How to distinguish the quality of aluminum sheet?

The surface of the aluminum sheet is not allowed to have cracks, corrosion, cracked edges, and the surface of the aluminum sheet with a thickness of more than 0.6mm is not allowed to have diffusion spots.
The surface of the aluminum sheet is allowed to have defects such as slight pressure scratches, metal and non-metal indentations, insertion marks, scratches, roll marks, pine dendritic patterns and emulsion marks. However, the depth of various defects shall not exceed the allowable negative deviation of the thickness of the aluminum sheet, and the total area of bubbles shall not exceed 100mm2 on the surface of the aluminum sheet with the minimum thickness per square meter.
Process package aluminum aluminum sheet, allowing exposed parts and surface bubbles without coating layer.
Aluminum sheet defects are allowed to use 400# sandpaper for inspection grinding, and the grinding depth shall not exceed the allowable deviation of thickness; the edges of the aluminum sheetshould be neat and free of burrs.