(c) Nisshin - the 257 Patent
1112 Nisshin was published on 28 November 2000 and stands in the name of Nisshin Steel Co Ltd. Nisshin claimed the following:
[Claim 1]
An Mg-containing hot-dip Zn-Al alloy plated steel sheet having high corrosion resistance and good surface appearance, the Mg-containing hot-dip Zn-Al alloy plated steel sheet comprising: a plating layer formed on a surface of a steel sheet, wherein the plating layer contains, by mass%, Al: 25 to 70%, Mg: 1.5 to 5.0%, Sr: 0.01 to 1.0%, and contains Si in a range satisfying the following Equation (1) and the balance being Zn and unavoidable impurities:
Al (mass%)x0.005□Si (mass%)□10 · · ·(1) [sic].
[Claim 2]
An Mg-containing hot-dip Zn-Al alloy plated steel sheet having high corrosion resistance and good surface appearance, the Mg-containing hot-dip Zn-Al alloy plated steel sheet comprising: a plating layer formed on a surface of a steel sheet, wherein the plating layer contains, by mass%, Al: 25 to 70%, Mg: more than 5.0 to 6.0%, Sr: 0.07 to 1.0%, and contains Si in a range satisfying the following Equation (1) and the balance being Zn and unavoidable impurities:
Al (mass%)x0.005□Si (mass%)□10 · · ·(1) [sic].
[Claim 3]
The Mg-containing hot-dip Zn-Al alloy plated steel sheet of claim 1 or 2, wherein Si is contained in a range satisfying the following Equation (1)':
Al (mass%)x0.03□Si (mass%)□10 · · ·(1)' [sic].
[Claim 4]
The Mg-containing hot-dip Zn-Al alloy plated steel sheet of any one of claims 1 to 3, wherein a plating amount per one surface of the steel sheet is 40 to 120 (g/m2).
1113 The discussion of the background was as follows:
[0002] A hot-dip Al plated steel sheet has an advantage in that corrosion resistance of a plated surface is excellent as compared to a hot-dip Zn plated steel sheet. However, since Al does not have a sacrificial protection effect on Fe, unlike Zn, the Al plated steel sheet is inferior to the Zn plated steel sheet in that red rust may easily occur in an exposed portion of base steel such as a damaged portion of a plated surface, a cut cross section of the steel sheet, or the like.
[0003] As a steel sheet in which the advantage of the Al steel sheet, that is, excellent corrosion resistance of the plated surface, and the advantage of the Zn plated steel sheet, that is, the sacrificial protection effect are balanced and introduced, a hot-dip Zn-Al alloy plated steel sheet containing 25 to 70 mass% of Al is disclosed in Japanese Patent Laid-Open Publication No. S46-7161, and as the hot-dip Zn-Al alloy plated steel sheet described above, for example, a Zn-Al (55 mass%) - Si (1.6 mass%) alloy plated steel sheet has been put to practical use.
1114 So, the context concerned the question of corrosion resistance rather than mottling. Nevertheless the body of the specification discussed the question of a wrinkle like defect.
1115 A brief summary of the invention stated the following:
[0005] However, generally, a plated steel sheet in which Mg is added to hot-dip Zn-Al alloy plating (hereinafter, referred to as Mg-containing hot-dip Zn-Al alloy plated steel sheet) has not yet been widely used in spite of an excellent effect of improving characteristics as described above. Particularly, a hot-dip Zn-Al alloy plated steel sheet containing Mg in a large amount (at least several % order) in a plating layer has not yet been commercialized as an industrial product in spite of significantly excellent corrosion resistance.
[0006] The main reason for the delay in industrial distribution of the Mg-containing hot-dip Zn-Al alloy plated steel sheet is that a technology of manufacturing a Mg-containing hot-dip Zn-Al alloy plated steel sheet having good surface appearance using a general hot-dip plating line is not established.
