RO134133B1 - Method of electrodeposition of zinc-nickel alloy on stainless steel substrate - Google Patents

Description

The invention relates to a process for electrodeposition of zinc-nickel alloy on the surface of stainless steel parts.

Electrolytic coatings with Zn-Ni alloys have been developed and developed due to their special properties of corrosion resistance, as well as very good mechanical properties. From the group of these alloys, the most used are about 2% Ni and those with 25-30% Ni, (Conrad H., Corbett J., Goldenz T.D., Electrochemical Deposition of y-Phase Zinc-Nickel Alloys from Alkaline Solution, Journal of The Electrochemical Society, 159, 2012).

The electrodeposition of zinc-nickel alloy on stainless steel is important in applications where the stainless steel is to be connected to another metal, usually less noble. Electrodeposition of zinc-nickel alloy on stainless steel is mainly used in the automotive industry.

Methods of electrodeposition of zinc or zinc alloys on stainless steel are currently known, but these methods have high energy consumption and use substances that are hazardous to humans and the environment.

The usual methods of electrolytic deposition (electrodeposition) of zinc and zinc alloys on stainless steel operate in a pH range of 1 -M at temperatures of 4O70 ° C and current densities up to 200 A / dm ² , (Maresch G. , Krupicka U., European Patent: EP 0 360 781 B1, 1994).

At pH values above 2.5, a very poor adhesion of zinc to stainless steel is obtained, and the coating is exfoliated. In addition, the stainless steel alloying elements reduce the adhesion of the electrolytically deposited layers.

The lower electrical conductivity of stainless steel limits the current density required for electrodeposition.

A method of electrodeposition of zinc or zinc-nickel alloy on stainless steel, with applications in the automotive industry, is described in patent document EP-A-0269808. The method consists in electrodeposition of a layer of zinc or zinc-nickel alloy, on one or both sides, on stainless steel sheet, at a pH of less than 3.5. The protection of the uncovered part of the sheet is obtained by applying a protective layer that must be removed after the electrodeposition process. The current densities for the single-sided coating of the sheet are between 25 and 200 A / dm ² , preferably between 50 and 150 A / dm ² , and for the coating on both sides between 10 and 100 A / dm ² , preferably , between 25- ^ 75 A / dm ² .

Another method for electrodeposition of zinc on stainless steel, according to EP 0360781, is to use an electrolyte (zinc sulfate solution) with a pH between 1.5- ^ 2.0, the current density between 25- ^ 75 A / dm ² and the temperature between 45- ^ 60 ° C, after which the part is subjected to a heat treatment at a temperature between 200- ^ 300 ° C for 30 minutes. The disadvantages of this method are the maintenance of a low pH of the electrolytic bath, a high current density, a high temperature of the electrolytic bath as well as post-galvanizing treatments that are high energy consumers.

Another method of electrodeposition of zinc-nickel alloy on stainless steel substrate is ultrasonic degreasing - washing - activation - washing - electrodeposition of nickel on stainless steel followed by electrodeposition of zinc, (Liu X.D., Zhou Y., Nie C. Liu J., Xiao C. Y., Effect of Nickel pre-plating on the Plating of Zn-Ni Alloy Coating on Stainless Steel Substrate, 2nd Annual International Conference on Advanced Material Engineering, China, 2016).

RO 134133 Β1

The disadvantage of this method is the multitude of operations prior to galvanizing, which are energy consuming. Also, the zinc-nickel layer is actually electrodeposited on the intermediate nickel layer. 3

It is also known a method of electrodeposition of zinc-nickel alloy which involves before electrodeposition the following steps: 1) grinding the piece of 5 stainless steel with SiC of granulation 600; 2) sanding the part with alumina (particle size 0.05 pm) and 3) ultrasonic degreasing. The disadvantage of this method is 7 in the use of pre-galvanizing treatments that consume energy and a deposition potential that must be modified at certain intervals, (Conrad H., 9

Corbett J., Goldenz T.D., Electrochemical Deposition of y-Phase Zinc-Nickel Alloys from Alkaline Solution, Journal of The Electrochemical Society, 159, 2012). 11

It should be noted that steel is naturally passivated by the formation of a layer of complex oxides on the surface which prevents corrosion but prevents coating with another metal or alloy by electrodeposition, in the sense that if the electrodeposition of Zn alloy is attempted. Neither directly on the stainless steel substrate by classical methods, the obtained layer 15 is exfoliated.

