Werkstoffe auf Gold-Basis

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Reines Gold ist neben Platin das chemisch beständigste aller Edelmetalle. Gold in unlegierter Form ist für die Verwendung als Kontaktwerkstoff in elektromechanischen Bauelementen aufgrund seiner Neigung zum Kleben und Kaltschweißen auch bei kleinen Kontaktkräften weniger gut geeignet. Außerdem ist Feingold nicht ausreichend mechanisch verschleißfest und widerstandsfähig bei elektrischer Belastung (Table 4). Daher beschränkt sich sein Einsatz meist auf dünne, galvanisch oder vakuumtechnisch aufgebrachte Schichten.

In der Praxis werden daher üblicherweise schmelztechnisch hergestellte Gold- Legierungen eingesetzt. Der Schmelzvorgang erfolgt dabei je nach Legierungskomponente in reduzierender Atmosphäre oder im Vakuum. Die Wahl der Legierungszusätze hängt wesentlich von der Anwendung der Werkstoffe ab. Aus der breiten Palette von Gold-Legierungen sind die binären Legierungen mit Zusätzen < 10 Massen-% an Edelmetallen wie Pt, Pd oder Ag bzw. Unedelmetallen wie Ni, Co, Cu hervorzuheben (Table 2). Diese Zusätze erhöhen einerseits die mechanische Festigkeit und wirken sich vorteilhaft auf das Schaltverhalten aus, verringern andererseits je nach Legierungspartner mehr oder weniger stark die elektrische Leitfähigkeit und die Korrosionsbeständigkeit (Figure 1).

Vor allem unter dem Aspekt der Goldeinsparung sind die ternären Legierungen mit Goldgehalten von ca. 70 Massen-% und Zusätzen von Ag und Cu bzw. Ag und Ni, z.B. AuAg25Cu5 oder AuAg20Cu10 zu sehen, die für viele Anwendungsfälle bei guten mechanischen Eigenschaften ausreichende Beständigkeit gegenüber Fremdschichtbildung bieten (Table 3). Weitere ternäre Legierungen, die aus dem AuAg-System hervorgehen, sind die Werkstoffe AuAg26Ni3 und AuAg25Pt6. Diese Legierungen ähneln in ihren mechanischen Eigenschaften den AuAgCu-Legierungen, sind aber bei höheren Temperaturen deutlich oxidationsbeständiger.

Table 1: Überblick über die gebräuchlichsten Gold-Qualitäten

Bezeichnung

Zusammensetzung Au

(Mindestanteil)

Beimengungen in ppm/p>

Hinweise für die Verwendung

Spektralreines Gold

Gold

99.999

Cu < 3

Ag < 3

Ca < 1

Mg <1

Fe < 1

Drähte, Bleche, Legierungszusätze für Halbleiter, elektronische Bauelemente

Hochreines Gold

99.995

Cu < 10

Ag < 15

Ca < 20

Mg < 10

Fe < 3

Si < 10

Pb < 20

Granalien für hochreine Legierungen, Bleche, Bänder, Rohre, Profile

Barren-Gold

99.95

Cu < 100

Ag < 150

Ca < 50

Mg < 50

Fe < 30

Si < 10

Legierungen, übliche Qualität

Table 2: Physikalische Eigenschaften von Gold und Goldlegierungen
Figure 1: Einfluss von 1-10 Atom-% verschiedener Zusatzmetalle auf den spez. elektrischen Widerstand p von Gold (nach Linde)


