Method for stably eliminating primary MgZn2 phase in hot-dip zinc-aluminum-magnesium alloy by utilizing synergistic effect of silicon and titanium

Abstract

The invention relates to the technical field of hot-dip galvanizing, in particular to a method for stably eliminating a primary MgZn2 phase in a hot-dip galvanized aluminum-magnesium alloy through the synergistic effect of silicon and titanium. According to the invention, silicon and titanium elements are added into a Zn-6Al-3Mg alloy, and the alloy comprises the following components: 6% of Al, 3% of Mg, 0.05-0.2% of Si, 0.05-0.3% of Ti and the balance of Zn, preferably 0.07-0.1% of Si and 0.2% of Ti. According to the method, the primary MgZn2 phase in the Zn-6Al-3Mg alloy coating is eliminated through the synergistic effect of silicon and titanium elements, and meanwhile the problem that hard intermetallic compounds such as TiAl3 and Mg2Si are introduced due to improper element adding is effectively solved. More importantly, the synergistic effect shows excellent tissue stability and can effectively inhibit the tissue heredity effect of the primary MgZn2 phase, and the method has important application value in the industry.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-dip galvanized alloys, and particularly relates to a method for eliminating primary MgZn2 in a hot-dip galvanized aluminum-magnesium alloy by utilizing the synergistic effect of silicon and titanium elements. Background Art

[0002] Hot-dip galvanizing is widely used in industries such as automotive and home appliances due to its simple process, excellent coating protection, economical efficiency, and development potential. The zinc-aluminum-magnesium alloy coating, with its high corrosion resistance and easy processing and forming properties, is widely used in the automotive and home appliance industries. The hot-dip galvanized coating consists of a free-solidifying layer and an alloy layer on the surface. Its solidification structure is formed according to the following steps: first, the matrix iron partially dissolves in the molten zinc liquid, then the iron and zinc react to form an Fe-Zn metal compound. During cooling, the zinc liquid attached to the surface of the compound layer solidifies and crystallizes to form a free-solidifying layer.

[0003] Zn-6Al-3Mg (wt.%) (ZAM for short) alloy is a zinc-aluminum-magnesium alloy for hot-dip coating developed at the beginning of this century. In the corrosion resistance comparison of the International Zinc Association, the weight loss of ZAM alloy coating is significantly less than that of zinc-aluminum alloy coating products such as Zn-0.2Al (wt.%) (GI) and Zn-5Al-0.1RE (wt.%) (Galfan). Compared with the Zn-11Al-3Mg (wt.%) (SuperDyma) alloy coating of the same "China Aluminum", the corrosion resistance of ZAM alloy coating still has certain advantages.

[0004] However, zinc-aluminum-magnesium alloys, including ZAM alloys, are prone to forming a metastable primary MgZn2 phase during the actual solidification process. Due to its inherent hardness and brittleness, this phase can significantly reduce the overall mechanical properties of the zinc alloy coating. Furthermore, the MgZn2 phase has a lower potential, meaning that the coarse MgZn2 phase in the structure is more susceptible to microgalvanic corrosion as the positive electrode. Therefore, refining and ultimately eliminating the primary MgZn2 phase is an effective method to improve the overall performance of zinc-aluminum-magnesium alloy coatings.

[0005] Research has shown that introducing an appropriate amount of Si into zinc-aluminum-magnesium alloys through a specific process can refine the microstructure. For example, Chinese invention patent CN118773461A discloses a method for preparing a hot-dip Zn-6Al-3Mg-Si alloy using a silicon-containing, melt-in-place master alloy. This patent first prepares a silicon-containing, melt-in-place master alloy, which is then used to prepare a Zn-6Al-3Mg-0.09Si alloy. This method can refine the Al-rich phase and primary MgZn2 phase in the alloy structure. However, the alloy preparation process in this patent is complex, requiring additional smelting processes, and it is difficult to increase the area fraction of the ternary eutectic structure in the alloy structure.