[0007] FIG. 1 is three photographs illustrating surface appearance of a hot-dip Zn-Al alloy plated steel sheet having a plate width of 60 mm, manufactured using a continuous hot-dip plating simulator (test line). Here, in all of the photographs, left and right end portions correspond to edges of the steel sheet, and a plate passing direction in each of the photographs is a direction from the bottom to the top.
[0008] A photograph in the upper part of FIG. 1 illustrates an example of a hot-dip Zn-Al alloy plated steel sheet that does not contain Mg. The Mg-free hot-dip Zn-Al alloy plated steel sheet has almost smooth and good surface appearance. Further, white parts seen as a spangle shape (some of them are seen as a stem shape) in the photograph in the upper part, which reflect crystal grains in the plating layer, are not defects. A photograph in the middle part of FIG. 1 illustrates an example of a hot-dip Zn-Al alloy plated steel sheet containing about 1% of Mg. A white stem extended from both edge portions to a lower portion of an oblique line is observed. This stem is a portion having a wrinkle-like uneven surface. In the case of adding Mg to a hot-dip Zn-Al alloy plating bath, the above-mentioned wrinkle-like unevenness (hereinafter, referred to as a wrinkle-like defect, or wrinkle-like unevenness defect) is generally formed in a plated surface, which deteriorates surface appearance of a product, thereby deteriorating a value of the product. A photograph in the lower part of FIG. 1 illustrates an example of a hot-dip Zn-Al alloy plated steel sheet containing about 6% of Mg. When a large amount of Mg is contained as described above, the wrinkle-like defect is formed in the vicinity of a central portion of the plate in a width direction as well as edge portions thereof, such that surface appearance is significantly deteriorated.
[0009] An object of the present invention is to provide an Mg-containing hot-dip Zn-Al alloy plated steel sheet having high corrosion resistance and good surface appearance in which a wrinkle-like defect is suppressed, capable of being manufactured using a general hot-dip plating line in which a surface of a plating bath is under air atmosphere.
[0010] The wrinkle-like defect is significantly prevented by allowing an Mg-containing hot-dip Zn-Al alloy plating layer to contain a trace amount of Sr. That is, according to claim 1 of the present invention, there is provided an Mg-containing hot-dip Zn-Al alloy plated steel sheet having high corrosion resistance and good surface appearance, including: a plating layer formed on a surface of a steel sheet, wherein the plating layer contains, by mass%, Al: 25 to 70%, Mg: 1.5 to 5.0%, Sr: 0.01 to 1.0%, and contains Si in a range satisfying the following Equation (1) and the balance being Zn and unavoidable impurities:
Al (mass%) x0.005□Si (mass%)□10 · · ·(1) [sic].
[0011] Here, a chemical composition of a hot-dip plating layer may be specified by dissolving the plating layer in a solution such as an HCl solution, or the like, and analyzing the solution using inductively coupled plasma (ICP) atomic emission spectrometry. Since in manufacturing of a hot-dip plated steel sheet, a surface of the steel sheet generally reacts with a plating metal to thereby be slightly dissolved, elements (iron, and the like) derived from the steel sheet are slightly contained in the plating layer. In the present invention, these elements are also considered as the unavoidable impurities. An Si content in the plating layer may be specified by Equation (1). More specifically, for example, in the case in which an Al content in the plating layer is 25 mass%, the Si content may be specified in a range of 0.125 to 10 mass%, and in the case in which the Al content in the plating layer is 70 mass%, the Si content may be specified in a range of 0.35 to 10 mass%.
1116 In a detailed description of the illustrated embodiments the following was said:
[0016] Mg serves to cover a surface of a plating layer and an exposed portion of base steel with a corrosion product when a hot-dip Zn-Al alloy plated steel sheet is under a corrosion environment, thereby further improving original corrosion resistance of the hot-dip Zn-Al alloy plated steel sheet. That is, Mg in the plating layer serves to form intermetallic compounds with Zn and Si, that is, MgZn2 and Mg2Si, and these intermetallic compounds serve as Mg sources promoting formation of stable protective corrosion products in the corrosion environment. Therefore, the surface of the plating layer is rapidly covered with uniform corrosion products, and these corrosion products are stably present and exhibit their protective film functions, such that corrosion resistance of a plated surface is improved. Further, since the exposed portion such as a cut cross section, or the like, of the base steel is also covered with these corrosion products, early disappearance of the plating layer caused by a galvanic effect between Zn in the plating layer and Fe in a plating back plate may also be suppressed. That is, Mg serves to maintain the sacrificial protection effect while improving corrosion resistance of the plated surface.
