Hydrogen embrittlement resistant high-magnesium aluminum alloy containing complex metal nanophase and preparation method of hydrogen embrittlement resistant high-magnesium aluminum alloy

Abstract

The invention discloses a hydrogen embrittlement-resistant high-magnesium aluminum alloy containing a complex metal nanophase and a preparation method of the hydrogen embrittlement-resistant high-magnesium aluminum alloy. The alloy comprises the following main components in percentage by mass: 5.50 to 8.00 percent of Mg, 0.10 to 0.30 percent of X (X is Sc, Zr or Ti), 0.005 to 0.50 percent of Si, 0.05 to 0.85 percent of Mn, 0.01 to 0.60 percent of Fe and the balance of Al. Through regulation and control of the preparation method and the processing and heat treatment process, high-density Al3 (Mg, X) 2 complex metal nanophase particles are obtained and serve as excellent hydrogen traps to capture and stabilize hydrogen atoms and inhibit hydrogen-induced fracture, and the hydrogen embrittlement resistance of the alloy is greatly improved. While the alloy density is reduced and a small amount of rare earth elements are used, the total tensile elongation of the target alloy under the hydrogen content of 7ppmw can be reduced by less than 15%, and the tensile uniform elongation is greater than 10%.

Description

Technical Field

[0001] The present invention relates to the technical field of non-ferrous metals, and particularly to a high-magnesium Al-Mg-X (X = Sc, Zr, Ti) alloy containing Al3(Mg, X)2 complex metal nanophases and having hydrogen embrittlement resistance, and a preparation method thereof. Background Art

[0002] The hydrogen energy economy is a global development trend. While hydrogen is being produced, how to safely and efficiently store and transport hydrogen has become the focus of attention. Against the backdrop of material lightweighting and energy conservation, lightweight and high-strength aluminum alloys have become the main materials for hydrogen storage and transportation tanks. However, traditional high-strength aluminum alloys have a very strong hydrogen embrittlement sensitivity, undergoing early brittle fracture during tensile testing at a hydrogen content of 1 ppmw (ppmw: parts per million by weight), with the tensile elongation far lower than that of the non-hydrogenated material; at a hydrogen content of 3 ppmw, the tensile elongation is usually reduced by more than 50% compared to the non-hydrogenated material. The higher the hydrogen content, the greater the degree of hydrogen embrittlement, severely restricting the large-scale application of lightweight and high-strength aluminum alloys in the hydrogen energy field. The proposed hydrogen embrittlement mechanisms for aluminum alloys mainly include: hydrogen segregation at grain boundaries leading to grain boundary cracking, hydrogen segregation at particle interfaces leading to interface cracking, hydrogen accumulation at crack tips promoting cracking, hydrogen distribution causing changes in local plastic deformation ability, and hydrogen pinning and hindering dislocation slip. In the design of aluminum alloy materials to inhibit or prevent hydrogen embrittlement, forming a microstructure with a hydrogen trapping effect to capture hydrogen and disperse it within the grains, reducing or alleviating the high-concentration segregation of hydrogen at interfaces, is currently the most commonly used method. Recent research has found that second-phase particles with intermetallic compound characteristics are potentially the most effective hydrogen traps in aluminum alloys, not only capturing hydrogen at interfaces but also stabilizing hydrogen within the particles, achieving multi-site hydrogen dispersion. However, the reported second-phase particles of this type have a hydrogen binding energy (reflecting the ability to capture hydrogen) of less than 0.8 eV / atom, a small variety, and are basically large-size (micrometer-scale) crystalline phase particles formed during the solidification of aluminum alloys, with a limited total capture amount of hydrogen atoms. To further increase the number of hydrogen traps and thus improve the hydrogen embrittlement resistance of aluminum alloys, it is necessary to design and prepare second-phase particles with a high fractional density, small size (nanometer scale), and higher hydrogen binding energy.