[0006] Titanium also has a refining effect on ZAM alloys. For example, Chinese invention patent CN103422041A discloses a titanium-containing ZAM hot-dip galvanized alloy, which achieves the refinement of the ZAM alloy structure by adding titanium to the Zn-6Al-3Mg alloy through microalloying of the titanium element. However, its traditional smelting process only achieves the refinement of the primary MgZn2 phase, and does not completely eliminate the primary MgZn2 phase.

[0007] In addition, CN118374717A discloses a hot-dip galvanized alloy containing titanium and a preparation method thereof. When the Ti content is high, the primary MgZn2 phase still exists. The primary MgZn2 phase is eliminated, but a harmful hard TiAl3 compound phase is introduced simultaneously, which will lead to problems such as reduced toughness and increased brittleness of the coating.

[0008] Existing Zn-Al-Mg coating alloys containing both Si and Ti elements essentially use traditional microalloying methodologies to consider the synergistic refinement of the Si and Ti elements on the Zn-Al-Mg coating alloy structure, namely, the formation of tiny particles of high-melting-point, insoluble intermetallic compounds to increase the nucleation rate and refine the alloy structure, making it difficult to eliminate the primary MgZn2 phase. Simultaneously, the specificity of Si and Ti for the Zn-Al-Mg ternary alloy system is not considered, and there is no reasonable control over the introduction of new hard intermetallic compound phases such as TiAl3 and Mg2Si phases caused by the addition of Si and Ti elements. Summary of the Invention

[0009] The present invention mainly controls the size of the harmful primary MgZn2 phase that is very easy to form in the intrinsic Zn-Al-Mg ternary alloy, and controls the formation of intermetallic compound phases such as TiAl3 and Mg2Si in the alloy by reasonably matching the Si and Ti elements, while eliminating the primary MgZn2 phase in the Zn-Al-Mg ternary coating alloy and forming a fine ternary eutectic structure.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is: The invention provides a method for eliminating primary MgZn2 in hot-dip galvanized aluminum-magnesium alloy by utilizing the synergistic effect of silicon and titanium elements.

[0011] The hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg (wt.%) alloy composition is calculated by mass percentage: 6% Al, 3% Mg, 0.05~0.2% Si, 0.05~0.3% Ti, and the balance Zn.

[0012] Preferably, the Zn-6Al-3Mg alloy composition (wt.%) is: 6% Al, 3% Mg, 0.07-0.1% Si, 0.2% Ti, and the balance Zn, calculated by mass percentage.

[0013] (1) Weigh the Zn-6Al-3Mg alloy ingot, pure Zn ingot, pure Mg particles, Al-10Ti alloy block, Al-10Si alloy block, and pure Zn foil according to mass percentage; (2) Place the weighed Zn-6Al-3Mg alloy ingot and pure Zn ingot in a pit furnace with a CO2 / SF6 mixed protective atmosphere and heat until melted (440-460°C), stir thoroughly, and keep warm for 8-12 minutes; (3) Heat the furnace to 710-750°C, press Al-10Ti alloy blocks and Al-10Si alloy blocks into the alloy melt in sequence until they are completely melted, stir thoroughly, and keep warm for 10-20 minutes; (4) Cool the furnace to 500-550°C, press pure Mg particles wrapped in pure Zn foil into the alloy melt until it is completely melted, stir thoroughly, and keep warm for 5-15 minutes; (5) The temperature of the furnace is lowered to 440°C-460°C, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Through the precisely controlled synergistic effect of low silicon and titanium contents, coupled with a simple single-melting preparation method, the present invention not only more thoroughly eliminates the performance-damaging primary MgZn2 phase in the hot-dip galvanized Zn-6Al-3Mg alloy, but also effectively avoids the introduction of other hard intermetallic compounds, such as TiAl3 and Mg2Si, due to improper element additions. More importantly, this synergistic effect exhibits excellent structural stability and effectively suppresses the structural inheritance effects of the primary MgZn2 phase, demonstrating that the Si-Ti synergistic effect in the present invention is endogenous and stable, ensuring the excellent alloy structure under conditions close to those encountered in actual applications.

