WO2023279493A1 - High-strength and high-toughness impact-resistant energy-absorbing al-mg-si alloy - Google Patents

Abstract

A high-strength and high-toughness impact-resistant energy-absorbing Al-Mg-Si alloy. The Al-Mg-Si alloy comprises, in percentage by mass: 0.40-1.00% of Mg, 0.50-0.90% of Si, 0.60% or less of Mn, 0.30% or less of Cr, 0.25% or less of Fe, and 96.8-99.1% of Al, wherein Sifree=Si-0.3×(Mn+Fe+Cr), the mass ratio of Mg/Sifree is 0.72-1.40, and the percentage by mass of Mg+2Sifree is 1.40% to 2.40%. The aluminum alloy has not only excellent conventional mechanical properties but also good bending toughness, and also has outstanding crushing and impact resistance and energy absorption properties.

Description

A high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy technical field

The invention belongs to the technical field of aluminum alloy materials, and in particular relates to a high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy.

Background technique

With the continuous rapid development of human economy and society, energy issues and environmental issues continue to emerge, and green, low-carbon, environmentally friendly and sustainable development has become the development direction of today's society. The fuel consumption of motor vehicles occupies a considerable proportion in the total consumption of crude oil. The rapid development of the automobile industry not only poses a huge challenge to my country's oil supply, but also brings unprecedented pressure on the environment due to the emission of automobile exhaust. Energy saving and emission reduction is the key to the transformation and upgrading of the automobile industry, and lightweight is an important means to achieve energy saving and emission reduction.

Al-Mg-Si alloy belongs to heat-treatable and strengthened aluminum alloy. It has the advantages of high specific strength, good formability, excellent corrosion resistance and high weldability. It is an important material for realizing the lightweight of automobiles. Has been widely used, such as: body panels, engine pistons, anti-collision beams and bumpers and so on. However, the service conditions of different components are different. In addition to improving the conventional mechanical properties of the material, it is also necessary to improve the relevant performance under the corresponding service conditions for different service conditions of the components, such as new energy vehicle battery trays and automotive anti-collision beams. The key safety structural parts, such as steel, may be shattered by violent collisions from the outside under service conditions, and even cause serious loss of personnel and property. Therefore, the impact resistance and energy absorption performance of aluminum alloys used under such working conditions is particularly important.

At present, the main focus of industrial production is still on the strength of aluminum alloys, and there is little research on the impact and energy absorption properties of aluminum alloys. Although the Chinese patent CN109504870B provides an aluminum alloy for lightweight automobile anti-collision beams, the synthesis reaction process and solidification process are regulated by direct melt reaction technology combined with ultrasonic magnetic coupling field technology, and a compound with uniform distribution of nanoparticles in situ is obtained. The material is formed by hot extrusion and heat treatment. The preparation process is relatively complicated, difficult and costly, and is not suitable for wide application. And the study found that the impact resistance of the material is not only related to the strength of the material, but also closely related to its plasticity and toughness. In addition, the microstructure of the material is also crucial to its impact resistance and energy absorption performance.

Contents of the invention

Aiming at the problems in the above-mentioned prior art, the present invention provides an Al-Mg alloy with high bending toughness, impact toughness, crushing performance and energy-absorbing capacity under the premise of ensuring alloy strength, corrosion resistance and thermal stability. - Si alloy.

The above object of the present invention is implemented through the following technical solutions: a high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy, said Al-Mg-Si alloy comprising Mg0.40-1.00%, Si0. 50～0.90%, Mn≤0.60%, Cr≤0.30%, Fe≤0.25%, Al 96.8～99.1%, among them, Si _free =Si-0.3×(Mn+Fe+Cr), Mg/Si _free mass ratio is 0.72-1.40, and the mass percentage of Mg+2Si _free is 1.40%-2.40%.