Table 3: Festigkeitseigenschaften von Gold und Goldlegierungen
Werkstoff Festigkeitszustand Zugfestigkeit Rm [MPa] min. Dehnung A10 [%] min. Vickershärte HV
Au R 140
R 170
R 200
R 240
140
170
200
240
30
3
2
1
20
50
60
70
AuAg20 R 190
R 250
R 320
R 390
190
250
320
390
25
2
1
1
38
70
95
115
AuAg30 R 220
R 260
R 320
R 380
220
260
320
380
25
3
1
1
45
75
95
110
AuAg25Cu5 R 400
R 470
R 570
R 700
400
470
570
700
25
4
2
2
90
120
160
185
AuAg20Cu10 R 480
R 560
R 720
R 820
480
560
720
820
20
3
1
1
125
145
190
230
AuAg26Ni3 R 350
R 420
R 500
R 570
350
420
500
570
20
2
1
1
85
110
135
155
AuAg25Pt6 R 280
R 330
R 410
R 480
280
330
410
480
18
2
1
1
60
90
105
125
AuCo5 R 340
R 390
R 450
R 530
340
390
450
530
10
2
1
1
95
105
120
150
AuCo5 prec.hardened heterogeneous 360 3 110-130
AuNi5 R 380
R 450
R 560
R 640
380
450
560
640
25
3
2
1
115
135
160
190
AuPt10 R 260
R 310
R 370
R 410
260
310
370
410
20
2
1
1
80
90
100
105
AuCu14Pt9Ag4 R 620
R 700
R 850
R 950
prec.hardened
620
700
850
950
900
20
3
2
1
3
190
225
260
270
280

Other ternary alloys based on the AuAg system are AuAg26Ni3 and AuAg25Pt6. These alloys are mechanically similar to the AuAgCu alloys but have significantly higher oxidation resistance at elevated temperatures Table 4.

Table 4: Contact and Switching Properties of Gold and Gold Alloys

Material

Properties

Au

Highest corrosion resistance, low

hardness

High electr. conductivity,

strong tendency to cold welding

AuAg8

High corrosion resistance, low thermo

e.m.f.

Low contact resistance

AuPt10

AuPd5

Very high corrosion resistance

High hardness

AuAg10 - 30

Mostly corrosion resistant

Higher hardness

AuNi5

AuCo5

High corrosion resistance, low

tendency to material transfer

High hardness

AuAg25Pt6

High corrosion resistance, low contact resistance

High hardness

AuAg26Ni3

AuAg25Cu5

AuAg20Cu10

Limited corrosion resistance

High hardness

AuPd40

AuPd35Ag10

AuCu14Pt9Ag4

High corrosion resistance

High hardness and mechanical

wear resistance

Caused by higher gold prices over the past years the development of alloys with further reduced gold content had a high priority. The starting point has been the AuPd system which has continuous solubility of the two components. Besides the binary alloy of AuPd40 and the ternary one AuPd35Ag9 other multiple component alloys were developed. These alloys typically have < 50 wt% Au and often can be solution hardened in order to obtain even higher hardness and tensile strength. They are mostly used in sliding contact applications.

Gold alloys are used in the form of welded wire or profile (also called weldtapes), segments, contact rivets, and stampings produced from clad strip materials. The selection of the bonding process is based on the cost for the joining process, and most importantly on the economical aspect of using the least possible amount of the expensive precious metal component.

Besides being used as switching contacts in relays and pushbuttons, gold alloys are also applied in the design of connectors as well as sliding contacts for potentiometers, sensors, slip rings, and brushes in miniature DC motors Table 5.

Table 5: Application Examples and Forms of Gold and Gold Alloys

Material

Application Examples

Form of Application

Pure Gold

(electroplated)

Corrosion protection layer for contact parts, stationary contacts, bonding surfaces

Electroplated coatings, bond surface layers

Hard Gold

(sputtered)

Contact parts for connectors and switches, sliding contact tracks, bonding surfaces

Electroplated coatings on contact rivets and stamped parts

Hard Gold

(sputtered)

Contacts in switches and relays for low loads, electronic signal relays

Contact surface layer on miniature

profiles (weld tapes)

AuAg8

Dry circuit switching contacts, electronic

signal relays

Contact rivets, welded contact

parts

AuAg20

Switching contacts for low loads, electronic

signal relays

Contact rivets, welded contact

parts

AuAg25Cu5

AuAg25Cu10

AuAg26Ni3

Contact parts for connectors, switches and relays

Claddings on Cu alloys, contact rivets, contact layer on micro profiles (weld tapes)

AuNi5

AuCo5 (heterogen)