[0015] The alloy prepared by the present invention has a finer and more uniform ternary eutectic structure, which lays a solid microstructural foundation for improving the comprehensive mechanical properties, corrosion resistance and processing performance of the coating, and has significant cost and process convenience advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : A microstructure photograph of the Zn-6Al-3Mg alloy prepared in Comparative Example 1 of the present invention; Figure 2 : A microstructure photograph of the Zn-6Al-3Mg-0.1Si-0.05Ti alloy prepared in Example 1 of the present invention; Figure 3: A microstructure photograph of the Zn-6Al-3Mg-0.1Si-0.1Ti alloy prepared in Example 2 of the present invention; Figure 4 : A microstructure photograph of the Zn-6Al-3Mg-0.1Si-0.15Ti alloy prepared in Example 3 of the present invention; Figure 5 : A microstructure photograph of the Zn-6Al-3Mg-0.1Si-0.2Ti alloy prepared in Example 4 of the present invention; Figure 6 : A microstructure photograph of the Zn-6Al-3Mg-0.07Si-0.2Ti alloy prepared in Example 5 of the present invention; Figure 7 : A microstructure photograph of the Zn-6Al-3Mg alloy prepared in Comparative Example 2 of the present invention; Figure 8 : A microstructure photograph of the Zn-6Al-3Mg-0.07Si alloy prepared in Comparative Example 3 of the present invention; Figure 9 : A microstructure photograph of the Zn-6Al-3Mg-0.1Si alloy prepared in Comparative Example 4 of the present invention; Figure 10 : A microstructure photograph of the Zn-6Al-3Mg-0.13Si alloy prepared in Comparative Example 5 of the present invention; Figure 11 : A microstructure photograph of the Zn-6Al-3Mg-0.2Ti alloy prepared in Comparative Example 6 of the present invention; Figure 12 : A microstructure photograph of the Zn-6Al-3Mg-0.1Si-0.23Ti alloy prepared in Comparative Example 7 of the present invention; Figure 13 : A microstructure photograph of the Zn-6Al-3Mg-0.13Si-0.2Ti alloy prepared in Comparative Example 8 of the present invention; Figure 14 : A microstructure photograph of the Zn-6Al-3Mg-0.07Si-0.2Ti alloy prepared in Application Example 1 of the present invention; Figure 15 : Statistical photographs showing the area fraction of eutectic structures of alloys prepared in the embodiments, comparative examples, and application examples of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0018] The pure Mg particles in the following examples of the present invention were purchased from Qinghe County Dingyuan Metal Products Co., Ltd.

[0019] The pure Zn blocks used in the following examples of the present invention were purchased from Qinghe County Dingyuan Metal Products Co., Ltd.

[0020] The pure Zn foils used in the following examples of the present invention were purchased from Hefei Jinentropy Technology Co., Ltd.

[0021] The Zn-6Al-3Mg alloy blocks used in the following examples of the present invention were purchased from Jiangsu Research Institute of Rare Metals.

[0022] The Al-10Si alloy blocks used in the following examples of the present invention were purchased from Jiangsu Research Institute of Rare Metals.

[0023] The Al-10Ti alloy blocks used in the following examples of the present invention were purchased from Jiangsu Research Institute of Rare Metals.

[0024] Example 1: A hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is 6% Al, 3% Mg, 0.1% Si, 0.05% Ti, and the balance Zn, in terms of mass percentage.

[0025] The preparation method of the hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block and the Al-10Ti alloy block into the alloy melt until they are completely melted, stirring them thoroughly and keeping them warm for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.1Si-0.05Ti with coordinated silicon and titanium elements.

[0026] The scanning electron microscope image of the cross section of the hot-dip galvanized aluminum-magnesium alloy with silicon and titanium elements obtained in Example 1 is shown in the attached specification. Figure 2Scanning electron microscopy results show that the primary MgZn2 phase in the alloy structure has significantly decreased in number and become finer in size, reaching a maximum size of 41.23 µm. Primary Al dendrites have also become finer and more numerous. This is likely due to the addition of Ti increasing the undercooling during melt solidification, significantly boosting the nucleation rate of primary Al dendrites. Furthermore, the black needle-like structure appearing in the alloy structure is the Mg2Si phase.

[0027] Example 2: A hot-dip galvanized aluminum-magnesium alloy with synergistic silicon and titanium elements, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is as follows: 6% Al, 3% Mg, 0.1% Si, 0.1% Ti, and the balance Zn, in terms of mass percentage.

