Semi-finished products for the brazing of aluminium heat exchangers must satisfy a number of requirements with extreme variations in stringency, depending on the product and on the design of the heat exchanger.
Aluminium clad strip is used for corrugated fins (0.08–0.10 mm) in all-aluminium brazed heat exchangers.
Manufacturing
Aluminium braze-clad strip for fins is manufactured by roll-bonding a package consisting of a core alloy ingot that is covered on two sides by plates of an AlSi alloy that melts at a lower temperature than the core alloy.
The whole package is subjected to preheating, hot rolling and cold rolling down to the final thickness of the respective products.
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| Sketch of a double-side braze-clad aluminium strip. |
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| Cross-section morphology of a double-side braze-clad strip. |
Depending on the requested final properties, the material is subjected to final annealing and / or intermediate annealing operation(s).
The core provides structural integrity. It is common to use a variety of aluminium alloys, examples being
AA 3xxx (AlMn), and more particularly modified versions of AA 3003 with additions of zinc.
The thickness of each braze-clad layer is typically 10 percent of the total sheet thickness. The layers melt and flow during the brazing process, to provide upon cooling a metallic bond between the fins and the tubes. It is common that the braze clad alloys are from the AA 4xxx series of alloys and more particularly AA 4343 (Al-6.8~8.2 wt.% Si).
Dimensions
| Alloy |
Width (mm) |
Thickness (mm) |
|
HA3968-K – both sides clad with HA 4343-E, clad ratio 10% +/- 2% each side
|
18 |
0.1 |
| 25 |
0.1 |
| 30 |
0.1 |