[0017] When the Mg content in a Zn-Al alloy plating layer is less than 1.5 mass%, this corrosion resistance improvement effect is not sufficiently obtained. Further, when the Mg content is more than 6 mass%, it is difficult to sufficiently suppress a wrinkle-like unevenness defect in the surface of the plating layer even in the case of adding Sr to be described below. Therefore, the present invention relates to an Mg-containing hot-dip Zn-Al alloy plated steel sheet in which the Mg content in the plating layer is in the range of 1.5 to 6.0 mass%.
[0018] At the time of manufacturing the hot-dip Zn-Al alloy plated steel sheet containing a large amount of Mg as described above, generally, the wrinkle-like unevenness defect may occur as described above, thereby significantly deteriorating surface appearance of the hot-dip Zn-Al alloy plated steel sheet. The reason is that growth of an oxide film on a surface of a molten metal is significantly promoted by adding Mg to the plating bath, and thus the oxide film inhibits a uniform flow of a plating metal in a molten state.
[0019] The present inventors found that when a suitable amount of Sr is contained in a plating layer, a wrinkle-like defect problem as described above may be solved. The reason may be that in a non-solidified surface of the plating layer picked out from the plating bath, Sr is preferentially oxidized than Mg, and thus oxidation of Mg is suppressed.
[0020] It is preferable that a Sr content in the plating layer is 0.01 to 1.0 mass% when the Mg content is 1.5 to 5.0 mass%. When the Sr content is less than 0.01 mass%, an effect of suppressing the wrinkle-like defect is hardly exhibited. However, when the Sr content is more than 1.0 mass%, spot-like unevenness caused by an Al-Si-Sr based intermetallic compound may occur, thereby deteriorating surface appearance of the plating layer . In the case in which the Mg content is high (more than 5.0 to 6.0 mass%), it is preferable that a lower limit of the Sr content is increased to 0.07 to 1.0 mass%. When the Si content is less than 0.07 mass%, the wrinkle-like defect may not be sufficiently suppressed.
…
[0024] The Mg-containing hot-dip Zn-Al alloy plated steel sheet according to the present invention may be manufactured using a general continuous hot-dip plating line. The present inventors confirmed through a separate experiment that in the Mg- containing hot-dip Zn-Al alloy plating, a composition of the plating bath is almost reflected as it is in a composition of the plating layer in the plated steel sheet. Therefore, at the time of manufacturing the Mg-containing hot-dip Zn-Al alloy plated steel sheet according to the present invention, there is a need only to adjust the Al content, the Si content, the Mg content, and the Sr content in the plating bath so as to coincide with the composition of the plating layer to be desired.
1117 Importantly, Table 1 reported on the following results:
1118 I will discuss Table 1 and some of the entries in more detail later. But I should make some observations at this point in terms of what Table 1 displays. The description for Example 1 gives the following explanation:
[0025] Hot-dip Zn-Al alloy plated steel sheets in which Mg and Sr contents were variously changed were manufactured using a continuous hot-dip plating simulator (continuous hot-dip plating test line). Plating conditions were as follows.
• Base steel sheet: cold-rolled Al killed steel (thickness: 0.8 mm, width: 60 mm)
• Maximum Temperature Reached by Sheet in Reduction Furnace: 700°C , Dew point: -35°C
• Sheet passing rate: 50 m/min
• Composition (mass%) of plating bath: Al:55%, Si:1.6%, Mg:0-7%, Sr:0-1.5%, and the balance being Zn and avoidable impurities
• Temperature of plating bath: 605°C
• Immersion time : 3 seconds
• Cooling after plating: air cooling (cooling rate: 20°C/s)
[0026] Surface appearance of the manufactured hot-dip plated steel sheets was observed by the naked eyes, and an occurrence degree of a wrinkle-like defect was ranked into four levels (⦾, ⚪, △, and x) As an evaluation standard, the surface appearance was ranked as follows using samples illustrated in the photographs in FIG. 1.