[0028] The preparation method of the hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block and the Al-10Ti alloy block into the alloy melt until they are completely melted, stirring them thoroughly and keeping them warm for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.1Si-0.1Ti with coordinated silicon and titanium elements.

[0029] The scanning electron microscope image of the cross section of the hot-dip galvanized aluminum-magnesium alloy with silicon and titanium elements obtained in Example 2 is shown in the attached specification. Figure 3 As shown in Figure 2, scanning electron microscopy results show that the amount of primary MgZn2 phase in the alloy structure further decreases and its size further refines, reaching a maximum size of 39.30 µm. The number of primary Al dendrites decreases and transforms into short and thick dendrites. This may be due to the increase in Ti content leading to an excessive number of nucleation cores, which limits the growth space of dendrites and leads to competitive growth, resulting in a short and thick morphology. In addition, the original black needle-shaped Mg2Si phase in the alloy structure also transforms into a black dot-like structure uniformly distributed in the Zn-Al-Mg alloy structure due to the increase in Ti content. This indicates that the Ti-Si is fully bonded, reducing the free Si and suppressing the precipitation of the Mg2Si phase. The remaining small amount of Mg2Si forms a nanoscale dot-like phase under rapid solidification.

[0030] Example 3: A hot-dip galvanized aluminum-magnesium alloy with synergistic silicon and titanium elements, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is as follows: 6% Al, 3% Mg, 0.1% Si, 0.15% Ti, and the balance Zn, in terms of mass percentage.

[0031] The preparation method of the hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block and the Al-10Ti alloy block into the alloy melt until they are completely melted, stirring them thoroughly and keeping them warm for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.1Si-0.15Ti with coordinated silicon and titanium elements.

[0032] The scanning electron microscope image of the cross section of the hot-dip galvanized aluminum-magnesium alloy obtained in Example 3 is shown in the attached specification. Figure 4 Scanning electron microscopy (SEM) results show that the nucleation driving force of the primary MgZn2 phase in the alloy structure has further decreased, making it more difficult for it to form and grow, reaching a maximum size of 16.69µm. The primary Al dendrites have become finer and more numerous, likely due to the excessive Ti content, which further hinders dendrite growth and leads to the dominance of a short, thick morphology. Furthermore, the black dots in the alloy structure represent the Mg2Si phase, which is even finer in size.

[0033] Example 4: A hot-dip galvanized aluminum-magnesium alloy with synergistic silicon and titanium elements, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is 6% Al, 3% Mg, 0.1% Si, 0.2% Ti, and the balance Zn, in terms of mass percentage.

[0034] The preparation method of the hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block and the Al-10Ti alloy block into the alloy melt until they are completely melted, stirring them thoroughly and keeping them warm for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.1Si-0.2Ti with coordinated silicon and titanium elements.

[0035] The scanning electron microscope image of the cross section of the hot-dip galvanized aluminum-magnesium alloy obtained in Example 4 is shown in the attached specification. Figure 5 Scanning electron microscopy (SEM) results show the absence of hard phases such as TiAl₃ and Mg₂Si, and the complete disappearance of the primary MgZn₂ phase in the alloy structure. This suggests that excess Ti strongly inhibits Mg atomic diffusion, blocking the nucleation of the MgZn₂ phase. Simultaneously, Si and the ternary eutectic structure completely consume Mg. Primary Al dendrites become finer and denser, likely due to the formation of a large number of nanoscale Ti-Al or Ti-Si compounds from the excess Ti, providing ultra-high-density nucleation sites and leading to further refinement of the Al dendrites. Mg₂Si disappears from the alloy structure, while deep-contrast Si-rich regions appear at the edges of the eutectic structures with varying orientations. This is likely due to the near-saturation of the binding of further Ti and Si, leading to the segregation of residual Si at the eutectic boundaries.

[0036] Example 5: A hot-dip galvanized aluminum-magnesium alloy with synergistic silicon and titanium elements, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is 6% Al, 3% Mg, 0.07% Si, 0.2% Ti, and the balance Zn, in terms of mass percentage.

