Electronic – Soldering specific wire, solder won’t stick + makes iron tip black

soldering

When I solder a specific wire, solder won't stick and it leaves my iron tip black.

With many years of hobby electronics, I have never experienced this before.
The wire is from a silicone encased LED strip and is dull silver in colour. I stripped back the silicone so that the wires were sticking out in free air. On attempting to solder them, I have the following issues:

  • The solder won't stick. I've tried scraping the wire to remove any coating, rubbing with my flux pen etc, but no luck. The wire has been hot enough to melt solder when touching only the wire, so plenty of heat.
  • The iron tip goes black. It appears as though anywhere that the solder "blob" has touched the iron and wire, the tip ends up black (not happy).

I'm not using any exotic solder. And like I said, I'm not new to this, but this has me stumped.

Has anyone seen this before? Can you offer any suggestions? At this point I don't want to go near it again without an idea of what I'm up against.

Additional info:

LED strip back
LED strip front

Best Answer

All of the mentioned symptoms (not accepting solder, silverish gray colour, non magnetic, cheap stuff) make me conclude that it most likely is aluminum.

Soldering properly to aluminum is almost impossible due its tendency to quickly form some oxide layer.

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