• ⦾: The hot-dip plated steel sheet had good surface appearance equivalent to or more excellent than that of a sample at the top in FIG. 1.
• ⚪: The hot-dip plated steel sheet had surface appearance worse than that of the sample at the top but equivalent to or more excellent than that of a sample in the middle in FIG. 1.
• △: The hot-dip plated steel sheet had surface appearance worse than that of the sample in the middle but more excellent than that of a sample at the bottom in FIG. 1.
• x: The hot-dip plated steel sheet had surface appearance equivalent to or worse than that of the sample at the bottom in FIG. 1.
[0027] A case in which the wrinkle-like defect occurred was also evaluated as "⚪". However, even in this case, surface appearance was significantly improved as compared to a material according to the related art, and it is considered that a product value of the hot-dip plated steel sheet was sufficient depending on the uses. Therefore, in the present invention, when the surface appearance was evaluated as "⦾" or "⚪", it was determined that surface appearance was good. However, since a case in which spot-like unevenness attributed to an Al-Si-Sr based intermetallic compound was formed means that even though occurrence of the wrinkle-like defect was sufficiently suppressed, a novel defect that did not occur in the material according to the related art occurred, this case was evaluated as unevenness exists.
[0028] Further, after each of the plated steel sheets was exposed in a coastal industrial belt in Sakai City, Osaka Prefecture for 3 months in a state in which a 2t bending processing part and a cross-cut part (a portion at which an X-shaped scratch was formed on a surface of the plating layer) were formed in each of the plated steel sheets, and at the same time, the base steel was exposed in a cut cross section thereof, a degree of inconspicuousness of red rust was evaluated. A commercial Zn-Al (55 mass%)-Si (1.6 mass%) alloy plated steel sheet that did not contain Mg was used as a standard sample, and the degree of inconspicuousness of red rust was observed by the naked eyes and was ranked into four levels (⦾, ⚪, △, and x) as follows.
• ⦾: Red rust was hardly seen.
• ⚪: Red rust was more inconspicuous than that of the standard sample.
• △: Red rust was inconspicuous similarly to that of the standard sample.
• x: Red rust was more conspicuous than that of the standard sample.
[0029] Further, a composite cyclic corrosion test (CCT) was performed on each of the plated steel sheets. CCT conditions were determined according to Japan Automobile Standards Organization (JASO) M609-91 standardized by the Society of Automotive Engineers of Japan, and one cycle was composed of salt water spray (5% normal saline) at 35°C for 2 hours → drying at 60°C and relative humidity 30% for 4 hours → wetting at 50°C and relative humidity 95% for 2 hours. A cross section and an entire inner surface of the test sample were sealed with an insulating tape and used in the test. After completing CCT 200 cycles, corrosion products were removed by a 10% ammonium chloride aqueous solution (solution temperature: 60°C), and a corrosion mass loss (g/m2) was calculated from a mass difference before and after the test, thereby evaluating corrosion resistance of the plated surface. These results were illustrated in Table 1.
1119 I will return to this later, but samples 27 to 30 are shown as the optimum samples in terms of good surface appearance and more modest corrosion mass loss. I should also note that sample 1 is galvalume. It would also seem from these results that surface appearance deteriorates as Mg increases. So it might be said that Nisshin teaches away from the 257 Patent and the 258 Patent.
1120 Now Dongkuk points out that Nisshin concerns a hot-dip coating method for coating a steel strip, with the method having Al-Zn-Si-Mg in the coating in the ranges claimed in claim 9 of the 257 Patent; see especially Example 1 Table 1 samples 20 to 22 and 27 to 29. Mg2Si is formed in the coating alloy. Dongkuk says that the distribution of Mg2Si would fall within claims 1, 3 and 15 of the 257 Patent in accordance with each or all of the methods set out in the 257 Patent. Dongkuk says this for the following reasons.
