Joining Techniques Soldering and Welding

Filler alloys used for soldering or brazing melt at a temperature lower than that of the metal or alloy soldered. A filler fills in gaps between areas of the parts to be joined and, as it cools down, solidifies and adheres to each part, providing a permanent and stable join between them. Two soldering 

All soft solders are alloys composed mainly of lead and tin mixed in proportions that vary from as little as 30% lead (and 70% tin), to as much as 98% lead (and only 2% tin). The brazing metals are mostly alloys of copper or silver their composition, as well as that of other alloys used since antiquity for soldering, are listed in Table 48 (Zhadkevich 2004). 

Fusion welding is possible because copper, a component of most gold and silver alloys, easily forms eutectics, alloys that melt at a temperature lower than any of the metals composing them (Duval et al. 1989 Wolters 1983, 1981). To attach granules or wires to a surface of gold or silver alloy 

As the assemblage is further heated and reaches a temperature of about 850°C, the carbon reacts with copper oxide on the surface of the alloy, reducing the copper to metallic copper, while the carbon is oxidized to carbon monoxide (it should be noted that practically all exposed copper surfaces acquire a thin layer of copper oxide formed by the oxidation of the metal when exposed to oxygen in the atmosphere)  

The carbon monoxide prevents reoxidation of the hot copper. A further temperature rise to about 900°C results in the copper and gold (or silver) at the surface of the parts interacting to form a eutectic. The eutectic melts and runs freely, wetting the surface as well as the attached wires or granules. When the assemblage is finally cooled, the eutectic solidifies, firmly joining the wires or granules to the now decorated surface. 

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