[0037] The preparation method of the hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block and the Al-10Ti alloy block into the alloy melt until they are completely melted, stirring them thoroughly and keeping them warm for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.07Si-0.2Ti with coordinated silicon and titanium elements.

[0038] The scanning electron microscope image of the cross section of the hot-dip galvanized aluminum-magnesium alloy with silicon and titanium elements obtained in Example 5 is shown in the attached specification. Figure 6 As shown in the figure, the scanning electron microscopy results show that there is no hard phase such as TiAl3 and Mg2Si, and the primary MgZn2 phase in the alloy structure disappears completely. At the same time, reducing the content of Si element reduces the primary Al dendrites and increases the fine ternary eutectic structure in the alloy structure. This shows that controlling the Si content can reasonably control the supercooling of the melt, thereby eliminating the primary MgZn2 phase while increasing the ternary eutectic structure.

[0039] Comparative Example 1: Comparative Example 1 is a commercially available ZAM alloy ingot (i.e., Zn-6Al-3Mg alloy ingot) purchased from Jiangsu Research Institute of Rare Metals. The scanning electron microscope cross-section of Comparative Example 1 is shown in the attached manual. Figure 1 As shown in Figure 2, the scanning electron microscopy results show that there is a coarse MgZn2 phase in the Zn-6Al-3Mg alloy ingot structure.

[0040] Comparative Example 2: Comparative Example 2 is a zinc-aluminum-magnesium alloy prepared by remelting a Zn-6Al-3Mg alloy ingot, and the preparation steps are as follows: (1) Place the Zn-6Al-3Mg alloy ingot in a pit furnace with a general CO2 / SF6 mixed protective gas, heat and melt it, and stir it thoroughly. The melting temperature is 450℃. (2) The alloy melt obtained in step (1) is kept warm for 1 hour and then cast to obtain a remelted and kept warm zinc-aluminum-magnesium alloy Zn-6Al-3Mg.

[0041] The scanning electron microscope of the cross section of Comparative Example 2 is shown in the attached specification. Figure 7 As shown in Figure 2, the scanning electron microscopy results show that the various structures in the remelted and held Zn-6Al-3Mg alloy are significantly refined, but due to the influence of the organizational genetic effect, coarse MgZn2 phase still exists in Zn-6Al-3Mg, with a maximum size of 76.49μm.

[0042] Comparative Example 3: A hot-dip galvanized aluminum-magnesium alloy containing only silicon, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is: 6% Al, 3% Mg, 0.07% Si, and the balance Zn, calculated in terms of mass percentage.

[0043] The method for preparing the silicon-containing hot-dip galvanized aluminum-magnesium alloy comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block into the alloy melt until it is completely melted, stirring thoroughly, and then keeping the temperature for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a silicon-containing hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.07Si.

[0044] The scanning electron microscope of the cross section of Comparative Example 3 is shown in the attached specification. Figure 8 As shown in the figure, scanning electron microscopy results show that the primary Al dendrites in the Zn-6Al-3Mg-0.07Si alloy are significantly refined and their number increases significantly, indicating that when the Si content is 0.07%, the Si element can provide a large degree of undercooling for the alloy. However, the primary MgZn2 phase still exists in the alloy structure, only slightly refined, with a maximum size of 50.29μm.

[0045] Comparative Example 4: A hot-dip galvanized aluminum-magnesium alloy containing only silicon, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is: 6% Al, 3% Mg, 0.1% Si, and the balance Zn, in terms of mass percentage.

[0046] The method for preparing the silicon-containing hot-dip galvanized aluminum-magnesium alloy comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block into the alloy melt until it is completely melted, stirring thoroughly, and then keeping the temperature for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a silicon-containing hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.1Si.

[0047] The scanning electron microscope of the cross section of Comparative Example 4 is shown in the attached specification. Figure 9 As shown in Figure 2, scanning electron microscopy results show that the primary MgZn2 phase in the remelted and held Zn-6Al-3Mg-0.1Si alloy has been further refined and its amount has been significantly reduced, with its maximum size reaching 31.51 μm. At the same time, black needle-like structures with a contrasting black structure have appeared in the solidified structure. According to the literature, these black needle-like structures are Mg2Si phases.

