A zinc-aluminum-bismuth-rare earth alloy for hot-dip galvanizing and its preparation and application method

Abstract

The present invention provides a zinc-aluminum-bismuth-rare earth alloy for hot-dip galvanizing and a preparation and application method thereof, and belongs to the technical field of alloys for hot-dip galvanizing. The alloy provided by the present invention contains aluminum, bismuth and rare earth elements at the same time, and the three elements can be added simultaneously when added to zinc liquid, and the required alloy addition amount is reduced by more than 50%, which can reduce the cost of galvanizing. By controlling the content of each element in the alloy, the content and proportion of each element in the zinc liquid can be better controlled at the same time, and the surface quality and corrosion resistance of the galvanized workpiece can be improved. After the zinc-aluminum-bismuth-rare earth alloy of the present invention is added to the zinc liquid, the surface quality of the galvanized layer is significantly improved: the surface is bright and the particulate matter is significantly reduced; the corrosion resistance of the galvanized layer is greatly improved, and the galvanized workpiece is subjected to a 96h neutral salt spray test, and the corrosion weight loss is below 0.137g, which is significantly less than the corrosion weight loss of 0.175g of the comparative example.

Description

Technical Field

[0001] The invention relates to the technical field of alloys for hot-dip galvanizing, and in particular to a zinc-aluminum-bismuth-rare earth alloy for hot-dip galvanizing and a preparation and application method thereof. Background Art

[0002] The method of hot-dip galvanizing steel workpieces to prevent substrate corrosion has been discovered for a long time. So far, with the development of the power and transportation industries and the increase in the service life requirements, many steel workpieces such as power towers and highway guardrails need to be hot-dip processed before they can be used. However, these workpieces have different shapes, and it is difficult to reduce the zinc slag and excess free zinc liquid on the surface of the galvanized layer by blowing with an air knife to control the surface quality and thickness of the galvanized layer. The thickness of the alloy layer can only be controlled by controlling the galvanizing time of the workpiece in the zinc liquid. By knocking the galvanized workpiece just taken out of the zinc liquid, the free zinc liquid on the surface flows back to the zinc pot under the action of gravity, and the thickness and surface quality of the free zinc layer can be controlled to a limited extent. In order to further improve the quality of the galvanized workpiece, some other elements are usually added in the form of alloys. At present, the alloys used in the galvanizing industry are binary alloys, mainly zinc-aluminum alloys, zinc-bismuth alloys, zinc-rare earth alloys, and zinc-nickel alloys. Since each alloy can actually only provide one alloying element in addition to the base zinc, if three elements need to be added at the same time, three alloys need to be added to the zinc liquid. However, the solubility of each alloying element in zinc is limited, so the total amount of alloy to be added is large, which not only causes high alloy production costs and transportation costs, but also a large workload during use, and is easy to confuse. Multiple additions of alloys bring more air into the zinc liquid, resulting in excessive oxidation losses of alloying elements, and the content of alloying elements cannot be well controlled, resulting in mediocre performance of galvanized workpieces. Therefore, how to reduce the cost of galvanizing and improve the performance of galvanized workpieces has become a difficult problem in the prior art. Summary of the invention

[0003] The purpose of the present invention is to provide a zinc-aluminum-bismuth-rare earth alloy for hot-dip galvanizing and a preparation and application method thereof. The alloy provided by the present invention contains aluminum, bismuth and rare earth elements at the same time, which can reduce the amount of alloy used in galvanizing production, reduce the galvanizing cost, and improve the surface quality and corrosion resistance of the galvanized workpiece.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The invention provides a zinc-aluminum-bismuth-rare earth alloy, which comprises, by mass content, 7.5-11% of Al, 0.5-1.5% of Bi, 0.4-0.6% of rare earth and the balance of zinc.

[0006] Preferably, the rare earths include lanthanum and cerium.

[0007] Preferably, the mass ratio of lanthanum to cerium is 1:(1.5-2).

[0008] The present invention provides a method for preparing the zinc-aluminum-bismuth-rare earth alloy described in the above technical solution, comprising: smelting a zinc ingot, an aluminum ingot, a zinc-rare earth alloy and an aluminum-bismuth alloy and then casting to obtain a zinc-aluminum-bismuth-rare earth alloy.

[0009] Preferably, the smelting temperature is 630-700° C., and the smelting holding time is 15-40 min.

