TWI575085B - Alloy coated workpieces - Google Patents

Description

Alloy coated workpiece

The present invention relates to a method for providing a workpiece or member having an alloy coating. The present invention is primarily directed to the manufacture of iron articles by providing a zinc-containing coating using a coating, particularly zinc powder or a zinc-based powder containing a mixture of elements or zinc alloys, to protect the iron article from corrosion.

A wide variety of coating methods are available to impart acceptable corrosion resistance to ferrous components. The method used can vary depending on the nature of the ferrous component, the composition of the coating, and the nature experienced during operation of the protective member. Decades of research have continually pursued better and more economical systems in order to achieve corrosion resistance that meets stringent requirements. The requirements for corrosion resistance (measured by the number of non-corrosive operating hours of ferrous components) are gradually increasing, and the early acceptable corrosion resistance is no longer satisfactory.

There are several different processes for coating zinc-containing coatings that can impart corrosion resistance to ferrous components. Processes such as electroplating and hot-dipping have been used for decades to coat zinc and zinc alloys. In the case of hot dip plating, it has been found in recent decades that aluminum-containing zinc alloys can greatly improve the degree of corrosion resistance that can be obtained. The discovery was originally based on a zinc alloy containing a low aluminum content, such as Zn-(3%-7%) Al. however It has been found that the use of high aluminum content alloys (eg, Zn-55% Al) may result in better corrosion resistance. Even more complex hot dip coatings (such as those containing a small amount of Cu, Mg and Si) have been developed and advantageous microstructures have been achieved.

The zinc coating applied by hot dip plating and electroplating (less used) has achieved brilliant achievements in protecting iron members and iron products. These zinc coatings provide good protection against the formation of white zinc corrosion products and prevent red rust from rusting the iron substrate. However, electroplating and hot dip coating require a large amount of capital and are suitable for large iron products and elongated iron materials such as plates, strips and threads.

Another process for forming a zinc or zinc alloy coating to protect the ferrous component from corrosion is to use a powder or shard of zinc or zinc alloy dispersed in the liquid. The powder dispersion can be applied by soaking, brushing, spraying or any other suitable means. The member is then heated to a temperature at which the liquid can evaporate, decompose or solidify to provide a zinc coating or a zinc-containing coating. The process is carried out in some cases to form a hard, wear resistant coating on the component. In other cases, the iron of the substrate is diffused into the coating by heating at a certain temperature for a period of time. Examples of this type of process that can be used in various metal powders and component forms are provided in the following patent references: GB 1,071,624 to Imperial Smelting Corp (NSC) Ltd; US 1,815,638 to Watkins; US 4,391,855 to Geeck; US 4,628,004 to Nickola et al. US Patent No. 2003/0059542 to Kircher et al., and US Patent Application No. 2003/0059542 to Creech et al. U.S. Patent Application Serial No. 2012/0006450, filed by Graf et al.

The zinc coating can also be applied using the Sherardising method, which was invented in 1900 and is well known. The Sherardising method is named after the inventor, and the Sherardising method involves burying the iron member in a bed of inert particulate filler (such as cerium oxide or alumina) dispersed with a small amount of zinc-containing powder. The packed bed may also contain materials such as clay. The housing containing the packed bed and the embedded member is then heated for several hours while rotating the container. The heating step is such that the temperature is such that zinc can diffuse in the gas phase and react with iron on the surface of the member to form a diffusion coating on the members. Oxygen must be excluded from the process to prevent oxidation of the zinc.

Several modern examples of the Sherardising method are disclosed in the following patent documents: US Pat. No. 3,808,031 to Brill-Edwards; US 6,171,359 to Levinski et al; US 7, 192, 624 to Shtikan et al.; US Pat. No. 7,241,350 to Rosenthul; U.S. Patent Application No. 2005, to Danger et al. U.S. Patent Application Serial No. 2009/0266454 to Graf et al., and U.S. Patent Application Serial No. 2010/0215980, filed on Jan.

The development of the Sherardising method was attributed to the first inventor of U.S. Patent No. 7,192,624, and the method was successfully commercialized under the Armor Galv trademark. It is understood that the advancement provided by the ArmorGalv process lies in the "special zinc powder formula". The process (also known as thermal diffusion galvanizing) can be described as a habit Know the improved version of the Sherardising zinc/iron vapor diffusion process. It has been quite common to successfully achieve an anti-corrosion effect of more than 1000 hours in a salt spray test. As in the general Sherardising process, the ArmorGalv process involves tumbling the components in a container placed in an oven while heating to a temperature between 310 ° C and 450 ° C. Heating was continued at this temperature for 3 hours to 4 hours, after which the members were slowly cooled for a similar length of time.

An alternative to the Sherardising method is disclosed in the following patent documents: U.S. Patent Application Serial No. 2006/0159859 to Danger et al. In the latter document, the profiled structure of the steel sheet is enveloped in a metal powder which is electrostatically deposited on the steel sheet, the steel sheet is heat treated to form a coating by a diffusion process, and then the steel sheet is cooled. The words "fogged" or "fogging" are not explained in the text, but these terms appear to be intended to express exposure to smoke-like zinc dust.

Yet another process suitable for providing a protective coating is known as mechanical plating, also known as peel plating or cold welding. Mechanical coating is effective for applying zinc, tin or other ductile metals to the component. A batch of components is loaded into the bucket and a coating is formed on the components using glass beads and fine powder or dust of the expanded metal. By rotating the barrel, the impact and impact energy is transmitted to the members by glass beads, and the fine powder or dust particles are cold welded to the surfaces of the members. In the case where the components are not at risk of hydrogen embrittlement or without the use of heat, the process produces a coating that is strongly adherent, has some microporosity and has a matte finish, and the coating may be the The coated component provides an anti-corrosion effect. The process is suitable for protecting a variety of relatively small components and can be widely used to provide corrosion protection for fasteners such as screws and self-tapping screws, including high strength fasteners for use in automotive body structures, particularly Some Rockwell C scales are higher than about 40 fasteners.

As described by ASTM International in ASM Handbook, Volume 5, "Surface Engineering," published in 1994, mechanical coating provides a means of achieving desired mechanical properties and galvanic properties. A straightforward method that has a very low risk of hydrogen embrittlement and can be completed at room temperature. The coating may be a single layer or at least two layers depending on, for example, the environment in which the anti-corrosion effect is to be obtained and whether another property (for example, low friction) is desired.

Published by Demyashev et al. and published by Swinburne Institute of Technology (IRIS) of Swinburne University of Technology in April 2011 titled "The Effect of Tin Alloying on Corrosion Resistance of High Carbon Steel Treated by Sherardising (Effect The paper on the Sn-alloying on Corrosion Resistance of Sherardised High Carbon Steel) further expands the field of technology. This IRIS paper attempts to improve the corrosion resistance of steel surfaces using zinc for conventional Sherardising zinc infiltration and is said to be suitable for automotive applications. It has been reported that the conventional Sherardising method using zinc can be modified by (1) using the conventional Sherardising method but using a Zn-10% Sn powder mixture; or (2) in the intermediate stage, ie in After the Sherardising phase but in addition Prior to the hot phase, mechanical coating was applied using Zn-10% Sn for further heat treatment.

The red rust corrosion resistance achieved by the modification (1) was as long as 174 hours compared to the 42-hour corrosion resistance achieved by the conventional Sherardising method (using zinc but not using tin).

The modification scheme (2) showed a further improvement effect of no red rust for 290 hours and no white rust for 99 hours.

It is an object of the present invention to provide an alternative process for forming a protective coating on an ferrous member to enhance corrosion resistance.

According to the present invention, there is provided a process for coating an iron member, wherein the uncoated iron member is subjected to the following steps: (a) using a metal zinc-containing powder such as zinc powder or zinc alloy powder or zinc or a powder mixture of a zinc alloy and at least one other metal as a coating medium for mechanical coating to accumulate a strong adhesion coating formed by the coating medium on the exposed surface of the members; (b) heating The members having the firmly adhered coating layer form a solid-solid diffusion effect on the surface to form a Fe/Zn intermetallic (Fe/Zn intermetallic) in at least the underlayer of the coating formed by the coating. And; (c) cooling the components.

As described herein, the process is applied to ferrous components. That is, the exposed surface of the members to be coated on the surface by mechanical coating is a bare metal surface, and the bare metal surfaces must be capable of forming Fe/Zn intermetallic The diffusion effect required by the genus layer. Thus, prior to mechanical coating of such members in accordance with the present invention, the members are free of any film or layer, such as a film or layer that is formed by applying a corrosion resistant treatment or applying a phosphate treatment, painting, or the like. In contrast to the second modification proposed in the IRIS paper, these components were not subjected to zinc rust protection prior to mechanical coating. However, prior to mechanical coating, the members are preferably treated as generally described below in order to ensure that the exposed surfaces are clean and conditioned ferrous metal surfaces of the members.

In commonly used routines, such components are typically processed according to standard mechanical coating procedures recommended in conjunction with formulations (eg, formulations sold under the registered trademark ALZIN). Thus, the hot alkaline cleaners can be used and then the components can be treated with an acid wash and rinsed. The grease-free component is loaded into a coating vessel, which is typically a bucket that is slanted, open at the top, and has a cross-section such as a hexagon or an octagonal shape. If necessary, the components can be cleaned in the container using a dedicated descaling/degreasing agent. However, some components may be subjected to mechanical coating without cleaning, relying on the initiator formulation for cleaning. The members are loaded into the container at an approximately equal volume ratio to the impact medium, or a larger volume of medium can be used when the member is heavier or if a thicker coating is desired. Preferred media include mixed size glass beads ranging in size from about 4 mesh to up to about 60 mesh. A liquid (most commonly water) is added to the container such that the amount of liquid added during coating is more than about 20 mm to 50 mm above the contents of the container as the container is rotated.

In this general procedure, the contents of the container may be at a temperature of from about 20 ° C to 30 ° C, although temperatures may exceed this range during coating. Coated The speed increases with temperature so that if the initial temperature is lower, gentle heating may be required. In addition to this, no heating is required, and it is conceivable to obtain a gentle cooling under extremely hot conditions, in particular when the temperature of the contents of the container generally rises during coating.

At the beginning of the general procedure, a starter formulation was added to the vessel to determine the correct conditions for the coating. These starters can be used in combination with different acid sources. The initial rotation of the container can last for a few minutes to allow the starter to spread throughout the contents of the container. A copper formulation and/or a tinning formulation is then added to the vessel and mixed with the initiator to provide a base on the components that facilitates controlled coating. Copperation and/or tinning takes a few minutes. After copperation and/or tinning, a promoter formulation is added to the vessel to facilitate continued coating of the components. At this stage, the metal zinc-containing medium has not been added to the container. A small amount of zinc medium is added to form a "flash" coating that provides a good base layer for further coating. All of the zinc medium is then added, and although all of the zinc medium can be added at once, the coating results obtained by adding a small amount of zinc medium several times in succession are preferred. During the coating, the pH was monitored to ensure that the coating was not stopped due to an increase in pH above 2.0. The thickness of the coating is also monitored, and when the desired thickness is reached, the remaining powder is removed to reinforce the resulting coating. Thereafter, the components are rinsed, and the components are separated from the plating solution, and the components are coated with a chromate finish and a sealant, which substantially enhances the components. The duration of the anti-corrosion effect.

As noted in the IRIS paper, mechanical coatings may have pores, while 30% to 35% porosity (cited data) for high quality work. Industrial coatings are already the limit. In any event, porosity is likely to be a major factor in the conventional mechanical coating process that is believed to be only suitable for achieving a good and usable but relatively low degree of corrosion protection on ferrous components. Therefore, this IRIS paper proposes that mechanical coating is one of the feasible methods to improve the anti-corrosion effect provided by the previous Sherardising step, because most of the outside world acknowledges that the Sherardising zinc-wetting rust alone provides better corrosion protection than the use of conventional knowledge. The anti-corrosion effect achieved by mechanical coating. In this regard, a distinction is made between the conventional mechanical coating method and the mechanical coating method proposed by the IRIS paper, on the one hand that the conventional mechanical coating method does not perform the steps after the first step of the process of the present invention and As with the present invention, it is applied to an uncoated iron member, and on the other hand, the mechanical coating method proposed by the IRIS paper is applied to a member having a protective coating which has been previously provided by the Sherardising method. In this proposal, the mechanical coating method is not a conventional mechanical coating because (a) the mechanical coating method is applied to the coated member produced by the previous Sherardising method, and (b) The mechanical coating process is followed by heating of the component for a second period of time (this is because in the Sherardising process itself there is a heating step that continues for a first time). The present invention uses a heating step after the mechanical coating step, rather than heating when the bare surface of the original uncoated member is coated.

The first solution provided by the present invention is to use a heating step after conventional mechanical coating on the component. As described herein, conventional mechanical coating provides a less effective void coating than other coating methods. However, it has unexpectedly been found that the use of a heat treatment step after the mechanical coating step on the component (the component is uncoated prior to coating) provides an anticorrosive effect over the machine. Mechanical coatings have been significantly improved without heat treatment.

The improved corrosion resistance obtained by the process of the present invention is attributed to the nature of the Fe/Zn intermetallic itself generated by solid-solid diffusion. Although the coating formed by the mechanical coating method has porosity, the Fe/Zn intermetallic can exhibit better corrosion resistance. It was found that the intermetallic formed by solid-solid diffusion is substantially void-free. This is apparently due to the solid-solid diffusion from the point where the solid component is in contact with each of the individual powder particles at each of the solid-solid, metal-to-metal contact, and the diffusion from each point. The front end continues to advance toward the interior of the component surface and the entire surface, so the front ends overlap and create a substantially non-porous metal-conducting surface region.

The degree of improvement provided by the process of the present invention allows the obtained anti-corrosion effect to be at least better than that obtained by the Sherardising method, and is superior to the anti-corrosion effect obtained by the Sherardising method in many cases, and the process of the present invention is at least comparable to the US. The corrosion resistance provided by the proposed modification of this IRIS paper. The process of the present invention not only provides a simpler anti-corrosion process, but also avoids the large amount of time and expense involved in previous coating stages (e.g., coating using the Sherardising method), which has great benefits. This IRIS paper conservatively says that the cost of the Sherardising method is only 50% of the cost of the Zn-plating process. The cost of the Sherardising method itself is enormous. Also, the Sherardising process is a relatively slow process due to the slower diffusion of steam to solids. Moreover, the Sherardising method is wasteful in the use of zinc, and the Sherardising method undoubtedly requires a large capital expenditure and operating costs, and the process of the present invention is exempt from these two expenditures for many component forms.

In the process of the present invention, the metal zinc-containing powder may simply comprise zinc powder, and it has been found that the application of such a powder according to the present invention provides an excellent anti-corrosion effect. While other powders provide comparable corrosion resistance, certain powder mixtures composed of zinc and at least one other metal and certain zinc alloys provide a higher degree of corrosion protection, at least in accordance with ASTM B117 using a salt spray test. This is the case. A powder mixture of zinc and up to about 25% by weight tin (e.g., from about 6% to 20% by weight tin) is particularly beneficial for further enhancing the corrosion resistance, while zinc alloys containing up to the same amount of tin are similar. Behavioral performance. The particle size of the metal zinc-containing powder can be varied as in the conventional mechanical coating method. The powder may range in size from 2 micrometers (μm) to 30 micrometers, preferably from 3 micrometers to 8 micrometers.

In addition to zinc powder, a mixture of zinc powder and tin powder, and a zinc/tin alloy, other metals may be present. Thus, each of these options may comprise up to about 15% by weight aluminum, up to about 6% by weight magnesium, and a combination of magnesium and aluminum having a magnesium aluminum content up to respective limits. Not more than 0.8% by weight of cerium may be present in the alloy powder, but strontium is preferably not used in the powder mixture. Further, when a powder mixture or alloy is used, up to about 0.8% by weight of copper may be present, and depending on the case, magnesium may be present, but the magnesium content is not more than 0.1% by weight.

The zinc powder, the zinc powder mixture or the zinc alloy powder preferably does not contain a hard metal, and the hard metal is not suitable for the mechanical coating method. Such hard metals include nickel, titanium, tungsten and molybdenum. Several other metals may be present in the powders, but overall it is not possible to provide an improvement to such powders that can be used. The individual content of the other metals is preferably not more than 0.5% by weight, and the total content of the other metals is not more than about 2.5% by weight.

