Handling and Storage of Aluminium

Becanse of the excellent corrosion resistance of the 1000, 3000, 4000, 5000, and 6000 series alloys, nsers occasionally have not employed good practice in the handling and storage of these alloys. This can resnlt in water stains or in pitting. Methods to avoid these unsightly surface effects are described in the chapter Cleaning and Finishing of Aluminium and Aluminium Alloys in Volume 5 of the 9th Edition of Metals Handbook. 

Water stain is superficial corrosion that occurs when sheets of bare metal are stacked or nested in the presence of moisture. The source of moisture may be condensation from the atmosphere that forms on the edges of the stack and is drawn between the sheets by capillary action. Aluminium should not be stored at temperatures or under atmospheric conditions conducive to condensation. When such conditions cannot be avoided, the metal sheets or parts should be separated and coated with oil or a suitable corrosion inhibitor. Once formed, water stain can be removed by either mechanical or chemical means, but the original surface brightness may be altered. 

Outdoor storage of aluminium, even under a tarpaulin, is generally not desirable for long periods of time this varies with the alloy, the end product, and the local environment. Moisture can collect on the surface, sometimes at relative humidities helow the dew point, because of the hygroscopic nature of the dust or particles that deposit on the metal from the atmosphere. 

Mechanical damage can he easily avoided hy good housekeeping practices, proper equipment, and proper protection during transportation. When transporting flat sheets or plates, the aluminium should be oiled or interleaved with approved paper to prevent traffic marks, where fretting action at points of contact causes surface abrasion. 

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