CN112940554A

CN112940554A - Zn-Al coating with sintered neodymium-iron-boron as base body and preparation method thereof

Info

Publication number: CN112940554A
Application number: CN202110272590.3A
Authority: CN
Inventors: 谢发勤; 胡娜; 吴向清; 王少青; 李淑良; 郝涛
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2021-03-12
Filing date: 2021-03-12
Publication date: 2021-06-11

Abstract

A Zn-Al coating based on sintered NdFeB and a preparation method thereof. The Zn-Al coating is composed of A component, B component, C component and D component, wherein A component is composed of Zn powder, Al powder dispersant, γ-(2,3-glycidoxy) Propyltrimethoxysilane, deionized water, emulsifier and isooctanol; component B is composed of γ-(2,3-glycidoxy)propyltrimethoxysilane, methanol and deionized water; C component consists of sodium phosphomolybdate and deionized water; D component consists of thickener and deionized water. The Zn-Al coating obtained by the invention has strong corrosion resistance, no rust spots on the surface after 1000h neutral salt spray resistance test, and has the characteristics of high hardness and strong bonding force, the hardness is 5H, the bonding force is grade 1, and the surface Has metallic luster. The preparation process of the invention has the advantages of low cost, green environmental protection, no three wastes discharge, and meets the development requirements of green and environmental protection surface treatment technology.

Description

Zn-Al coating with sintered neodymium-iron-boron as base body and preparation method thereof

Technical Field

The invention relates to the field of metal corrosion prevention, in particular to a Zn-Al coating which takes sintered neodymium iron boron as a matrix and has neutral salt spray resistance test of more than 1000 h.

Background

The sintered Nd-Fe-B is a rare earth permanent magnetic material, has high cost performance, good mechanical property, high energy density and extremely high magnetic energy and coercive force. The advantages enable the neodymium iron boron to have wide application in the fields of medical equipment, modern industry, new energy automobiles, aerospace and the like. However, neodymium iron boron is easy to corrode and pulverize due to poor high temperature resistance, and the expansion of the application field of the magnet is severely limited. Therefore, it is urgent to improve the corrosion resistance of the steel sheet to meet the requirements of practical use.

Currently, there are two methods for improving the corrosion resistance of sintered neodymium iron boron: the first is adding alloy elements; the second is to add a coating on the surface of the magnet. The first addition of alloying elements increases the corrosion resistance of the magnet, generally destroys the magnet, and does not significantly improve the corrosion resistance. For example, electroplating and chemical plating, although the two methods have low cost, three serious problems exist, firstly, the discharge of the electroplating waste liquid seriously pollutes the environment; secondly, because the plating solution is deposited in the plating solution, the plating solution can permeate into the substrate, so that the magnet is corroded; thirdly, the hydrogen evolution reaction of electroplating can cause the surface of the neodymium iron boron substrate to be loose, thereby causing the film-substrate bonding force to be poor. Therefore, the corrosion resistance of the magnet is improved by adding a protective layer on the surface. The principle of the protective coating is to slow down the corrosion of the magnet by preventing the corrosive medium from coming into direct contact with the substrate.

A Zn-Al coating is a new green and environment-friendly surface treatment process, and the principle is that flaky Zn powder and flaky Al powder are dissolved in an organic solvent and deionized water, a binder, a passivator and other auxiliaries are added, the mixture is uniformly stirred, the mixture is coated on the surface of a matrix, and the Zn-Al coating is formed after preheating and curing. The Zn-Al coating is not only environment-friendly, but also plays a role in physical shielding, cathode protection and passivation on the surface of the matrix. However, the problems of low hardness, poor corrosion resistance and the like of the existing Zn-Al coating for sintering neodymium iron boron still exist, and the problems need to be solved.

