Patent Publication Number: US-4149883-A

Title: Electrical contact

Description:
The present invention relates to silver-palladium alloys and more particularly to electrical contacts utilizing silver-palladium alloys. 
     Alloys of silver and palladium are known contact materials in the measuring and control technology. With a palladium content of 30% they are substantially resistant to the effects of sulfur. Their strength characteristics can be improved by additions of copper. A known copper-containing silver-palladium contact alloy consists of 65% silver, 30% palladium and 5% copper (A. Keil: Werkstoffe fuer elektrische Kontakte, &#34;Materials for Electrical Contacts,&#34; Springer-Verlag, Berlin/Gottingen/Heidenlberb, 1960, page 157). If, for further improvement of the strength, the copper content of these alloys is increased, the danger arises that their resistance to tarnishing and to corrosion is considerably decreased. 
     It is an object of the invention to provide silver-palladium alloys having improved strength without decreasing the resistance to attack by corrosion. It is a further object of the invention to provide contact materials with at least one contact surface comprising an alloy of the present invention. 
     THE INVENTION 
     The present invention provides alloys consisting essentially of between about 10% and 60% preferably between 10% and 50% by weight palladium, about 0.1% and 8% copper, about 0.1% and 6% indium, about 0.1% and 6% tin, and the balance essentially silver. 
     Particularly preferred alloys contain (i) 59.8% by weight silver, 30% palladium, 5% copper, 5% indium and 0.2% tin; and (ii) of 59.8% by weight silver, 30% palladium, 5% copper, 0.2% indium and 5% tin. 
     The aforesaid alloys have good electrical contact utility and excellent resistance characteristics. They have also very good elasticity, i.e., springlike characteristics, which makes them suitable for use in miniaturized components, especially for use as switch contacts. This utilizes both their excellent contact and elasticity characteristics. They are also useful for other contacts, such as output contacts, pick-off contacts, etc. 
     The excellent physical characteristics of the two preferred alloys set forth hereinbefore are illustrated in the Table which is the last page of the specification. For comparison purposes, the Table also specifies the corresponding properties of the known contact alloys containing (i) 70% slver-30% palladium, and (ii) 65% silver, 30% palladium, and 5% copper. 
     The invention, particularly with reference to the contacts, will be described by way of example with reference to the accompanying drawing, wherein the single figure is a schematic, cross-section view of a contact. 
     Normally open switch 1 includes spring contact sheet 2 comprising the silver-palladium of this invention held in insulating block 3, which also holds the rigid contact 4. Terminals 5 and 6 are connected to contacts 2 and 4, respectively. When pressure is applied to spring contact 2 in the direction of the arrow, the circuit is closed, and when the pressure is removed, contact is broken. 
     Preferred alloys of the present invention contain between about 20% and 35% palladium, about 2% and 6% copper, about 0.2% and 5% indium, about 0.2% and 5% tin, and balance is silver. 
     
                                           TABLE                                   
__________________________________________________________________________
              AgPd                                                        
                  AgPdCu                                                  
                       AgPdCuInSn                                         
                               AgPdCuInSn                                 
              70/30                                                       
                  65/30/5                                                 
                       59.8/30/5/5/0,2                                    
                               59.8/30/5/0.2/5                            
__________________________________________________________________________
Density                                                                   
[g . cm.sup.-3 ]                                                          
              10.9                                                        
                  10.8 10.5    10.5                                       
Electrical Conductivity                                                   
            a 6.5 6.4  5.7     6.3                                        
[mΩ.sup.-1 mm.sup.-2 ]                                              
            b 6.3 6.6  5.6     6.3                                        
Hardness    a 180 225  255     265                                        
[kp . mm.sup.-2 ]                                                         
            b 55  90   145     135                                        
            c --  245  345     330                                        
Tensile Strength                                                          
            a 630 810  905     970                                        
[N . mm.sup.-2 ]                                                          
            b 310 420  535     510                                        
            c --  --   1050    1095                                       
Elasticity Limit                                                          
             a&#39;                                                           
              --  330  430     420                                        
[N . mm.sup.-2 ]                                                          
            c --  --   800     850                                        
__________________________________________________________________________
 a = hard                                                                 
 a&#39; = 70% deformed                                                        
 b = soft                                                                 
 c = tempered