First of all,is to see if there are obvious distortion, if the surface is smooth. If there is any crack，scratches, or burrs，you'd better not to buy..
Second, is to check carefully whether the aluminum surface have different shades of color, if so the quality is not up to standard. Also can put the same kind of profiles together to compare, if color difference is too obvious, it is best not to choose and buy. Don’t forget to check whether the section thickness of the aluminum profile is the same as its annotation type.
Finally, you can use smooth hard tool to draw a aluminum surface, leaving a white scratch, the hand gently wipe and observe, if not erased, material may have quality problems, but if it can be easily erased, then the thickness of the oxide film is qualified.
Consumers can use the simple way to identify extrusions, which allows you to use better.