DE19548183C1 - Process for applying a fire retardant layer to a magnesium component - Google Patents

Description

The invention relates to a method for application a fire-retardant layer on a magnesium component by thermal spraying an oxide. Under magnesium Components are both components made of pure magnesium how to understand from magnesium alloys.

Magnesium alloys are important materials for that Automotive engineering, engine construction, aerospace technology and other lightweight construction, as in the computer industry, chainsaws and household appliances. The reason is the low specific weight of magnesium Alloys with very good strength properties, where through a significant weight reduction of the magnesium Components compared to aluminum and steel is possible. The, compared to aluminum materials, significantly better Castability of magnesium alloys also leads to a reduction in process steps and a rise tion of productivity, so that magnesium alloys geometrically complex shaped, thin-walled components in high Quantity can be produced inexpensively. Of the Use of magnesium materials in vehicle technology therefore opens up a high potential for cost reduction, Fuel savings and increased payload.  

However, thin-walled magnesium components are particularly popular aerospace, but also in the automotive sector due to the possible fire risk only with restrictions usable. Thin-walled magnesium components, for example wise components with a wall thickness of 3 mm or less can cause fire elsewhere ignite. Problematic when dealing with magnesium materials is the fact that magnesium in can ignite molten state when access to oxygen. The melting point of magnesium is approx. 650 ° C. Thicker Magnesium components dissipate enough heat so that a local melting from another source of fire practically does not occur. However, with thin walls ke local melting of the magnesium component another source of fire is possible and therefore the danger of Magnesium fire.

It is known to fire magnesium components line to reduce the risk of fire. The like fire protection coatings, however, have a significant Thickness of 2 mm and more, which makes it particularly thin the magnesium components achieved by the magnesium Weight reduction of the component at least partially again is nullified. In addition, fire protection dashes optically unappealing, on the other hand But not with conventional paints like car paints be painted over.

From DE-OS 38 36 614 it is known to be thermally stressed Magnesium components by thermal spraying with a Diffusion barrier made of a metal, e.g. B. titanium, one or multi-phase layer, e.g. B. from Ni₃Al and a functi onsschicht from ZrO₂ with proportions of Y₂O₃, MgO or CaO coat.

The object of the invention is to provide a method len, with which thin-walled magnesium Components inexpensively with a fire retardant coating high effectiveness without significant weight increase can be provided.

This is known according to the invention with that in claim 1 recorded procedures achieved. In the subclaims are advantageous embodiments of the invention specified.

That is, according to the invention, aluminum oxide (Al₂O₃), whatever modification, used as a spray material puts.

In contrast to aluminum oxide, pure silicon dioxide the disadvantage that there is no defined melting point and into one even at relatively high temperatures pasty condition with which it is difficult to spray is.

Accordingly, according to the invention, in addition to aluminum oxide, a Ge mix of silicon oxide and at least one other metal loxid used as spray material, the content of Silicon oxide in the spray material at least 20 is preferably at least 50% by weight and the mixture is egg pressure softening point between 400 ° C and 1000 ° C points.

The other metal oxides in the mixture can be sodium oxide (Na₂O), potassium oxide (K₂O), calcium oxide (CaO), magnesium oxide (MgO), zinc oxide (ZnO), lead oxide (PbO), lithium oxide (Li₂O), Alumina (Al₂O₃) and / or boron oxide (B₂O₃).

These oxide mixtures include mixtures in particular Production of enamel, that is, of melt mixtures with sili catenate and possibly borates and fluorides as glass-forming  Elements, particularly those mentioned above with the rest metal oxides that have a pressure softening point between 400 and 1000 ° C, in particular between 450 and 800 ° C sen. The glass-forming material of the enamel forms above all SiO₂ or feldspar, which contains about 70 wt .-% SiO₂. Vastness re glass pictures are B₂O₃, Al₂O₃ and PbO and possibly GeO₂ and BeF₂. To improve the liability, Email may have a minor increase sets of adhesive oxides, for example cobalt or nickel oxide contain.

The composition of the enamel used according to the invention for thermal spraying, according to the Seger formula, is preferably in moles for lead-containing enamel:
0-0.7 mol in Na₂O
0-0.3 mol K₂O
0-0.6 mol CaO
0-0.3 mol of MgO
0-0.7 mol ZnO
0.2-1.5 moles of PbO
0-0.3 mol of Al₂O₃
0.2-3.0 moles of SiO₂
0-2.0 moles of B₂O₃
and with lead-free email
0-1.5 moles in Na₂O
0-0.7 mol K₂O
0-1.0 mol CaO
0-0.6 mol of MgO
0-0.4 mol ZnO
0-0.2 mol of Li₂O
0-0.8 mol of Al₂O₃
1.5-5.0 moles of SiO₂
0-3.0 moles of B₂O₃.