The invention with the publication number of CN 109439187A discloses a graphene modified chromium-free Dacromet coating, which improves the corrosion resistance and hardness of a coating by adding graphene, but cannot be produced on a large scale at present because the graphene is expensive. In the invention with the publication number of CN 106700701A, the high-temperature-resistant environment-friendly Dacromet coating and the coating are improved in high-temperature corrosion resistance and thermal shock resistance by replacing part of zinc powder with magnesium-manganese powder and replacing water with absolute ethyl alcohol, but the rapid corrosion test of ammonium nitrate is only 162min, and the corrosion resistance is poor. In the doctor's academic paper of Jiang in Nanjing aerospace university, namely the research on preparation and corrosion resistance mechanism of Zn-Al-based alloy coating based on Dacromet technology, sodium phosphomolybdate is adopted as a passivating agent, ethylene glycol is adopted as a dispersing agent, and the sodium phosphomolybdate is matched with flaky zinc-aluminum powder to prepare a chromium-free Dacromet coating, so that the defect of complex process exists.

Disclosure of Invention

In order to overcome the defect that the prior art is extremely easy to corrode in high-temperature, humid and hydrogen environments, the invention provides a Zn-Al coating taking sintered neodymium-iron-boron as a base body and a preparation method thereof.

The Zn-Al coating taking the sintered neodymium iron boron as the matrix consists of a component A, a component B, a component C and a component D. The component A comprises 35 parts by weight of flaky Zn powder and flaky Al powder, 6.72-20.06 parts by weight of dispersant, 5-15 parts by weight of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, 5-15 parts by weight of deionized water, 1-5 parts by weight of emulsifier and 0.1-0.5 part by weight of isooctanol defoaming agent;

the component B consists of 5-20 parts by weight of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, 5-20 parts by weight of methanol and 5-20 parts by weight of deionized water;

the component C consists of 0.3-1.2 parts by weight of sodium phosphomolybdate and 10 parts by weight of deionized water;

the component D consists of a thickening agent and deionized water; the thickening agent is: deionized water at a ratio of 1: 25; the proportion is the weight portion ratio.

In the component A, Zn powder: al powder 6: 1. the particle size of the Zn powder is 10-17 mu m; the granularity of the Al powder is 10-20 mu m.

The dispersing agent is one or a mixture of two of polyethylene glycol 200, polyethylene glycol 400 and sodium dodecyl sulfate; the emulsifier is one or a mixture of two of OP-10, Tween 20 and AE 0-9; the defoaming agent is isooctyl alcohol; the thickening agent is hydroxyethyl cellulose.

The specific process for preparing the Zn-Al coating with the sintered neodymium-iron-boron as the matrix provided by the invention is as follows:

step 1, preparing the following components:

preparing a component A:

and weighing various materials in the component A according to the proportion. Sequentially putting the weighed Zn powder, the dispersant, the emulsifier and the gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane into a beaker, adding one material, uniformly stirring, and then adding the next material; and (3) completely adding Zn powder, a dispersing agent, an emulsifying agent and the gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane powder, and stirring for 5-30 min. Adding Al powder into the beaker, stirring for 5-30 min, adding deionized water, and stirring for 1-6 h. During stirring after adding deionized water, if bubbles appear in the mixture, adding 0.1-0.5 part by weight of a defoaming agent; if there are no bubbles in the mixture, the addition of the defoamer is not required. Obtaining the component A for later use.

II, preparing a component B:

and weighing various materials in the component B according to the proportion.

Adding weighed gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane and methanol into a beaker, stirring for 5-30 min at the rotating speed of 400r/min by a stirrer, adding deionized water, and stirring for 1-6 h for later use.

III, preparing a component C:

and weighing various materials in the component C according to the proportion. And adding weighed sodium phosphomolybdate and deionized water into a beaker, and heating for 2-10 h in a water bath. The temperature of the water bath is 20-70 ℃ for standby.

IV, preparing a component D:

and weighing various materials in the component D according to the proportion. And adding the weighed hydroxyethyl cellulose and deionized water into a beaker, and stirring for 1-6 h at the speed of 300-400 r/min to obtain the hydroxyethyl cellulose pulp. And (5) standby.

