Hard Anodizing

OX-HS is a hard anodizing treatment of aluminium in sulphuric acid in compliance with MIL-A-8625 Type III, ISO 10074, and UNI 7796 standards.

The OX-HS hard anodizing process transforms the aluminium alloy surface, creating an inert and compact layer of aluminium oxide. The electrochemical process takes place in a sulphuric acid solution at temperatures below 0°C, making it possible to reach very high treatment thicknesses.

The OX-HS treatment features surface hardness that protects the aluminium base from abrasive and adhesive wear. The coating is customarily used in the automotive sector and for industrial machinery to extend the lifetime of parts subject to wear and sliding motion.

The non-conductivity, compactness, and chemical resistance of the coating make it possible to protect the aluminium substrate from corrosion, exceeding 1000 hours of salt spray without the onset of corrosion. For this reason, the coating is used to protect submarine components and components in the maritime and military sectors.

Automotive brake drum with OX-HS hard anodized coating


The compact OX-HS film protects the substrate material from corrosion, exceeding 336 hours of salt spray exposure with flying colours with no trace of corrosive attack.


The hardness and compactness of the layer of aluminium oxide allows the achievement of high abrasive and adhesive wear resistance, comparable to that of hard chrome.


The high treatment thickness, typically 40-60µm, makes it possible to obtain extended durability in aggressive environments.


The OX-HS treatment can be pigmented to create a deep black colour, thus allowing all aluminium alloys to be given the same appearance.


To reduce the friction coefficient and impart non-stick properties, the OX-HS treatment can be impregnated with PTFE nanoparticles.


Composition and applicable standards

The OX-HS treatment transforms the aluminium substrate into a compact layer of aluminium oxide. The coating composition is thus strongly dependent on the starting alloy.
20÷40%50÷70%3÷5%Depending on the alloy
Product technical standards
ISO 10074
UNI 7796
MIL-A-8625 | Type III
RoHS compliance
RoHS compliant. No restricted substances present in amounts greater than the maximum tolerated concentrations.
REACH compliance
REACH compliant. No SVHCs present in amounts higher than 0.1% by weight.

Anodizable alloys

Wrought alloysCharacteristics
Series 2000Hardness★★★☆☆
Wear resistance★★★☆☆
Corrosion resistance★★★☆☆
Maximum thickness★★★☆☆
Series 5000 (with >2% Mg) and 7000Hardness★★★★☆
Wear resistance★★★★☆
Corrosion resistance★★★★☆
Maximum thickness★★★★★
Series 6000 (except 6082, 6061)Hardness★★★★★
Wear resistance★★★★★
Corrosion resistance★★★★★
Maximum thickness★★★★★
6082, 6061Hardness★★★★★
Wear resistance★★★★★
Corrosion resistance★★★★★
Maximum thickness★★★★☆
Casting alloysCharacteristics
Alloys with Si>8% or Cu>2%Hardness★☆☆☆☆
Wear resistance★☆☆☆☆
Corrosion resistance★☆☆☆☆
Maximum thickness★☆☆☆☆
Die castings with Si<8% or Cu< 2%Hardness★★☆☆☆
Wear resistance★★☆☆☆
Corrosion resistance★★☆☆☆
Maximum thickness★☆☆☆☆
Other alloysHardness★★☆☆☆
Wear resistance★★☆☆☆
Corrosion resistance★★★☆☆
Maximum thickness★★★☆☆

Treatment thickness and aesthetic appearance

Coating thickness
Standard thicknessTolerance
50% of the treatment thickness is due to external film growth and 50% is due to film growth in the surface of the aluminium part. The radial dimensional increase can thus be calculated as half the treatment thickness.
Adjustment of dimensional values following hard anodizing
Uniform thickness over the entire external surface. Reduced thickness in holes.
Aesthetic appearance
Slightly matt appearance with dark grey colour. The colour depends on the base alloy and the treatment thickness. Reproduces the morphology of the machined part.
Option of black colouration in the OX-HC version

Tribological properties

The OX-HS treatment produces high film hardness values. The value varies in accordance with the treated alloy.
Hardness valueAlloy
Series 2000
Series 5000 (with >2% Mg) and 7000
Other wrought alloys
Wear resistance
OX-HS offers very high resistance to abrasive and adhesive wear. The value varies in accordance with the treated alloy.
Wear value, TWI-CS17Alloy
The lower the number, the higher the performance – MIL-A-8625F and ISO 10074 C.3 – Taber Abraser wear test – CS 17 abrasive wheels – 1 kg load
< 35 mg / 10 000 cycles
Series 2000
< 25 mg / 10 000 cycles
Series 5000 (with >2% Mg) and 7000
< 15 mg / 10 000 cycles
Other wrought alloys
Friction coefficient
The OX-HS-PTFE variant has an impregnation treatment of the anodized layer with PTFE nanoparticles.
The impregnation process makes it possible to obtain a non-stick, self-lubricating surface with a low friction coefficient.

Chemical properties

Corrosion resistance
The OX-HS treatment makes it possible to achieve high corrosion and oxidation resistance. The treated surface passes 336 hours of salt spray exposure with flying colours, with no trace of corrosion.
Corrosion resistance valueSubstrate material
NSS in compliance with ISO 9227 and ISO 10074
≥336 hours without corrosion6000 alloy
Chemical resistance
Guideline environmental compatibility values. The actual environmental resistance must anyway be tested in the field.
Hydrocarbons (e.g. petrol, diesel, mineral oil, toluene)
Alcohol, ketones (e.g. ethanol, methanol, acetone)
Neutral saline solutions (e.g. sodium chloride, magnesium chloride, seawater)
Dilute reducing acids (e.g. citric acid, oxalic acid)
Acid oxidizing agents (e.g. nitric acid)
Concentrated acids (e.g. sulphuric acid, hydrochloric acid)
Dilute bases (e.g. dilute sodium hydroxide)
Base oxidizing agents (e.g. sodium hypochlorite)
Concentrated bases (e.g. concentrated sodium hydroxide)