The pressure softening point of the lead indicated above permanent or lead-free enamel is between 430 and 750 ° C. The lead-free enamel types are made from health and Environmental reasons preferred.

As attempts at melting have shown, the thermally sprayed layer of aluminum oxide or Email (with a layer thickness of 30 to 100 µm) the Ent Ignition time of a magnesium component with a layer thickness delayed by at least four times by 1 mm, so that the time span for fire fighting measures in the event of a fire is significantly expanded.

Furthermore, the Mg component according to the invention thermally sprayed oxide layer the resistance of the Component against corrosion significantly increased. Also forms the thermally sprayed oxide layer an excellent Primer for paintwork.

The aluminum oxide layer applied according to the invention has the advantage that they the magnesium component in addition Dimensional stability gives, even if the magnesi is softened um material.

The advantage of the silicon di applied according to the invention oxide-containing layer, in particular enamel layer, is in it to see that this layer softens with increasing temperature and tightly encloses the magnesium component. she can hence the thermal expansion of the magnesium component fol This prevents cracks in the protective layer. Should there still be cracks due to thermal expansion of the building sometimes occur with a correspondingly high level of heating, softens the SiO₂ or enamel layer, resulting in self-sealing leads.  

The thickness of the fire retardant applied according to the invention Protective layer is preferably 10 to 300 microns, in particular 30 to 100 µm.

If the layer thickness is less than 10 µm, it is fire inhibitory protective effect is no longer sufficient, d. H. the Protective layer is no longer dense enough, so that an open Beat a flame through the magnesium base material can. In addition, the oxide applied according to the invention acts layer of thermal insulation. With a layer below 10 µm this thermal insulation effect is no longer present.

With a layer thickness of more than 300 µm, the dimension suffers durability of the magnesium component. Even then the knockout most of the protective layer is relatively large. In addition, the Protective layer the brittle the thicker it is, it loses So elasticity, so that when the component is deformed rather cracks can be formed.

Magnesium materials are insulated due to their good castability special for making thin, large, complex Components having geometry are suitable. Accordingly, it is The method according to the invention, in particular for applying feu inhibiting layer on thin magnesium components with a Layer thickness of 3 mm or less determined.

For the thin-walled fireproofed according to the invention Magnesium components exist in a wide variety of applications opportunities, for example in vehicle construction as a frame or frame parts of seats, doors, etc.

According to the inventive method, the various most magnesium materials are fire-retardant coated den, for example AZ91 (9% Al, 1% Zn), AM50 (5% Al,  5% Mn), AM20 (2% Al, = 0.5 Mn) or AE42 (4% Al, 2% rare earth metals as cerium mixed metal).  

Because magnesium materials have a relatively low melting point point, the component is used in thermal spraying preferably cooled, for example with carbon dioxide, air or water.

Thermal spraying can be done by plasma Arc spraying or flame spraying. Since the Spray particles when plasma spraying at a higher temperature rature heated than with flame spraying, arise during Plasma spraying thicker oxide layers with correspondingly ho fire retardant effect. In contrast, the flame Spraying is cheaper than plasma arc spraying. Particularly dense oxide layers are achieved if the Oxide layer applied by high speed flame spraying is brought, in which the molten oxide particles with egg speed of 500 m / s and more on the component hit.

Claims (5)

1. A method for applying a fire-retardant layer to a magnesium component by thermal spraying of an oxide, characterized in that for thermal spraying aluminum oxide or a mixture of we at least 20 wt .-% silicon dioxide and at least one further metal oxide is used, which one Pressure softening point between 400 ° C and 1000 ° C. 2. The method according to claim 1, characterized in that the further metal oxide sodium oxide, potassium oxide, cal cium oxide, magnesium oxide, zinc oxide, lead oxide, lithium oxide, aluminum oxide and / or boron oxide. 3. The method according to claim 1 or 2, characterized net that the mixture of silicon dioxide and at least another metal oxide is an enamel melt mixture. 4. The method according to any one of the preceding claims characterized in that an oxide layer with a Layer thickness of 10 to 300 microns is applied. 5. The method according to any one of the preceding claims characterized in that the magnesium component at thermal spraying is cooled.