SU536257A1 - Electrolyte for anodizing magnesium and its alloys - Google Patents

Description

(54) ELECTROLYTE TO ANODIZE MAGNESIUM AND ITS ALLOYS of 100-115 V in the anodizing of wrought alloys. After the process is completed, the voltage in the bath is reduced to zero, the parts are removed from the electrolyte, washed in hot running water, and dried with warm air. To anodize products from the ML5 alloy obtained by the method of injection molding, the electrolytes of three compositions, shown in Table 1, were investigated. 1. When sulfosalicylic acid is introduced into the electrolyte of less than 30 g / l, there is no qualitative leap in the anticorrosion properties of the coating; with the introduction of sulfosalicylic acid over 100 g / l, a precipitate forms in the electrolyte, as a result of which the porosity of the coating increases and reduces its corrosive properties. In tab. Table 2 shows the data of the experiment carried out in the following mode: alternating current, current density 6, a / dm temperature 25 ° C and duration 8 minutes, current constant, current density 5 a / dm, temperature 2 5 ° C and duration 8 minutes. Corrosion tests were carried out in a chamber of salt (sea) fog during 30 days with a periodic inspection in 1-3 days. The solution was dispersed for 15 minutes every 45 minutes. The coatings obtained from the proposed electrolyte did not change the original appearance during the entire period of the tests performed. Traces of corrosion are not detected. On the coatings obtained and the known electrolyte, the first corrosive points of white color appeared on the 23rd day of testing. In the next 7 days of testing, an increase in corrosion foci was observed. The coatings obtained by anodizing products in each of the three electrolyte compositions under these conditions differ from coatings obtained from known electrolytes with high corrosion resistance, since they do not have bubbles, swellings, exfoliation and local white raids, as well as high mechanical strength. The coating is well fed with EP-541 epoxy lacquer followed by polymerization of the lacquer in the pores of the anode film when heated for 1 hour at 150 ° C. The thickness of the coating obtained varies from 25 to 60 µm under anodizing with alternating current and from 25 up to 8O µm under anodizing with direct current. The coating thickness with average values of the indicated current densities during anodization from 5 to 12 min is in the range from 25 to 80 µm. Anodizing in an electrolyte containing additionally sulfosalicylic acid in the amount of 30-100 g / l was subjected to magnesium slag ML5 products, obtained by casting under pressure or into the ground, products made of deformable magnesium alloy MA2-1, obtained by machining by cutting (turning and milling processing) and by stamping. In all cases, a high-quality corrosion-resistant coating was obtained on these products. The peculiarity of the anodizing process in the proposed electrolyte is that, when current is passed, the surface of the products is anodized and, in particular, the surface of the contacting devices at the electrolyte-air interface is enveloped with a stable yellow-brown foam that protects these places from possible cases of etching. The foam appears due to the surface-active properties of sulfosalicylic acid, the presence of which in the electrolyte weakens the sparking on the surface of the anodized product, makes it uniform and eliminates the occurrence of long sparks that go over into the arc causing the burn-through of the metal. The weakness of weak micro-crease ensures high-quality formation of the anode film. In addition, the presence of sulfosalicylic acid in the electrolyte causes its possible destruction in the growth zone of the anode film and at the bottom of the film pores with the formation of inert carbon dioxide, which protects these film sites from possible local overheating with uneven Joule heat removal. Sulfosalicylic acid forms soluble complexes with iron and other metallic impurities in magnesium castings and wrought alloys, and thus prevents products from local etching of impurities during their anad dissolution during anodization. For use in harsh atmospheric and marine tropical conditions, anodized products are impregnated with epoxy-phenol varnish and painted with epoxy enamels. In enclosed spaces and inside devices, anodized and impregnated parts can be applied without their subsequent painting with polymer resin enamels.

A characteristic feature and advantage of anodizing in the proposed electrolyte is the use of current-carrying suspension devices made of aluminum (instead of magnesium) alloys, which is unacceptable in the known processes of anodizing products made of magnesium and its alloys due to their etching. During the anodizing process, a very thin white anodic film is formed on the aluminum fixtures, which at the end of the process is easily removed by immersion for 5 g-10 sec in 10% sodium hydroxide solution heated to 7 O-8 O o. The anodic films formed on the magnesium alloy fixtures used in existing anodizing processes can be removed from the fixtures only by sandblasting or file stripping.

Anodizing in the proposed electrolyte can be used for the anode coating of magnesium alloy assemblies with welded seams or pressed parts of aluminum alloys AD1, AMg2, AMgZ, AMgb, AMts, B-95, etc. Such assemblies are widely used in modern instrument-making and machine-building. for increasing mechanical strength, for threading, especially for thin-walled castings.

35

58

42

65

4O

6O

Table 1

table 2

gray-white powder black years, loosening, no blistering

blackwhite powder raids, loosening, no blistering

black to sulfur with ash green shade

Claims (1)

Electrolyte for Magnesium Anodizing and its alloys, containing ammonium fluoride, sodium dichromate, phosphoric acid and water, which in order to increase the corrosion resistance of the coating, it additionally contains sulfosalicylic acid in the following ratio of components: 300-35О 60-70 50-60 30-10О up to 1