Mg and Si are the main additive elements of 6xxx alloys. During the aging process, the second phase particles such as GP area, β", β' and β are interacted and precipitated to strengthen the matrix. According to the latest research, the Al-Mg-Si alloy is in the aging process The evolution law of the precipitated phase is as follows: supersaturated solid solution → GP area → β” → β'(B', U1, U2) → β. Among them, the β" phase has the best strengthening effect and is the most important strengthening precipitate in the peak-aged alloy; the β' phase is the main precipitate in the overaging alloy, and the strengthening effect is not as good as that of the β" phase; the β phase is an equilibrium phase. It has a non-coherent relationship with the aluminum matrix, and the strengthening effect is limited.

Information on Precipitated Phases in 6xxx Alloys

Precipitates	coherent relationship with the matrix	chemical components
GP area	coherent	Mg 2+X Al 7-XY Si 2+Y
β”	coherent	Mg5Si6 _
β'	semi-coherent	Mg 5 Si 3
beta	Incoherent	Mg 2 Si

In the composition design of 6xxx alloys, the β(Mg ₂ Si) phase is often considered as the main strengthening precipitate in the alloy, so the Mg/Si atomic ratio = 2:1 is used as the principle of Mg and Si ratio design, which is a misunderstanding .

Because the β” phase has the best high-strength and high-strengthening effect in Al-Mg-Si alloys, and their Mg/Si atomic ratio is 5/6. In summary, a reasonable composition design should refer to the atomic ratio of the β” phase, that is Mg/Si atomic ratio = 5:6, converted to a mass ratio of 0.714:1 (the relative atomic mass of Mg is 24, and the relative atomic mass of Si is 28).

In the Al-Mg-Si alloy, if the alloy ratio is lower than this ratio, there will be excess Si in the aluminum matrix, and the excess Si is easy to segregate and precipitate on the grain boundary, reducing the grain boundary bonding force, and it is also easy to cause Stress concentration becomes the source of crack initiation in the deformation process, which will damage the plasticity and deformation energy absorption effect of the alloy, and a certain excess of Mg can help improve the thermal stability of the alloy, but if there is too much excess Mg, this part of the excess Mg does not have effective Si to combine with it to form a strengthening precipitate, and the strengthening effect will be weakened. At the same time, too much Mg will also reduce the extrudability of the alloy (as the alloy Mg/Si _free value increases, the alloy strain Hardening index increases, alloy processing formability decreases) and brings high quenching sensitivity, which is not conducive to mass production. The present invention comprehensively considers the consumption of elements such as Mn, Fe, Cr to Si element, can be used to form free silicon Si _free =Si-0.3*(Mn+Fe+Cr) of β " strengthened phase, the present invention will Mg/Si _free quality The ratio is controlled at 0.72-1.40 to avoid excess Si existing in the aluminum matrix, and at the same time ensure a certain amount of Mg to avoid excessive Mg from affecting the properties of the alloy.

Furthermore, the contents of Mg and Si jointly determine the strength level of the Al-Mg-Si alloy. It has been found that increasing the yield strength by adding 1% Si alone is about twice that of adding 1% Mg, so the strength level of the alloy is directly determined by (Mg+2Si _free ). In the Al-Mg-Si alloy of the present invention, the Mg/Si _free mass ratio is greater than 0.72, that is, Mg is excessive. In the alloy with excess Mg, when the Si content increases, more strengthening precipitates are formed by combining with the excess Mg, which significantly improves the yield strength of the alloy; when the Mg continues to increase, because there is no effective Si to combine with it to form strengthening phase, can only increase the nucleation rate of strengthening precipitates to a certain extent, thereby increasing the number of precipitates in a limited way, which has a limited contribution to the strength. But when Mg+2Si _free <1.40%, the number of precipitates is insufficient, the strengthening effect decreases, and the alloy strength cannot meet the development target (yield strength ≥ 240MPa); the higher the value of Mg+2Si _free , the worse the deformation performance of the alloy, when the Mg When the total content of +2Si _free is more than 2.40%, the alloy is prone to cracking in deformation energy absorption tests such as crushing and drop hammer, and the impact energy absorption performance is significantly reduced. Therefore, the reasonable total content range of Mg+2Si _free in the present invention is 1.40-2.40%. In summary, in the Al-Mg-Si alloy of the present invention, Si _free = Si-0.3×(Mn+Fe+Cr), the mass ratio of Mg/Si _free is controlled at 0.72-1.40, and the mass percentage of Mg+2Si _free is also To meet 1.40% ~ 2.40%.

