Difference between revisions of "Gold Based Materials"

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Pure Gold is besides Platinum the chemically most stable of all precious metals. In its pure form it is not very suitable for use as a contact material in electromechanical devices because of its tendency to stick and cold-weld at even low contact forces. In addition it is not hard or strong enough to resist mechanical wear and exhibits high materials losses under electrical arcing loads. This limits its use in form of thin electroplated or vacuum deposited layers.
 
  
−
For most electrical contact applications gold alloys are used. Depending on the alloying metal the melting is performed either under in a reducing atmosphere or in a vacuum. The choice of alloying metals depends on the intended use of the resulting contact material. The binary Au alloys with typically <10 wt% of other precious metals such as Pt, Pd, or Ag or non-precious metals like Ni, Co, and Cu are the more commonly used ones ''(Table 2.2)''. On one hand these alloy additions improve the mechanical strength and electrical switching properties but on the other hand reduce the electrical conductivity and chemical corrosion resistance ''(Fig. 2.2)'' to varying degrees.
+
Pure Gold is besides Platinum the chemically most stable of all precious metals. In its pure form it is not very suitable for use as a contact material in electromechanical devices because of its tendency to stick and cold-weld at even low contact forces. In addition it is not hard or strong enough to resist mechanical wear and exhibits high material losses under electrical arcing loads (<xr id="tab:Contact_and_Switching_Properties_of_Gold_and_Gold_Alloys"/>)<!--(Tab. 2.4)-->. This limits its use in form of thin electroplated or vacuum deposited layers.
  
−
[[File:Physical Properties of Gold and Gold-Alloys.jpg|right|thumb|Physical Properties of Gold and Gold-Alloys]]
+
For most electrical contact applications, gold alloys are used. Depending on the alloying metal, the melting is performed either under a reducing atmosphere or in a vacuum. The choice of alloying metals depends on the intended use of the resulting contact material. The binary Au alloys with typically < 10 wt% of other precious metals such as Pt, Pd, Ag or non-precious metals like Ni, Co and Cu are the more commonly used ones (<xr id="tab:Physical Properties of Gold and Gold-Alloys"/>)<!--(Tab. 2.2)-->.
−
[[File:Influence of 1-10 atomic of different.jpg|right|thumb|Influence of 1-10 atomic% of different alloying metals on the electrical resistivity of gold (according to J. O. Linde)]]
+
On one hand these alloy additions improve the mechanical strength and electrical switching properties but on the other hand reduce the electrical conductivity and chemical corrosion resistance (<xr id="fig:Influence_of_1_10_atomic_of_different"/>)<!--(Fig. 2.2)--> to varying degrees.
  
−
Under the aspect of reducing the gold content ternary alloys with a gold content of approximately 70 wt% and additions of Ag and Cu or Ag and Ni resp., for example AuAg25Cu5 or AuAg20Cu10 are used which exhibit for many applications good mechanical stability while at the same time have sufficient
+
Under the aspect of reducing the gold content, ternary alloys with a gold content of approximately 70 wt% and additions of Ag and Cu or Ag and Ni resp., for example AuAg25Cu5 or AuAg20Cu10 are used, which exhibit for many applications good mechanical stability, while at the same time have sufficient resistance against the formation of corrosion layers (<xr id="tab:Mechanical Properties of Gold and Gold-Alloys"/>)<!--(Table 2.3)-->.
−
resistance against the formation of corrosion layers ''(Table 2.3)''. 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 2.4)''.
 