[0010] The present invention also provides the use of the zinc-aluminum-bismuth-rare earth alloy described in the above technical solution or the zinc-aluminum-bismuth-rare earth alloy prepared according to the preparation method described in the above technical solution in a zinc plating solution.

[0011] Preferably, the method comprises the following steps:

[0012] (1) melting a zinc ingot and adding a zinc-aluminum-bismuth-rare earth alloy to obtain a zinc liquid;

[0013] (2) Immersing the workpiece to be plated in the zinc solution obtained in step (1) for zinc plating to obtain a galvanized workpiece.

[0014] Preferably, the zinc solution in step (1) contains, by mass content, 0.0010-0.0015% rare earth, 0.0021-0.0035% bismuth, 0.006-0.011% aluminum and the balance zinc.

[0015] Preferably, the galvanizing temperature in step (2) is 440-450°C.

[0016] Preferably, the galvanizing time in step (2) is 200 to 220 seconds.

[0017] The present invention provides a zinc-aluminum-bismuth-rare earth alloy, which includes 7.5-11% Al, 0.5-1.5% Bi, 0.4-0.6% rare earth and the balance of zinc by mass content. The alloy provided by the present invention contains aluminum, bismuth and rare earth elements at the same time. When added to zinc liquid, the three elements can be added at the same time, and the required alloy addition amount is reduced by more than 50%, which can reduce the cost of galvanizing, control the content of each element in the alloy, and better control the content and proportion of each element in the zinc liquid at the same time, thereby improving the surface quality and corrosion resistance of the galvanized workpiece. The results of the embodiment show that after the zinc-aluminum-bismuth-rare earth alloy of the present invention is added to the zinc liquid, the surface quality of the galvanized layer is significantly improved: the surface is bright and the particulate matter is significantly reduced; the corrosion resistance of the galvanized layer is greatly improved, and the galvanized workpiece is subjected to a 96h neutral salt spray test, and the corrosion weight loss is below 0.137g, which is significantly less than the corrosion weight loss of 0.175g in the comparative example. DETAILED DESCRIPTION

[0018] The invention provides a zinc-aluminum-bismuth-rare earth alloy, which comprises, by mass content, 7.5-11% of Al, 0.5-1.5% of Bi, 0.4-0.6% of rare earth and the balance of zinc.

[0019] The zinc-aluminum-bismuth-rare earth alloy provided by the present invention includes Al7.5-11%, preferably 8-10%, and more preferably 9-10%, by mass content. In the present invention, the aluminum element can make the surface of the zinc-plated layer brighter and improve the corrosion resistance of the galvanized workpiece. The present invention limits the content of the aluminum element in the zinc-aluminum-bismuth-rare earth alloy to the above range, so that the zinc liquid contains a suitable aluminum content, further improving the surface quality and corrosion resistance of the galvanized workpiece.

[0020] The zinc-aluminum-bismuth-rare earth alloy provided by the present invention includes Bi0.5-1.5%, preferably 0.6-1.2%, and more preferably 0.8-1.0%, by mass content. In the present invention, the bismuth element can improve the fluidity of zinc, reduce the size and number of zinc nodules, and achieve the effect of reducing zinc consumption and improving the quality of galvanizing. The present invention limits the content of bismuth in the zinc-aluminum-bismuth-rare earth alloy to the above range, so that the zinc liquid contains a suitable bismuth content, further improving the surface quality and corrosion resistance of the galvanized workpiece.

[0021] The zinc-aluminum-bismuth-rare earth alloy provided by the present invention includes 0.4-0.6% rare earth, preferably 0.5% by mass. In the present invention, the rare earth preferably includes lanthanum and cerium; the mass ratio of lanthanum to cerium is preferably 1: (1.5-2), more preferably 1: (1.8-2). In the present invention, the rare earth element can purify impurities, refine grains, improve the wettability and fluidity of zinc liquid, and improve the surface quality and corrosion resistance of galvanized workpieces.

[0022] The zinc-aluminum-bismuth-rare earth alloy provided by the present invention includes a balance of zinc by mass content. In the present invention, the zinc is a matrix element.

[0023] The alloy provided by the present invention contains aluminum, bismuth and rare earth elements at the same time. When added to zinc liquid, the three elements can be added at the same time, and the required alloy addition amount is reduced by more than 50%, which can reduce the galvanizing cost, control the content of each element in the alloy, and better control the content and proportion of each element in the zinc liquid at the same time, thereby improving the surface quality and corrosion resistance of the galvanized workpiece.

