SU618459A1 - Electrolyte for anode-plating of magnesium alloys - Google Patents

Description

The invention relates to the electrolytic deposition of oxide coatings (anodizing), in particular to the anodizing of magnesium alloys of the type MA-8, MA2-1, MA-12, MA-14. MA-15, ML-5, ML-6, ML-9, W1-10 and VDM-3.

A known electrolyte for anodizing magnesium alloys containing ammonium fluoride, sodium dichromate, phosphoric acid, and sulfosalicylic acid 1.

This electrolyte produces corrosion resistant oxide coatings with a thickness of 40-60 µm. However, coatings of this thickness change the dimensions of the parts and therefore cannot be used to protect parts of 1-2 grade accuracy and details with narrow channels. In addition, coatings with a thickness of more than 50 microns reduce the fatigue strength of the product.

Closest to the invention is a known electrolyte for anodizing magnesium alloys containing 300 g / l of potassium fluoride 2. The electrolyte also contains caustic potassium (80 r /;: t.

OjDiaKO coatings, obtained in the indication of electrolyte, are neo / ir / common, porous, named after IIH kis "lzipi ie properties ;. Incca is corrosive

the durability of the coating is due to the fact that the coating consists mainly of oxide and magnesium hydroxide.

The purpose of the invention is to increase the corrosion resistance of the oxide coating.

For this, the proposed electrolyte additionally contains chromic anhydride in the following ratio of components, g / l: potassium fluoride300-500

Chromic anhydride 5-50

In addition, the electrolyte according to the invention allows simultaneously with the application of the coating surface cleaning from various contaminants.

The anodizing process is recommended to be carried out, at room temperature, with a voltage of direct or alternating current of 60-80 V and current of 0.5-5.0 A / dm.

The duration of the process depends on the current density: the higher the current density, the less time it will take for the voltage to rise to a given value and, accordingly, the length of the process is reduced.

Thus, at a current density of 0.5 A / dm, the process length is 30 minutes, and iqjH current density of 5 A / dm is 15 minutes.

The introduction of chromic anhydride into the electrolyte allows the inclusion of chromium ions in the oxide film, which have a passivating effect on magnesium, which ensures high coating properties. The simultaneous increase in the concentration of potassium fluoride to 500 g / l permits the use of the proposed electrolyte for the anodizing of magnesium alloys of all systems, i.e. the proposed electrolyte is unnumbered.

In the proposed electrolyte, coatings of light yellow color with a thickness of 4-6 microns are obtained smooth, elastic, with high protective properties both in a humid atmosphere and when immersed in a 3% solution of sodium chloride. Coatings also have high adhesion to paintwork (LCP).

The invention can be illustrated with several gfimers presented in table. one.

Comparative protective and adhesive properties of oxide coatings obtained in the well-known

Experimental data

ML-5 JMA2Sksrost corrosion on hydrogen,

HI cm cm-hour 0.1100 0.0100 0.0053 0.0045

Note: Adhesion was determined according to GOST 15140-69, as a paint coating, a coating widely used in the industry for the protection of magnesium alloys, consisting of three layers of EP-076 primer and one layer of enamel.

EP-140. Corrosion tests are carried out by immersion in a 3% solution of sodium chloride according to GOST 9.020.74;

known and anticipated electrolytes are presented in table. 2

table 2

Proposed

product material

MA-5 | mA2-1 I ML-5 | mA2-1 | ML-51mA2J1G-1 1 0 .0056 0.004Y 0.0057 0.0040

As can be seen from the table, the protective properties of the coatings obtained in the proposed electrolyte are higher on the ML-5 alloy by 20 times, and on the MA2-1 alloy by 2.5 times while maintaining adhesion properties.

Claims (2)

1. Author's certificate of the USSR № 536257, cl. C25 D 11/30, 1975. 2. Timonov MA Corrosi and the protection of mechanical alloys M., Mashinostroenie, 1964, p. 198.