Aluminum sections are extruded from billets heated to 800-925F under high pressure and then pushed through a die.
During the entire process temperature is carefully controlled, because depending on the aluminum alloy and performance expected heat stages at the beginning and exit out of die are crucial.
here is the diagram of the extrusion machine.
Yes, as per comment, but you have to check current density to make sure sufficient temperature is achieved otherwise the bond between some layers becomes weak.
Making, welding then testing several examples with variations of parameters is usually the way to proceed.
If we talk about quality and 6-sigma (which roughly means 1 ppm defects), the 1 ppm refers to test escapes, not test rejects.
Even if a part only costs \$1, if testing fails to catch a bad part and we accidentally send it to a customer, where it fails in the field, the eventual cost (in failure analysis, corrective actions, documentation, time spent ...
1ppm is 4 times better than 4ppm. If 4ppm of parts are indicated it means that 0.0004% of these parts have to be discarded.
It is always better to have a lower number of discarded parts which means that 0.0001% of defects is better than having 4 times more. Lower ppm (in this case) means less costs and higher productivity.