[0024] The present invention provides a method for preparing the zinc-aluminum-bismuth-rare earth alloy described in the above technical solution, comprising: smelting a zinc ingot, an aluminum ingot, a zinc-rare earth alloy and an aluminum-bismuth alloy and then casting to obtain a zinc-aluminum-bismuth-rare earth alloy.

[0025] In the present invention, the mass content of rare earth in the zinc-rare earth alloy is preferably 0.4-2.5%, more preferably 1-2%. The present invention adds zinc-rare earth in the form of alloy, which can make the rare earth element more evenly dispersed in the zinc-aluminum-bismuth-rare earth alloy.

[0026] In the present invention, the preparation method of the zinc-rare earth alloy is preferably:

[0027] 1) mixing a zinc ingot, a rare earth and a covering agent and then smelting them to obtain a zinc-rare earth smelting solution;

[0028] 2) cooling the zinc-rare earth smelting liquid obtained in step 1), and then separating the covering agent to obtain a zinc-rare earth alloy liquid;

[0029] 3) Casting the zinc-rare earth alloy liquid obtained in step 2) to obtain a zinc-rare earth alloy.

[0030] In the present invention, the zinc ingot, the rare earth and the covering agent are preferably mixed and then smelted to obtain a zinc-rare earth smelting liquid.

[0031] In the present invention, the mass content of rare earth in the mixture obtained by mixing the zinc ingot and the rare earth is preferably 0.5-2.5%.

[0032] In the present invention, the covering agent is preferably potassium fluoride and aluminum trifluoride; the mass ratio of potassium fluoride to aluminum trifluoride is preferably 1: (1-1.5), more preferably 1: 1.18; the ratio of the mass of the covering agent to the total mass of the rare earth and the zinc ingot is preferably 0.50-3.0: 100, more preferably 1.0-2.0: 100. In the present invention, the melting point of aluminum trifluoride is 1290°C, and the melting point of potassium fluoride is 858°C. After the two are mixed in the above ratio, they become a eutectic, and the melting point is reduced to 580°C. During the alloy smelting process, the covering agent exists in liquid form, and its density is 3.0g / cm 3 Below, lower than the alloy density of 6.0g / cm 3 , can float on the surface of alloy liquid, isolate air, and reduce the oxidation of alloy components by air. The present invention limits the type and amount of covering agent to the above range, which can better isolate air and reduce the oxidation of alloy elements.

[0033] In the present invention, the mixing of the zinc ingot, the rare earth and the covering agent is preferably as follows: first, the zinc ingot is heated and melted in a medium frequency induction furnace, the covering agent is added, and then the rare earth is wrapped with aluminum foil, and then a graphite frame is pressed into the molten zinc liquid surface for smelting, and the rare earth is completely dissolved and evenly dispersed in the zinc liquid under the action of electromagnetic stirring to form a zinc-rare earth smelting liquid. The mixing method of the present invention has the advantages of high safety and small oxidation loss of rare earth elements. If the rare earth metal is directly added to the zinc liquid, since the density of the rare earth metal is less than that of the zinc liquid, it will float on the surface of the zinc liquid and explode with the air above 500°C, which is not only unsafe, but also causes the rare earth metal to be converted into oxides and lost. The present invention uses aluminum foil to wrap the rare earth, which can prevent the rare earth from deflagration and improve the yield of rare earth elements. In the present invention, the mass of the aluminum foil is deducted in the aluminum addition link in the subsequent preparation process of the zinc-aluminum-bismuth-rare earth alloy, and will not affect the content of each element in the final zinc-aluminum-bismuth-rare earth alloy.

[0034] In the present invention, the smelting temperature is preferably 600-650°C, more preferably 630°C; the smelting holding time is preferably 10-20 minutes, more preferably 15 minutes; the heating rate to the smelting temperature is preferably 10-20°C / min, more preferably 15°C / min. The present invention limits the smelting temperature, time, etc. within the above range, which can achieve the purpose of complete dissolution and uniform dispersion of rare earth metals, improve production efficiency, save energy consumption, and avoid the problem of excessive oxidation of rare earth elements caused by excessive temperature.