In the Al-Mg-Si alloy, the mass percentage of Mn+2Cr is 0.40%-1.0%. More preferably, the mass percentage of Cr is 0.10-0.20%. Production and processing is a process of deformation of external work materials. With the continuous input of energy and the increase of deformation, the material will accumulate a large amount of energy. When the energy reaches a certain critical value (≥recrystallization activation energy), the material will recrystallize , Recrystallization often first occurs on the surface in direct contact with the tool and mold and forms a surface coarse-grained layer. The formation of the coarse-grained layer will seriously affect the uniformity and consistency of material properties. Mn/Cr can form submicron-scale dispersed precipitates with Al, such as Al ₆ Mn(Fe), Al(CrFe)Si, etc. On the one hand, these precipitates can effectively refine the grain structure and inhibit recrystallization during processing. Stabilize the deformed structure in the product and reduce the thickness of the coarse grain layer on the surface of the product; on the other hand, it can also improve the plasticity of the alloy. However, too high Mn/Cr content will not only consume more main alloying element Si, reduce the strength of the alloy, but also significantly increase the quenching sensitivity of the alloy. In terms of overall performance, the Cr element is stronger than the Mn element, so the mass percentage of Mn+2Cr in the Al-Mg-Si alloy of the present invention needs to meet 0.40%-1.0%, and the mass percentage of Cr is preferably 0.10-0.20%.

The Al-Mg-Si alloy also includes V, and V≤0.20% by mass percentage. More preferably, the mass percentage of V is 0.05-0.15%. V can form a peritectic dispersed phase with Al and other related elements during the melting and casting process, and evenly distribute in the crystal, effectively improving the channel of dislocation movement during deformation and improving the impact toughness of the alloy; but when the amount of V added is too much, The AlV phase is easy to segregate, which affects the uniformity of the alloy and deteriorates the toughness of the alloy. In addition, the inclusion of V phase can effectively improve the high temperature performance of the alloy and improve the thermal stability of the alloy. Therefore, the V of the Al-Mg-Si alloy of the present invention is ≤0.20%, preferably 0.05-0.15%.

The Al-Mg-Si alloy also includes Cu, and Cu≤0.25% by mass percentage.

The Al-Mg-Si alloy also includes Ti, and Ti≤0.10% by mass percentage.

The other inevitable impurity elements in the Al-Mg-Si alloy are individually ≤0.05%, and the total ≤0.15%.

In the above-mentioned high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy, the Al-Mg-Si alloy has a multilayer structure of "coarse-grained layer/fibrous structure/coarse-grained layer", and the single-sided coarse-grained layer Thickness≤0.3×wall thickness. The core fiber structure of the middle layer of the multi-layer structure can effectively ensure the longitudinal bending performance and impact resistance of the product, while the coarse-grained layers on the inner and outer surfaces can improve the anisotropy and corrosion performance of the product to a certain extent.

Preferably, the wall thickness of the aluminum alloy product obtained in the present invention is ≤10mm, and when the wall thickness is too thick, the performance may be low, and it is difficult to meet the requirement of yield strength of 240MPa.

The processing method of the high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy of the present invention includes aging treatment, and the aging treatment is T6 treatment or T7 treatment.

The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy of the present invention can adopt conventional aluminum alloy processing methods, including smelting, casting, heat treatment, extrusion molding and the like.

During the smelting process, raw materials are added in the form of aluminum ingots, magnesium ingots, and intermediate alloy ingots such as Al-Si, Al-Mn, Al-Cr, and Al-V.

The aluminum rod is preheated before extrusion molding, and the preheating temperature is 480-530°C.

The yield strength of the high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy of the present invention is ≥240MPa, and has good thermal stability. After the final state alloy is kept at 150°C/1000h, the yield strength is ≥230MPa, and at the same time, it has excellent bending toughness. , alloy transverse (perpendicular to extrusion direction) bending angle ≥ 75 °, alloy longitudinal (parallel to extrusion direction) bending angle ≥ 65 °.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention optimizes the content of alloy elements such as Mg/Si, Mn, Cr and even V in the Al-Mg-Si alloy, on the premise of ensuring the alloy strength, corrosion resistance and thermal stability It can effectively improve the bending toughness and crushing performance of Al-Mg-Si alloy, significantly improve the impact energy absorption performance of the alloy, and the alloy profile will not produce a penetration greater than 30mm under the impact of a 250Kg weight at a speed of 40Km/h crack.

(2) The Mg/Si ratio and the total amount of the main alloying element of the present invention are reasonably designed, which can improve the strain hardening index of the alloy, improve the deformation behavior of the alloy, reduce local stress concentration, and improve the uniformity of deformation while ensuring the strength of the alloy performance and energy-absorbing capacity.

(3) The Mn, Cr atoms of the present invention have strong attraction with Al and Si atoms, and are easy to form dispersed second-phase particles. These particles can effectively pin the migration of grain boundaries and inhibit the recrystallization of the alloy during processing. V is easy to interact with Al and Si atoms to form intermetallic compounds, which are evenly distributed in the grain, effectively improving the channel of dislocation movement and the uniformity of deformation during deformation, and improving the plasticity and impact toughness of the alloy.

Description of drawings

Fig. 1 is the comparison effect diagram of crushing and cracking of the product made of the impact-resistant and energy-absorbing Al-Mg-Si alloy of Example 1 and the alloy product of Comparative Example 1;

Fig. 2 is the high-speed impact test and the result of embodiment 3 anti-impact energy-absorbing Al-Mg-Si alloy product;

Fig. 3 is a schematic diagram of the flexural toughness test of the impact-resistant and energy-absorbing Al-Mg-Si alloy product.

detailed description

The technical solutions of the present invention will be further described and illustrated through specific examples below. Unless otherwise specified, the raw materials used in the examples of the present invention are commonly used raw materials in the art, and the methods used in the examples are conventional methods in the art. It should be understood that the specific embodiments described here are only used to help the understanding of the present invention, and are not intended to specifically limit the present invention.

The Al-Mg-Si alloy in the present invention is applicable to various other conventional aluminum alloy processing methods in terms of processing methods, such as smelting, casting, heat treatment, extrusion molding and the like.

During the smelting process, raw materials are added in the form of aluminum ingots, magnesium ingots, and intermediate alloy ingots such as Al-Si, Al-Mn, Al-Cr, and Al-V. Refining agent is added during the smelting process.

For extrusion molding, the aluminum rod is firstly preheated, and the preheating temperature is 480-530°C.

Examples 1-11

Melt the components of the Al-Mg-Si alloy described in Examples 1-11 in Table 2, semi-continuously cast it into an ingot, cut the head and tail of the ingot and homogenize it, and then use a mold with a corresponding section to extrude and cool. Finally, the extruded profile is subjected to aging treatment by T7 treatment.

Example 12

The difference between Example 12 and Example 3 lies in the difference in the aging process, and the aging in Example 12 adopts T6 treatment.

Comparative example 1-4

The only difference between Comparative Examples 1-4 and Example 1 is that the composition of the aluminum alloy is different, see Table 2 for details, and the preparation method is the same as that of Example 1.

Comparative example 5-6

The difference between Comparative Examples 5-6 and Example 3 lies in the difference in the aging process, which is treated by natural aging T4 and underaging T6X respectively. The alloy samples treated by underaging T6X have only part of the precipitation of solid solution alloy atoms, and the performance is low, and the impact performance is poor.