[0003] Al-Mg alloys are a type of aluminum alloy system with Mg solid solution strengthening as the main strengthening mechanism. They have advantages such as weldability and corrosion resistance, and are widely used in fields such as aerospace, marine ships, and hydrogen energy storage and transportation. The presence of water or hydrogen in their long-term service environment makes hydrogen embrittlement resistance an important indicator for safe service. In traditional Al-Mg alloys, the Mg content is less than about 5.5% (mass percentage). When the Mg content exceeds this value, even in an Al-Mg alloy with complete Mg solid solution, coarse β-Al3Mg3 equilibrium phase particles will precipitate at grain boundaries at a relatively low temperature (~50 °C), resulting in easy cracking at grain boundaries and early fracture, and at the same time, the corrosion resistance of the material is significantly reduced. However, the Al3Mg3 second phase itself is a special type of intermetallic compound with a Samson crystal structure. Its unit cell contains 1832 atomic sites, and only 1168 atomic sites are occupied by Al or Mg atoms, containing a large number of structural vacancies or crystal defects. It is an excellent hydrogen trap, and its hydrogen binding energy can theoretically reach more than 1.0 ev / atom. The precipitation sequence of Al3Mg3 is supersaturated solid solution → Al3Mg (L12 crystal structure) → β′-Al3Mg2 → β-Al3Mg2. Once the large nucleation energy barrier is overcome, it can precipitate in a high-density, uniformly dispersed manner in the grains in the form of nanoparticles, which will improve the material strength, corrosion resistance, and more importantly, significantly improve the hydrogen embrittlement resistance. The present invention proposes to add a small amount of X (X = Sc, Zr, Ti) microalloying elements. Through two-stage heat treatment, during the first-stage heat treatment, high-density distributed Al3X nanoparticles with an L12 crystal structure precipitate; during the second-stage heat treatment, the Al3Mg phase nucleates on the Al3X phase in a template manner and gradually grows into the β-Al3Mg2 phase, forming composite nano second-phase particles with an Al3X / β-Al3Mg2 core-shell structure. While pinning dislocations to increase strength, the β-Al3Mg2 shell layer captures a large number of hydrogen atoms and stabilizes them inside, inhibiting the segregation of hydrogen atoms at grain boundaries or phase boundaries, significantly improving the hydrogen embrittlement resistance. At a hydrogen content as high as 7.0 ppmw, the tensile elongation decreases by less than 15%, and the uniform elongation reaches 10%, which is better than all reported cast aluminum alloys. Summary of the Invention

[0004] An anti-hydrogen embrittlement high-magnesium aluminum alloy containing complex metal nano-phases and its preparation method mentioned in the present invention aims at the urgent needs of serving in a high-hydrogen harsh environment. Through the microalloying effect of adding element X (X = Sc, or Zr, or Ti), a two-stage heat treatment system is formulated and the process parameters are optimized to achieve the first precipitation of high-density Al3X nano-particles. Then, the in-situ precipitation of β-Al3Mg2 on the Al3X nano-particles is induced by the template effect, in which part of the Mg atoms are replaced by X atoms to form a complex metal nano-phase Al3(Mg,X)2 with a similar structure. The Al3(Mg,X)2 nano-phase has a high density and a large interface, and its hydrogen binding energy is greater than 1.0 ev / atom, which can effectively capture and stabilize hydrogen atoms, significantly reduce the hydrogen embrittlement tendency of the alloy, and obtain excellent mechanical properties at a high hydrogen content of 7.0 ppmw.

[0005] The present invention is realized by the following technical solutions:

[0006] An anti-hydrogen embrittlement high-magnesium Al-Mg-X alloy containing complex metal nano-phases, with the mass percentage of Mg being 5.50–8.00%, the mass percentage of X (X = Sc, Zr, Ti) being 0.10–0.30%, the mass percentage of Si being 0.005–0.50%, the mass percentage of Mn being 0.05–0.85%, the mass percentage of Fe being 0.01–0.60%. For the remaining impurities including Ni and Zn, their mass percentage needs to be strictly controlled to be less than 0.2%, and the rest is Al. The ingot is cast by sub-rapid solidification water-cooled copper mold, and the solidification rate is 100 - 300 K / s.

[0007] A preparation method of an anti-hydrogen embrittlement high-magnesium aluminum alloy containing complex metal nano-phases. The ingot is cast by the sub-rapid solidification method, and then homogenized to eliminate the alloy composition segregation. Thin plate materials are prepared by hot working deformation. After solution treatment, artificial aging treatment is carried out. It includes two parts: homogenization and hot deformation. The homogenization treatment is carried out at 480 - 520 °C for 20 h - 26 h, and cooled in the furnace to avoid internal stress caused by too fast cooling, which may lead to composition segregation; the hot deformation is carried out after homogenization, at a temperature of 200 °C - 480 °C, and the hot deformation is multi-pass, with the deformation amount of each pass less than 20%. After deformation to the required thickness, it is air-cooled to room temperature.

