05 and 0.4%.
6. Process according to claim 2, wherein the titanium content is between 0.035 and 0.6%.
7. Process according to claim 2, wherein the titanium is introduced in mother alloy form following the introduction of the boron, so as to avoid titanium losses and obviate melting and vacuum casting.
8. Process according to claim 2, wherein the precipitation heat treatment is carried out at a temperature, below the temperature TM, for which the gradient of the conductivity curve in % IACS as a function of the temperature is between 0.1 and 0.3%IACS/°C.
9. Alloy obtained according to any one of the claims 1 to 8.
10. Alloy according to claim 9, characterized in that it contains less than 10 ppm boron.
11. Application of the alloy according to any one of the claims 9 and 10 to the production of conductor elements for electronics and the connector industry and in particular component support grids, contact springs and connections.

Images