  
−
Caused by higher gold prices over the past years the development of alloys with
+
<figtable id="tab:Commonly Used Grades of Gold">
−
further reduced gold content had a high priority. The starting point has been the
+
<caption>'''Commonly Used Grades of Gold<!--(2.1)-->'''</caption>
−
AuPd system which has continuous solubility of the two components. Besides
+
<table class="twocolortable">
−
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),
+
<tr><th><p class="s11">Designation</p></th><th><p class="s11">Composition Au</p><p class="s11">(min. content)</p></th><th><p class="s11">Impurites ppm</p></th><th><p class="s12">Remarks on forms and application</p></th></tr><tr><td><p class="s11">Electronic Gold</p><p class="s11">Gold</p></td><td><p class="s11">99.999</p></td><td><p class="s11">Cu &lt; 3</p><p class="s11">Ag &lt; 3</p><p class="s11">Ca &lt; 1</p><p class="s11">Mg &lt;1</p><p class="s11">Fe &lt; 1</p></td><td><p class="s12">Wires, strips, alloying metal for semiconductors, electronic components</p></td></tr><tr><td><p class="s11">Pure Gold</p></td><td><p class="s11">99.995</p></td><td><p class="s11">Cu &lt; 10</p><p class="s11">Ag &lt; 15</p><p class="s11">Ca &lt; 20</p><p class="s11">Mg &lt; 10</p><p class="s11">Fe &lt; 3</p><p class="s11">Si &lt; 10</p><p class="s11">Pb &lt; 20</p></td><td><p class="s12">Granulate for high purity alloys, strips, tubing, profiles</p></td></tr><tr><td><p class="s11">Ingot Grade-Gold</p></td><td><p class="s11">99.95</p></td><td><p class="s11">Cu &lt; 100</p><p class="s11">Ag &lt; 150</p><p class="s11">Ca &lt; 50</p><p class="s11">Mg &lt; 50</p><p class="s11">Fe &lt; 30</p><p class="s11">Si &lt; 10</p></td><td><p class="s12">Alloys, commonly used grade</p></td></tr></table>
−
segments, contact rivets, and stampings produced from clad strip
+
</figtable>
−
materials. The selection of the bonding process is based on the cost for the
+
<br/>
−
joining process, and most importantly on the economical aspect of using the
+
<br/>
−
least possible amount of the expensive precious metal component.
 
  
−
Besides being used as switching contacts in relays and pushbuttons, gold
+
<figtable id="tab:Physical Properties of Gold and Gold-Alloys">
−
alloys are also applied in the design of connectors as well as sliding contacts for
+
<caption>'''Physical Properties of Gold and Gold-Alloys'''</caption> 
−
potentiometers, sensors, slip rings, and brushes in miniature DC motors
 
−
''(Table 2.5)''.
 
  
−
[[File:Mechanical Properties of Gold and Gold Alloys.jpg|right|thumb|Mechanical Properties of Gold and Gold Alloys]]
+
{| class="twocolortable" style="text-align: left; font-size: 12px"
 +
|-
 +
!Material
 +
!Gold<br/>Content<br/>[wt.%]
 +
!Density<br/>[g/cm<sup>3</sup>]
 +
!Melting Point<br/>or Range<br/>[°C]
 +
!Electrical<br/>Resistivity<br/>[µΩ*cm]
 +
!Electrical<br/>Conductivity<br/>[MS/m]
 +
!Thermal<br/>Conductivity<br/>[W/(m*K)]
 +
!Temp. Coeff. of<br/>the electr. Resistance<br/>[10<sup>-3<sup/>/K]
 +
!Modulus of<br/>Elasticity<br/>[GPa]
 +
|-
 +
|Au (99,95)
 +
| >99,95
 +
|19,3
 +
|1064
 +
|2,32
 +
|43
 +
|317
 +
|4,0
 +
|79
 +
|-
 +
|AuAg8
 +
|92
 +
|18,1
 +
|1058
 +
|6,13
 +
|16,3
 +
|147
 +
|1,25
 +
|82
 +
|-
 +
|AuAg20
 +
|80
 +
|16,4
 +
|1035 - 1045
 +
|10,0
 +
|10
 +
|75
 +
|0,86
 +
|89
 +
|-
 +
|AuNi5
 +
|95
 +
|18,3
 +
|995 - 1018
 +
|13,5
 +
|7,4
 +
|53
 +
|0,71
 +
|83
 +
|-
 +
|AuCo5
 +
|95
 +
|18,2
 +
|1010 - 1015
 +
|55,6
 +
|1,8
 +
|
 +
|0,68
 +
|88
 +
|-
 +
|AuCo5 (het.)
 +
|95
 +
|18,2
 +
|1010 - 1015
 +
|5,99
 +
|16,7
 +
|
 +
|
 +
|
 +
|-
 +
|AuAg25Cu5
 +
|70
 +
|15,2
 +
|950 - 980
 +
|12,2
 +
|8,2
 +
|
 +
|0,75
 +
|89
 +
|-
 +
|AuAg20C10
 +
|70
 +
|15,1
 +
|865 - 895
 +
|13,3
 +
|7,5
 +
|66
 +
|0,52
 +
|87
 +
|-
 +
|AuAg26Ni3
 +
|71
 +
|15,4
 +
|990 - 1020
 +
|11,0
 +
|9,1
 +
|59
 +
|0,88
 +
|114
 +
|-
 +
|AuPt10
 +
|90
 +
|19,5
 +
|1150 - 1190
 +
|12,5
 +
|8,0
 +
|54
 +
|
 +
|
 +
|-
 +
|AuAg25Pt6
 +
|69
 +
|16,1
 +
|1060
 +
|15,9
 +
|6,3
 +
|46
 +
|0,54
 +
|93
 +
|-
 +
|AuCu14Pt9Ag4
 +
|73
 +
|16,0
 +
|955
 +
|14,3 - 25
 +
|4 - 7
 +
|
 +
|
 +
|
 +
|-
 +
|}
 +
</figtable>
  
