The physical-chemical and mechanical characteristics of aluminum make it particularly difficult to weld.
Regardless of the league, therefore from the presence of silicon or magnesium, or whether it is pure aluminum, the main characteristic that distinguishes it is the presence of aluminum oxide: a superficial layer that covers the true aluminum and that commonly he's calledAlumina.
Why the alumina "disturbs" welding?
We press that generally the melting point of oxides is lower than the material from which they come. Oxides are formed in contact with oxygen in the external part of the material to be welded. For example: carbon oxide, so-called rust, it forms on the iron (carbon steel) in the part exposed to the presence of oxygen and has a fusion temperature of 900 ° C, then lower than iron (carbon steel) which is 1535 ° C.
What does this mean? That the merger of oxide will be simpler than the underlying material.
In the event of the aluminum exactly the opposite. From here the difficulty that many find, especially in the first weapons is born. In fact the alumina flies to over 2000 ° C while the underlying aluminum at 660 ° C!
The thermal conductivity of aluminum is five times higher than that of steel, so the heat must be high.
What does this mean? It is intuitable to understand that once the alumina is merged, the underlying aluminum is literally disintegrated from a temperature three times higher than that of the necessary fusion. Hence the phenomenon of "bacing" in the aluminum welding process.
What to do to weld aluminum well?
First remove alumina.
Regardless of the process with which you decide to weld it (which is MMA, MIG / MAG or TIG), which depends on many untreated factors in this article, the first indispensable thing is the superficial cleaning of the part subject to welding, ie L Allumina removal.
We remind you that alumina has a fusion point three times that of aluminum, which is very hard and tenacious is also porous and is also a thermal insulator. All property certainly not compatible with a welding process.
The decapant action of the electric arc is not always sufficient since in the porosity of alumina can be retained pollutants such as oils and paints that in turn constitute a disturbing element in the merger process.
Once the alumina layer with abrasive products (Click here to see for example the Disco 3M Scotch Brite Clean & Strip and a demonstration video of the same) It is advisable to prepare the welding process through a preheating at 150-200 ° C.
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