[0035] After obtaining the zinc-rare earth smelting liquid, the present invention preferably cools the zinc-rare earth smelting liquid, and then separates the covering agent to obtain the zinc-rare earth alloy liquid.

[0036] In the present invention, the zinc-rare earth smelting liquid is preferably cooled to 550-580° C. The present invention cools the zinc-rare earth smelting liquid to the above temperature so that the covering agent on the surface of the alloy liquid solidifies into a solid state, which is convenient for separation.

[0037] The present invention has no special limitation on the operation of separating the covering agent, and the covering agent can be fully separated by using a technical solution well known to those skilled in the art.

[0038] After separating the covering agent, a zinc-rare earth alloy liquid is obtained. In the present invention, the zinc-rare earth alloy liquid is cast to obtain the zinc-rare earth alloy.

[0039] The present invention preferably pours the alloy liquid into the mold, and then uses indirect water on the outer wall of the mold for cooling and casting; the mold is preferably a low-alloy steel mold; the low-alloy steel is preferably 4Cr5MoSiV, and its chemical composition includes: 0.32-0.45% C, 4.75-5.50% Cr, 1.10-1.75% Mo, 0.8-1.2% Si, 0.80-1.20% V, 0.2-0.5% Mn, S≤0.030%, P≤0.030%, the material has good corrosion resistance to zinc liquid, and can reduce the pollution of the alloy caused by the dissolution of the mold material; the temperature of the indirect water is preferably 25-30°C. The casting method of the present invention can accelerate the cooling speed of the alloy, reduce the oxidation of the alloy components; and reduce the dissolution of the mold material by the alloy liquid, so as to prevent the impurity iron content in the alloy from exceeding the standard.

[0040] The method for preparing the zinc-rare earth alloy of the present invention can achieve a higher yield of rare earth.

[0041] In the present invention, the mass content of bismuth in the aluminum-bismuth alloy is preferably 7-17%. In the present invention, aluminum-bismuth is added in the form of an alloy, so that the bismuth element can be more evenly dispersed in the zinc-aluminum-bismuth-rare earth alloy.

[0042] In the present invention, the preparation method of the aluminum-bismuth alloy is preferably: heating aluminum ingots and bismuth in a medium frequency induction furnace to melt into alloy liquid and then casting to obtain the aluminum-bismuth alloy.

[0043] In the present invention, in the mixture obtained by mixing the aluminum ingot and bismuth, the mass content of bismuth is preferably 7-16% of the total mass of the aluminum ingot and bismuth.

[0044] In the present invention, the smelting temperature is preferably 720-750°C, more preferably 720-740°C; the holding time of the smelting is preferably 10-20 minutes, more preferably 15 minutes; the smelting is preferably carried out under stirring conditions. The present invention has no special restrictions on the stirring method and rate, and the stirring method and rate well known to those skilled in the art can be used. The present invention limits the smelting temperature and time within the above range, which can make the alloy raw materials mixed more uniformly.

[0045] In the present invention, the mold during casting is preferably a 4Cr5MoSiV low alloy steel mold. The present invention has no special limitation on other operations of the casting, and a casting scheme well known to those skilled in the art can be used.

[0046] The method for preparing the aluminum-bismuth alloy of the present invention can achieve a higher yield of bismuth.

[0047] In the preparation process of the zinc-aluminum-bismuth-rare earth alloy of the present invention, the mass ratio of the zinc ingot, the aluminum ingot, the zinc-rare earth alloy and the aluminum-bismuth alloy is preferably (485-520): (20-25): 200: (40-72).

[0048] In the preparation process of the zinc-aluminum-bismuth-rare earth alloy of the present invention, the smelting temperature of the zinc ingot, the aluminum ingot, the zinc-rare earth alloy and the aluminum-bismuth alloy is preferably 630-700°C, more preferably 630-670°C; the holding time of the smelting is preferably 15-40 minutes, more preferably 15-35 minutes; the smelting is preferably carried out under stirring conditions. The present invention has no special restrictions on the stirring mode and rate, and the stirring mode and rate well known to those skilled in the art can be used.

[0049] The preparation process of the zinc-aluminum-bismuth-rare earth alloy of the present invention is preferably as follows: the zinc ingot and the aluminum ingot are melted, then the zinc-rare earth alloy is added, and then the aluminum-bismuth alloy is added. The addition method of the present invention can make the alloy elements mixed more uniformly.

