MAGOXID-COAT®

MAGOXID-COAT® is a plasma chemical coating that improves magnesium alloys.

Coating takes place in a saline solution electrolyte. The workpiece is connected in series to an external source of electricity and acts as an anode. During anodisation oxygen plasma discharges itself on the workpiece surface and briefly melts the surface thus forming 2 oxide ceramic layers that bond tightly with the outer metallic layer. A barrier layer with a thickness of about 100 nm constitutes the direct bond with the magnesium workpiece. Then come an oxide ceramic layer with low porosity density followed by one with high porosity density. This layer bond protects the magnesium against wear and corrosion and, thanks to its surface structure, it allows the absorption of lubricants as well as following workpiece treatments such as, for instance, paintwork or impregnation.

The MAGOXID-COAT® layer is a crystalline oxide ceramic with a high content of extremely resistant compounds such as spinels, e.g. MgAl2O4. The plasma chemical process produces oxide ceramic layers, which, in addition to providing a high level of protection against wear and corrosion, also meets other requirements such as hardness, uniform layer formation, fatigue strength, dimensional accuracy and temperature load capacity. 

Wear behaviour of anodic oxide layers, Taber-Abraser Test (wheels: CS 10, load: 10 N, alloy: AZ 91) 
Wear behaviour of anodic oxide layers

Friction wear test with pin-disc-tribometer according to DIN 50 324 (test conditions: FN = 10 N, v = 0.1 m/s, s = 1,000 m)
Friction wear test

Corrosion test on MAGOXID-COAT® layers according to DIN EN ISO 9227 and assessment according to DIN EN ISO 10 289.

SystemCorrosion resistance (in h)
MAGOXID-COAT® 80 - 100
MAGOXID-COAT® + sodium water glass 250 - 300
MAGOXID-COAT® + silane 430 - 600
MAGOXID-COAT® + epoxide powder coating 750 - 1.000
MAGOXID-COAT® + silane + epoxide powder coating > 1,000

The MAGOXID-COAT® plasma chemical process is suitable for the coating of almost any magnesium alloy as well as for the treatment of alloys containing noble earths and zirconium.

With a density of just 1.74 g/cm3, magnesium is the lightest of the metals used for construction. MAGOXID-COAT® can improve almost any magnesium alloy and it combines the variety of the materials perfectly with a wide range of layer properties. This coating makes it possible to use coated magnesium products in different sectors such as, for instance, rollers, clutch components, sealing units or conveyor guide rails.

  • Automotive sector
  • Valves and fittings
  • Office and data technology
  • Food processing industry
  • Energy technology
  • Household appliance industry
  • Aviation and space industry
  • Telecommunications

Process variant MAGOXID-COAT® black  

One variant of the MAGOXID-COAT® process is MAGOXID-COAT® black. This layer contains fade-resistant, chemically inert spinels of magnesium-aluminium oxide minerals and it is well suited for the treatment of virtually any magnesium-based material. For instance, MAGOXID-COAT® black is used for the inner coating of optical components or precision screw threads. It is ideal for heating radiators, for use in vacuum technology, microelectronics and in the aviation and space industry.

Surface roughness: after coating with 10 μm of MAGOXID-COAT® black an initial roughness value of Ra= 0.5 μm is increased to Ra= 1.1 μm (measurements according to DIN 4768).

Fatigue strength: owing to the layer's crystalline structure the base material's fatigue strength is only slightly affected.

Temperature resistance: temperature resistance depends only on the base material.

Outgassing rate: in specific vacuum conditions it amounts to: 10-6 Pa · l · s-1 · cm-2.

The analysis of the residual gas showed slight traces of H2O. 

Layer
(Thickness)
Degree of absorption
α
Degree of reflexion ρColour DifferenceBrightnessEmissivity ξ
MAGOXID-COAT®
black (10 μm)
> 95 % ≤ 5 % 24 % 7 % 81 %

Remarks: Absorption coefficient, reflection, colour difference, and brightness value were determined at room temperature and within the visible range. The colour difference indicates the degree of blackness (0 % = theoretically absolute black, 100 % = absolute white).

The emissivity value was determined at 85 °C and it refers to emissions in the infrared range.