Table 2. Embodiment 1-12 and comparative example 1-4 alloy component mass percent (wt%)

alloy	Mg	Si	mn	Cr	V	Cu	Fe	Ti	Mg/Si free	Mg+2Si free
Example 1	0.58	0.92	0.37	0.12	/	0.08	0.17	0.03	0.83	1.98
Example 2	0.75	0.80	0.35	0.14	/	0.12	0.18	0.04	1.30	1.90
Example 3	0.56	0.67	0.37	0.17	0.08	0.13	0.14	0.02	1.26	1.45
Example 4	0.83	0.87	0.27	0.15	/	0.15	0.18	0.02	1.24	2.17
Example 5	0.82	0.89	0.56	0.16	/	0.13	0.14	0.02	1.36	2.03
Example 6	0.81	0.88	0.29	0.08	/	0.11	0.17	0.03	1.16	2.21
Example 7	0.57	0.68	0.37	0.15	/	0.12	0.15	0.03	1.25	1.48
Example 8	0.55	0.67	0.36	0.16	0.10	/	0.14	0.02	1.22	1.45
Example 9	0.80	0.89	0.53	0.26	/	0.13	0.14	0.02	1.38	1.96
Example 10	0.57	0.68	0.08	0.04	/	0.12	0.15	0.03	0.97	1.75
Example 11	0.57	0.69	0.36	0.17	0.07	0.28	0.15	0.03	1.23	1.50
Example 12	0.56	0.67	0.37	0.17	0.08	0.13	0.14	0.02	1.26	1.45
Comparative example 1	0.85	0.50	0.07	/	0.10	0.09	0.12	0.04	1.95	1.72
Comparative example 2	0.48	0.78	0.06	/	0.13	0.12	0.16	0.07	0.68	1.89
Comparative example 3	0.51	0.48	0.03	/	/	0.01	0.17	0.03	1.23	1.34
Comparative example 4	0.85	1.04	0.46	0.12	/	0.05	0.14	0.02	1.06	2.45

The product made of the Al-Mg-Si alloy in Example 1 is compared with the alloy product of Comparative Example 1 for crushing and cracking. The alloy product of Comparative Example 1 was severely cracked after being crushed, and part of the block was crushed and separated from the matrix. In summary, the crushing performance of the alloy of Example 1 is much better than that of the alloy of Comparative Example 1.

The product is made of Al-Mg-Si alloy in Example 3, and the high-speed impact test is carried out. The test results are shown in Figure 2. After the alloy product of Example 3 is subjected to high-speed collision (40Km/h), no penetration cracks of ≥ 20 mm have been produced. , indicating that the alloy of Example 3 has excellent impact resistance.

The aluminum alloy products in Examples 1-12 and Comparative Examples 1-6 were tested for mechanical properties, bending toughness, and crushing performance. Among them, the bending toughness test standard is VDA238-100, the test sample size is 60mm×60mm, and the test direction is parallel (longitudinal)/perpendicular (transverse) to the extrusion direction. When the maximum load of the indenter drops 60N, the test ends. The specific test schematic diagram See Figure 3. The size of the alloy bending angle α is closely related to the thickness t of the test sample. When comparing, it needs to be converted into the angle α' of the standard sample thickness t ₀ (2mm) according to the following formula:

The evaluation of the crushing properties of aluminum alloys is done by quasi-static compression tests (along the extrusion direction of the profile). The original length of the crushed sample is 300mm, and it is compressed to 100mm at a speed of 100mm/min. The crushing performance of the alloy is evaluated by measuring the length of the crack on the sample after the test. There is no penetrating crack for grade A, the existence of ≤10mm penetrating crack is grade B, and the existence of >10mm penetrating crack is grade C. Products with crush ratings of A and B indicate excellent crush performance.

