Extruded and a drawn aluminum tube differentiation

[erssk]

Is it possible to differentiate between an extruded and a drawn aluminum tube by a metallurgical examination of the microstructure? I do not know if the tube has been artificially aged after drawing / extruding. Surface finish is smooth and shiny ID and OD with some longitudonal marking.

 

[Goahead]

A shining external surface might point in the direction of drawn tube. Maybe swabbing with a clean cotton wool wad will show drawing oil residuals. Extrusions should be clean, as well as heat treated material. Extruded material is probably recristallized, while drawn and not heat treated might shaw elongated microstructure. But what is the point?

http://www.welding-advisers.com/

 

[erssk]

The point is. I have a sample of tube and a client who wants to know.

 

[swall]

Much aluminum tube is extruded through a "porthole" die, which has the inner plug attached to the outer ring at four points around the circumference. During extrusion, the metal flows past the attachment arms and welds back together. You would be able to see the welds on a transverse macro section.

 

[kenvlach]

I agree that shininess indicates (cold) drawn. Beer cans are drawn, the process is more suitable for precision thickness & finish, while extrusion is used for long lengths.

Extrusion of Al tubing is done hot as part of the heat treatment process. E.g., 6061 exits the extrusion die at the solutionizing temperature, then is water sprayed & cooled prior to artificial aging to T6. Not shiny.

 

[TVP]

erssk,

Yes, it is possible to differentiate tubes produced by the two different processes. If you obtain both a transverse and a longitudinal cross-section and etch them appropriately, the microstructure will reveal whether or not the parts were cold drawn, etc. Goahead correctly pointed out that extruded tubes will show a recrystallized microstructure. Cold drawing will obviously change this microstructure. Macroetching may also be useful. ASM HANDBOOK Volume 9 [I/Metallography and Microstructures[/I] is an excellent reference on the subject.