Hard Anodizing (version 5)
N.B.: The information contained in this sheet comes from reliable sources. Nevertheless, it is provided without any guarantee, express or implied, of its accuracy.
Principle:
Hard anodizing is a special case of sulfuric anodizing. This process is usually carried out in a 10 to 20% (by volume) sulfuric acid bath at low temperature, usually -5 to 5°C.
The use of low temperature allows the application of higher current densities (typically 3 A/dm²) and minimizes the dissolution of the oxide, which allows the achievement of significant thicknesses (from 25 to 100 μm) and especially dense structures. An increase in hardness, abrasion resistance, electrical and thermal insulation is noted for layers formed in hard anodizing.
This treatment is therefore particularly recommended when resistance to abrasive or erosive wear is paramount. Coloration and clogging of the oxide layer are possible but decrease hardness and wear resistance.
ASPECT: gray, brown (black coloring possible)THICKNESS: 5 to 60 μmMICRODURITY: 300 to 500HV for 50 μm, depending on the alloy
SURFACE CONDITION: Roughness degradation, depending on the alloy
ELECTRICAL INSULATION: 500 to 1000 volts ~ COEF OF COOLING: good under high load
FATTENING : 30 to 50% depending on the alloy
CORROSION RESISTANCE :
- without clogging : ~ 50 h
- nickel salt sealing : ~ 300 h
- chromium VI salt sealing : ~ 500 h
SUBSTRATE:
Aluminum alloys with a maximum of 4 to 5% copper.
The alloy used has a strong influence on the performance level obtained and the appearance.
Thickness limited to 20/25 μm for alloys made by die casting.
VARIANTS:
Use of baths consisting of mixtures of sulfuric acid and organic acids (Sanford), superimposition of alternating current (Hardas) or use of pulsed or periodic current (Durkalu).
Possibility of black coloring
PTFE impregnation (Nituff, Tufram...): reduction of the friction coefficient
APPLICATIONS :
Resistance to abrasive or erosive wear, ability to rub
Electrical insulation
Thermal insulation
Applications: aeronautics, automotive, defense, household appliances...
SELECTION CRITERIA - LIMITATIONS :
Due to the high thickness of the oxides formed in hard anodizing, it may be necessary to take into account variations in the dimensions of the parts. It is sometimes necessary to rectify the layer after anodizing to restore a surface condition
ENVIRONMENTAL IMPACT:
The process used has no critical influence on the environment, no heavy metals, no chlorinated solvents, etc. There is therefore no threat to the sustainability of this process.
REFERENCE:
EN 2536 : aeronautical sector
ISO 10 074 : building sector
EN 12 373-2 /17 : methods for measuring the anodic layer
ISO 9227-NSS : neutral salt spray test
EN 12 373-18 : Pitting corrosion rating system
ISO 4516: Vickers and Knoop microhardness measurement method
FED. TEST METHOD STD.141C Method 6192-1: Abrasive wear resistance TABER method
Implementation
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