CH682327A5 - - Google Patents

Description

1

CH 682 327 A5

2nd

description

The anodic oxidation of aluminum alloys is well known and is used to increase the corrosion resistance and physical properties such as wear resistance, hardness etc. of aluminum materials.

Wear-resistant objects made of aluminum materials are known to be produced, in particular, by making them wholly or at least partially from a eutectic or hypereutectic Al-Si alloy. The surface layer - up to about 1 mm - of objects of this type contain Si or Si-containing and thus electrically conductive crystals in the order of magnitude of 10 μm, which protrude up to the surface or partially form the same. If one wants to anodize such surfaces, it is found that the Si or Si-containing crystals conduct the electrical current from the anode to the cathode and thus cause a short-circuit current, which prevents an anodic oxidative layer build-up.

It is an object of the present invention to produce an object which consists at least superficially of a eutectic or hypereutectic Al-Si alloy and which can be anodically oxidized and thus has increased corrosion resistance and improved wear resistance and hardness properties at least compared to a comparable object that cannot be anodized.

According to the invention, the object is achieved by the characterizing features of claim 1.

Advantageous further developments of the method according to the invention result from the characterizing features of claims 2 to 9.

example 1

An object made of an AISi7 cast alloy was melted on the surface by a C02 laser, at the same time aluminum-silicon powder was introduced into the melting zone, which bonded to the substrate. The laser beam was focused on the surface with a power of 1500 watts at 1 mm diameter and passed over the object at a speed of 2 meters per minute. This process was repeated 3 to 4 times, a 0.7 mm thick layer of aluminum with 13% by weight of silicon being built up.

Then about 0.1 mm was mechanically twisted off the porous surface and then the object was degreased and anodized in a sulfuric acid electrolyte with 200 g HaSO ^ liters at 20 ° C and 1.5 A / dm2 for 40 minutes. After the compression process in boiling water, the article had an oxide layer thickness of 12 microns.

Example 2

The procedure was as in Example 1, but a composition of the aluminum / silicon powder was chosen such that the layer contained 25% by weight of silicon. Mechanical preparation, anodic oxidation and compression were carried out as in Example 1. The oxide layer thickness was 19 micrometers.

Example 3

The procedure was again as in Examples 1 and 2, but the surface of the article was subjected to a heat treatment with the CO 2 laser after the coating process. The object was then mechanically turned off, degreased and anodized as in Example 1.

The articles according to all three examples were able to determine surface-covering anodically produced oxide layers which have the desired chemical and physical properties.

The reason that it was previously not possible to anodize Si-rich Al alloys was that the Si precipitates were too large to form a compact anodically oxidative layer structure. Shock-like heat treatments on the surface of the Si-rich phases make it possible, according to the invention, to reduce the size of the deposited Si particles to a measure, with the effect that subsequent anodization of an object of this type is possible.

Claims (9)

Claims 1. A process for producing an object consisting of at least one surface layer made of a eutectic or hypereutectic Al-Si alloy, characterized in that the particle size of the Si- or Si-containing crystals of the surface layer having a content of 13% by weight or more Si of the object is brought to a size of around 5 .mu.m by melting or melting, or that in the case of an object with a surface layer with an Si content of less than 13% by weight, by introducing Si, a surface layer with a content of 13% by weight. % or more Si is produced and the particle size of the Si or Si-containing crystals in the surface layer is brought to a size of around 5 μm by melt treatment. 2. The method according to claim 1, characterized in that the introduction of Si and the melt treatment take place simultaneously. 3. The method according to claim 1 or 2, characterized in that the Si content of the surface layer is at least 20 wt .-%, preferably 25 wt .-%. 4. The method according to any one of claims 1 to 3, characterized in that the particle size of the Si or Si-containing crystals is less than 5 microns. 5. The method according to claim 4, characterized in that the particle size of the Si or Si-containing crystals is less than / equal to 3 µm. 6. The method according to any one of claims 1 to 5, 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 2nd 3rd CH 682 327 A5 characterized in that the particle size of the Si- or Si-containing crystals is brought about with high-energy radiation. 7. The method according to claim 6, characterized in that the high-energy radiation is laser radiation. 8. The method according to claim 7, characterized in that the laser radiation is brought about by a CO2 laser. 9. The method according to claim 6, characterized in that the high-energy radiation is electron radiation. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd