阅读说明：本技术 一种可免助镀剂的钢用Sn基镀层或软钎料 (Sn-based plating layer or soft solder for steel without plating assistant agent ) 是由 张晓峰 刘春燕 李建文 陈宇 于 2021-06-07 设计创作，主要内容包括：本发明公开一种可免助镀剂的钢用Sn基镀层或软钎料,合金包括如下质量百分比的组分：Zn为1～20％,Cu为1～20％,Ni为1～5％,Ti为1～5％,余量为Sn。本发明的SnZnNiCuTi五元合金中活性元素的选择是针对钢材中的主要组织铁素体与珠光体来提升Sn基镀层或软钎料的润湿性：Zn兼有降低镀层或钎料熔点与改善润湿性的作用；Cu、Ni、B(由Ni带入的微量硼元素)则主要用于改善对铁素体及其晶界的润湿性；Ti主要用作对铁素体晶粒的脱氧还原以及对珠光体中渗碳体的反应润湿；同时利用Sn对Cu、Ni、Ti的溶解能力,使之均匀分散,并呈液态,以保证这些合金元素具备必要的活度。(The invention discloses an auxiliary plating agent-free Sn-based plating layer or soft solder for steel, which comprises the following components in percentage by mass: 1-20% of Zn, 1-20% of Cu, 1-5% of Ni, 1-5% of Ti and the balance of Sn. The active elements in the SnZnNiCuTi quinary alloy are selected to improve the wettability of an Sn-based plating layer or a soft solder aiming at the main structures of ferrite and pearlite in steel: zn has the functions of reducing the melting point of a plating layer or a brazing filler metal and improving the wettability; cu, Ni and B (trace boron elements brought by Ni) are mainly used for improving the wettability to ferrite and a grain boundary thereof; ti is mainly used for deoxidizing ferrite grains and wetting cementite in pearlite through reaction; meanwhile, the Sn is uniformly dispersed and is in a liquid state by utilizing the dissolving capacity of the Sn to Cu, Ni and Ti, so that the alloy elements have necessary activity.)

1. The Sn-based plating layer or soft solder for the steel without the plating assistant agent is characterized in that the alloy comprises the following components in percentage by mass: 1-20% of Zn, 1-20% of Cu, 1-5% of Ni, 1-5% of Ti and the balance of Sn.

2. The Sn-based plating or soldering flux for steel free from plating assistant of claim 1, wherein Ni is added by way of Ni-based brazing filler BNi-2 intermediate alloy.

3. The Sn-based plating or solder for use in a plating-assistant free steel as claimed in claim 1, wherein Ti is added as an Sn-Ti master alloy.

4. The Sn-based plating or solder for use in a plating-assistant free steel as claimed in claim 1, wherein Sn, Zn and Cu are added as pure metals.

5. The Sn-based plating or solder for use in a plating-assistant free steel as claimed in claim 1, wherein the alloy is based on Sn-9 Zn.

6. The Sn-based plating or solder for use in a plating-assistant free steel according to claim 1, wherein the alloy is obtained by a method comprising: sn-9Zn is taken as a matrix, and BNi-2 intermediate alloy, Sn-Ti intermediate alloy and Cu metal are added into the matrix.

Technical Field

The invention relates to the field of materials, in particular to a plating assistant-free Sn-based plating soft solder for steel.

Background

The Sn-plated base coating layer coated on the surface of the steel can play a role in corrosion prevention and service life extension, can provide convenience conditions for subsequent application (such as welding) of the steel, and further expands the application range of the steel. The preparation technology of the coating and the plating layer comprises two important aspects: firstly, coating the formula of a plating layer; the second is coating method.

At present, according to different shapes of steel, the coating method of industrialized tinning mainly comprises steel strip continuous tinning and bearing steel back centrifugal casting tinning technology, wherein tinned steel plates are commonly called tinplate and are divided into hot-dip tinned steel plates and electroplated tin steel plates according to production processes. While the formula of the traditional coating layer is mainly pure Sn, commercial Sn-based soft solder (Sn-37Pb, Sn-0.7Cu) and Babbitt (SnSbCu).

The interface of the tin coating and the steel strip of the hot dip plating method is metallurgically bonded (a FeSn2 layer generated by the reaction of the plating assistant agent and Sn is bonded with liquid tin), the thickness is thick and uneven, the thickness of the coating is difficult to control, the tin consumption is large, and the efficiency is low; meanwhile, before plating, a plating assistant agent with a chloride salt aqueous solution is needed.

