The method of coating

 

(57) Abstract:

The invention relates to methods gasometrical coating on parts made of aluminum alloys. The objective of the invention is to improve the quality of the sprayed coatings by increasing the strength of adhesion of the coating to the substrate. The method involves the following operations: mechanical surface preparation, epidemiologie, heating the parts up to 60 - 450oC and the coating. table 1.

The invention relates to methods of thermal coating on parts made of aluminum alloys.

The known method of coating metals, which consists in gasometrical the coated substrate preheated surface of the substrate and subsequent deposition of the base layer (1). Preheating of the substrate leads to a reduction of thermal stress in the coating caused by the difference in the coefficients of thermal expansion of the coating and the substrate. This increases the adhesion strength. However, for a number of cases, this adhesion does not provide the required performance characteristics of the components with coatings. In addition, with increasing temperature above a certain level is

The closest way to the invention is a method including pre-machined surface with ultrasonic impact and a coating (2). The disadvantage of the prototype method is that to increase the adhesion strength of the coating to the base to almost simultaneous operations preliminary machining with ultrasonic impact and coating as described interval is 0.5 seconds. When increasing the interval again begins to grow the oxide film is destroyed under the influence of ultrasonic vibrations. As a result, the adhesion strength may fall even below the level provided by the method-analogue of (1) for some modes.

While performing machining and coating of the sprayed particles by radiation will heat the tool for machining and sticking to it, which will cause it to heat and change the geometry. This will cause a change in the parameters of ultrasonic treatment and the loss of precision machining that will reduce the strength of adhesion.

The objective of the invention is to improve the quality of the sprayed coatings of testing the method of coating, including preliminary mechanical surface treatment and coating, after preliminary machining surface carry out its epidemiologie and before coating produce heating of the parts that are exposed to spraying, to a temperature 60.450 degrees Celsius.

Unlike the prototype, the mechanical surface preparation and coating are performed sequentially, with the inclusion of intermediate operations epidemiologia that simplifies the process of preliminary preparation of the surface due to the appearance of the specified interval. During the time between machining and epidemiologies will go undesirable process of growing the oxide film on the surface due to the high affinity of aluminum for oxygen, which causes a decrease in the adhesion strength of the coating to the base. To compensate for this, the proposed method introduces an additional, in comparison with the prototype, the operation pre-heating increases the strength of the coupling by reducing thermal stress in the coating. Note also that Eelam is a solution parfocality acid. With increasing temperature improves smuul its mechanical destruction. In addition, the flux increases the activity of the fluoride film, which also contributes to the destruction of aluminum oxide. These factors also lead to an increase in the adhesion strength.

As the upper limit of the heating you can choose to 450 degrees Celsius - the temperature of decomposition of epilame. When this limit heating for each class of alloys must be individually selected. So, for example, aluminum wrought alloys are suitable as the upper limit of heating to use the softening temperature of aluminum alloys, caused by the aging process before the formation of stable phases. Usually thermal alloys wrought aluminium alloys begins at temperatures of components of 0.24.0.3 of the melting temperature, that is, 160.200 degrees Celsius, depending on the content of alloying elements. We also note that overheating higher temperature aging alloyed aluminium alloys leads to a fall in the resistance against intergranular corrosion associated with precipitation at the grain boundaries insoluble dispersed particles of the second phase, formed during the decomposition of solid solution. For casting aluminum alloys, it is advisable to heat det the s), which leads to warping and swelling of the castings. For the lower limit adopted on the basis of experimental data (see specific example), the heating temperature of 60 degrees Celsius, which begins a noticeable increase in the strength of adhesion of the coating to the core in comparison with the prototype.

After machining to epidemiologia inevitable that there be some time interval, if these operations are not combined. This interval is necessary, on the one hand, to reduce to a minimum to avoid excessive growth of the oxide film. On the other hand, this interval should be enough technologically to perform the operation of epidemiologia. The tests showed that when the interval to 15 seconds between machining operations and epidemiologia for aluminum alloy V containing 1.6% of magnesium, a positive effect of the proposed method does not disappear. Deposition of large parts of the alloy V, such as disks with a diameter of 670 mm, showed that the interval in 5.10 seconds are enough for the preparation and operation of epidemiologia of the proposed method.

Depending on the content of alloying elements the growth rate of the oxide film can both increase and reduce, the REE content in the aluminum alloy to 0.7% magnesium oxidation is increased 9.5 times, and the introduction of 0.7% beryllium in aluminum alloy with 10% magnesium reduces the oxidation of the alloy in 160 times. Experience shows that the choice of the time interval between the machining and epidemiologies, which is the oxidation of the surface without protective film epilame, and when the protective effect of epidemiologia is technologically determined for a particular alloy, the criterion of "reduced strength".

An example of a specific implementation.

The proposed method of coating were tested on prismatic samples of size HH mm, made of aluminum alloy V. The coating was applied by the proposed method on the prototype method and by the method similar. For samples deposited sublayer with a thickness of 0.1.0.15 mm nichrome HN, wire of 1.6 mm diameter, method of electric arc metallization on the following modes: a current of 200 A, voltage 32B. Then nubilalis main floor 2 mm thick steel HF, wire diameter 1.8 mm, for the following modes: a current of 200 A, voltage 32 b In the coating by the method similar mechanical preparation was performed using the abrasive tape. Before IPO interval between mechanical preparation and coating was 15 seconds. In the coating process of the proposed method after the mechanical preparation using abrasive belt surface 15 seconds were covered with a solution of epilame BSFC-180-05 dipping. Before deposition the samples the proposed method was heated to temperatures of 60, 100, 200 degrees Celsius. After coating was determined by the strength of adhesion "to cut" in a special fixture. Each value was determined according to the test results of 7 samples. The obtained data are given in the table.

Analysis of the data shows an increase in the strength of the proposed method in comparison with the prototype in 2.4 times. The table shows that when heated to 200 degrees Celsius by the method similar starts to decrease the adhesion strength associated with excessive growth of the oxide film. When heated to this temperature on the proposed method of reducing the adhesion strength does not occur, indicating the reliability of the protective film from epolamine in the claimed temperature range.

The use of the proposed technical solution during the deposition of thermal spray coating provides increased adhesion in comparison with the existing methods for aluminum is termicheskimi coatings.

The method of application of thermal spray coatings on parts made of aluminum alloys, including mechanical surface preparation and coating, characterized in that after mechanical surface preparation spend her epidemiologie and before coating the workpiece is heated to 60 - 450oC.

 

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