Step 2, preparing the Zn-Al coating:

mixing the prepared component A and the component B, stirring for 1-6 h, adding the component C, and continuously stirring for 1-6 h; and adding a certain amount of the component D, and then continuously stirring for 2-15 h. Obtaining the Zn-Al paint for later use. The stirring speed is 200-400 r/min.

Step 3, pretreatment of the base material:

polishing the sintered neodymium iron boron substrate, removing oil stains on the surface of the substrate, removing an oxidation film and a rust layer on the surface, ultrasonically cleaning the polished substrate material for 5-20 min by using de-rusting water at 30-70 ℃, ultrasonically cleaning for 3-15 min by using acetone or absolute ethyl alcohol, washing by using deionized water, and naturally drying.

Step 4, preparing a coating:

putting the pre-treated sintered neodymium iron boron substrate into a Zn-Al coating in stirring, and standing for 5-30 s; taking out and standing for 1min until the Zn-Al coating on the surface of the dipped neodymium-iron-boron substrate is uniformly leveled and has no Zn-Al coating dropping, putting the neodymium-iron-boron substrate into an oven box for preheating for 5-20 min at 70-100 ℃, and curing for 5-35 min at 260-320 ℃ to complete the coating, preheating and curing processes of preparing the coating; and (6) taking out. And repeating the coating, preheating and curing processes for three times after natural or artificial accelerated cooling. And obtaining the Zn-Al coating with the sintered neodymium iron boron as the matrix.

The Zn-Al coating prepared by using the sintered neodymium iron boron as the matrix has strong corrosion resistance, high hardness and metallic luster on the surface.

Compared with the prior art, the invention has the beneficial effects that:

after the component A and the component B are mixed, the silane can be fully hydrolyzed by continuously stirring, and the scaly Zn powder and the scaly Al powder in the coating liquid are coupled together to finally form uniform, continuous, glossy and stable coating liquid, as shown in figure 1. Polyethylene glycol is used as a dispersing agent, and the scaly Zn powder and the scaly Al powder are uniformly dispersed in the solution, so that the coating liquid shows good fluidity and is beneficial to forming a layered structure during coating, as shown in figure 4b, the layered structure of the Zn-Al coating is obvious, and the flaky Zn powder and the flaky Al powder are uniformly distributed. The passivating agent is added and continuously stirred to be fully dissolved in gaps of the scaly Zn powder and the scaly Al powder, the defect of poor corrosion resistance of the Zn-Al coating is overcome, the corrosion resistance of the Zn-Al coating is greatly improved, and as shown in figure 5b, the surface of the Zn-Al coating does not have rusty spots after a neutral salt spray test reaches 1000 h. In fig. 6a, a polarization curve 1 of the Zn-Al coating and a polarization curve of the sintered nd-fe-b substrate are respectively given, and it can be seen that the potential of the polarization curve of the Zn-Al coating is shifted forward and the current density is reduced. In fig. 6b, an electrochemical impedance spectrum 3 of the Zn-Al coating and an electrochemical impedance spectrum 4 of the sintered neodymium-iron-boron substrate are respectively given, and it can be seen that the impedance radius is increased, which strongly proves that the corrosion resistance of the invention is greatly improved.

Compared with the prior sintered neodymium iron boron surface treatment method, the method has the advantages that:

1. the Zn-Al coating disclosed by the invention is strong in corrosion resistance, and the surface of the Zn-Al coating does not have rust spots after a neutral salt spray resistance test is carried out for 1000 hours;

2. the Zn-Al coating has high hardness, and the hardness is 5H measured by a pencil hardness tester;

3. the Zn-Al coating has high binding force, and the binding force measured by a paint film scriber is grade 1;

4. the Zn-Al coating disclosed by the invention is low in preparation process cost, green and environment-friendly, has no three-waste emission, and meets the development requirement of a green and environment-friendly surface treatment technology.