When babbitt metal is poured on the inner surface of a tile back (generally a steel back) by centrifugal casting, in order to prevent the defects that the interface is not compact and even the steel back is separated from the babbitt metal due to poor wettability of a liquid/solid interface formed by a solid steel back and the liquid babbitt metal, the inner surface of the steel back needs to be cleaned, then a chloride saline solution is coated as a solvent to remove an oxidation film on the inner surface of the steel back, then a tin hanging procedure is carried out firstly, and finally the babbitt metal is poured.

The traditional coating and plating pure Sn, commercial Sn-based soft solder (Sn-37Pb, Sn-0.7Cu) and Babbitt metal (SnSbCu) have poor film removing capability on the surface of steel materials during coating and plating the steel materials, and the reasons are mainly two aspects: firstly, the contained alloy elements do not have the capability of breaking the oxide film on the surface of the steel plate through a chemical reaction path; and the second is restricted by an alloy system and process temperature, and the Fe dissolution capacity is not obvious, so that a way of removing the film by using a physical mechanism is lost. Therefore, the densification and wetting of the liquid/solid (L/S) interface are usually achieved by means of solvent (plating assistant), chemical assistance of flux and mechanical action of the tool (e.g. ultrasonic vibration) to break the oxide film on the surface of the solid steel substrate.

In addition, when the thickness of the steel is thicker (such as more than or equal to 3mm), the time required by the activation of the atoms on the surface of the steel is prolonged due to the aggravation of the heat dissipation of the liquid coating metal on the surface to the inside of the steel; especially, the winding becomes difficult, so that the existing coil hot dip coating line process of tinplate cannot be adopted. In view of the above, the necessity of developing an Sn-based plating layer that can eliminate the need for a plating assistant is more prominent for thicker steel sheets.

Disclosure of Invention

The prior art has the problems that the traditional pure Sn, commercial Sn-based soft solder (Sn-37Pb, Sn-0.7Cu) and babbit alloy (SnSbCu) have poor film removing capability on the surface of steel, a large number of laminar peeling conditions can occur during coarse surface grinding under the working condition of hot dip plating without using a plating assistant, and the aqueous solution of chloride is required to be used as the plating assistant, so that the process is increased, and the environment is not facilitated. The invention aims to provide a plating assistant-free Sn-based plating layer or soft solder for steel, which improves the wettability on the surface of steel by selecting different active elements and adding the active elements into a low-melting-point Sn-based alloy by adopting a proper way, does not need to be coated with any chloride plating assistant, and has the characteristics of self-stripping, emission reduction and environmental protection.

The invention is realized by the following technical scheme:

an Sn-based plating layer or soft solder for steel without plating assistant comprises the following components in percentage by mass: 1-20% of Zn, 1-20% of Cu, 1-5% of Ni, 1-5% of Ti and the balance of Sn.

The active elements in the SnZnCuNiTi quinary alloy are selected to improve the wettability of an Sn-based plating layer or soft solder aiming at the main tissues of ferrite and pearlite in steel: zn has the functions of reducing the melting point of a plating layer or a brazing filler metal and improving the wettability; cu, Ni and B (trace boron elements brought by Ni) are mainly used for improving the wettability to ferrite grain boundaries and crystal grains thereof; ti is mainly used for deoxidizing ferrite grains and wetting cementite in pearlite through reaction; meanwhile, the Sn is uniformly dispersed and is in a liquid state by utilizing the dissolving capacity of the Sn to Cu, Ni and Ti, so that the alloy elements have necessary activity.

Considering that Sn has certain dissolving capacity to Ni, Ni is added in a mode of Ni-based brazing filler metal BNi-2 intermediate alloy, so that the addition of Ni and deoxidizing element boron B can be ensured simultaneously, and the chemical reaction stripping can be realized by using the boron element B in the Ni-based brazing filler metal as an active element; secondly, for ferrite grains, because Ni and Fe in the Ni-based brazing filler metal are homologous elements, the Ni-based brazing filler metal has good metallurgical compatibility and is easy to deposit compactly, and the interface compactness can be improved, so that the wettability of a plating layer or the brazing filler metal at low temperature is improved. Meanwhile, below 500 ℃, Sn has less than 5% solubility for Ni, which is advantageous for obtaining liquid Ni atoms at coating temperatures.

The invention can improve the wettability to the ferrite grain boundary by utilizing the characteristic that Cu is easy to diffuse into the ferrite grain boundary.