In carrying out step (a) of the process of the invention, the uncoated ferrous member together with the glass beads used to provide the impinging medium and a sufficient amount of the desired metal-containing zinc powder are loaded into the open and tilted rotatable end. In the container. Unlike the Sherardising process (for example, the ArmorGalv process), the metal zinc-containing powder is not mixed with the inert particulate material, and is different from the process of coating the member using the powder dispersed in the liquid, the zinc-containing powder. Contains no binder. The powder preferably contains adjuvants commonly used in mechanical coating methods, such as those described above. The container may be in the form conventionally employed for mechanical coating. Also, the mechanical coating step does not require heating. Instead, the mechanical coating step is carried out without heating and under ambient environmental conditions. These conditions include operation in a prevailing ambient atmosphere. Unlike the Sherardising method, the mechanical coating step does not necessarily have a moderately low oxygen content (eg, no more than about 100 ppm) in order to meet the Sherardising requirements (to avoid the oxygen contamination that would otherwise occur during the heating process). In the atmosphere of the operation.

The mechanical coating of step (a) of the present invention is continued for a suitable period of time to achieve the desired coating thickness. The coating thickness can range from 2 microns to 150 microns, such as from 10 microns to 75 microns. For conventional coating thicknesses, the length of mechanical coating can range from 0.5 hours to preferably no more than 2.5 hours. Since the temperature is not a relevant parameter, this length of time is determined only by the required coating thickness. Temperature is an important parameter when using the Sherardising method and the range of data presented is broad, for example from about 200 ° C to 500 ° C, but more often between 300 ° C and 450 ° C, according to published data from the ArmorGalv process, 315 ° C to 450 ° C (or The temperature expressed as 600 °F to 850 °F) takes 3 hours to 4 hours (there is a vague inverse relationship between time and temperature). Not only available The mechanical coating step of the present invention is carried out at a substantially constant temperature, and the progress of the step is relatively short and the time may range from about 0.5 hours to 4 hours, preferably from 0.5 hours to 3.5 hours, for example from 1.5 hours to 2.5 hours. . The time required to lay the coating using this mechanical coating step is usually due to the impact and impact energy transmitted by the glass beads to form the coating, rather than relying on a relatively slow thermal diffusion galvanizing mechanism (Sherardising method) It is based on a thermal diffusion galvanizing mechanism).

In carrying out step (b) of the present invention, the coated components are heated in a vessel that is open to the atmosphere or maintained at a low oxygen content (e.g., less than about 100 ppm) positive pressure atmosphere. This heating step is a heating to a temperature at which solid-solid diffusion can occur to form a Fe/Zn intermetallic. The temperature may range from 315 ° C to 415 ° C, but is preferably from 360 ° C to 380 ° C. Depending on the temperature, the heating time may be from about 0.4 hours to 3 hours, preferably from 1.5 hours to 2.5 hours. Upon completion of the heating step, the coated components are cooled in the atmosphere in which the coated components are heated in step (b) or in the surrounding atmosphere. While it is sufficient and acceptable to naturally cool such components (e.g., air cooling), forced cooling (e.g., water quenching) can also be used.

After the step (b) of the present invention, the coating is cracked like a coating made by the Sherardising method. However, unlike the Sherardising coating, the coatings made in step (a) have porosity. The components after step (a) of the present invention generally exhibit a degree of corrosion resistance that is good and can be used in a variety of applications, generally as mechanically coated members, although such corrosion resistance is less than that achieved by the Sherardising process. Nevertheless, it was unexpectedly found that after the step (a), After completing steps (b) and (c) of the present invention, the resultant coating formed by the solid-solid diffusion imparts a higher degree of corrosion resistance to the members, such that the members Suitable applications are more widely used. Thus, although the coatings produced by the overall process of the present invention may still have some surface porosity, this does not impair the corrosion resistance of the present invention as compared to the corrosion resistance that can be achieved using only conventional mechanical coating methods. A significant increase in substance has been achieved. This degree of lift is achieved by using the present invention to achieve an anti-corrosion effect at least comparable to the Sherardising method.

Information on Sherardising methods, particularly those of ArmorGalv method is disclosed in the book DELNORTH Products: ArmorGalv® (see the following URL: www.armorgalv.com.au/SiteFiles/armorgalvcomau/DELNORTH_ARMORGALV_PRESENTATION.pdf).

In the table on page 12 of this Delnorth document, the corrosion resistance of the coating formed by mechanical coating is classified as "medium" as in the case of hot dip coating and immersion/spin coating, and in contrast, The electroplating method is classified as "middle and upper" for the alloy and the ArmorGalv thermal diffusion method is classified as "excellent". Page 6 of the Delnorth document mentions that the trial is still in progress until July 1, 2009, confirming that the document provides relatively modern data. Also on page 7 indicates that salt spray test results over 1000 hours are common for ArmorGalv coatings. On page 6, a 25 micron ArmorGalv bronze coating is available for up to 4000 hours of salt spray test duration and a 40 micron ArmorGalv natural coating can be used to achieve a 5000 hour salt spray test durability. time. Depending on the thickness, the coating provided by the present invention is tested in salt spray. It can support more than 1000 hours in the test, and at least when it is the same as the ArmorGalv coating, when the coated component has a modified coating (for example, the chromate treatment agent and sealant detailed above), it can reach close or More than 4000 hours.

The solid-solid diffusion in step (b) of the present invention is achieved under conditions which are significantly different from those in the Sherardising process. In the step (a) of the process of the present invention, the coating formed by the mechanical coating is such that the individual particles of the metal zinc-containing powder are cold-welded to the surface of the member in the form of a micro-flat sheet and cold welded to the previously cold-welded The thin slices are accumulated. The progressive accumulation of the flakes is due to the impact and beating action of the glass beads and no solid-solid diffusion occurs. In the present invention, the solid-solid diffusion during step (b) occurs in the finished coating formed by step (a). Thus, the diffusion of iron from the component can be advanced through the coating from the interface between the surface of the component and its coating. Conversely, a coating formed using a Shearddising process (e.g., ArmorGalv) can be such that zinc vapor contacts the components such that zinc initially condenses on the surface of the components to form a Fe/Zn intermetallic. As zinc continues to compress and solidify, iron can diffuse out of the surface of the component and pass through the intermetallic coating that is accumulating, and the continuously compressed solidified zinc can also diffuse through the forming intermetallic coating to reach the surface of the component.

The coating produced in step (a), particularly a coating made using a coating medium containing pure zinc, may exhibit porosity. The coating prepared by using the mixture of zinc powder and tin powder or the coating medium containing zinc-tin alloy by step (a) may have no pores, and as the tin content is increased, the coating is more favorable for forming a non-porous coating. Floor. Where porosity is prone to occur, the porosity may decrease with the length of time during which step (a) is performed, as the coating being formed is gradually thickened and because The percentage of the surface area of the member on which the sheet is cold welded to form a coating is increased. However, increasing the thickness of the coating tends to inevitably leave some residual porosity after step (a). However, the results of the salt spray test using the member coated with the coating according to the present invention show that the solid-solid diffusion effect achieved in the step (b) of the present invention can alleviate the influence of porosity even if it is not completely offset.

The reason why the enhanced corrosion resistance achieved by the present invention outweighs the conventional mechanical coating method is not fully understood at this stage. In contrast to the conditions used in the Sherardising process, various indications indicate that this advancement is caused by the different conditions of solid-solid diffusion in step (b). At least to some extent, the solid-solid diffusion in step (b) appears to reduce the size of the pores (the coating formed in step (a) has pores), while zinc may also occur during step (b) The coating migrates from the coating to the surface of the component exposed by the holes. However, at least under certain conditions, the components treated by the process of the present invention exhibit a little red rust after the initial stage of the salt spray test, but this condition does not deteriorate during further long-term testing, and the final result is These components exhibit excellent long-term corrosion resistance. The small amount of rust is not so severe as, for example, that the nut and bolt assembly protected by the coating formed in accordance with the present invention is difficult to unscrew. The small amount of rust does not mean that the base metal is corroded (i.e., the member under the coating is corroded), but rather the color produced by the oxidation of iron in the surface intermetallic.

1 to 4 are cross-sectional views showing the formation of a clear intermetallic layer in accordance with an embodiment of the present invention.

An anti-corrosion coating is provided for a plurality of batches of components using the process of the present invention. In each case, a standard mechanical coating procedure was performed using an aqueous solution and a cleaning process added to clean and pH-controlled inhibited acid to remove all oxides and create a surface suitable for further processing. Perform step (a) of the process. The cleaning steps include: (1) performing copper immersion coating; (2) performing tin immersion coating; (3) adding a coating accelerator and a zinc "coloring" agent (zinc) Flash"); (4) adding metal powder at regular time intervals to achieve a desired thickness; (5) flushing the solution and performing several additional rinses upon completion of the coating cycle; and (6) separating the member with Hit the medium.