1121 First, the thickness of the Nisshin product would be controlled by ordinary good practice.
1122 Second, the cooling rate in Nisshin is only 20°C/sec.
1123 Third, the samples include Sr in the range 0.05-0.3% by wt (500-3000ppm).
1124 Now Nisshin is directed towards an Mg-containing hot-dip Zn-Al alloy plated steel sheet having high corrosion resistance and good surface appearance.
1125 Nisshin discloses that a plated steel sheet in which Mg has been added to hot dip zinc and alloy had not yet been widely used in spite of its excellent effect in improving characteristics, which relates to corrosion resistance. Nisshin explains that the product has not been commercialised because it has not been possible to produce a sheet having a good surface appearance.
1126 Nisshin is particularly directed towards suppressing a "wrinkle-like" defect associated with the addition of Mg to Al-Zn alloy coatings.
1127 Nisshin discloses an Mg-containing hot-dip Zn-Al alloy plated steel sheet where the plating layer contains, by mass %:
(a) 25 to 70 wt.% Al;
(b) 1.5% to 5 wt.% Mg;
(c) 0.01 to 1.0 wt.% Sr;
(d) Si according to the following formula:
Al (mass%) x 0.005 ≤ Si (mass%) ≤ 10%,
and the balance being Zn and unavoidable impurities.
1128 Figure 1 of Nisshin contains three images illustrating the surface appearance of three Zn-Al alloy plated steel sheets. In my view the images are of such poor quality that they provide little assistance with understanding the nature of the defect.
1129 The "wrinkle-like" defect is described as a defect which arises when Mg oxidises with O2. This forms Mg-oxides that grow as an oxide film on the surface of the molten bath. As the metal strip is drawn out of the molten bath, the Mg-oxides inhibit the uniform flow of the molten metal onto the strip.
1130 The "wrinkle-like" defect is associated with oxide drag out which causes the Mg-oxide film to adhere to the coated surface of the strip as it exits the molten bath, or to form on the molten metal after the strip exits the bath. The following evidence was given:
MR CAINE: Thank you. Then if we come across to paragraph 18 on page 13, they refer again to the wrinkle-like unevenness defect, and then at about 5 line 18 they say the reason is that the growth of an oxide film on the surface of the molten metal is significantly promoted by adding magnesium to the plating bath and thus the oxide film inhibits a uniform flow of a plating metal in a molten state. So that that's telling us that there's an oxide film that forms on the surface of the molten bath; that's right, isn't it?
MR ROMMAL: It's telling us that there is an oxide film that forms on the molten coating metal that could be on the surface of the bath or it could be on the surface of the molten metal after the strip exits the bath.
MR CAINE: As the metal strip is drawn out of the bath, I wanted to put to you the magnesium oxides inhibit the uniform flow of the molten metal on to the strip.
MR ROMMAL: It says inhibits the uniform flow of a plating metal. It doesn't say flow of the metal from the bath to the strip. It could be flow of the metal once it's on the surface of the strip in terms of its motion in response to gravity or other airflow in the vicinity above the bath.
MR CAINE: So the description of the wrinkle defect is one that's not clear to you?
MR ROMMAL: It's not clear to me whether the wrinkle defect is magnesium oxide patches pulled out on the surface of the coating or whether it's non-uniform coating thickness on a small scale caused by magnesium oxide getting in the way of the molten metal flowing freely somewhere either on the bath or once it's applied to the - to the coated strip.
1131 This causes the surface appearance to deteriorate, resulting in a "wrinkle-like" surface defect.
1132 Nisshin indicates that additions of Sr to the molten bath may solve the "wrinkle-like" defect. Nisshin suggests that because Sr is more favourably oxidised than Mg, the oxidation of Mg is suppressed. This reduces the amount of Mg-oxide film available for drag out onto the coated surface, suppressing the "wrinkle-like" defect.