Ti active element as strong deoxidizing element can improve p-cementite (Fe)₃C) The wettability of the ferrite is favorable for breaking an oxide film on the surface of ferrite grains; because the active element Ti has a higher melting point and Sn has certain dissolving capacity to Ti, Ti is added in a Sn-Ti intermediate alloy mode, and the preparation mode of the Sn-Ti intermediate alloy mainly comprises the following steps: melting Ti with high melting point and Sn with low melting point into Sn-Ti alloy with higher Ti content by adopting electric arc, further carrying out induction heating and heat preservation, and adding more Sn to realize uniform distribution of Ti in Sn.

Sn, Zn and Cu are added in a pure metal mode.

The alloy takes Sn-9Zn as a base material.

The alloy smelting method comprises the following steps: sn-9Zn is taken as a matrix, and BNi-2 intermediate alloy, Sn-Ti intermediate alloy and Cu metal are added into the matrix.

The invention takes Sn-9Zn eutectic with low melting point as a base material, is beneficial to reducing the melting point of Sn-based alloy, and is more active to Fe and beneficial to improving the wettability compared with Sn, so that the low melting point Sn-9Zn is taken as a base body, BNi-2, Sn-Ti intermediate alloy and Cu which have certain solid solubility in Sn are added into the base body, the added main deoxidizing element B, Ti and the elements Ni and Cu with high metallurgical compatibility can be ensured to be in liquid state at the temperature of A1 (the austenitizing starting temperature of steel is 727 ℃), the activity of a coating layer or brazing filler metal is ensured, and the film removal and the subsequent densification wetting and deposition are ensured.

The Sn-based plating layer or soft solder of the invention adds different active elements B and Ti to improve the wettability of the Sn-based plating layer or soft solder from the aspect of chemical reaction stripping aiming at ferrite and pearlite areas in steel materials so as to ensure that each area and crystal boundary can be well wetted. In order to realize the addition of a high-activity oxidizing element B and a high-melting-point easily-oxidizable element Ti into a Sn-based plating layer or brazing filler metal, the commercial Ni-based brazing filler metal BNi-2 master alloy and the arc melting Sn-Ti master alloy are respectively adopted, and the method has the advantages that: (1) the steel has excellent wettability, and the plating assistant agent of chloride salts is not required to be coated before hot dipping, so that the coating has the advantages of self-stripping, emission reduction and environmental protection; (2) the temperature required by hot dip plating is lower (below 550 ℃); (3) the bonding strength with the interface of the common steel matrix is high; (4) the plating process is flexible, and the modes of hot dipping, gravity casting, centrifugal casting and the like can be adopted; (5) even under the condition of no plating assistant agent, the copper-based alloy has excellent wettability with the steel backing, is firmly combined, and can save the process of tin coating; (6) the Sn-based quinary alloy can be used as a hot dip coating or a centrifugal casting composite layer of steel and can also be used as soft solder of the steel.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the invention provides an Sn-based plating layer or soft solder for steel without plating aids, which can realize good wetting of the Sn-based plating layer or the Sn-based soft solder on the surface of steel and realize green coating or green soft soldering without using the plating aids or solvents.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is an appearance diagram of a hot dip coating obtained by using the SnZnCuNiTi of the invention without plating assistant;

FIG. 2 is an appearance diagram of a hot dip coating obtained by using the SnZnCuNiTi of the invention without plating assistant;

FIG. 3 is an appearance diagram of a hot dip coating obtained by using the SnZnCuNiTi of the invention without plating assistant;

FIG. 4 is an appearance diagram of a hot dip coating obtained using Sn-based babbitt alloy without a plating aid;

FIG. 5 is an appearance diagram of a hot dip coating obtained using pure Sn without a plating assistant;

FIG. 6 is an external view of a hot dip coating obtained using Sn-37Pb without a plating assistant;

FIG. 7 is a hot dip coating interface microstructure of SnZnCuNiTi system coating/steel without plating assistant agent;

FIG. 8 is a hot dip coating interface microstructure of SnZnCuNiTi system coating/steel without plating assistant agent;

FIG. 9 shows the melting point test results (DSC curve) of SnZnCuNiTi-based coating melting blocks;

FIG. 10 shows the microstructure of a SnZnCuNiTi-based plated ingot.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

The effectiveness of the SnZnCuNiTi quinary plating layer provided by the invention relative to the traditional Sn-based plating layer under the condition of no plating assistant agent is evaluated through the following aspects: (1) comparing the hot dip plating appearance with the plating leakage defects; (2) evaluating and comparing the bonding strength of the coating and the matrix after hot dip coating; (3) observing and analyzing the microscopic structure of the coating/steel matrix interface after hot dipping; (4) the melting point, structure and properties (shear properties) of the coating itself.