[0048] Comparative Example 5: A hot-dip galvanized aluminum-magnesium alloy containing only silicon, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is: 6% Al, 3% Mg, 0.13% Si, and the balance Zn, calculated in terms of mass percentage.

[0049] The method for preparing the silicon-containing hot-dip galvanized aluminum-magnesium alloy comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Si alloy block into the alloy melt until it is completely melted, stirring thoroughly, and then keeping the temperature for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a silicon-containing hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.13Si.

[0050] The scanning electron microscope of the cross section of Comparative Example 5 is shown in the attached specification. Figure 10 As shown in Figure 2, scanning electron microscopy (SEM) results show that the primary Al dendrites in the remelted and held Zn-6Al-3Mg-0.13Si alloy further refine and increase in number. The primary MgZn2 phase also slightly refines, reaching a maximum size of 29.83 μm. As the Si content increases, more black, dot-like Mg2Si phases appear in the microstructure.

[0051] Comparative Example 6: A hot-dip galvanized aluminum-magnesium alloy containing only titanium, wherein the alloy composition of Zn-6Al-3Mg (wt.%) is: 6% Al, 3% Mg, 0.2% Ti, and the balance Zn, calculated in terms of mass percentage.

[0052] The preparation method of the titanium-containing hot-dip galvanized aluminum-magnesium alloy comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing the Al-10Ti alloy block into the alloy melt until it is completely melted, stirring thoroughly, and then keeping the temperature for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a silicon-containing hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.2Ti.

[0053] The scanning electron microscope of the cross section of Comparative Example 6 is shown in the attached specification. Figure 11 As shown in the figure, the addition of Ti element refines the dendritic Al phase, but has a weaker effect on the refinement of the primary MgZn2 phase. The microstructure can still form a primary MgZn2 phase with a size of up to 132.11 μm.

[0054] Comparative Example 7: Comparative Example 7 is a silicon-titanium hot-dip galvanized aluminum-magnesium alloy with a titanium content exceeding 0.2%. The alloy composition of Zn-6Al-3Mg (wt.%) is: 6% Al, 3% Mg, 0.1% Si, 0.23% Ti, and the balance Zn, calculated in terms of mass percentage.

[0055] The method for preparing the silicon-containing hot-dip galvanized aluminum-magnesium alloy comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing Al-10Ti and Al-10Si alloy blocks into the alloy melt until completely melted, stirring thoroughly, and then keeping the temperature for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a silicon-containing hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.1Si-0.23Ti.

[0056] The scanning electron microscope of the cross section of Comparative Example 7 is shown in the attached specification. Figure 12 As shown in the figure, the Zn-6Al-3Mg-0.1Si-0.23Ti alloy is mainly composed of dendritic Al phase, black short rod-shaped TiAl3 phase and eutectic structure. The primary coarse MgZn2 phase is absent in the silicon-titanium synergistic ZAM alloy with excess Ti, indicating that the silicon-titanium synergistic effect can eliminate the primary MgZn2 phase. However, when excessive Ti is added, the aluminum-titanium intermetallic compound phase TiAl3 phase appears in the structure.

[0057] Comparative Example 8: Comparative Example 8 is a silicon-titanium hot-dip galvanized aluminum-magnesium alloy with a silicon content exceeding 0.1%. The alloy composition of Zn-6Al-3Mg (wt.%) is as follows: 6% Al, 3% Mg, 0.13% Si, 0.2% Ti, and the balance Zn, calculated in terms of mass percentage.

[0058] The method for preparing the silicon-containing hot-dip galvanized aluminum-magnesium alloy comprises the following steps: (1) According to the formula of each element in the raw material, pure Zn block and Zn-6Al-3Mg alloy block are placed in a general CO2 / SF6 mixed protective gas pit furnace in turn, heated and melted, and then stirred thoroughly. The melting temperature is 450℃ and kept warm for 10 minutes. (2) heating the alloy melt obtained in step (1) to 720°C, pressing Al-10Ti and Al-10Si alloy blocks into the alloy melt until completely melted, stirring thoroughly, and then keeping the temperature for 10 minutes; (3) The alloy melt obtained in step (2) is cooled to 550°C in the furnace, and pure Mg particles coated with pure Zn foil are pressed into the total melt until it is completely melted, and then the mixture is stirred thoroughly and kept warm for 10 minutes; (4) The alloy melt obtained in step (3) is cooled to 450° C. in a furnace, and the alloy melt is cast to obtain a silicon-containing hot-dip galvanized aluminum-magnesium alloy Zn-6Al-3Mg-0.13Si-0.2Ti.