[0008] A heat treatment process of an anti-hydrogen embrittlement high-magnesium Al-Mg-X alloy containing complex metal nano-phases, including two parts: solution treatment and artificial aging treatment. 1. Solution treatment is carried out at 300 - 450 °C for 2 - 6 h, and water quenched to room temperature; 2. Rapidly carry out artificial aging treatment at 150 - 300 °C for 8 - 24 h to complete.

[0009] Through the regulation of the preparation method, processing, and heat treatment process, the present invention has obtained Al3(Mg,X)2 complex metal nanophase particles with a high-density intragranular dispersion distribution. Their hydrogen binding energy exceeds 0.9 eV / atom, which is the maximum value reported in aluminum alloys. These nanophase particles act as strong hydrogen traps to capture and stabilize hydrogen atoms, inhibit hydrogen-induced fracture, and greatly improve the hydrogen embrittlement resistance of the alloy. While reducing the alloy density and using a small amount of rare earth elements, the present invention enables the target alloy to have a total elongation reduction of less than 15% and a uniform elongation of 10% under a hydrogen content of 7 ppmw, exceeding all known aluminum alloy materials. Brief Description of the Drawings

[0010] Figure 1 It is the precipitation phase microstructure of Example 1 and Comparative Example 5 provided by the present invention;

[0011] (a) Low-magnification transmission image of intragranular nano-precipitation phase particles in Example 1;

[0012] (b) High-resolution transmission image of the precipitation phase in Example 1. The inner circle is Al3Sc, and the outer circle is Al3(Mg,Sc)2;

[0013] (c) Crystal structure characterization of the inner-circle Al3Sc and outer-circle Al3(Mg,Sc)2 phases of the precipitation phase in Example 1;

[0014] (d) Transmission image of the precipitation phase in Comparative Example 5. Coarse Al3Mg2 particles are mainly distributed at the grain boundaries

[0015] Figure 2 It is the precipitation phase microstructure of Example 3 and Comparative Example 7 provided by the present invention;

[0016] (a) Low-magnification transmission photograph of intragranular nano-precipitation phase particles in Example 3;

[0017] (b) High-resolution transmission photograph of the precipitation phase in Example 3. The lower part is Al3Ti, and the upper part is Al3(Mg,Ti)2;

[0018] (c) Crystal structure characterization of the upper-part Al3Ti and lower-part Al3(Mg,Ti)2 phases of the precipitation phase in Example 3;

[0019] (d) Transmission photograph of the precipitation phase in Comparative Example 7. Coarse Al3Mg2 particles are mainly distributed at the grain boundaries

[0020] Figure 3 It is the engineering stress-engineering strain curves of Example 1 and Comparative Example 5 provided by the present invention before and after hydrogen charging at 7.0 ppmw;

[0021] Figure 4 It is the engineering stress-engineering strain curves of Example 2 and Comparative Example 6 provided by the present invention before and after hydrogen charging at 7.0 ppmw;

[0022] Figure 5 Examples 1-4 of the present invention are provided for comparison of the uniform elongation after hydrogen charging at 7.0 ppmw with the results of aluminum alloys reported by predecessors. Detailed implementation manners

[0023] The following examples are intended to illustrate the present invention rather than further limit the present invention.

[0024] Refer to Figure 1 As shown, according to the accompanying drawings, after adding Sc element, a high-density precipitation of Al3(Mg,Sc)2 nanophase is formed inside the grains in the Al-Mg-Sc alloy of Example 1, while in the Al-Mg alloy of Comparative Example 5 without adding Sc element, only coarse Al3Mg2 phase particles are formed at the grain boundaries.

[0025] Refer to Figure 2 As shown, according to the accompanying drawings, after adding Ti element, a high-density precipitation of Al3(Mg,Ti)2 nanophase is formed inside the grains in the Al-Mg-Ti alloy of Example 3, while in the Al-Mg alloy of Comparative Example 7 without adding Ti element, only coarse Al3Mg2 phase particles are formed at the grain boundaries.