Example 1 - Zinc Coating

A large number of components were treated in a 2 liter impact medium (40% 5 mm impact medium, 40% 3 mm impact medium and 20% 0.7 mm impact medium) using the standard procedure described above. 12 x 50 hex head T17 steel roof screws. A 90 gram zinc powder having a nominal particle size of 4.5 microns was used to achieve the desired coating thickness. The zinc powder was added in six portions by adding 15 grams of zinc powder every 3 minutes. After the last zinc powder is added, coating is continued for a further 10 to 12 minutes to complete the coating and polishing. The components are then rinsed and separated without any additional treatment. The coating thickness achieved was approximately 55 microns.

Example 2 - Zinc/Tin Coating

A large number of components were treated in a 2 liter impact medium (40% 5 mm impact medium, 40% 3 mm impact medium and 20% 0.7 mm impact medium) using the standard procedure described above. 12 x 50 hex head T17 steel roof screws and 200 gram 5 mm x 10 mm long flat head half pipe steel rivets. A 60 gram zinc-tin mixed powder was used to achieve the desired coating thickness. The zinc powder has a nominal particle size of 4.5 microns and the tin powder size is less than 325 mesh (-325 mesh). The composition of the mixed powder was 80% Zn and 20% Sn. The mixed powder was added in six portions by adding 10 gram of powder every 3 minutes. After the last powder is added, the coating is continued for 10 to 12 minutes to complete the coating and polishing. The components are then rinsed and separated without any additional treatment. The coating thickness achieved was approximately 35 microns.

Example 3 - Temperature

A fan oven having a diameter of 1 m was preheated to a temperature of 320 ° C, and 10 zinc coated member samples prepared in Example 1 were placed in the oven. These components are placed in a steel cage. The components were left in the oven for 120 minutes and then the components were removed along with the cage and the components were allowed to cool in air. The screws were cut, the screws were polished using a 1 micron abrasive, and the screws were etched in a mild caustic solution. A clear intermetallic layer is formed as shown in Fig. 1 of the accompanying drawings.

Example 4 - Time Comparison

Example 3 was repeated using an additional 10 zinc coated members made by Example 1, except that the oven temperature was changed to 380 ° C and the members were left at this temperature for 30 minutes. Also cut the screws, polish the screws with a 1 micron abrasive, and etch the solution in a mild caustic solution Wait for the screws. A clear intermetallic layer formation is seen as seen in Figure 2.

Example 5 - Atmosphere

Ten zinc coated screw member samples made using Example 1 were placed in a glass tube, and then the glass tube was filled with argon. One end of the glass tube is closed, and after loading the members, the other end is sealed to seal the screws in an argon atmosphere. A fan oven having a diameter of 1 meter was preheated to a temperature of 380 ° C, and the screws housed in the glass were placed in a wire mesh basket and placed in the oven. The articles were left in the oven for 120 minutes and then removed along with the basket and cooled in air. The glass capsules are then broken and the screws are removed.

Truncate the screws, polish the screws with a 1 micron abrasive, and etch the screws in a mild caustic solution. A clear intermetallic layer formation is provided as shown in Figure 3.

Example 6 - Alloy

A fan oven having a diameter of 1 m was preheated to a temperature of 380 ° C, and 10 Zn/Sn coated screw members (all of which were screws) of Example 2 were placed in the oven. These screws are placed in a steel cage. The components were left in the oven for 120 minutes and then the components were removed along with the cage and the components were quenched in water. Truncate the screws, polish the screws with a 1 micron abrasive, and etch the screws in a mild caustic solution. A clear intermetallic layer formation is seen as seen in Figure 4.

Extensive standard salt spray testing has been performed on components made in the manner detailed in the previous examples, and this test is ongoing. So far, this test has confirmed the process capability of the present invention. Provides excellent corrosion resistance for ferrous components. Excellent protection can be obtained by mechanical coating alone, and the degree of protection obtained by mechanical coating is at least comparable to that obtained by the Sheardsising method. The present invention provides iron members with corrosion resistance that is highly suitable for a wide range of applications and in a variety of environments.