[0059] The scanning electron microscope of the cross section of Comparative Example 8 is shown in the attached specification. Figure 13 As shown in the figure, the microstructure of the Zn-6Al-3Mg-0.13Si-0.2Ti alloy is mainly composed of Al dendrites, black Mg2Si phase and eutectic structure. When the Si content exceeds 0.1wt.%, the primary coarse MgZn2 phase does not exist in the silicon-titanium synergistic ZAM alloy structure, indicating that the silicon-titanium synergistic effect can eliminate the primary MgZn2 phase. However, when the Si element is added exceeding 0.1wt.%, the silicon-magnesium intermetallic compound phase Mg2Si phase appears in the structure.

[0060] Application Example 1: Application Example 1 is a zinc-aluminum-magnesium alloy prepared by remelting the silicon-titanium-synergistic zinc-aluminum-magnesium alloy Zn-6Al-3Mg-0.07Si-0.2Ti prepared in Example 5. The preparation steps are as follows: (1) The Zn-6Al-3Mg-0.07Si-0.2Ti alloy was heated and melted in a pit furnace with a general CO2 / SF6 mixed protective gas and stirred thoroughly. The melting temperature was 450°C. (2) The alloy melt obtained in step (1) is kept warm for 1 hour and then cast to obtain a remelted and kept warm zinc-aluminum-magnesium alloy Zn-6Al-3Mg-0.07Si-0.2Ti.

[0061] Application Example 1 Scanning electron microscope cross section as shown in the instruction manual Figure 14 As shown, the scanning electron microscopy results show that there is no primary MgZn2 phase in the remelted and heat-insulated Zn-6Al-3Mg-0.07Si-0.2Ti alloy structure, indicating that the organizational inheritance effect of the primary MgZn2 phase is completely suppressed by the synergistic effect of silicon and titanium elements. At the same time, the ternary eutectic structure in the remelted Zn-6Al-3Mg-0.07Si-0.2Ti alloy structure is fine and no other intermetallic compound phases are formed. The remelting of the alloy obtained in Example 5 can illustrate that Zn-6Al-3Mg-0.07Si-0.2Ti has the ability to stably eliminate primary MgZn2 and refine the eutectic structure at the same time.

[0062] Refinement effect analysis: Statistical analysis of the area fraction of eutectic structure of alloys prepared in the embodiments, comparative examples and application examples of the present invention is shown in the following results: Figure 15 The length of each column represents the average area fraction of the eutectic structure in four micrographs taken at different areas of the ingot sample at 250 times magnification, and the broken line represents the average area fraction of the original ZAM alloy ingot, the ZAM alloy with the addition of Si or Ti single element, and the ZAM alloy with the synergistic addition of Si and Ti elements. Figure 15 The specific composition and corresponding examples of each alloy number are shown in Table 1.

