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Inside the radiator, clear residues of potassium aluminum fluoride (flux) are detectable and even clearly visible as a visible encrustation. Discrete particles of potassium aluminum fluoride are also trapped in the outlet of the channels, which can not only extremely disrupt the flow of water over time, but also lead to complete blockages. You only have to look at the pictures once.
In the top image, we also see significant amounts of the gelled coolant additives. That which lies almost like a kind of skin on the aluminum body and has settled as a layer is also potassium aluminum fluoride, or flux for short. And for those who still don’t know what flux actually is: it is a corrosive flux that is absolutely necessary for the inexpensive soldering of aluminum parts. It would also work without (non-corrosive process), but then the costs would also increase.
Scanning electron microscopy
Let us now look at such an attacked surface under the scanning electron microscope and marvel at the bizarre landscape! This is chemical fallout of the very highest order, unfortunately. Smooth aluminum or even a coated surface would certainly look different (better).
Energy dispersive X-ray spectroscopy (EDX)
But what chemical elements are actually in it? That’s exactly why there are such analyses, which you still know from my article on the MX-4. So let’s take a closer look at the composition:
We see aluminum, fluorine and potassium in large quantities, clearly indicating the extremely corrosive flux. In addition, there is the usual carbon, some oxygen and magnesium. Of course, the whole thing could be solved non-corrosively, but we’ll see that on the next page. Incidentally, you can’t just flush these things out without leaving a residue. A supposedly thorough cleaning can certainly alleviate the symptoms and, with the use of suitable additives in the coolant, suppress them quite well for a longer period of time, but unfortunately even this rework is not really safe.
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