−
Table 2.3: Mechanical Properties of Gold and Gold-Alloys
+
<div class="multiple-images">
 +
<figure id="fig:Influence_of_1_10_atomic_of_different">
 +
[[File:Influence of 1-10 atomic of different.jpg|left|thumb|<caption>Fig 2.2 Influence of 1-10 atomic% of different alloying metals on the electrical resistivity of gold (according to J. O. Linde)</caption>]]
 +
</figure>
 +
</div>
 +
<div class="clear"></div>
  
−
[[File:Commonly Used Grades of Gold.jpg|right|thumb|Mechanical Commonly Used Grades of Gold]]
 
  
−
Table 2.1: Commonly Used Grades of Gold
+
<figtable id="tab:Mechanical Properties of Gold and Gold-Alloys">
 +
<caption>'''<!--Tab.2.3:-->Mechanical Properties of Gold and Gold-Alloys'''</caption>
 +
{| class="twocolortable" style="text-align: left; font-size: 12px"
 +
|-
 +
!Material
 +
!Hardness Condition
 +
!Tensile Strength Rm [MPa] min.
 +
!Elongation A<sub>10</sub> [%] min.
 +
!Vickers Hardness HV
 +
|-
 +
|Au
 +
|R 140<br />R 170<br />R 200<br />R 240
 +
|140<br />170<br />200<br />240
 +
|30<br />3<br />2<br />1
 +
|20<br />50<br />60<br />70
 +
|-
 +
|AuAg20
 +
|R 190<br />R 250<br />R 320<br />R 390
 +
|190<br />250<br />320<br />390
 +
|25<br />2<br />1<br />1
 +
|38<br />70<br />95<br />115
 +
|-
 +
|AuAg30
 +
|R 220<br />R 260<br />R 320<br />R 380
 +
|220<br />260<br />320<br />380
 +
|25<br />3<br />1<br />1
 +
|45<br />75<br />95<br />110
 +
|-
 +
|AuAg25Cu5
 +
|R 400<br />R 470<br />R 570<br />R 700
 +
|400<br />470<br />570<br />700
 +
|25<br />4<br />2<br />2
 +
|90<br />120<br />160<br />185
 +
|-
 +
|AuAg20Cu10
 +
|R 480<br />R 560<br />R 720<br />R 820
 +
|480<br />560<br />720<br />820
 +
|20<br />3<br />1<br />1
 +
|125<br />145<br />190<br />230
 +
|-
 +
|AuAg26Ni3
 +
|R 350<br />R 420<br />R 500<br />R 570
 +
|350<br />420<br />500<br />570
 +
|20<br />2<br />1<br />1
 +
|85<br />110<br />135<br />155
 +
|-
 +
|AuAg25Pt6
 +
|R 280<br />R 330<br />R 410<br />R 480
 +
|280<br />330<br />410<br />480
 +
|18<br />2<br />1<br />1
 +
|60<br />90<br />105<br />125
 +
|-
 +
|AuCo5
 +
|R 340<br />R 390<br />R 450<br />R 530
 +
|340<br />390<br />450<br />530
 +
|10<br />2<br />1<br />1
 +
|95<br />105<br />120<br />150
 +
|-
 +
|AuCo5 prec.hardened
 +
|heterogeneous
 +
|360
 +
|3
 +
|110-130
 +
|-
 +
|AuNi5
 +
|R 380<br />R 450<br />R 560<br />R 640
 +
|380<br />450<br />560<br />640
 +
|25<br />3<br />2<br />1
 +
|115<br />135<br />160<br />190
 +
|-
 +
|AuPt10
 +
|R 260<br />R 310<br />R 370<br />R 410
 +
|260<br />310<br />370<br />410
 +
|20<br />2<br />1<br />1
 +
|80<br />90<br />100<br />105
 +
|-
 +
|AuCu14Pt9Ag4
 +
|R 620<br />R 700<br />R 850<br />R 950<br />prec.hardened
 +
|620<br />700<br />850<br />950<br />900
 +
|20<br />3<br />2<br />1<br />3
 +
|190<br />225<br />260<br />270<br />280
 +
|}
 +
</figtable>
  