[0050] The present invention preferably pours the alloy liquid into the mold, and then uses indirect water on the outer wall of the mold for cooling and casting; the mold is preferably a low-alloy steel mold; the low-alloy steel is preferably 4Cr5MoSiV, which has good corrosion resistance to zinc liquid and can reduce the pollution of the alloy caused by the dissolution of the mold material; the temperature of the indirect water is preferably 25-30°C. The casting method of the present invention can accelerate the cooling speed of the alloy, reduce the oxidation of the alloy components, and reduce the dissolution of the mold material by the alloy liquid, preventing the impurity iron content in the alloy from exceeding the standard.

[0051] The present invention also provides the use of the zinc-aluminum-bismuth-rare earth alloy described in the above technical solution or the zinc-aluminum-bismuth-rare earth alloy prepared according to the preparation method described in the above technical solution in zinc liquid.

[0052] In the present invention, the use of the zinc-aluminum-bismuth-rare earth alloy in zinc liquid preferably includes the following steps:

[0053] (1) melting a zinc ingot and adding a zinc-aluminum-bismuth-rare earth alloy to obtain a zinc liquid;

[0054] (2) Immersing the workpiece to be plated in the zinc solution obtained in step (1) for zinc plating to obtain a galvanized workpiece.

[0055] The present invention preferably melts the zinc ingot and then adds the zinc-aluminum-bismuth-rare earth alloy to obtain zinc liquid.

[0056] In the present invention, the mass ratio of the zinc-aluminum-bismuth-rare earth alloy to the zinc ingot is preferably (1.2-2.1):580, and more preferably (1.5-2.1):580. The present invention limits the mass ratio of the zinc-aluminum-bismuth-rare earth alloy to the zinc ingot within the above range, so that the zinc liquid contains appropriate amounts of aluminum, bismuth and rare earth, thereby improving the surface quality and corrosion resistance of the galvanized workpiece.

[0057] In the present invention, the zinc liquid preferably contains 0.0010-0.0015% rare earth, 0.0021-0.0035% bismuth, 0.006-0.011% aluminum and the balance zinc, and more preferably contains 0.0012-0.0015% rare earth, 0.0026-0.0035% bismuth, 0.007-0.011% aluminum and the balance zinc. The present invention limits the content of rare earth, bismuth and aluminum in the zinc liquid to the above range, which can further improve the surface quality and corrosion resistance of the galvanized workpiece.

[0058] In the present invention, the temperature of the liquid zinc obtained after the zinc ingot is melted is preferably 440-450°C; the dissolution time after the zinc-aluminum-bismuth-rare earth alloy is added is preferably 30-40 minutes. The present invention limits the temperature of the liquid zinc and the dissolution time of the alloy within the above range, so that the alloy elements can be evenly dispersed in the liquid zinc and the oxidation of the alloy elements can be reduced. Moreover, the temperature is the optimal temperature range for normal galvanizing.

[0059] After obtaining the zinc solution, the present invention preferably immerses the workpiece to be plated in the zinc solution for zinc plating to obtain a galvanized workpiece.

[0060] In the present invention, the workpiece to be plated is preferably subjected to acid pickling, water washing and plating-assist treatment in sequence before use.

[0061] In the present invention, the pickling solution is preferably hydrochloric acid with a mass concentration of 15-20%; the pickling time is preferably 10-15 minutes. In the present invention, the pickling can remove the rust on the surface of the workpiece and convert it into ferrous chloride, exposing a clean steel surface, which is conducive to the galvanizing process and avoids the "zinc leakage" phenomenon.

[0062] The purpose of the water washing operation of the present invention is to remove the pickling solution containing hydrochloric acid and ferrous chloride adhering to the surface of the workpiece from the pickling tank. In the present invention, the water used for the water washing is preferably ordinary tap water. The present invention preferably soaks the workpiece in water and then takes it out.

[0063] The present invention preferably immerses the workpiece to be plated in a plating aid for plating treatment. In the present invention, the plating aid is preferably a mixed aqueous solution of zinc chloride and ammonium chloride; the concentration of zinc chloride in the plating aid is preferably 80-100 g / L; the concentration of ammonium chloride in the plating aid is preferably 100-120 g / L; the temperature of the plating aid is preferably 60-70°C; the pH value of the plating aid is preferably 3.5-4.0. In the present invention, the time of the plating treatment is preferably 150-180 seconds. After the plating is completed, the present invention preferably lifts the workpiece after the plating treatment out of the plating aid and stays in the air for 200-250 seconds to dry the workpiece. In the present invention, during the plating treatment, the workpiece exchanges heat with the plating aid, increases its own temperature and adsorbs the plating aid, which is beneficial to the subsequent galvanizing process.