KR 20100083623 A / 2010 also discloses a process of 17 electrodeposition of a Zn-Ni alloy plating layer to increase corrosion resistance and hardness, which includes a preliminary stage of preparation of the 19 plated metal surface by degreasing alkaline chemical, electrolytic degreasing, pickling and washing with water, followed by electrodeposition of Zn-Ni alloy in additive NaOH electrolytic solution, 21 electrodeposition composition also including a complexing agent, a brightening agent and an additive, the complexing agent improving the electrodeposition property of Zn and Ni 23 on the basic composition Zn-Ni and comprising sodium citrate, the brightening agent comprising sulfonic acid agent, and the basic composition of Zn-Ni deposition being 25 composed of ZnO ₃ ~ 10% by weight, NaOH, 81 ^ -94% by weight and NiSO ₄ x6H ₂ O ₃ ~ 9% by weight, the additive comprising a mixed solution of nitrilotriethanol and nickel sulphate, 27 electrodep the joining being carried out at 10-35 ° C, for 10 minutes, at a cathodic current intensity of 0.5 ^ -4.5 A / dm ² and anodic current intensity of 2 ^ -3 A / dm ² . 29

RO 114646 B1 / 1999 also presents a process for electrodeposition of zinc-nickel-phosphorus alloy with high corrosion resistance and having 31 composition Zn (5 ^ -15%), Ni (0.5 ^ -5%) and P, which uses an alkaline electrolyte containing the addition of 5 ^ -70 g / l sodium salt of one of the phosphoric acids, 0.1 ^ -3 g / l 33 polysulfonic copolymer of dialyldimethylamine with sulfur dioxide and 0.1 ^ - 5 g / l of a hydrocarboxylic or polyhydroxycarboxylic acid, the process taking place at a temperature of 18 ^ -50 ° C and below a current density of 0.5 ^ -6 A / dm ² .

The technical problem solved by the proposed invention is the establishment of 37 phase parameters for the treatment of the electrodeposition surface of a stainless steel that would allow a reliable electrodeposition, resistant to exfoliation, of a Zn-Ni alloy, directly on the treated substrate, through a simple, low-energy process and the use of environmentally friendly, low-polluting chemicals. 41

The process according to the invention, for electrodeposition of zinc-nickel alloy on steel substrate, solves this technical problem in that it is carried out by the steps of: 43

- preparation of the surface of the parts for electrodeposition, by chemical degreasing; - washing in water to remove degreasing solutions for 30 s; 45

- surface treatment in solution and washing in water to remove sodium hydroxide solution for 30 s;

RO 134133 Β1

- the preparation of an alkaline electrolyte for electrodeposition of zinc-nickel alloy, such as an additive NaOH electrolytic solution containing a conditioner, and

- subjecting the stainless steel part to the process of electrodeposition of an alkaline solution Zn-Ni alloy, at a current density of 2-3 A / dm ² and at a working temperature of 22-28 ° C, in a electrodeposition tank with stainless steel or nickel anodes, chemical degreasing of the deposition surface taking place at a temperature of 60 ° C for 10 min, alkaline treatment of the surface being carried out in sodium hydroxide solution of concentration 350-450 g / l, at a temperature of 70-100 ° C for 30-50 min, and the electrodeposition electrolyte being a mixture of: 4.9-7.5 g / l Zn, 130-145 g / l NaOH, 10 g / l Envirozin Conditioner, 0.5 ml / l Enviralloy Ni, 12-15 LCD, 50 ml / l NiSpeed Complexor, 5-7 ml / l NiSpeed Additive Ni, 0.2 ml / l Ni Speed Leveler and 5 ml / l Enviralloy Ni 12-15 Part B.