 +
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 (<xr id="tab:Contact_and_Switching_Properties_of_Gold_and_Gold_Alloys"/>)<!--(Table 2.4)-->.
  
−
[[File:Phase diagram of goldplatinum.jpg|right|thumb|Phase diagram of goldplatinum]]
+
<figtable id="tab:Contact_and_Switching_Properties_of_Gold_and_Gold_Alloys">
 +
<caption>'''<!--Table 2.4:-->Contact and Switching Properties of Gold and Gold Alloys'''</caption>
 +
<table class="twocolortable">
 +
<tr><th><p class="s11">Material</p></th><th><p class="s12">Properties<th colspan="2"></p></th></tr><tr><td><p class="s11">Au</p></td><td><p class="s12">Highest corrosion resistance, low</p><p class="s12">hardness</p></td><td><p class="s12">High electr. conductivity,</p><p class="s12">strong tendency to cold welding</p></td></tr><tr><td><p class="s11">AuAg8</p></td><td><p class="s12">High corrosion resistance, low thermo</p><p class="s12">e.m.f.</p></td><td><p class="s12">Low contact resistance</p></td></tr><tr><td><p class="s11">AuPt10</p><p class="s11">AuPd5</p></td><td><p class="s12">Very high corrosion resistance</p></td><td><p class="s12">High hardness</p></td></tr><tr><td><p class="s11">AuAg10 - 30</p></td><td><p class="s12">Mostly corrosion resistant</p></td><td><p class="s12">Higher hardness</p></td></tr><tr><td><p class="s11">AuNi5</p><p class="s11">AuCo5</p></td><td><p class="s12">High corrosion resistance, low</p><p class="s12">tendency to material transfer</p></td><td><p class="s12">High hardness</p></td></tr><tr><td><p class="s11">AuAg25Pt6</p></td><td><p class="s12">High corrosion resistance, low contact resistance</p></td><td><p class="s12">High hardness</p></td></tr><tr><td><p class="s11">AuAg26Ni3</p><p class="s11">AuAg25Cu5</p><p class="s11">AuAg20Cu10</p></td><td><p class="s12">Limited corrosion resistance</p></td><td><p class="s12">High hardness</p></td></tr><tr><td><p class="s11">AuPd40</p><p class="s11">AuPd35Ag10</p><p class="s11">AuCu14Pt9Ag4</p></td><td><p class="s12">High corrosion resistance</p></td><td><p class="s12">High hardness and mechanical</p><p class="s12">wear resistance</p></td></tr></table>
 +
</figtable>
  
−
Fig. 2.3:
+
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.
−
Phase diagram
 
−
of goldplatinum
 
  
−
[[File:Phase diagram of gold-silver.jpg|right|thumb|Phase diagram of gold-silver]]
+
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.
  
