Apparent residues and changes
Inside the radiator, clear residues of potassium aluminum fluoride (flux) are detectable as visible incrustations and are even clearly visible. Discrete particles of potassium aluminum fluoride are also trapped in the outlet of the ducts, which can not only extremely disrupt the flow of water over time, but can also lead to complete blockages. One only has to look at the pictures once.
In the top picture, 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 be possible without it (non-corrosive process), but then the costs would also increase.
Scanning electron microscopy
Let’s take a 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 is actually in the chemical elements? Exactly for this there are such analyses, which you know from my article about the MX-4. Let’s take a closer look at the composition:
We see large amounts of aluminum, fluorine and potassium, which clearly points to 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 will see that on the next page. Incidentally, you can’t just flush these things out without residue either. A supposedly thorough cleaning after corrosive brazing can certainly alleviate the symptoms and, if suitable additives are used in the coolant, suppress them quite well for a longer period of time, but unfortunately even this rework is not really safe. And especially in Germany, the whole thing would also be really expensive for environmental reasons (keyword disposal). In China, however, this plays a subordinate role.
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