Drawings

FIG. 1 macroscopic view of Zn-Al coating solution

FIG. 2 is a Zn-Al coating and a manufacturing scheme;

FIG. 3a is a microscopic morphology of flaky Zn powder;

FIG. 3b shows the microstructure of flaky Al powder;

FIG. 4a is a microscopic morphology of a Zn-Al coating surface prepared with sintered NdFeB as a substrate;

FIG. 4b is a microscopic morphology of a Zn-Al coating section prepared with sintered NdFeB as a substrate;

FIG. 5a is a macroscopic view of a Zn-Al coating before being placed in a neutral salt spray box;

FIG. 5b is a macroscopic appearance of the Zn-Al coating after being placed in a neutral salt fog box for 1000 hours;

FIG. 6a is a polarization curve of a sintered NdFeB substrate and a polarization curve of a Zn-Al coating;

FIG. 6b is the electrochemical impedance spectrum of the sintered NdFeB substrate and the electrochemical impedance spectrum of the Zn-Al coating;

FIG. 7 is a flow chart of the present invention.

In the figure: polarization curve of Zn-Al coating; 2. sintering the polarization curve of the neodymium iron boron substrate; electrochemical impedance spectroscopy of the Zn-Al coating; 4. electrochemical impedance spectroscopy of the sintered neodymium iron boron substrate.

Detailed Description

The invention relates to a Zn-Al coating with strong corrosion resistance by taking sintered neodymium iron boron as a substrate. The present invention will be described in detail with 43 embodiments.

The component A comprises 35 parts by weight of flaky Zn powder and flaky Al powder, 6.72-20.06 parts by weight of dispersant, 5-15 parts by weight of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, 5-15 parts by weight of deionized water, 1-5 parts by weight of emulsifier and 0.1-0.5 part by weight of isooctanol defoaming agent;

the component D consists of a thickening agent and deionized water; the hydroxyethyl cellulose: deionized water at a ratio of 1: 25; the proportion is weight ratio.

In the component A, flaky Zn powder: flaky Al powder 6: 1. the particle size of the Zn powder is 10-17 mu m; the granularity of the Al powder is 10-20 mu m.

Table 1: components of the examples

TABLE 1

TABLE 1

TABLE 1

The invention also provides a method for preparing the Zn-Al coating with the sintered neodymium-iron-boron as the matrix, and the preparation process is explained in detail through 9 specific embodiments:

step 1, preparing the following components:

preparing a component A:

The coating liquid can become dark by changing the adding sequence of the raw materials, the coated surface has no metallic luster, a proper amount of antifoaming agent is added according to the situation in the process, the coating liquid foams due to the excessively high stirring speed, and the coating effect is poor.

II, preparing a component B:

and weighing various materials in the component B according to the proportion.

III, preparing a component C:

IV, preparing a component D:

Step 2, preparing the Zn-Al coating:

Step 3, pretreatment of the base material:

polishing the sintered neodymium iron boron substrate by using No. 120-No. 600 abrasive paper, removing oil stains on the surface of the substrate, an oxidation film on the surface and a rust layer on the surface, ultrasonically cleaning the polished substrate material for 5-20 min by using de-rusting water at 30-70 ℃, ultrasonically cleaning for 3-15 min by using acetone or absolute ethyl alcohol, washing by using deionized water, and naturally drying.