−
Fig. 2.4:
+
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 (<xr id="tab:Application Examples and Forms of Gold and Gold Alloys"/>)<!--(Table 2.5)-->.
−
Phase diagram
 
−
of gold-silver
 
  
−
Fig. 2.5:
+
<figtable id="tab:Application Examples and Forms of Gold and Gold Alloys">
−
Phase diagram
+
<caption>'''<!--Table 2.5:-->Application Examples and Forms of Gold and Gold Alloys'''</caption>
−
of gold-copper
 
  
−
Fig. 2.6: Phase diagram of gold-nickel
+
<table class="twocolortable">
 +
<tr><th><p class="s11">Material</p></th><th><p class="s12">Application Examples</p></th><th><p class="s12">Form of Application</p></th></tr><tr><td><p class="s11">Pure Gold</p><p class="s11">(electroplated)</p></td><td><p class="s12">Corrosion protection layer for contact parts, stationary contacts, bonding surfaces</p></td><td><p class="s12">Electroplated coatings, bond surface layers</p></td></tr><tr><td><p class="s11">Hard Gold</p><p class="s11">(sputtered)</p></td><td><p class="s12">Contact parts for connectors and switches, sliding contact tracks, bonding surfaces</p></td><td><p class="s12">Electroplated coatings on contact rivets and stamped parts</p></td></tr><tr><td><p class="s11">Hard Gold</p><p class="s11">(sputtered)</p></td><td><p class="s12">Contacts in switches and relays for low loads, electronic signal relays</p></td><td><p class="s12">Contact surface layer on miniature</p><p class="s12">profiles (weld tapes)</p></td></tr><tr><td><p class="s11">AuAg8</p></td><td><p class="s12">Dry circuit switching contacts, electronic</p><p class="s12">signal relays</p></td><td><p class="s12">Contact rivets, welded contact</p><p class="s12">parts</p></td></tr><tr><td><p class="s11">AuAg20</p></td><td><p class="s12">Switching contacts for low loads, electronic</p><p class="s12">signal relays</p></td><td><p class="s12">Contact rivets, welded contact</p><p class="s12">parts</p></td></tr><tr><td><p class="s11">AuAg25Cu5</p><p class="s11">AuAg25Cu10</p><p class="s11">AuAg26Ni3</p></td><td><p class="s12">Contact parts for connectors, switches and relays</p></td><td><p class="s12">Claddings on Cu alloys, contact rivets, contact layer on micro profiles (weld tapes)</p></td></tr><tr><td><p class="s11">AuNi5</p><p class="s11">AuCo5 (heterogen)</p></td><td><p class="s12">Contacts in switches and relays for low and medium loads, material transfer resistant contacts</p></td><td><p class="s12">Contact rivets, welded contact parts, contact layer on miniature profiles (weld tapes)</p></td></tr><tr><td><p class="s11">AuPt10</p><p class="s11">AuAg25Pt6</p></td><td><p class="s12">Contacts for highest chemical corrosion resistance in switches and relays</p></td><td><p class="s12">Contact rivets, contact layer on micro profiles (weld tapes)</p></td></tr><tr><td><p class="s11">AuCu14Pt9Ag4</p></td><td><p class="s12">Sliding contacts for measurement data transfer</p></td><td><p class="s12">Wire-formed parts</p></td></tr></table>
 +
</figtable>
  
−
Fig. 2.7: Phase diagram of gold-cobalt
 
  
−
Fig. 2.8:
+
<div class="multiple-images">
−
Strain hardening
+
<figure id="fig:Phase diagram of goldplatinum">
−
of Au by cold working
+
[[File:Phase diagram of goldplatinum.jpg|left|thumb|<caption>Phase diagram of goldplatinum</caption>]]
 +
</figure>
  
