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1 2004

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Analiza przyczyn perforacji rur ze stopu Al z lutowniczą powłoką Al-Si.

Nowak S., Żaba K., Bronicki M., Kąc S.

Rudy i Metale Nieżelazne

2004

R. 49, nr 10-11

568-572

W artykule zamieszczono analizę problemu i wyniki badań, zmierzających do wyjaśnienia przyczyn awarii (perforacji) rur formowanych z taśmy ze stopu Al z powłoką lutowniczą Al-Si. Do awarii dochodzi podczas lutowania elementów wymiennika ciepła w temperaturze około 600 stopni Celsjusza.

The paper includes methods and results of tests aiming at explanation of the cause of failure (perforation) of tubes formed from Al alloy strip with small content of Mn, Fe, Cu with Al-Si coating soldered in temperature about 600 degrees centigrade. A problem occurred in production of vehicle coolers made of Al alloy, where tubes for the exchanger were made of an Al-Si coated strip soldered with elements of the radiator in temperature of about 600 degrees centigrade. Initial analysis and microscopic observation excluded mechanical damages, so we concentrated on material the tube has been made of and high temperature of the soldering process. One cause of damage may be locally disturbed chemical content, which may always happen, that is increased content of needle-shaped silicon may weaken the strip at certain points on next production stages. The observed perforation may take place in the increased temperature, higher than eutectic temperature, especially in a local change of coat thickness. Local disturbance of chemical content not in the coat but in the base may be another reason for damage. We observed with an electronic scanning microscope and made micro-analysis of chemical content of characteristic points at the strip section near the perforation. The observations confirmed influence of high temperature (melted edges of the hole). So it may be assumed that perforation takes place during soldering. Analysis of the chemical content indicates what a probable cause of perforation is. It is locally excessive copper content. Perforation mechanism may be more complex. Existence of Al2Cu phase may result in earlier disturbance of material cohesion, as early as in, for instance, rolling phase. Flux agent operation is also possible.