BG1465U1 - A coating on aluminium and aluminium alloys components - Google Patents

Abstract

The coating is used for applying on aluminium and aluminium alloys components that work in conditions of liquid and border friction. By it is secured high bearing ability, irrespective of the contentof silicium in the aluminium or aluminium alloy. The coating includes a conversion film, composed of a mixture of NH4MgAlF6 and MgAlF5.1.5H2O, and/or a mixture of NH4MgAlF6 and MgAl2F8.2H2O, where according to the useful model, the conversion layer with thickness 2 to 20 microm is applied on a pad with aluminium oxides anode coating. The thickness of the anode coating is 5 to 100 microm.

Description

Technical field

The utility model relates to a coating on aluminum and aluminum alloy parts and in particular on aluminum pistons or aluminum surfaces operating under fluid and boundary friction conditions.

BACKGROUND OF THE INVENTION

From US 5884600, a coating is known on the aluminum piston skirts for internal combustion engines consisting of an anodic aluminum oxide coating on which a polymer layer is applied.

The disadvantage of this known anodic coating of aluminum oxides is that it increases the initial roughness of the friction surfaces. Surfaces with increased roughness of the coating, on which no polymer layer (grooves for piston rings, etc.) is applied, leads to deterioration of conditions for liquid, semi-liquid and boundary lubrication, increased abrasive wear in the case of co-working surfaces (grooves for piston rings). ring - piston ring). The high micro-irregularities on the forehead and the piston belt of the piston overheat and become centers of self-ignition due to the presence of a polymer layer, causing improper combustion of the air / fuel mixture and buildup.

US 6951691 discloses a conversion coating on aluminum and aluminum alloy articles consisting of a thin layer of a mixture of NH ₄ MgAlF ₆ and MgAlF _5. 1.5H ₂ O or a mixture of NH ₄ MgAlF ₆ and MgAl ₂ F _g. 2H ₂ O. The coating is 1-20 micrometer thick and is a corrosion-resistant film with good firing and anti-scratching properties. It works as a solid lubricant and its load-bearing capacity (stability to mechanical degradation) is ensured by undissolved silicon grains passed from the aluminum alloy into the conversion coating.

The disadvantage of this known coating is that the amount of its carrying capacity is determined by the content of silicon in the aluminum alloy (1 to 24 wt.%) That remains in the conversion coating. Coating on parts made of an aluminum alloy with a low content of silicon grains has a lower bearing capacity. When this coating is applied to aluminum pistons, it cannot serve as a thermal barrier and prevent thermal overload of those areas that operate at elevated temperatures, such as compression ring ducts, fire belts and foreheads.

The technical nature of the utility model

The object of the utility model is an anti-scratch and corrosion-resistant coating on parts of aluminum or aluminum alloys, which has a high bearing capacity regardless of the content of silicon in aluminum or aluminum alloy.

The coating on aluminum and aluminum alloy parts includes a conversion film consisting of a mixture of NH ₄ MgAlF ₆ and MgAlF ₅ .1.5H ₂ O and / or a mixture of NH ₄ MgAlF ₆ and MgAl ₂ F ₈ .2H ₂ O, as appropriate model conversion film 2 to 20 microns thick is deposited on an anodic aluminum alumina substrate.

The thickness of the anode coating is from 5 to 100 µm.

The method for surface treatment of aluminum and aluminum alloys consists in initially applying the anodic coating of aluminum oxide on the working surfaces of the parts and subsequent chemical treatment to convert a portion of the anodic coating in the conversion film containing a mixture of NH ₄ MgAlF ₆ and MgAlF ₅ .1.5H ₂ O or a mixture of NH ₄ MgAlF ₆ and MgAl ₂ F ₈ .2H ₂ O.