[0063] Table 1 Alloy number name Alloy composition Corresponding example Average area fraction of the ternary eutectic structure A ZAM alloy ingot Zn-6Al-3Mg Comparative Example 1 73.58% B ZAM (remelting) Zn-6Al-3Mg Comparative Example 2 71.82% C ZAM-0.07Si Zn-6Al-3Mg-0.07Si Comparative Example 3 64.65% D ZAM-0.1Si Zn-6Al-3Mg-0.1Si Comparative Example 4 73.67% E ZAM-0.13Si Zn-6Al-3Mg-0.13Si Comparative Example 5 64.12% F ZAM-0.2Ti Zn-6Al-3Mg-0.2Ti Comparative Example 6 67.21% G ZAM-0.1Si-0.05Ti Zn-6Al-3Mg-0.1Si-0.05Ti Example 1 74.59% H ZAM-0.1Si-0.1Ti Zn-6Al-3Mg-0.1Si-0.1Ti Example 2 81.19% I ZAM-0.1Si-0.15Ti Zn-6Al-3Mg-0.1Si-0.15Ti Example 3 84.29% J ZAM-0.1Si-0.2Ti Zn-6Al-3Mg-0.1Si-0.2Ti Example 4 79.85% K ZAM-0.1Si-0.23Ti Zn-6Al-3Mg-0.1Si-0.23Ti Comparative Example 7 74.64% L ZAM-0.13Si-0.2Ti Zn-6Al-3Mg-0.13Si-0.2Ti Comparative Example 8 78.49% M ZAM-0.07Si-0.2Ti Zn-6Al-3Mg-0.07Si-0.2Ti Example 5 84.52% N ZAM-0.07Si-0.2Ti(remelting) Zn-6Al-3Mg-0.07Si-0.2Ti Application Example 1 81.45% like Figure 15As shown in the figure, the black broken line indicates that while the addition of Si or Ti alone can homogenize the alloy structure and refine the single phase, the increased nucleation rate caused by the individual elements reduces the area fraction of eutectic structure in the ZAM alloy, even lower than that of the original ZAM alloy. However, even when the synergistic addition of Si and Ti elements exceeds a threshold, the area fraction of eutectic structure in the alloy remains higher than that in the ZAM alloy ingots containing either Si or Ti alone. Comparison of ZAM alloys with synergistic Si and Ti elements reveals that the preferred ZAM alloys, ZAM-0.1Si-0.2Ti (alloy number J) and ZAM-0.07Si-0.2Ti (alloy number M), both eliminate the primary MgZn2 phase while exhibiting a high area fraction of eutectic structure. In particular, ZAM-0.07Si-0.2Ti (alloy number M) exhibits the highest area fraction of eutectic structure. It can be found from the alloy number N that the refining effect of the ZAM-0.07Si-0.2Ti alloy after remelting is well maintained, indicating that the preferred ZAM-0.07Si-0.2Ti can stably eliminate the primary MgZn2 phase and refine the structure.

[0064] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for stably eliminating the primary MgZn2 phase in hot-dip galvanized aluminum-magnesium alloy by utilizing the synergistic effect of silicon and titanium, characterized in that: Hot-dip galvanized aluminum-magnesium alloy, the composition is calculated in mass percentage, the Zn-6Al-3Mg (wt.%) alloy composition is: 6% Al, 3% Mg, 0.05~0.2% Si, 0.05~0.3% Ti, and the balance Zn.

2. The method according to claim 1, characterized in that The composition of Zn-6Al-3Mg (wt.%) alloy is: 6%Al, 3%Mg, 0.07~0.1%Si, 0.2%Ti, and the balance Zn.

3. The method according to claim 1, characterized in that (1) Weigh the Zn-6Al-3Mg alloy ingot, pure Zn ingot, pure Mg particles, Al-10Ti alloy block, Al-10Si alloy block, and pure Zn foil according to mass percentage; (2) Place the weighed Zn-6Al-3Mg alloy ingot and pure Zn ingot in a pit furnace with a CO2 / SF6 mixed protective atmosphere and heat until melted, stir thoroughly, and keep warm for 8-12 minutes; (3) Heat the furnace to 710-750°C, press Al-10Ti alloy blocks and Al-10Si alloy blocks into the alloy melt in sequence until they are completely melted, stir thoroughly, and keep warm for 10-20 minutes; (4) Cool the furnace to 500-550°C, press pure Mg particles wrapped in pure Zn foil into the alloy melt until it is completely melted, stir thoroughly, and keep warm for 5-15 minutes; (5) The temperature of the furnace is lowered to 440°C-460°C, and the alloy melt is cast to obtain a hot-dip galvanized aluminum-magnesium alloy with coordinated silicon and titanium elements.

4. The hot-dip galvanized aluminum-magnesium alloy prepared by the method according to claim 3, characterized in that: There is no primary MgZn2 phase in hot-dip galvanized Zn-6Al-3Mg alloy.

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