Step 4, preparing a coating:

Table 2 process parameters for the examples:

in the invention, the dispersing agent is polyethylene glycol 200, polyethylene glycol 400, sodium dodecyl sulfate, a mixture of polyethylene glycol 200 and polyethylene glycol 400, a mixture of polyethylene glycol 200 and sodium dodecyl sulfate, and a mixture of polyethylene glycol 400 and sodium dodecyl sulfate. The results are in the form of a coating solution, and the neutral salt spray resistance test, hardness and adhesion are as follows:

dispersing agent	State of application	Neutral salt spray test	Hardness of	Adhesion force
					Polyethylene glycol 200	Stabilization	40h	3H	Stage	2
Polyethylene glycol 400	Stabilization	Over 120h	4H	Stage							2
					Sodium dodecyl sulfate	Stabilization	63h	4H	Stage	2
Polyethylene glycol 200 and polyethylene glycol 400	Stabilization	40h	3H	Stage							2
					Polyethylene glycol 200 and sodium dodecyl sulfate	Stabilization	40h	3H	Stage	2
Polyethylene glycol 400 and sodium dodecyl sulfate	Stabilization	63h	4H	Stage							2

In the present invention, the dispersant polyethylene glycol 400 was contained in amounts of 6.72 parts by weight, 10.08 parts by weight, 12.32 parts by weight, and 20.06 parts by weight, respectively. The results are in the form of a coating solution, and the neutral salt spray resistance test, hardness and adhesion are as follows:

content of dispersant	State of application	Neutral salt spray test	Hardness of	Adhesion force
					6.72 parts by weight	Viscosity of viscous material	40h	4H	Stage	2
10.08 parts by weight	Good effect	63h	4H	Stage							2
					12.32 parts by weight	Superior food	300h	4H	Stage	2
16.80 weight percent	Difference (D)	40h	4H	Stage							2
					20.06 parts by weight	Difference (D)	40h	4H	Stage 2

In the invention, the contained emulsifiers are OP-10, Tween 20, AE0-9, a mixture of OP-10 and Tween 20, a mixture of OP-10 and AE0-9 and a mixture of AE09 and OP-10 respectively. The results are in the form of a coating solution, which has the following resistance to neutral salt spray test, hardness and adhesion:

in the present invention, the contents of the emulsifier tween 20 were 1.00 part by weight, 2.53 parts by weight, 3.03 parts by weight, 3.54 parts by weight, 4.04 parts by weight, and 5.00 parts by weight, respectively. Results the coating state, the neutral salt spray resistance test, the hardness and the adhesion were as follows:

emulsifier content	State of application	Neutral salt spray test	Hardness of	Adhesion force
					1.00 part by weight	The coating liquid has no bubble stability	40h	4H	Stage	2
2.53 parts by weight	The coating liquid has no bubble stability	280h	5H	Level							1
					3.03 parts by weight	The coating liquid has no bubble stability	1000h	5H	Level	1
3.54 parts by weight	The coating liquid has no bubble stability	300h	4H	Stage							2
					4.04 parts by weight	The coating liquid has no bubble stability	40h	4H	Stage	2
5.00 parts by weight	The coating liquid has no bubble stability	40h	4H	Stage							2

Claims

1. a Zn-Al coating with sintered neodymium iron boron as matrix, is characterized in that, is made up of A component, B component, C component and D component; Described A component is made up of 35 parts by weight of Flake Zn powder and flake Al powder, 6.72-20.06 parts by weight of dispersant, 5-15 parts by weight of γ-(2,3-glycidoxy)propyltrimethoxysilane, 5-15 parts by weight of Deionized water, 1-5 parts by weight of emulsifier and 0.1-0.5 parts by weight of isooctyl alcohol defoamer;

The B component is composed of 5-20 parts by weight of γ-(2,3-glycidoxy)propyltrimethoxysilane, 5-20 parts by weight of methanol and 5-20 parts by weight of deionized water;

The C component is composed of 0.3-1.2 parts by weight of sodium phosphomolybdate and 10 parts by weight of deionized water;

The D component is composed of a thickening agent and deionized water; the thickening agent: deionized water=1:25; the ratio is the ratio of parts by weight.

2 . The Zn-Al coating based on sintered NdFeB as claimed in claim 1 , wherein, in the A component, Zn powder:Al powder=6:1. 3 .