The benefits of a utility model coating are as follows. The conversion film of a mixture of NH ₄ MgAlF ₆ and MgAlF ₅ .1.5H ₂ O and / or a mixture of NH ₄ MgAlF ₆ and MgAl ₂ F ₈ .2H ₂ O is deposited on a heat-resistant substrate of A1 ₂ O ₃ with the two layers in the combination is a thermal barrier with load-bearing and anti-locking ability. The amount and shape of the silicon grains in the aluminum alloy do not play a decisive role in the bearing capacity of the coating. In the chemical treatment to achieve a conversion film working solution penetrates microcapillary depth of the anodic coating, there were obtained mixtures of NH ₄ MgAlF ₆ and MgAlF ₅ .1.5H ₂ O or NH ₄ MgAlF ₆ and MgAl ₂ F ₈ .2H ₂ O, who play the role

1465 Ul of solid lubricant for both triggering and operating modes. Another advantage of the utility model is that the chemical treatment reduces the height of the micro-irregularities of the anode coating, modifying their tips in a rigid lubricant and avoiding the risk of abrasive wear of the co-working surfaces during actuation, as well as reducing the tendency to build up. self-ignition of the fuel-air mixture.

Explanation of the annexed figures

Figure 1. Results of X-ray diffraction analysis of an aluminum piston alloy surface after coating according to the utility model.

Figure 2. Tribological tests for determining the load of a friction pair of aluminum alloy and cast iron, whereby the liquid and semi-liquid lubrication is converted into boundary lubrication: (a) - aluminum piston alloy with anode coating of A1 ₂ O ₃ ; (b) - Coated aluminum alloy according to the utility model.

Figure 3. Surface profiles: (a) - Aluminum piston alloy with anode coating of A1 ₂ O ₃ ; (b) - Coated aluminum alloy according to the utility model.

Examples of implementation of the utility model

Example. Samples made of an aluminum piston alloy are anodized for 45 minutes in sulfuric acid electrolyte at a concentration of 180 g / Ι at -2 ° C ± 1 ° C and an anode current density of 4-6 A / dm ² . The resulting anode coating is 50 µm thick. After completion of the anodizing test pieces were washed with water and treated in an aqueous solution of 7 g / 1 MgSiF ₆ .6H ₂ O and 3 g / 1 NH ₄ C1 for 5 min at the working temperature of 90 ° C. The resulting coating consists of an anode coating of 50 μm thick aluminum oxide coated with a conversion film consisting of a mixture of OTNH ₄ MgAlF ₆ and MgAlF _5. 1.5H ₂ O and a mixture of NH ₄ MgAlF ₆ and MgAl ₂ F ₈ .2H ₂ O with a thickness of 5 microm.

An X-ray diffraction analysis was performed on the surface layer of one of the sample bodies (Fig. 1) confirming the presence of a conversion film containing a mixture of NH ₄ MgAlF ₆ and MgAlF ₅ .1.5H ₂ O, as well as a mixture of NH ₄ MgAlF ₆ and MgAl / ^ Hp.

In FIG. 2 shows the results of a comparative tribological study to determine the loading of a friction pair of aluminum alloy and cast iron, whereby the liquid and semi-liquid lubrication goes to the limit: (a) - aluminum piston alloy with anode coating of A1 ₂ O ₃ , (b) - the aluminum alloy after machining according to the utility model. The aluminum-alloy pair machined according to the utility model can withstand higher loads under liquid and semi-liquid lubrication conditions.

In FIG. In Fig. 3 the profiles obtained from the surfaces of Taylor Hobson apparatus are shown: (a) - Aluminum piston alloy with anode coating of A1 ₂ O ₃ , (b) - Aluminum alloy after treatment according to the utility model. As a result of the machining, the heights of the roughness obtained after the anodic machining are reduced and their tips are rounded.

Claims (2)

Claims 1. A coating on aluminum and aluminum alloy parts comprising a conversion film consisting of a mixture of NH ₄ MgAlF ₆ and MgAlF ₅ .1.5H ₂ O and / or a mixture of NH ₄ MgAlF ₆ and MgAl ₂ F ₈ .2H ₂ O, characterized in that the conversion film having a thickness of from 2 to 20 micrometer is deposited on a support made of an anodic coating of aluminum oxides. A coating according to claim 1, characterized in that the thickness of the anode coating substrate is from 5 to 100 µm.