[0026] Refer to Figure 3 As shown, according to the accompanying drawings, in Example 1, for the Al-Mg-Sc alloy containing Al3(Mg,Sc)2 nanophase with dispersed distribution inside the grains, after hydrogen charging at about 7 ppmw, its tensile elongation decreases by less than 10% compared with the non-hydrogen-charged material. While for the Al-Mg alloy of Comparative Example 5, after hydrogen charging at about 7 ppmw, its tensile elongation decreases by about 50% compared with non-hydrogen charging. It shows that the high-density Al3(Mg,Ti)2 nanophase plays an excellent anti-hydrogen embrittlement effect.

[0027] Refer to Figure 4 As shown, according to the accompanying drawings, in Example 2, for the Al-Mg-Ti alloy prepared by sub-rapid solidification and containing Al3(Mg,Sc)2 nanophase with dispersed distribution inside the grains, after hydrogen charging at about 7 ppmw, its tensile elongation decreases by less than 8% compared with the non-hydrogen-charged material. While in Comparative Example 6, for the Al-Mg-Sc alloy with the same composition prepared by conventional cooling rate, due to the absence of Al3(Mg,Sc)2 nanophase inside the grains, after hydrogen charging at about 7 ppmw, its tensile elongation decreases by more than 50% compared with non-hydrogen charging. It shows that high-density Al3(Mg,Ti)2 nanophase can be formed only by the sub-rapid solidification preparation method and plays an excellent anti-hydrogen embrittlement effect.

[0028] Refer to Figure 5As shown, after charging hydrogen at about 7 ppmw, the tensile uniform elongation of the Al-Mg-Sc alloy in Example 1 and Example 2 containing intragranular dispersion of Al3(Mg,X)2 (X = Sc, Zr, Ti) nano-phases, the Al-Mg-Zr alloy in Example 3, and the Al-Mg-Ti alloy in Example 4 reached 10%, which was significantly better than other aluminum alloys prepared by casting under the same hydrogen content, and even exceeded the tensile uniform elongation of other aluminum alloys at low hydrogen content (less than 3 ppmw), showing extremely strong resistance to hydrogen embrittlement.

[0029] Example 1

[0030] A high-magnesium Al-Mg-Sc alloy with complex metal nano-phases and hydrogen embrittlement resistance, comprising the following steps: (1) An Al-6.2Mg-0.2Sc-0.1Si-0.16Mn-0.3Fe (by mass percentage) alloy ingot was prepared by water-cooled copper mold casting. Subsequently, the ingot was homogenized at 520 °C for 20 hours, cooled in the furnace, and hot-rolled 8 passes in the temperature range of 350 °C - 480 °C, and air-cooled to room temperature. (2) Solution treatment was carried out at 450 °C for 2 h, quenched in water to room temperature, and rapidly artificially aged at 200 °C for 16 h.

[0031] Example 2

[0032] A high-magnesium Al-Mg-Sc alloy with complex metal nano-phases and hydrogen embrittlement resistance, comprising the following steps: (1) An Al-5.8Mg-0.3Sc-0.3Si-0.5Mn-0.1Fe (by mass percentage) alloy ingot was prepared by water-cooled copper mold casting. Subsequently, the ingot was homogenized at 480 °C for 26 hours, cooled in the furnace, and hot-rolled 10 passes in the temperature range of 200 °C - 350 °C, and air-cooled to room temperature. (2) Solution treatment was carried out at 300 °C for 6 h, quenched in water to room temperature, and rapidly artificially aged at 300 °C for 8 h.

[0033] Example 3

[0034] A high-magnesium Al-Mg-Zr alloy with complex metal nano-phases and hydrogen embrittlement resistance, comprising the following steps: (1) An Al-7.8Mg-0.2Zr-0.5Si-0.8Mn-0.5Fe (by mass percentage) alloy ingot was prepared by water-cooled copper mold casting. Subsequently, the ingot was homogenized at 500 °C for 22 hours, cooled in the furnace, and hot-rolled 8 passes in the temperature range of 300 °C - 400 °C, and air-cooled to room temperature. (2) Solution treatment was carried out at 400 °C for 3 h, quenched in water to room temperature, and rapidly artificially aged at 300 °C for 12 h.

