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→Composite Contact Rivets
During ''cold bonding'' and heading the bond between the contact material and the copper is achieved without external heat energy by high plastic deformation at the face surfaces of the two wire segments <xr id="fig:Cold_bonding_of_bimetall_rivets"/> (Fig. 3.1). The bonding pressure must be high enough to move the lattice components of the two metals within a few atom radii so that the adhesion forces between atoms become effective.
Therefore the head to shank diameter ratio of 2:1 must be closely met for a strong bond between the two metals. (s. Picture "Cold bonding of bimetall rivets")
<figure id="fig:Cold_bonding_of_bimetall_rivets">
[[File:Cold_bonding_of_bimetall_rivets.jpg|right|thumb|Cold bonding of bimetall rivets (schematic)]]
</figure>
During ''hot bonding'' the required heat energy is applied by a short term electrical current pulse ''<xr id="fig:Hot_bonding_of_bimetal_rivets"/> (Picture Hot bonding of bimetall rivetsFig. 3.2)''. In the case of Ag and Cu a molten eutectic alloy of silver and copper is formed in the constriction area between the two wire ends. When using metal oxide containing contact materials the non-soluble oxide particles tend to coagulate and the bonding strength between the component materials is greatly reduced. Therefore the cold bonding technology is preferred for these contact materials. The during cold bonding required high surface deformation ratio can be reduced for the hot bonding process which allows the head to shank diameter ratio to be reduced below 2:1. For composite rivets with AgPd alloys as well as alloys on the basis of Au, Pd, and Pt the above methods cannot be used because of the very different work hardening of these materials compared to the base material copper. The starting material for such composite rivets is clad strip material from which the contact rivets are formed in multiple steps of press-forming and stamping. Similar processes are used for larger contact rivets with head diameters > 8 mm and Ag-based contact materials. (s. Picture "Hot bonding of bimetall rivets")
For composite rivets with AgPd alloys as well as alloys on the basis of Au, Pd, and Pt the above methods cannot be used because of the very different work hardening of these materials compared to the base material copper. The starting material for such composite rivets is clad strip material from which the contact rivets are formed in multiple steps of press-forming and stamping. Similar processes are used for larger contact rivets with head diameters > 8 mm and Ag-based contact materials.
<figure id="fig:Hot_bonding_of_bimetal_rivets">
[[File:Hot_bonding_of_bimetal_rivets.jpg|right|thumb|Hot bonding of bimetall rivets (schematic)]]
</figure>
*Typical contact shapes for composite rivets (s. Picture "Typical contact shapes for composite rivets")