3 . The Zn-Al coating based on sintered NdFeB as claimed in claim 2 , wherein the particle size of the Zn powder is 10-17 μm; the particle size of the Al powder is 10-20 μm. 4 .

4. The Zn-Al coating based on sintered NdFeB as claimed in claim 1, wherein the dispersant is polyethylene glycol 200 or polyethylene glycol 400 or sodium dodecyl sulfonate one or a mixture of both;

Described emulsifier is one or the mixture of two in OP-10 or Tween 20 or AEO-9;

The defoamer is isooctanol; the thickener is hydroxyethyl cellulose.

5. a method for preparing the Zn-Al coating of claim 1 with sintered NdFeB as matrix, is characterized in that, concrete process is:

Step 1, prepare each component:

Step 2, the preparation of Zn-Al coating:

Mix the prepared component A and component B and stir for 1 to 6 hours, then add component C, and continue to stir for 1 to 6 hours; take a certain amount of component D and add it and continue to stir for 2 to 15 hours; obtain a Zn-Al coating for use; The stirring speed is 200～400r/min;

Step 3, pretreatment of base material:

The base material is a sintered NdFeB base; the base material is pretreated by grinding and cleaning;

Step 4, Prepare the coating:

Put the pre-treated sintered NdFeB substrate into the stirring Zn-Al paint and let it stand for 5-30s; after taking it out, let it stand for 1 min until the Zn-Al paint on the surface of the dipped NdFeB substrate flows evenly. Flat and no Zn-Al coating dripping, put it in an oven at 70～100℃ to preheat for 5～20min, and cure at 260～320℃ for 5～35min to complete the coating, preheating and curing process of the prepared coating; take out; naturally Or after artificially accelerated cooling, repeat the coating, preheating, and curing process three times to obtain a Zn-Al coating based on sintered NdFeB.

6. the method for preparing the Zn-Al coating with sintered neodymium iron boron as matrix as claimed in claim 5, is characterized in that, when described preparing each component:

Ⅰ Preparation of component A:

Weigh the various materials in the A component according to the proportion; put the weighed Zn powder, dispersant, emulsifier and γ-(2,3-glycidoxy)propyltrimethoxysilane into the beaker in turn inside, and add one material and stir evenly before adding the next material; Zn powder, dispersant, emulsifier and γ-(2,3-glycidoxy)propyltrimethoxysilane powder are all added and stirred for 5 ～30min; add Al powder to the beaker and stir for 5～30min, add deionized water and stir for 1～6h; in the stirring after adding deionized water, if bubbles appear in the mixture, add 0.1～0.5 parts by weight of defoamer ; If there are no bubbles in the mixture, then there is no need to add the defoamer; Component A is obtained, for subsequent use;

Ⅱ Preparation of component B:

Weigh the various materials in the B component according to the proportion;

Add the weighed γ-(2,3-glycidoxy)propyltrimethoxysilane and methanol into the beaker, stir at a speed of 400r/min for 5-30min, add deionized water and stir for 1-6h, spare;

Ⅲ Preparation of C component:

Weigh the various materials in the C component according to the proportion; add the weighed sodium phosphomolybdate and deionized water into the beaker, and heat it in a water bath for 2 to 10 hours; the temperature of the water bath is 20 to 70 ° C, for use;

Ⅳ Preparation of D component:

Weigh the various materials in the D component according to the proportion; add the weighed hydroxyethyl cellulose and deionized water into the beaker, and stir at 300-400 r/min for 1-6 hours to obtain hydroxyethyl cellulose Slurry; reserve.

7. the method for preparing the Zn-Al coating of matrix with sintered NdFeB as claimed in claim 5, is characterized in that, the cleaning in described matrix material pretreatment is to use rust-removing water 30 for the matrix material after grinding. Ultrasonic cleaning at ~70°C for 5 to 20 minutes, ultrasonic cleaning with acetone or absolute ethanol for 3 minutes to 15 minutes, rinsed with deionized water, and air-dried.