[0035] Example 4

[0036] A high-magnesium Al-Mg-Ti alloy with complex metal nanophases resistant to hydrogen embrittlement, comprising the following steps: (1) An Al-7.1Mg-0.3Ti-0.4Si-0.8Mn-0.5Fe (in mass percentage) alloy ingot is prepared by water-cooled copper mold casting. Subsequently, the ingot is homogenized at 500 °C for 22 hours, cooled in the furnace, and hot-rolled 8 passes in the temperature range of 300 °C - 400 °C and air-cooled to room temperature. (2) Solution treatment is carried out at 400 °C for 3 h, water-quenched to room temperature, and rapidly artificially aged at 300 °C for 12 h.

[0037] Comparative Example 5

[0038] A high-magnesium Al-Mg alloy without Sc, comprising the following steps: (1) An Al-6.1Mg-0.1Si-0.16Mn-0.3Fe (in mass percentage) alloy ingot is prepared by water-cooled copper mold casting. Subsequently, the ingot is homogenized at 520 °C for 20 hours, cooled in the furnace, and hot-rolled 8 passes in the temperature range of 350 °C - 480 °C and air-cooled to room temperature. (2) Solution treatment is carried out at 450 °C for 2 h, water-quenched to room temperature, and rapidly artificially aged at 200 °C for 16 h.

[0039] Comparative Example 6

[0040] A high-magnesium Al-Mg-Sc alloy prepared by a conventional casting method, comprising the following steps: (1) An Al-7.8Mg-0.3Sc-0.3Si-0.5Mn-0.1Fe (in mass percentage) alloy ingot is prepared by conventional metal iron mold casting. Subsequently, the ingot is homogenized at 480 °C for 26 hours, cooled in the furnace, and hot-rolled 10 passes in the temperature range of 200 °C - 350 °C and air-cooled to room temperature. (2) Solution treatment is carried out at 300 °C for 6 h, water-quenched to room temperature, and rapidly artificially aged at 300 °C for 8 h.

[0041] Comparative Example 7

[0042] A high-magnesium Al-Mg alloy without Ti, comprising the following steps: (1) An Al-8.0Mg-0.4Si-0.8Mn-0.5Fe (in mass percentage) alloy ingot is prepared by water-cooled copper mold casting. Subsequently, the ingot is homogenized at 500 °C for 22 hours, cooled in the furnace, and hot-rolled 8 passes in the temperature range of 300 °C - 400 °C and air-cooled to room temperature. (2) Solution treatment is carried out at 400 °C for 3 h, water-quenched to room temperature, and rapidly artificially aged at 300 °C for 12 h.

[0043] For the aluminum alloy materials of Examples 1 - 4 and Comparative Examples 5 - 7, the room temperature tensile mechanical properties are measured according to the national standard GB / T1173-1995 (tensile rate 10 -5 / s). The tensile property results before hydrogen charging are summarized in Table 1. It can be seen that before hydrogen charging, Examples 1-4 (all containing complex metal nanophases) designed in the present invention have more excellent room temperature yield and tensile strength than Comparative Examples 3-7 (all without complex metal nanophases), but the tensile elongation rate decreases.

[0044] For the aluminum alloy materials of Examples 1-4 and Comparative Examples 5-7, they are electrochemically charged with hydrogen to 7.0 ppmw, and their room temperature tensile mechanical properties are measured according to the national standard GB / T 1173-1995 (tensile rate 10 -5 / s). The tensile property results after hydrogen charging are summarized in Table 2. It can be seen that before and after hydrogen charging, the strength of Examples 1-4 (all containing complex metal nanophases) designed in the present invention changes little, and at the same time, the decrease amplitude of the tensile elongation rate is less than 10%; while for Comparative Examples 3-7 (all without complex metal nanophases), although the strength changes little, the decrease amplitude of the tensile elongation rate is greater than 40%. It shows that the design of complex metal nanophases effectively inhibits the hydrogen embrittlement of the material.