Examples

Melting the SnZnNiCuTi quinary alloy to 500-560 ℃ to obtain alloy liquid and protecting the alloy liquid with inert gas; wherein Ni and B are added through commercial Ni-based brazing filler metal BNi-2; ti is added through Sn-Ti alloy; sn, Zn and Ti are added in the form of pure metals.

And then cutting a steel plate with the thickness of 3-5 mm into small blocks with the thickness of 15mm multiplied by 15mm by electric sparks, polishing and ultrasonically cleaning, directly immersing the steel plate into the alloy liquid in a hot dipping mode without preheating or brushing a chloride aqueous solution plating assistant agent, and preserving heat for 5 minutes to enable the temperature of the steel plate to rise and realize a wetting reaction with the Sn-based alloy.

Comparative example

Three common commercially available tin-based metals, namely pure Sn, Sn-37Pb and ZSnSb11Cu6 (babbitt metal), are selected, heated to 400 ℃, 400 ℃ and 500 ℃ respectively under the protection of inert gas, and are preserved for preparing for hot dipping.

And then cutting a steel plate with the thickness of 3-5 mm into small blocks with the thickness of 15mm multiplied by 15mm by electric sparks, polishing and ultrasonically cleaning, directly immersing the steel plate into the alloy liquid in a hot dipping mode without preheating or brushing a chloride aqueous solution plating assistant agent, and preserving heat for 5 minutes to enable the temperature of the steel plate to rise and realize a wetting reaction with the Sn-based alloy.

(1) Hot dip (no plating aid) appearance and plating-missing defect contrast

The following results were obtained by observing the appearance of the hot dip plated steel sheets of examples and comparative examples: FIG. 1, FIG. 2 and FIG. 3 show the appearance of hot dip coatings obtained by using three Sn-based SnZnCuNiTi quinary alloy plating baths, 74.5Sn-7Zn-16Cu-1.5Ni-1Ti plating bath (560 ℃ C.. times.5 min), 71Sn-9Zn-18Cu-1Ni-1Ti plating bath (560 ℃ C.. times.5 min) and 79Sn-9Zn-10Cu-1Ni-1Ti plating bath (550 ℃ C.. times.5 min), respectively. As can be seen from the figures 1 to 3, the plating layer provided by the invention is uniform, the bonding force is good, the plating leakage area is avoided, the tin layer is fine and white, and the plating leakage defect is avoided even under the condition that the plating assistant agent is not suitable; and the steel substrate is roughly ground by using sand paper, the situation of flaking does not occur, and the phenomenon of high-temperature oxidation blackening is not found on the surface of the steel substrate after the plating layer is removed by grinding (see the right picture of figure 1). From FIGS. 4 to 6, it can be seen that the three commercially available Sn-based alloys have poor wettability without using a plating assistant agent, and cannot wet the steel sheet, so that there are significant plating missing regions.

The comparison of the hot dip coating appearance defects proves that the SnZnNiCuTi quinary alloy has good wetting capacity on the surface of solid steel under the conditions of no preheating and no use of any plating assistant agent.

(2) Evaluation and comparison of bonding strength between coating and matrix after hot dip coating (without plating assistant agent)

Because the plating layer is very thin (50-100 mu m), normal tensile and shearing samples cannot be prepared, and the method of bonding by using super glue and then stretching is adopted for evaluation. When in bonding, uniformly stirring the two components (multifunctional epoxy resin and curing agent) of the E-7 adhesive A and B according to the proportion of 7:1, and pumping out redundant air in the adhesive by using a vacuum box (the time is 30 min); then uniformly coating the prepared glue on two stainless steel adhesive clamps with internal tapping, gently placing the sample on the clamps coated with the glue and extruding air; and winding the clamp interface by using an adhesive tape to ensure the center alignment of the two clamps.