[0064] In the present invention, the galvanizing temperature is preferably 440-450°C; the galvanizing time is preferably 200-220s; and the thickness of the galvanized layer obtained by galvanizing is preferably 80-100 μm. The present invention limits the galvanizing temperature, time and galvanized layer thickness within the above ranges, which can make the galvanized workpiece have better quality and corrosion resistance, and control the galvanizing cost.

[0065] After the galvanizing is completed, the present invention preferably allows the galvanized workpiece to remain in the air for 110 to 130 seconds to allow the zinc liquid on the surface of the workpiece to cool and solidify, and then immerses it in water to cool to below 60° C. to obtain a galvanized workpiece.

[0066] The invention adds a zinc-aluminum-bismuth-rare earth alloy containing aluminum, bismuth and rare earth elements to the zinc liquid. Compared with adding zinc-aluminum alloy, zinc-bismuth alloy and zinc-rare earth alloy separately, the required alloy addition amount is reduced by more than 50%, which can reduce the cost of galvanizing. By controlling the addition amount of zinc-aluminum-bismuth-rare earth alloy, the content of various alloy elements in the zinc liquid can be guaranteed to reach the optimal value, thereby improving the surface quality and corrosion resistance of the galvanized workpiece.

[0067] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] Embodiments 1 to 5

[0069] The amounts of zinc ingots and rare earth, the theoretical content of rare earth, the actual content of rare earth in the prepared zinc-rare earth alloy and the yield of rare earth in Examples 1 to 5 are shown in Table 1.

[0070] The preparation method of zinc-rare earth alloy is specifically as follows:

[0071] (1) adding a zinc ingot into a graphite crucible of a coreless medium frequency induction furnace, and adding covering agents of potassium fluoride and aluminum trifluoride into the crucible (the mass ratio of potassium fluoride to aluminum trifluoride is 1:1.18, and the ratio of the total mass of potassium fluoride and aluminum trifluoride to the total mass of the zinc ingot and the rare earth is 1.5:100), heating to 630° C. at a rate of 15° C. / min, and keeping the temperature for 15 min, and then wrapping a rare earth RE (a mixture of lanthanum and cerium, wherein the mass content of lanthanum in the mixture is 35%, the mass content of cerium is 65%, and the mass ratio of lanthanum to cerium is 1:1.86) with aluminum foil, and pressing it below the zinc liquid surface with a graphite frame until the rare earth is completely dissolved, and under the stirring action of the electromagnetic force of the medium frequency induction furnace, the rare earth element reacts metallurgically with the liquid zinc to obtain an intermetallic compound, which is evenly dispersed in the liquid zinc to obtain a zinc-rare earth alloy molten liquid;

[0072] (2) cooling the molten liquid to 560° C., removing the covering agent on the surface of the alloy liquid, and obtaining the alloy liquid;

[0073] (3) The alloy liquid is poured into a low alloy steel 4Cr5MoSiV mold, and indirect water cooling is adopted on the outer wall of the mold. The indirect water temperature is 28° C., and the zinc-rare earth alloy ingots of 10 kg / piece are cast.

[0074] Table 1 The amount of zinc ingot and rare earth used, the theoretical content of rare earth, the actual content of rare earth in the prepared zinc-rare earth alloy and the yield of rare earth in Examples 1 to 5

[0075]

[0076] As can be seen from Table 1, the yield of rare earth in Example 4 is the highest.

[0077] Embodiments 6 to 10

[0078] The amounts of aluminum ingots and bismuth blocks, the theoretical content of bismuth, the actual content of bismuth in the prepared aluminum-bismuth alloys, and the yield of bismuth in Examples 6 to 10 are shown in Table 2.

[0079] The specific preparation method of aluminum-bismuth alloy is as follows: adding aluminum ingots to a medium frequency induction furnace, heating to 720°C, then adding metal bismuth blocks to the aluminum liquid, stirring at 720°C for 15 minutes under electromagnetic stirring, and casting into a low alloy steel mold to obtain 4kg / block aluminum-bismuth alloy ingots.