1133 The specification explains that the wrinkle-like defect is significantly prevented by allowing the coating to contain Sr, in an amount from 0.1 to 1%.
1134 Nisshin refers to an upper limit for Sr of 1 wt.% (10,000 ppm). This is to ensure that another defect, described as "a spot-like unevenness" caused by Al-Si-Sr, does not occur. The lower limit for Sr is dependent on the amount of Mg. A lower limit for Sr of 0.01 wt.% is described where the Mg content is 1.5 to 5 wt.%. A lower limit for Sr of 0.07 wt.% is described where the Mg content is 5 to 6 wt.%.
1135 Now it would seem that the "wrinkle-like" defect described in Nisshin is a surface defect. But as Mr Dutton observed, the defect is not the surface defect mottle to which the 257 Patent is addressed. The "wrinkle-like" defect is a defect resulting from the formation of Mg-oxides on the molten bath which inhibit the uniform flow of the molten metal onto the strip. In contrast, mottle is a defect resulting from the formation of a non-uniform distribution of Mg2Si particles in the surface of the coating microstructure.
1136 Nisshin provides three examples of the Mg-Al-Zn alloy coating of the invention. The examples are assessed by reference to the naked eye. Table 1, which contains the results of 49 different samples, relates to compositions with 55 wt.% Al, 1.6 wt.% Si, Mg from 0 to 7wt. %, and Sr from 0 to 1.5 wt.%. Table 2 relates to compositions with 25 wt.% Al. And Table 3 relates to compositions with 70 wt.% Al.
1137 Let me say something about Table 1.
1138 Sample 1 of Table 1 is the composition equivalent to galvalume, which is used as a comparator. The results for samples 1, 2 and 3 showed that as Mg was increased (from 0 wt.% to 1.0 wt.%), corrosion resistance improved, that is, mass loss reduced. However, at Mg levels of 5 wt.% and above, surface appearance issues started to arise. Samples 27 to 30 appear to have been the "best". They have the optimal balance of surface appearance, minimal red rust and corrosion resistance. Those samples contain Al in the amount of 55 wt.%, Si in the amount of 1.6 wt.%, Mg in the amount of 4 wt.%, Sr in amounts up to 1 wt.% (that is, up to 10 000ppm), and Zn in the amount of up to 39.4 wt.%. No coating mass for the samples is given.
1139 In my view it seems reasonably clear that insofar as the results in Table 1 direct the reader to any particular samples, they are samples 27 to 30. This is fatal to Dongkuk's assertion of anticipation.
1140 Now Dongkuk relies on samples 20 to 22 as anticipatory, but I disagree as I will explain shortly.
1141 Let me say something about the other Tables. Mr Rommal's earlier evidence was that "the results set out in Table 1 in terms of surface appearance and red rust are superior to those set out in Table 2 and Table 3", but Dr Prošek did not agree. In my view, the results set out in Tables 1, 2 and 3, in relation to surface appearance and red rust are consistent and do not vary despite the change in Al and Si composition. I accept that Mr Rommal later corrected his early statement stating that his "intention was to say that the results set out in Table 1 are nearly identical in terms of surface appearance and red rust compared to Table 2 and Table 3, but the corrosion mass loss results in Table 1 are superior to those set out in Tables 2 and 3".
1142 Let me now deal with a number of points.
1143 First, Nisshin does not focus on developing a specific coating microstructure. Rather, Nisshin focuses on controlling a production issue that causes oxide to build up, giving rise to the "wrinkle-like" defect. The "wrinkle-like" defect is not the result of microstructural issues.
1144 Second, Nisshin refers only briefly to Mg2Si. The context of this brief discussion is that Mg2Si is said to promote the formation of a stable product with improved corrosion resistance. Mr Rommal explained that Nisshin is talking about products of oxidation of magnesium spreading across the surface of the coating. If those corrosion products are not easily redissolved, because they are stable, then they can serve as a barrier to further corrosion. Mg2Si is a source of the magnesium which forms the barrier. At least some must be present at the surface of the coating to provide corrosion protection. Further, both Dr Prošek and Mr Dutton understood from the brief reference to Mg2Si that it was desirable to have Mg2Si at the surface of the coating in order to improve corrosion resistance.