−
Fig. 2.9:
+
<figure id="fig:Phase diagram of gold-silver">
−
Softening of Au after annealing
+
[[File:Phase diagram of gold-silver.jpg|left|thumb|<caption>Phase diagram of gold-silver</caption>]]
−
for 0.5 hrs after 80%
+
</figure>
−
cold working
 
  
−
Fig. 2.10:
+
<figure id="fig:Phase diagram of gold-copper">
−
Strain hardening of
+
[[File:Phase diagram of gold-copper.jpg|left|thumb|<caption>Phase diagram of gold-copper</caption>]]
−
AuPt10 by cold working
+
</figure>
  
−
Fig. 2.11:
+
<figure id="fig:Phase diagram of gold-nickel">
−
Strain hardening
+
[[File:Phase diagram of gold-nickel.jpg|left|thumb|<caption>Phase diagram of gold-nickel</caption>]]
−
of AuAg20 by cold working
+
</figure>
  
−
Fig. 2.12:
+
<figure id="fig:Phase diagram of gold-cobalt">
−
Strain hardening of
+
[[File:Phase diagram of gold-cobalt.jpg|left|thumb|<caption>Phase diagram of gold-cobalt</caption>]]
−
AuAg30 by cold working
+
</figure>
  
−
Fig. 2.13:
+
<figure id="fig:Strain hardening of Au by cold working">
−
Strain hardening of AuNi5
+
[[File:Strain hardening of Au by cold working.jpg|left|thumb|<caption>Strain hardening of Au by cold working</caption>]]
−
by cold working
+
</figure>
  
−
Fig. 2.14:
+
<figure id="fig:Softening of Au after annealing for 0.5 hrs">
−
Softening
+
[[File:Softening of Au after annealing for 0.5 hrs.jpg|left|thumb|<caption>Softening of Au after annealing for 0.5 hrs after 80% cold working</caption>]]
−
of AuNi5 after annealing
+
</figure>
−
for 0.5 hrs after 80%
 
−
cold working
 
  
−
Fig. 2.15:
+
<figure id="fig:Strain hardening of AuPt10 by cold working">
−
Strain hardening
+
[[File:Strain hardening of AuPt10 by cold working.jpg|left|thumb|<caption>Strain hardening of AuPt10 by cold working</caption>]]
−
of AuCo5 by cold working
+
</figure>
  
−
Fig. 2.16:
+
<figure id="fig:Strain hardening of AuAg20 by cold working">
−
Precipitation hardening of
+
[[File:Strain hardening of AuAg20 by cold working.jpg|left|thumb|<caption>Strain hardening of AuAg20 by cold working</caption>]]
−
AuCo5 at 400°C hardening
+
</figure>
−
temperature
 
  
−
Fig. 2.17:
+
<figure id="fig:Strain hardening of AuAg30 by cold working">
−
Strain hardening
+
[[File:Strain hardening of AuAg30 by cold working.jpg|left|thumb|<caption>Strain hardening of AuAg30 by cold working</caption>]]
−
of AuAg25Pt6 by cold working
+
</figure>
  
−
Fig. 2.18:
+
<figure id="fig:Strain hardening of AuNi5 by cold working">
−
Strain hardening
+
[[File:Strain hardening of AuNi5 by cold working.jpg|left|thumb|<caption>Strain hardening of AuNi5 by cold working</caption>]]
−
of AuAg26Ni3 by cold working
+
</figure>
  
−
Fig. 2.19:
+
<figure id="fig:Softening of AuNi5 after annealing for 0.5 hrs">
−
Softening
+
[[File:Softening of AuNi5 after annealing for 0.5 hrs.jpg|left|thumb|<caption>Softening of AuNi5 after annealing for 0.5 hrs after 80% cold working</caption>]]
−
of AuAg26Ni3 after
+
</figure>
−
annealing for 0.5 hrs
 