[0080] Table 2 The amount of aluminum ingots and bismuth blocks used in Examples 6 to 10, the theoretical content of bismuth, the actual content of bismuth in the prepared aluminum-bismuth alloys, and the yield of bismuth

[0081]

[0082]

[0083] As can be seen from Table 2, the yield of bismuth is the highest in Example 8.

[0084] Examples 11 to 15

[0085] The amounts of zinc ingot, aluminum ingot, zinc-rare earth alloy and aluminum-bismuth alloy used in Examples 11 to 15, and the actual contents of aluminum, bismuth and rare earth in the prepared zinc-aluminum-bismuth-rare earth alloy are shown in Table 3.

[0086] The preparation method of the zinc-aluminum-bismuth-rare earth alloy is as follows: a zinc ingot and an aluminum ingot are heated to 630° C. in a medium frequency induction furnace to melt, and then the zinc-rare earth alloy in Example 4 is added and stirred for 15 minutes, and then the aluminum-bismuth alloy in Example 8 is added and stirred at 630° C. for 15 minutes to obtain a zinc-aluminum-bismuth-rare earth alloy liquid, which is then cast into a 10 kg / piece zinc-aluminum-bismuth-rare earth alloy ingot in a low alloy 4Cr5MoSiV mold.

[0087] Table 3 Amounts of zinc ingot, aluminum ingot, zinc-rare earth alloy and aluminum-bismuth alloy used in Examples 11 to 15, and actual contents of aluminum, bismuth and rare earth in the prepared zinc-aluminum-bismuth-rare earth alloy

[0088]

[0089]

[0090] Application Examples 1 to 4

[0091] A zinc ingot is placed in a medium frequency induction furnace for melting, and the temperature is controlled at 443° C. to obtain liquid zinc. The zinc-aluminum-bismuth-rare earth alloy in Example 14 is added to the liquid zinc in a certain proportion and moved back and forth to dissolve the alloy in the liquid zinc. After the alloy elements diffuse, a zinc liquid with uniform composition is obtained. The zinc liquid is used to galvanize a steel workpiece that has been pickled, washed, and assisted plating. The amounts of the zinc ingot and the zinc-aluminum-bismuth-rare earth alloy, the rare earth content, bismuth content and aluminum content in the zinc liquid, the galvanizing temperature, and the galvanizing time are shown in Table 4.

[0092] The specific steps of the galvanizing process are as follows: a steel pipe with a material of Q235A and a specification of DN50mm*3mm is cut into a workpiece with a length of 50mm, and the workpiece is pickled in hydrochloric acid with a mass concentration of 18% for 15 minutes, and the pickled workpiece is lifted out of the pickling tank and lifted into a cleaning tank for water washing; then the workpiece is lifted into a plating aid, and the plating aid is a mixed aqueous solution of zinc chloride and ammonium chloride, wherein the concentration of zinc chloride is 100g / L, the concentration of ammonium chloride is 120g / L, the temperature of the plating aid is 70°C, and the pH value is 4, the workpiece is immersed in the plating aid for 180s, and after the plating is completed, the workpiece is lifted out of the plating aid, and stays in the air for 250s to dry the workpiece, and finally the workpiece is lifted into the zinc liquid in the zinc pot for galvanizing, and after the galvanizing is completed, the workpiece is lifted out, stays in the air for 120s, and then enters the cooling tank, and is cooled to below 60°C in water to obtain a galvanized workpiece.

[0093] Observe the surface brightness and particle size of the galvanized workpiece, and measure the thickness of the galvanized layer with a magnetic thickness gauge; place the galvanized workpiece in a neutral salt spray test box, and conduct a neutral salt spray test according to the national standard GB6458-86 "Neutral Salt Spray Test for Metal Covering Layers", and test continuously for 96 hours. Weigh each sample before the test and record the initial weight. After the test, rinse each sample with tap water, remove the corrosion products with a hard brush, remove the moisture on the surface of the sample with ethanol, dry it, and bake it in an oven at 105°C for 1 hour. Weigh the sample after the test again, calculate the sample corrosion weight loss, and use it to judge the corrosion resistance of the galvanized layer. The less weight loss, the better the corrosion resistance. The results are shown in Table 4.

