Anodizing defects: storage and transportation conditions
See. Classification anodization defects aluminum
Various types of corrosion can occur at different stages of the production process: from the method and conditions of storage of profiles during their storage before anodizing to the shipment of finished products.. defects anodizing, corrosion related, presented in decreasing order of probability.
Fretting corrosion
English term
Fretting corrosion (traffic marking)
defect Source
Moving - Storage - Transportation
Defect manifestation:
Factory displacement – Storage – Transportation – Anodizing
Details of the defect
Small, very dense black spots, consisting of groups of very short scratches, strips and recesses, visible on pressed surface. These minor defects are oriented approximately at right angles to the pressing direction., and spots often line up along the pressing direction, as shown in Figure 1.
Figure 1
Friction corrosion occurs in the friction contact between the protruding points of two adjacent profiles during relative movement from relative to each other, usually, when slippage between profiles occurs during transport. This leads to the formation of fine aluminum dust., which quickly oxidizes to very solid alumina, which the, in turn, leads to fast and targeted local abrasion. Usually arises in the absence of reliable fastening of profiles in containers and vehicles. Slight friction corrosion can be removed by grinding..
Preventing defect
The solution to the problem is to prevent the formation of a metal-metal contact during movements, packaging and transport by securely fastening, excluding moving profiles.
General atmospheric corrosion
English term
General atmospheric corrosion
defect Source
Inside- and inter-workshop movements - Storage - Transportation
The manifestation of the defect
Travlenye - Anodyrovanye
Details of the defect
Randomly located ulcers, appearing after etching and anodizing alloy profiles 6063, as shown in Figure 2.
Figure 2
Ulcers tend to be mostly along the tracks of the matrix and usually only on surfaces, weatherproof. They are almost invisible until, until the material is etched. Atmospheric corrosion occurs as a dissolution of a MgO / Al film2O3 on alloy profiles 6063 under the influence of acid dust particles, deposited on the profiles and leading to fairly rapid corrosion in these places.
Preventing defect
If a defect has already occurred, it can only be removed by grinding and reprocessing. It is very difficult to avoid this type of corrosion on alloy products such as 6063, since a magnesium oxide film on extruded profiles makes them very sensitive to corrosion even under relatively good storage conditions. The most appropriate solution is to etch and anodize the profiles as soon as possible after pressing..
Gasket corrosion
English term
Spacer marking.
defect Source
Storage
The manifestation of the defect
Anodizing.
Details of the defect
Cross strips in places, corresponding to the positions of spacers (spacers), used to separate batch profiles after satin, grinding and polishing (drawing 3). These stripes may be lighter or darker., than adjacent surfaces depending on the angle of incidence of light. These bands result from slight corrosion., usually starting under the influence of water or moisture from remaining on the surface of the grinding coolant or from gaskets.
Figure 3.3.
Preventing defect. Use paper-covered soft foam pads or rubber pads with a low moisture and acid content (see. below is the defect "Paper" corrosion). Profiles should be anodized as soon as possible after grinding and polishing..
Paper Corrosion
English term
Paper corrosion.
defect Source
Storage
The manifestation of the defect
Storage – Travlenye
Details of the defect
Open chamfered ulcers, formed after etching. “Paper” corrosion can be seen on pressed profiles, as shown in Figure 3.4.1, but more clearly - after anodizing (figure 3.4.2), when chamfers occur on ulcers. Sometimes these ulcers have a random distribution, sometimes - have an ordered look, and sometimes - concentrated along one face of the profile. If the ulcers are regular, this may be the result of placing the profile on corrugated paper with metal contact on the corrugation. These ulcers can be removed by grinding., but it can be expensive and not always effective, as often the pits are very deep.
Figure 3.4.1
Figure 3.4.2
“Paper” corrosion results from exposure to acid radicals in the presence of moisture, such as chlorides and sulfates, which are present in packaging and corrugated paper. When the pH is less than 5, intergranular corrosion occurs (see. also "acid corrosion"). Etching aggravates ulcers.
Preventing defect
“Paper” corrosion can be avoided by keeping the packaging paper as dry as possible., at low humidity and acidity, as well as measures, designed to remove moisture from packaging.
Source: Barry R. Ellard, Aluminum Extrusion Technology, 2000