[0045] Table 1. Summary of room temperature tensile properties before hydrogen charging of hydrogen embrittlement-resistant high-magnesium Al-Mg-X series alloys of Examples 1-4 and Comparative Examples 5-7 involved in the present invention

[0046] Alloy code Yield strength / MPa Tensile strength / MPa Tensile elongation / % Example 1 211 326 11.2 Example 2 258 367 11.8 Example 3 244 354 12.2 Example 4 228 341 10.7 Comparative example 5 105 260 13.1 Comparative example 6 171 276 7.8 Comparative example 7 164 257 8.6

[0047] Table 2. Summary of room temperature tensile properties after hydrogen charging to 7.0 ppmw of hydrogen embrittlement-resistant high-magnesium Al-Mg-X series alloys of Examples 1-4 and Comparative Examples 5-7 involved in the present invention

[0048] Alloy code Yield strength / MPa Tensile strength / MPa Tensile elongation / % Example 1 216 317 9.8 Example 2 244 367 10.7 Example 3 238 342 10.2 Example 4 220 332 9.2 Comparative example 5 104 224 7.0 Comparative example 6 164 236 2.9 Comparative example 7 155 228 3.5

Claims

1. A high-magnesium aluminum alloy resistant to hydrogen embrittlement containing complex metal nanophases, characterized in that: The mass percentage of Mg is 5.50–8.00%, the mass percentage of X (X = Sc, Zr, Ti) is 0.10–0.30%, the mass percentage of Si is 0.005–0.50%, the mass percentage of Mn is 0.05–0.85%, the mass percentage of Fe is 0.01–0.60%. For the remaining impurities including Ni and Zn, their mass percentage needs to be strictly controlled to be less than 0.2%, and the rest is Al.

2. The anti-hydrogen embrittlement high magnesium aluminum alloy containing complex metal nano-phases according to claim 1, wherein: A high-density Al3(Mg, X)2 (X = Sc, Zr, Ti) nano-phase is formed within the crystal grains. This nano-phase particle has an extremely complex crystal structure, contains a large number of lattice defects, is an excellent hydrogen trap, and significantly improves the hydrogen embrittlement resistance of the material.

3. The anti-hydrogen embrittlement high magnesium aluminum alloy containing complex metal nano-phases according to claim 1, wherein: The high-density Al3(Mg, X)2 (X = Sc, Zr, Ti) nano-phase nucleates heterogeneously on the pre-formed high-density Al3Sc nano-particles, forming a complex nano-phase with an Al3(Mg, X)2 / Al3Sc core-shell structure.

4. A method for preparing a hydrogen embrittlement-resistant high-magnesium aluminum alloy containing complex metal nanophases as described in claim 1, characterized in that, The ingot is cast by the sub-rapid solidification method, and then homogenized to eliminate alloy composition segregation. Thin plate materials are prepared by hot working deformation. After solution treatment, artificial aging treatment is carried out.

5. The preparation method of the hydrogen embrittlement-resistant high magnesium aluminum alloy containing complex metal nanophases according to claim 4, characterized in that, The sub-rapid solidification ingot is cast using a water-cooled copper mold, and the solidification rate is 100 - 300 K / s.

6. The preparation method of the hydrogen embrittlement-resistant high-magnesium aluminum alloy containing complex metal nanophases according to claim 4, characterized in that The homogenization treatment is to hold at a temperature in the range of 480 - 520 °C for 20 h - 26 h, and cool with the furnace to avoid internal stress caused by too fast cooling, which may lead to composition segregation.

7. The preparation method of the hydrogen embrittlement-resistant high-magnesium aluminum alloy containing complex metal nanophases according to claim 4, characterized in that The hot working deformation temperature is 200 °C - 480 °C, and the deformation is in multiple passes, with the deformation amount per pass less than 20%. After deforming to the required thickness of the thin plate, it is air-cooled to room temperature.

8. The preparation method of the hydrogen embrittlement-resistant high magnesium aluminum alloy containing complex metal nanophases according to claim 4, characterized in that, The solution treatment is to hold at a temperature in the range of 300 - 450 °C for 2 - 6 h, and then water-quenched to room temperature.

9. The preparation method of the hydrogen embrittlement-resistant high-magnesium aluminum alloy containing complex metal nanophases according to claim 4, characterized in that The artificial aging treatment needs to be carried out rapidly, hold at 150 - 300 °C for 8 - 24 h, and a muffle furnace can be used.

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