[0094] Comparative application example 1

[0095] The galvanizing was carried out in the same manner as in Application Examples 1 to 4, except that zinc-10% aluminum alloy was added to the zinc ingot to obtain zinc liquid. The thickness of the galvanized layer, the surface quality of the galvanized workpiece, and the weight loss data of the workpiece after the neutral salt spray test are shown in Table 4.

[0096] Table 4 The amount of zinc ingot, zinc-aluminum-bismuth-rare earth alloy, rare earth content, bismuth content and aluminum content in zinc solution, galvanizing temperature, time, galvanizing layer thickness, surface quality of galvanized workpiece, and weight loss data of workpiece after neutral salt spray test in application examples 1 to 4 and comparative application example 1

[0097]

[0098] As can be seen from Table 4, in the application example of galvanizing after adding the zinc-aluminum-bismuth-rare earth alloy of the present invention, the galvanized workpiece obtained has high surface brightness, less particulate matter and better surface quality; after 96h of neutral salt spray test, the corrosion weight loss of the galvanized workpiece in the application example is less than 0.137g, which is significantly less than the corrosion weight loss of 0.218g in the comparative example 1, indicating that the galvanized workpiece in the application example has better corrosion resistance.

[0099] Comparative Application Examples 2 to 5

[0100] The method of comparative application example 1 was used for galvanizing, except that three alloys were added to the zinc solution at the same time: zinc-10% aluminum alloy, zinc-1% bismuth alloy, and zinc-0.5% rare earth alloy. The dosage of zinc ingot, zinc-10% aluminum alloy, zinc-1% bismuth alloy, and zinc-0.5% rare earth alloy, the content of aluminum, bismuth, and rare earth in the zinc solution, the galvanizing temperature, time, the surface quality of the galvanized workpiece, and the weight loss due to corrosion are shown in Table 5.

[0101] Table 5 Comparison of the dosage of zinc ingot, zinc-10% aluminum alloy, zinc-1% bismuth alloy, zinc-0.5% rare earth, the content of aluminum, bismuth and rare earth in zinc solution, galvanizing temperature, time, surface quality of galvanized workpiece and corrosion weight loss in application examples 2 to 5

[0102]

[0103]

[0104] By comparing Table 4 and Table 5, it can be seen that in the application example in which the zinc-aluminum-bismuth-rare earth alloy of the present invention is added for galvanizing, the galvanized workpiece obtained has high surface brightness, less particulate matter and better surface quality; after 96h of neutral salt spray test, the corrosion weight loss of the galvanized workpiece of the application example is less than 0.137g, which is significantly less than the corrosion weight loss of more than 0.175g of the application control example, indicating that the galvanized workpiece of the application example has better corrosion resistance.

[0105] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A zinc-aluminum-bismuth-rare earth alloy, comprising, by mass content, 7.5-11% Al, 0.6-1.5% Bi, 0.4-0.6% rare earth and the balance zinc; the rare earth comprises lanthanum and cerium; the mass ratio of lanthanum to cerium is 1:(1.5-2).

2. The method for preparing the zinc-aluminum-bismuth-rare earth alloy according to claim 1, comprising: The zinc ingot, the aluminum ingot, the zinc-rare earth alloy and the aluminum-bismuth alloy are smelted and then cast to obtain the zinc-aluminum-bismuth-rare earth alloy.

3. The preparation method according to claim 2, characterized in that: The smelting temperature is 630-700° C., and the smelting holding time is 15-40 minutes.

4. Use of the zinc-aluminum-bismuth-rare earth alloy according to claim 1 or the zinc-aluminum-bismuth-rare earth alloy prepared by the preparation method according to claim 2 or 3 in zinc liquid.

5. The use according to claim 4, characterized in that: The steps include: (1) melting a zinc ingot and adding a zinc-aluminum-bismuth-rare earth alloy to obtain a zinc liquid; (2) Immersing the workpiece to be plated in the zinc solution obtained in step (1) for zinc plating to obtain a galvanized workpiece.

6. The use according to claim 5, characterized in that: Calculated by mass content, the zinc solution in step (1) contains 0.0010-0.0015% of rare earth, 0.0021-0.0035% of bismuth, 0.006-0.011% of aluminum and the balance of zinc.

7. The use according to claim 5, characterized in that: The galvanizing temperature in step (2) is 440-450°C.

8. The use according to claim 5 or 7, characterized in that: The galvanizing time in step (2) is 200 to 220 seconds.

Images