1145 Third, Nisshin does not identify where the Mg2Si particles are located in the coating microstructure.
1146 Fourth, Nisshin is not concerned with providing a surface which is free of visual defects such as mottle. The only reference to the appearance of the product is to a wrinkle-like defect, which is not mottle.
1147 Fifth, Nisshin makes no reference to controlling coating thickness variations. In terms of coating thickness, Nisshin claims a coating mass in the range of 40 to 120g/m2, but otherwise does not refer to coating mass. The coating mass used in the tabulated results is not known.
1148 Sixth, Nisshin does not suggest that controlling the cooling rate will impact upon the distribution of Mg2Si particles. Further, it does not describe that the cooling rate will affect the appearance of the coated strip. Similarly, Nisshin does not describe the effect of cooling rate on corrosion resistance and the resulting microstructure. The same bath temperature (605°C) is used throughout. The same cooling rate of 20°C/sec is used in all the samples, despite different coating bath compositions.
1149 Seventh, although Nisshin describes that Sr assists with the appearance of the coating, Nisshin does not describe what effect the addition of Sr has on the diffusion of the Mg2Si particles. Dr Prošek concludes that Sr has no effect on the microstructure. This is because if it did, there would be a change in the corrosion resistance results. But as was pointed out in the evidence, the samples in Nisshin do not show that there was any improvement to the corrosion resistance properties across a range of 0 to 1.5 wt.% Sr (15,000 parts per million) when the amount of Al, Si and Mg remained constant.
1150 Further, samples 27 to 30, which performed best against the criteria tested, namely surface appearance evaluation, red rust test and corrosion mass loss test, had less than 40 wt.% Zn and were therefore outside the scope of claim 9 of the 257 Patent.
1151 Now as Dongkuk pointed out, samples 20 to 22 had alloy ranges which corresponded with the alloy ranges set out in claim 9 of the 257 Patent. But although Dongkuk relies upon samples 20 to 22 as anticipatory, Dr Prošek would not have made those samples. Moreover, he did not accept that if he made samples 20, 21 and 22 and exercised ordinary good manufacturing practice, he would have arrived at the claimed Mg2Si distribution.
1152 Further, although Dr Prošek accepted that the addition of Sr would affect Mg2Si distribution, he considered that the structure disclosed in Nisshin clearly had large amounts of Mg2Si at the surface. This was necessary for the protection mechanism that was claimed, being a stable corrosion product. That protection mechanism would not work without Mg-rich phases exposed at the surface, including not only Mg2Si, but also MgZn2.
1153 Further, Mr Dutton also understood that there would be Mg2Si close to the surface, if not in the surface.
1154 Further, Mr Rommal considered that there would have been some Mg2Si or MgZn2 at the surface, but that the amount would depend on the dissolution rate in the corrosive environment and how much corrosion product was required to provide protection. He explained:
Nisshin is specifically calling out the two intermetallic compounds Mg2Si and MgZn2 as potential sources of the magnesium. In order for the stable magnesium corrosion product to cover the surface of the plating layer providing additional corrosion protection, you would have to have some source of magnesium present at the surface or close enough to the surface that when the corrosion of the coating begins - the very beginning of corrosion you've down to it and now you've got some magnesium available at the new surface. … So it has to be either at the surface or close to the surface in some quantity to be able to make that corrosion product.
1155 Now although Professor Marder observed that Nisshin does not say how much Mg2Si is present at the surface, and he speculated that MgZn2 could be the source of Mg, I agree with BlueScope that that observation does not assist Dongkuk. Nisshin does not clearly disclose a coating which contains only a small proportion of Mg2Si in or near the surface of the coating.
1156 In summary, Nisshin does not anticipate claims 1, 3 to 9 and 11 to 15 of the 257 Patent.