−
after 80% cold
 
−
working
 
  
−
Fig. 2.20:
+
<figure id="fig:Strain hardening of AuCo5 by cold working">
−
Strain hardening of
+
[[File:Strain hardening of AuCo5 by cold working.jpg|left|thumb|<caption>Strain hardening of AuCo5 by cold working</caption>]]
−
AuAg25Cu5
+
</figure>
−
by cold working
 
  
−
Fig. 2.21:
+
<figure id="fig:Precipitation hardening of AuCo5 at">
−
Strain hardening of
+
[[File:Precipitation hardening of AuCo5 at.jpg|left|thumb|<caption>Precipitation hardening of AuCo5 at 400°C hardening temperature</caption>]]
−
AuAg20Cu10
+
</figure>
−
by cold working
 
  
−
Fig. 2.22:
+
<figure id="fig:Strain hardening of AuAg25Pt6 by cold working">
−
Softening
+
[[File:Strain hardening of AuAg25Pt6 by cold working.jpg|left|thumb|<caption>Strain hardening of AuAg25Pt6 by cold working</caption>]]
−
of AuAg20Cu10 after
+
</figure>
−
annealing for 0.5 hrs
 
−
after 80% cold working
 
  
−
Fig. 2.23:
+
<figure id="fig:Strain hardening of AuAg26Ni3 by cold working">
−
Strain hardening of
+
[[File:Strain hardening of AuAg26Ni3 by cold working.jpg|left|thumb|<caption>Strain hardening of AuAg26Ni3 by cold working</caption>]]
−
AuCu14Pt9Ag4
+
</figure>
−
by cold working
 
  
−
Fig. 2.24:
+
<figure id="fig:Softening of AuAg26Ni3 after annealing for 0.5-hrs">
−
Precipitation
+
[[File:Softening of AuAg26Ni3 after annealing for 0.5-hrs.jpg|left|thumb|<caption>Softening of AuAg26Ni3 after annealing for 0.5 hrs after 80% cold working</caption>]]
−
hardening of
+
</figure>
−
AuCu14Pt9Ag4
 
−
at different
 
−
hardening
 
−
temperatures
 
−
after 50%
 
−
cold working
 
  
−
Table 2.4: Contact and Switching Properties of Gold and Gold Alloys
+
<figure id="fig:Strain hardening of AuAg25Cu5 by cold working">
 +
[[File:Strain hardening of AuAg25Cu5 by cold working.jpg|left|thumb|<caption>Strain hardening of AuAg25Cu5 by cold working</caption>]]
 +
</figure>
  
−
Table 2.5: Application Examples and Forms of Gold and Gold Alloys
+
<figure id="fig:Strain hardening of AuAg20Cu10 by cold working">
 +
[[File:Strain hardening of AuAg20Cu10 by cold working.jpg|left|thumb|<caption>Strain hardening of AuAg20Cu10 by cold working</caption>]]
 +
</figure>
 +
 
 +
<figure id="fig:Softening of AuAg20Cu10 after annealing for 0.5 hrs">
 +
[[File:Softening of AuAg20Cu10 after annealing for 0.5 hrs.jpg|left|thumb|<caption>Softening of AuAg20Cu10 after annealing for 0.5 hrs after 80% cold working</caption>]]
 +
</figure>
 +
 
 +
<figure id="fig:Strain hardening of AuCu14Pt9Ag4 by cold working">
 +
[[File:Strain hardening of AuCu14Pt9Ag4 by cold working.jpg|left|thumb|<caption>Strain hardening of AuCu14Pt9Ag4 by cold working</caption>]]
 +
</figure>
 +
 
 +
<figure id="fig:Precipitation hardening of AuCu14Pt9Ag4">
 +
[[File:Precipitation hardening of AuCu14Pt9Ag4.jpg|left|thumb|<caption>Precipitation hardening of AuCu14Pt9Ag4 at different hardening temperatures after 50% cold working</caption>]]
 +
</figure>
 +
</div>
 +
<div class="clear"></div>
  
 
==References==
 
==References==
 
[[Contact Materials for Electrical Engineering#References|References]]
 
[[Contact Materials for Electrical Engineering#References|References]]
 +
 +
[[de:Werkstoffe_auf_Gold-Basis]]

Latest revision as of 09:46, 11 January 2023

Pure Gold is besides Platinum the chemically most stable of all precious metals. In its pure form it is not very suitable for use as a contact material in electromechanical devices because of its tendency to stick and cold-weld at even low contact forces. In addition it is not hard or strong enough to resist mechanical wear and exhibits high material losses under electrical arcing loads (Table 4). This limits its use in form of thin electroplated or vacuum deposited layers.