The advantages of the electrodeposition process of zinc-nickel alloy on stainless steel substrate are:

- the procedure is simple and efficient;

- the zinc-nickel alloy layer has a very good adhesion (fig. 1b);

- the thickness of the zinc-nickel alloy layer is 10 pm;

- costs and energy consumption are minimal.

The invention is presented in more detail below in connection with FIG. 1, a-c, showing images of parts obtained by electrodeposition of zinc-nickel alloy on a stainless steel substrate, namely:

- fig. 1a, electrodeposition of zinc-nickel alloy without the use of the claimed process, on stainless steel substrate;

- fig. 1b, electrodeposition of zinc-nickel alloy by the claimed process, on stainless steel substrate;

- fig. 1c, stainless steel without electrodeposition.

The process for electrodeposition of the zinc-nickel alloy on a stainless steel substrate according to the invention consists of three steps:

1. Electrolyte preparation: The electrolyte used for electrodeposition of zinc-nickel alloy contains 4.9-7.5 g / l Zn, 130-145 g / l NaOH, 10 g / l Envirozin Conditioner, 0.5 ml / l Enviralloy Ni 12-15 LCD, 50 ml / l NiSpeed Complexor, 5-7 ml / l NiSpeed Additive Ni, 0.2 ml / l NiSpeed Leveler and 5 ml / l Enviralloy Ni 12-15 Part B. Mix the components at room temperature. The pH of the resulting electrolyte is 13-14.

2. Preparation of the surface of the parts by the following actions: chemical degreasing (only if the parts are dirty, oily) at a temperature of 60 ° C, for 10 min; washing in water to remove degreasing solutions for 30 s; surface treatment in sodium hydroxide solution of concentration 350-450 g / l, at a temperature of 70-100 ° C for 30-50 min; washing in water to remove sodium hydroxide solution for 30 s;

3. Electrodeposition of Zn-Ni alloy from alkaline solution: the current density for electrodeposition is between 2-3 A / dm ² , working temperature 22-28 ° C. Anodes used for electrodeposition of zinc-nickel alloy are made of steel or nickel.

RO 134133 Β1

Claim 1

Claims (1)

Process for electrodeposition of zinc-nickel alloy on a stainless steel substrate, 3 carried out by the phases of: - preparation of the surface of the parts for electrodeposition, by chemical degreasing; 5 - washing in water to remove degreasing solutions for 30 s; - surface treatment in solution and washing in water to remove sodium hydroxide 7 solution for 30 s; - preparation of an alkaline electrolyte for electrodeposition of zinc-nickel alloy, type 9 electrolytic solution of NaOH additive containing a conditioner, and - subjecting the stainless steel part to the process of electrodeposition of an 11 Zn-Ni alloy of alkaline solution, at a current density between 2- ^ 3 A / dm ² and at a working temperature of 22- ^ 28 ° C, in an electrode deposition tank with stainless steel 13 or nickel anodes, characterized in that the chemical degreasing of the deposition surface takes place at a temperature of 60 ° C for 10 min and the alkaline treatment of the stainless steel surface 15 for its passivation is carried out in a solution of sodium hydroxide with a concentration of 350- ^ 450 g / l, at a temperature of 70- ^ 100 ° C for 30- ^ 50 min, the electrode electrode chosen being a mixture of : 4.9- ^ 7.5 g / l Zn, 130- ^ 145 g / l NaOH, 10 g / l Envirozin Conditioner, 0.5 ml / l Enviralloy Ni, 12- ^ 15 LCD, 50 ml / l NiSpeed Complexor, 5- ^ 7 ml / l NiSpeed 19 Ni Additive, 0.2 ml / l Ni Speed Leveler and 5 ml / l Enviralloy Ni 12- ^ 15 Part B, the thickness of the deposited Zn-Ni layer being proportional to the holding time in the bathroom electrodeposition. 21