Is high temperature oxidation of copper detrimental?

[UkraineTrain]

We are resistance welding oxygen-free copper wire braid and it's changing colors to purple/red. We haven't seen this before but the supplier is trying to improve the strength of the weld and I think has increased time and/or temperature in their process. Does this oxidation have any negative effects on mechanical properties, particularly brittleness or cracking? The assembly is subjected to vibration loads and high current.

 

[metengr]

Have the supplier run some resistance weld coupons and perform mechanical tests regarding the strength and ductility of the weld joint. The results will dictate if this is suitable without guessing.

 

[MintJulep]

Maybe you can find a way to post a smaller picture.....

 

[WKTaylor]

Oxidation ruins the conductor capability of the copper strands.

I have never heard of successfully 'welding copper braid'. Typically twisted wires will be silver or tin-lead soldered for joints [wire splices or to connector ferrules]... or simply crimped-joined... with protective shrink-tubing jackets.

NOTE. The oxidation You noted is a classic sign of over heated wire due to excessive current flow. I have seen distressed wire like this that carrying 2Xs its rated current load... and the plastic insulative jacket was 'oozing/flowing' thru protective wire braiding. This was hair-raising-scary stuff in aircraft electrical systems. The wiring was discovered on the verge of igniting the liquefying/outgassing plastic jacket material.

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", Homebuiltairplanes.com forum]

 

[WKTaylor]

NOTE.

I suspect Your best option to try is resistance welding with inert-gas purge/cooling. Or perhaps ultrasonic welding with/WO inert-gas purge/cooling.

Problem: High level of cleanliness/deoxidation of the wire-braid-ends being splice welded together is probably a mandatory 'no-brainer'.

Found following reference for resistance welded [braided/twisted] wires to terminals... may provide insight... although it is specifically NOT for splice welding wires together.

SAE USCAR-38 PERFORMANCE SPECIFICATION FOR ULTRASONICALLY WELDED WIRE TERMINATIONS...

1. SCOPE
This specification defines test methods and performance criteria for evaluating ultrasonically welded wire-to-terminal
metallurgical bonds. The examples used are specific to the linear weld type of process equipment. USCAR-38 is not
applicable for 'splice welding'. The specification is applicable to wire-on-pad configurations with a typical weld shown in
Figure 1. This test specification subjects parts under test to environmental exposures to simulate a lifetime of field
exposure for a road vehicle. Exposures called-out in this specification include Thermal Shock, Temperature Humidity
Cycling and mechanical abuse. This test specification is intended to evaluate the strength and performance of the
interface between wires to an electrical terminal. Validation of the performance of the Terminal is a separate task and can
be accomplished using a component validation test such as SAE/USCAR-2, which evaluates whether the entire
connection system is acceptable.

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", Homebuiltairplanes.com forum]