What is the bonding mechanism in Soldering and Brazing?

[metalman8357]

I think this is a pretty basic question but I'm curious about the type of bond that is formed in soldering and brazing processes. Take a tin/lead solder onto copper for example; does a metallurgical bond form between the tin/lead solder alloy and the copper even though the copper is not melted? What type of bond is this? Is this the same type of a bond that forms if the same tin/lead solder alloy were put into contact with a molten copper alloy?

Can a parallel be drawn to cold welding? If two perfectly flat, solid metal bars are brought into contact at room temperature in a vacuum they will bond if the oxide layer is removed from each bonding surface. Is this true for liquid solder bonding to solid copper since the flux removes the oxide layer on both metals and the solder wets out onto the imperfect surface of the solid?

If this theory is true, could a tiny droplet of molten metal in vacuum bond to a much larger solid metal even though the droplet does not have enough thermal energy to melt the solid (assuming it is dropped with enough velocity to properly wet out)?

 

[metengr]

Look this information up in Welding, Brazing, and Soldering, Vol 6, ASM Handbook, ASM International, 1993, p 109–113

Brazed joint strength is high. The nature of the interatomic (metallic) bond is such that even a simple joint, when properly designed and made, will have strength equal to or greater than that of the as-brazed parent metal. The natural shapes of brazing fillets are excellent

you can look the remaining information up yourself.

 

[Coctyle]

Vacuum is not necessary if velocity is high enough. Are you familiar with cold spray coatings? Solid powder is accelerated to supersonic speed and plastically deforms on contact with substrate to form metallurgical bond without melting either material. Can be done with metals, ceramics, polymers, etc.

 

[EdStainless]

Or the explosive bonding of plates.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metman]

Quote:

"...strength equal to or greater than that of the as-brazed parent metal."

We proved this to be true at Metallurgical Consultants Inc. with a tensile test of two stainless steel pieces brazed in hydrogen furnace with nioro braze alloy (Nickel - Gold if memory serves. Failed in parent metal.

Design for RELIABILITY, manufacturability, and maintainability

 

[WKTaylor]

The AWS also has two excellent handbooks on these topics, if serious info is required.

AWS BH Brazing Handbook
AWS SH Soldering Handbook

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can b

 

[tbuelna]

A bit off-topic, but one of the most beautiful examples of fabrication work I have ever seen was bronze TIG brazing of an alloy steel tube chassis structure.