For most electrical contact applications, gold alloys are used. Depending on the alloying metal, the melting is performed either under a reducing atmosphere or in a vacuum. The choice of alloying metals depends on the intended use of the resulting contact material. The binary Au alloys with typically < 10 wt% of other precious metals such as Pt, Pd, Ag or non-precious metals like Ni, Co and Cu are the more commonly used ones (Table 2). On one hand these alloy additions improve the mechanical strength and electrical switching properties but on the other hand reduce the electrical conductivity and chemical corrosion resistance (Figure 1) to varying degrees.

Under the aspect of reducing the gold content, ternary alloys with a gold content of approximately 70 wt% and additions of Ag and Cu or Ag and Ni resp., for example AuAg25Cu5 or AuAg20Cu10 are used, which exhibit for many applications good mechanical stability, while at the same time have sufficient resistance against the formation of corrosion layers (Table 3).

Table 1: Commonly Used Grades of Gold

Designation

Composition Au

(min. content)

Impurites ppm

Remarks on forms and application

Electronic Gold

Gold

99.999

Cu < 3

Ag < 3

Ca < 1

Mg <1

Fe < 1

Wires, strips, alloying metal for semiconductors, electronic components

Pure Gold

99.995

Cu < 10

Ag < 15

Ca < 20

Mg < 10

Fe < 3

Si < 10

Pb < 20

Granulate for high purity alloys, strips, tubing, profiles

Ingot Grade-Gold

99.95

Cu < 100

Ag < 150

Ca < 50

Mg < 50

Fe < 30

Si < 10

Alloys, commonly used grade



Table 2: Physical Properties of Gold and Gold-Alloys
Material Gold
Content
[wt.%] 		Density
[g/cm3] 		Melting Point
or Range
[°C] 		Electrical
Resistivity
[µΩ*cm] 		Electrical
Conductivity
[MS/m] 		Thermal
Conductivity
[W/(m*K)] 		Temp. Coeff. of
the electr. Resistance
[10-3/K] 		Modulus of
Elasticity
[GPa]
Au (99,95) >99,95 19,3 1064 2,32 43 317 4,0 79
AuAg8 92 18,1 1058 6,13 16,3 147 1,25 82
AuAg20 80 16,4 1035 - 1045 10,0 10 75 0,86 89
AuNi5 95 18,3 995 - 1018 13,5 7,4 53 0,71 83
AuCo5 95 18,2 1010 - 1015 55,6 1,8 0,68 88
AuCo5 (het.) 95 18,2 1010 - 1015 5,99 16,7
AuAg25Cu5 70 15,2 950 - 980 12,2 8,2 0,75 89
AuAg20C10 70 15,1 865 - 895 13,3 7,5 66 0,52 87
AuAg26Ni3 71 15,4 990 - 1020 11,0 9,1 59 0,88 114
AuPt10 90 19,5 1150 - 1190 12,5 8,0 54
AuAg25Pt6 69 16,1 1060 15,9 6,3 46 0,54 93
AuCu14Pt9Ag4 73 16,0 955 14,3 - 25 4 - 7
Figure 1: Fig 2.2 Influence of 1-10 atomic% of different alloying metals on the electrical resistivity of gold (according to J. O. Linde)


Table 3: Mechanical Properties of Gold and Gold-Alloys
Material Hardness Condition Tensile Strength Rm [MPa] min. Elongation A10 [%] min. Vickers Hardness 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: 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

References

References

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