Contacts in switches and relays for low and medium loads, material transfer resistant contacts

Contact rivets, welded contact parts, contact layer on miniature profiles (weld tapes)

AuPt10

AuAg25Pt6

Contacts for highest chemical corrosion resistance in switches and relays

Contact rivets, contact layer on micro profiles (weld tapes)

AuCu14Pt9Ag4

Sliding contacts for measurement data transfer

Wire-formed parts


Figure 2 Fig. 2.3: Phase diagram of goldplatinum


Figure 3 Fig. 2.4: Phase diagram of gold-silver


Figure 4 Fig. 2.5: Phase diagram of gold-copper


Figure 5 Fig. 2.6: Phase diagram of gold-nickel


Figure 6 Fig. 2.7: Phase diagram of gold-cobalt


Figure 7 Fig. 2.8: Strain hardening of Au by cold working


Figure 8 Fig. 2.9: Softening of Au after annealing for 0.5 hrs after 80% cold working


Figure 9 Fig. 2.10: Strain hardening of AuPt10 by cold working


Figure 10 Fig. 2.11: Strain hardening of AuAg20 by cold working


Figure 11 Fig. 2.12: Strain hardening of AuAg30 by cold working


Figure 12 Fig. 2.13: Strain hardening of AuNi5 by cold working


Figure 13 Fig. 2.14: Softening of AuNi5 after annealing for 0.5 hrs after 80% cold working


Figure 14 Fig. 2.15: Strain hardening of AuCo5 by cold working


Figure 15 Fig. 2.16: Precipitation hardening of AuCo5 at 400°C hardening temperature


Figure 16 Fig. 2.17: Strain hardening of AuAg25Pt6 by cold working


Figure 17 Fig. 2.18: Strain hardening of AuAg26Ni3 by cold working


Figure 18 Fig. 2.19: Softening of AuAg26Ni3 after annealing for 0.5 hrs after 80% cold working


Figure 19 Fig. 2.20: Strain hardening of AuAg25Cu5 by cold working


Figure 20 Fig. 2.21: Strain hardening of AuAg20Cu10 by cold working


Figure 21 Fig. 2.22: Softening of AuAg20Cu10 after annealing for 0.5 hrs after 80% cold working


Figure 22 Fig. 2.23: Strain hardening of AuCu14Pt9Ag4 by cold working


Figure 23 Fig. 2.24: Precipitation hardening of AuCu14Pt9Ag4 at different hardening temperatures after 50% cold working


Figure 2: Phase diagram of goldplatinum
Figure 3: Phase diagram of gold-silver
Figure 4: Phase diagram of gold-copper
Figure 5: Phase diagram of gold-nickel
Figure 6: Phase diagram of gold-cobalt
Figure 7: Strain hardening of Au by cold working
Figure 8: Softening of Au after annealing for 0.5 hrs after 80% cold working
Figure 9: Strain hardening of AuPt10 by cold working
Figure 10: Strain hardening of AuAg20 by cold working
Figure 11: Strain hardening of AuAg30 by cold working
Figure 12: Strain hardening of AuNi5 by cold working
Figure 13: Softening of AuNi5 after annealing for 0.5 hrs after 80% cold working
Figure 14: Strain hardening of AuCo5 by cold working
Figure 15: Precipitation hardening of AuCo5 at 400°C hardening temperature
Figure 16: Strain hardening of AuAg25Pt6 by cold working
Figure 17: Strain hardening of AuAg26Ni3 by cold working
Figure 18: Softening of AuAg26Ni3 after annealing for 0.5 hrs after 80% cold working
Figure 19: Strain hardening of AuAg25Cu5 by cold working
Figure 20: Strain hardening of AuAg20Cu10 by cold working
Figure 21: Softening of AuAg20Cu10 after annealing for 0.5 hrs after 80% cold working
Figure 22: Strain hardening of AuCu14Pt9Ag4 by cold working
Figure 23: Precipitation hardening of AuCu14Pt9Ag4 at different hardening temperatures after 50% cold working

Referenzen

Referenzen