Tensile strength and macrofracture are shown in table 1. Tensile strength was first compared: the bonding strength of the two commercial Sn-based brazing solders with a steel matrix is not more than 4MPa under the condition of no plating assistant, while the bonding strength of the two SnZnCuNiTi coatings provided by the invention with the steel matrix under the condition of no plating assistant is 7MPa and 13MPa, which is 2-3 times of that of the commercial Sn-based brazing solder and is far superior to that of the commercial Sn-based brazing solder; then, the macro fractures were compared: the two commercial Sn-based solders are totally or mainly cracked from the surface of a steel matrix under the condition of no plating assistant; meanwhile, blackening of the surface of the steel matrix can be observed, which shows that after hot dip coating is finished, air enters an incompact interface to cause the oxidation blackening of the steel matrix interface at high temperature (the instantaneous temperature of a sample just taken out from a molten pool is still higher); the above cracking position and the color after cracking both indicate that the wettability of two commercial Sn-based solders to the surface of a steel substrate is poor without plating aids. The two SnZnCuNiTi plating layers provided by the invention are broken inside the plating layer but not on the surface of the steel matrix in the stretching process, which shows that the two SnZnCuNiTi plating solutions have strong wetting capacity on the surface of the steel matrix under the condition of no plating assistant.

The combination of the strength and the macroscopic fracture analysis shows that the SnZnCuNiTi plating solution has much better surface wetting capability on a steel matrix than a commercial Sn-based plating layer under the condition of no plating assistant agent.

TABLE 1 bonding Strength and macroscopic fractures of commercial coatings with the inventive coatings and Steel substrates without plating promoters

(3) Microscopic structure observation and analysis of coating/steel matrix interface after hot dip coating

The upper graph in FIG. 7 shows the distribution of the 78.5Sn-9Zn-10Cu-1.5Ni-1Ti plating layer (hot dip 550 ℃ C. times.5 min) in the "full width range (15 mm)" of the hot dip plating sample and the interface macrostructure (20X) under the condition of no plating assistant, and the plating layer has no interface clearance everywhere. The lower left image of fig. 7 is an interface microstructure of a region B, which is partially enlarged to 1000 times, and the lower right image of fig. 7 is an interface microstructure of a region E, which is partially enlarged to 2000 times. The result shows that the interface of the plating layer/steel matrix is compact and good in wetting, and the defect of poor wetting property is not observed even if the interface is amplified to 1000-2000 times; the plating layer is compact and has the thickness of 100 mu m; the plating layer mainly comprises a Sn matrix which has good plasticity and is in a net shape and a second phase which is discretely distributed in the Sn matrix. The Sn matrix with good plasticity is in a continuous network shape, so that the second phase particles are isolated, and the harm of the second phase particles is reduced.

FIG. 8 shows the macroscopic (upper diagram in FIG. 8) and macroscopic (back-scattered image in C region in the left lower diagram in FIG. 8 and the macroscopic secondary electron image in C region in the right lower diagram in FIG. 8) interface structure of the 74.5Sn-7Zn-16Cu-1.5Ni-1Ti plating layer (560 ℃ C. × 5min under hot dip plating) and steel matrix provided by the invention under the condition of no plating assistant.

The interface structures of the two SnZnCuNiTi formulas are very similar, the interface wetting is good, no visible defect exists, and the alloy system has good stability and reproducibility in the aspect of wetting property.

(4) Melting point, structure and properties (shear properties) of the coating itself

FIG. 9 shows DSC curves of 78.5Sn-9Zn-10Cu-1.5Ni-1Ti (left) and 74.5Sn-7Zn-16Cu-1.5Ni-1Ti (right). The melting characteristics of the two are close to the parameters, and the solidus is 233 ℃; although the liquidus is high, the added alloy elements can be significantly dissolved below the transformation temperature (A1) of the steel and remain in an activated state.

FIG. 10 shows the microstructure of a 74.5Sn-7Zn-16Cu-1.5Ni-1Ti smelted block, and it can be seen that the brazing filler metal has uniform structure and consists of a Sn matrix with good plasticity and in a net shape and second phases which are discretely distributed in the Sn matrix, and because the Sn matrix with good plasticity is in a continuous net shape and separates second phase particles, the harm of the second phase particles is reduced.

Wherein, the shear strength of the brazing filler metal can be measured by a displacement-load curve:

the solder 78.5Sn-9Zn-10Cu-1.5Ni-1Ti shear strength is as follows:

the shear strength of the solder 74.5Sn-7Zn-16Cu-1.5Ni-1Ti is as follows:

the shear strength of the solder is actually measured to be about 20 MPa.

Through the hot dip coating appearance defect inspection, the bonding strength and fracture analysis and the comparative analysis of the interface microstructure, an evidence chain supporting each other can be formed, which shows that the surface wetting capability of the SnZnCuNiTi quinary coating provided by the invention to a steel matrix is far better than that of a commercial Sn-based coating under the condition of no plating assistant.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.