Table 3. Examples 1-12 and comparative examples 1-6 alloy mechanical properties, flexural toughness, crushing properties

Compared with Comparative Examples 1-2 and 4, the alloy in the present invention has greatly improved longitudinal bending toughness and crushing performance, wherein the longitudinal bending angle has been increased from 50° to more than 65°, and the crushing performance level has been improved by C grade to grade B and above. Simultaneously, compared with Comparative Examples 3 and 5-6, the impact-resistant and energy-absorbing Al-Mg-Si alloy of the present invention also has obvious improvement in conventional mechanical properties (tensile strength, yield strength, elongation), and the average tensile strength is ≥ 265MPa , Average yield strength ≥ 240MPa, average elongation after fracture ≥ 11%. The alloy of Comparative Example 5 has excellent elongation, bending toughness and crushing performance, but the overall strength is too low, and the yield strength is only 115MPa, which is less than 50% of the alloy of Example 1, indicating that the T4 process cannot achieve the expected strength effect. The elongation and bending performance of the alloy in Comparative Example 6 are acceptable, but the crushing performance is extremely poor, and the alloy is difficult to form when crushed.

In summary, the aluminum alloy provided by the present invention not only has excellent conventional mechanical properties, yield strength ≥ 240MPa, elongation after fracture ≥ 10%; at the same time, it has good bending toughness, and the bending angle of the alloy in the transverse direction (perpendicular to the extrusion direction) ≥75°, alloy longitudinal (parallel to the extrusion direction) bending angle ≥65°; and outstanding crushing and impact resistance and energy absorption performance, the overall crushing performance of the alloy is ≥B level.

The inexhaustible point values in the parameter range of the technical solutions claimed in the present invention in the above embodiments and the new technical solutions formed by the equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also covered by the requirements of the present invention. Within the scope of protection, and if there is no special description among all the parameters involved in the scheme of the present invention, there is no irreplaceable unique combination among them.

The specific embodiments described herein are only to illustrate the spirit of the present invention, and are not intended to limit the protection scope of the present invention. Those skilled in the technical field to which the present invention belongs can obtain technical solutions similar or similar to the present invention by means of equivalent replacement or equivalent transformation, all of which fall within the protection scope of the present invention.

Claims (10)

1. A high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy, characterized in that the Al-Mg-Si alloy includes Mg 0.40-1.00%, Si 0.50-0.90%, Mn≤0.60%, Cr≤0.30%, Fe≤0.25%, Al 96.8～99.1%, among them, Si _free =Si-0.3×(Mn+Fe+Cr), Mg/Si _free mass ratio is 0.72-1.40, and Mg+2Si _free mass The percentage is 1.40%-2.40%.
2. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1, characterized in that, in the Al-Mg-Si alloy, the mass percentage of Mn+2Cr is 0.40%-1.0%.
3. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1 or 2, characterized in that, in the Al-Mg-Si alloy, the mass percentage of Cr is 0.10-0.20%.
4. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1 or 2, characterized in that the Al-Mg-Si alloy further includes V, and V≤0.20% in mass percentage.
5. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 4, characterized in that the mass percentage of V is 0.05-0.15%.
6. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1 or 5, characterized in that the Al-Mg-Si alloy further includes Cu, and Cu≤0.25% in mass percentage.
7. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 6 is characterized in that the Al-Mg-Si alloy further includes Ti, and Ti≤0.10% by mass percentage.
8. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1 or 2 or 5 or 7, characterized in that, other unavoidable impurity elements in the Al-Mg-Si alloy are individually ≤0.05% , total ≤0.15%.
9. The high-strength, high-toughness, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1 is characterized in that the Al-Mg-Si alloy has a multilayer structure of "coarse grain layer/fibrous structure/coarse grain layer" , and the thickness of the single-sided coarse-grained layer is ≤0.3×wall thickness.
10. The processing method of the strong, tough, impact-resistant and energy-absorbing Al-Mg-Si alloy according to claim 1, wherein the processing method of the Al-Mg-Si alloy includes aging treatment, and the aging treatment is T6 treatment or T7 processing.

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