Claims (27)

A process for providing an anticorrosive coating on an ferrous member, wherein the uncoated ferrous member undergoes the following steps: (a) (i) using a metal zinc-containing powder as a coating medium for mechanical operation Coating, whereby a firmly adhered coating formed by the coating medium is accumulated on the exposed surface of the members; (ii) the mechanical coating is performed under the following conditions, and the temperature is not exceeded at 30 ° C An uncoated iron member, together with glass beads, a sufficient amount of zinc-containing powder, and a sufficient amount of aqueous solution, are placed in a tilting rotating container, and the container is rotated for a suitable period of time by means of the glass The action of the bead hitting the members causes the powder particles to be cold welded to the members to achieve the desired coating thickness; and (iii) the metal zinc-containing powder has substantially no iron and is substantially composed of metal An elemental powder, a metal alloy powder or a combination of a metal element powder and a metal alloy powder, wherein the powder is mainly composed of zinc and optionally comprises tin, aluminum, magnesium, strontium, copper and manganese, and not more than 0.5% by weight Any other metal and The total content of the other metals is not more than 2.5% by weight; (b) heating the members having the firmly adhered coating to produce a solid-solid diffusion effect of the diffusion of iron from the members to the coating, and on the surfaces Forming a Fe/Zn intermetallic in at least one of the underlayers of the coating formed by mechanical coating; and (c) cooling the members. The process of claim 1 wherein the exposed surfaces of the members are intended to form the coating on the exposed surfaces by mechanical coating, the exposed surfaces of the members being capable of being formed for formation A bare metal surface required for diffusion of a Fe/Zn intermetallic layer, and the members do not have any film or layer prior to performing step (a). The process of claim 1 or claim 2, wherein prior to the mechanical coating, the oil of the components is removed and/or the components are treated to remove any surface rust. The process of claim 1, wherein the coated members produced by the process have a corrosion inhibiting effect that is significantly greater than when the mechanical coating step is performed but the heat treatment of the members is not performed. Upgrade. The process of claim 4, wherein the degree of corrosion resistance is at least comparable to the degree of corrosion resistance obtained by the Sherardising method. The process of claim 1, wherein the metal zinc-containing powder comprises zinc powder. The process of claim 1, wherein the metal zinc-containing powder comprises a powder mixture or a zinc alloy formed of zinc and at least one other metal. The process of claim 1 wherein the metal zinc-containing powder is a powder mixture of zinc and up to about 25% by weight tin. The process of claim 8, wherein the metal zinc-containing powder has from 6 to 20% by weight tin. The process of claim 1 wherein the metal zinc-containing powder is a zinc alloy powder containing up to about 25% by weight tin. The process of claim 10, wherein the powder has from 6% to 20% by weight tin. The process of any one of claim 7 to claim 9, wherein the metal zinc-containing powder comprises a powder mixture containing at least one of aluminum and magnesium, and each of the aluminum and magnesium has an upper limit of 15 Weight% and 6% by weight. The process of claim 7 or claim 10, wherein the metal zinc-containing powder comprises a zinc alloy containing at least one of aluminum, magnesium and bismuth, and each of the aluminum, magnesium and strontium has an upper limit of 15 Weight%, 6% by weight, and 0.8% by weight. The process of claim 11 wherein the metal zinc-containing powder contains up to about 0.8% by weight copper. The process of claim 1 wherein the coating has a thickness of from 2 microns to 150 microns. The process of claim 14 wherein the coating has a thickness of between about 10 microns and 75 microns. The process of claim 1, wherein the mechanical coating is performed for a period of time from about 0.5 hours to 4 hours. The process of claim 17, wherein the period of time is from 0.5 hours to 3.5 hours. The process of claim 17, wherein the period of time is from 1.5 hours to 2.5 hours. The process of claim 1, wherein after the mechanical coating, the coated components are heated in a container under a positive pressure in step (b), and the container is open to the atmosphere or Maintain a low oxygen content atmosphere. The process of claim 1, wherein the step of heating to produce solid-solid diffusion is performed at a temperature of 315 ° C to 415 ° C. The process of claim 21, wherein the heating step is at 360 ° C to It is executed at a temperature of 380 °C. The process of claim 1 wherein the heating step has a duration of from about 0.4 hours to about 3 hours. The process of claim 23, wherein the heating step has a duration of from about 1.5 hours to 2.5 hours. The process of claim 1 wherein, in the heating step, the coated components are cooled in the atmosphere in which the components are heated. The process of claim 1 wherein, upon completion of the heating step, the coated components are cooled in the atmosphere for one week. The process of claim 1 wherein the water quenching is used to force cooling for cooling the components.