Patent Application
20240287653
The present disclosure relates to the technical field of aluminum alloy materials, and in particular to a high-strength and high-toughness impact-resistant energy-absorbing Al—Mg—Si alloy.
With the rapid development of human economy and society, energy problems and environmental problems emerge one after another, the sustainable development of green low-carbon environmental protection has become the target of development of the society at present. Motor vehicle fuel consumption accounts for a considerable proportion of the total crude oil consumption. The rapid development of the automotive industry not only poses a great challenge to China'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 automobile industry, and lightweight is an important means to achieve energy saving and emission reduction.
Al—Mg—Si alloy is a heat-treatable strengthened aluminum alloy, which has the advantages of high specific strength, good formability, excellent corrosion resistance and high weldability, and is an important material for realizing the light weight of automobiles. At present, Al—Mg—Si alloy is widely used in (vehicle body) structural parts, such as a vehicle body cover part, an engine piston, an anti-collision beam, a bumper, and the like. However, the service conditions of different components are different. In addition to improving the conventional mechanical properties of the materials, it is also necessary to improve the relevant performance under different service conditions of the components, such as a battery tray of a new energy vehicle and a key safety structural component such as an automobile anti-collision beam, which may be broken by external violent impact under service conditions, and even cause serious personnel and property losses. Therefore, the impact-resistant energy-absorbing properties of aluminum alloys used under such conditions are particularly important.
At present, the focus in industrial production is still strength of aluminum alloys, and the impact-resistant energy-absorbing properties of aluminum alloys are rarely studied. Although a Chinese patent No. CN 109504870 B provides a lightweight aluminum alloy for automobile anti-collision beam, a direct melt reaction technology together with an ultrasonic magnetic coupling field technology is used to regulate the synthesis reaction process and solidification process to obtain the composite material with uniform distribution of in-situ nanoparticles. Then the composite material is prepared by hot extrusion forming and heat treatment, the preparation process is complex, difficult, and costly, and it is not suitable for wide application. It is found from study that the impact resistance of the material is not only related to the strength of the material, but also closely related to the plasticity and toughness of the material. In addition, the microstructure of the material is also important to the impact-resistant energy-absorbing property.
In view of the above-mentioned problems of the prior art, the present disclosure provides an Al—Mg—Si alloy having high bending toughness, impact toughness, crushing performance and energy absorption capacity while ensuring the strength, corrosion resistance and thermal stability of the alloy.
The above object of the present disclosure is achieved by the following technical solution: a high-strength and high-toughness impact-resistant energy-absorbing Al—Mg—Si alloy including Mg 0.40-1.00%, Si 0.50-0.90%, Mn≤0.60%, Cr≤0.30%, Fe≤0.25%, Al 96.8-99.1% in percentage by mass, wherein Sifree=Si-0.3×(Mn+Fe+Cr), a mass ratio of Mg/Sifree is 0.72-1.40, and a percentage by mass of Mg+2Sifree is 1.40%-2.40%.
Mg and Si are the main additive elements of 6xxx alloy, and the second phase particles of β″, β′ and β are precipitated by interaction in the aging process to strengthen the substrate. According to the latest study of Al—Mg—Si alloy in the aging process, the evolution of precipitated phases is as follows: supersaturated solid solution→GP region→β″→β′(B′, U1, U2)→β. Among them, the β″ phase has the best strengthening effect, which is the most significant strengthened precipitated phase in peak aged alloy. The β′ phase is the main precipitated phase in overaged alloy, and has an inferior strengthening effect compared with β″ phase; and the β phase is an equilibrium phase which is non-coherent with aluminum substrate and has a limited strengthening effect.
Information about the precipitated phases in 6xxx alloy
In the composition design of 6xxx alloy, β(Mg2Si) phase is often considered to be the main strengthened precipitated phase in the alloy, so it is a misunderstanding to use Mg/Si atomic ratio=2:1 as the principle of Mg, Si ratio design.
Because the best strengthening effect in Al—Mg—Si alloys is β″ phase, their Mg/Si atomic ratio is 5/6. From the above, the reasonable composition design should refer to the atomic ratio of β″ phase, i.e. Mg/Si atomic ratio=5:6, which is 0.714:1 if converted into a mass ratio (relative atomic mass of Mg is 24, and 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 substrate. The excess Si is easy to segregate on the grain boundary and reduce the grain boundary bonding force. At the same time, it will also easily cause stress concentration as the source of crack initiation in the deformation process, which will damage the plastic and deformation energy absorption effect of the alloy, and a certain excess of Mg will help to improve the thermal stability of the alloy. However, if there is too much Mg excess, this part of the excess Mg will not effectively combine with Si to form strengthened precipitated phases, and the strengthening effect will be weakened. At the same time, too much Mg can also reduce the extrudability of the alloy (with the increase of Mg/Sifee value, the strain-hardening index of the alloy increases, and the workability of the alloy decreases) and bring high quenching sensitivity, which is not conducive to mass production. In the present disclosure, by comprehensively considering the consumption of Si element by Mn, Fe, Cr and other elements, the free silicon Sifree=Si—0.3*(Mn+Fe+Cr) which can be used for forming a β″ strengthened phase can be used for forming a β″ strengthened phase. In the present disclosure, the mass ratio of Mg/Sifree is controlled to be 0.72-1.40, avoiding the presence of excess Si in the aluminum substrate while ensuring a certain amount of Mg, and avoiding the effect of excess Mg on the properties of the alloy.
Furthermore, the content of Mg and Si together determine the strength level of the Al—Mg—Si alloy. It has been found that the increase in yield strength with 1% Si alone is about twice that with 1% Mg, so the strength level of the alloy is directly determined by (Mg+2Sifree). The Mg/Sifree mass ratio in the Al—Mg—Si alloys of the present disclosure is all above 0.72, i.e. Mg is excess. In the Mg-excess alloy, when the Si content increases, more strengthened precipitated phases are formed by combining with the excess Mg, which significantly improves the yield strength of the alloy. When the addition of Mg is continued, since there is no effective Si to combine with it to form strengthened phase, the nucleation rate of the strengthened precipitated phase can be increased only to some extent, thereby increasing the number of precipitated phases to a limited extent, which has a limited contribution to strength. However, when the content of Mg+2Sifree is less than 1.40%, the number of precipitated phases is insufficient and the strengthening effect decreases, and the strength of the alloy cannot meet the development target (yield strength≥240 MPa). The higher the value of Mg+2Sifree is, the worse the deformation performance of the alloy is. When the total content of Mg+2Sifree is more than 2.40%, the alloy is easy to crack in the crushing and drop hammer deformation energy absorption test, and the impact-resistant energy-absorbing performance is significantly reduced. Therefore, a reasonable total content of Mg+2Sifree in the present disclosure is in the range of 1.40%-2.40%. In summary, in the Al—Mg—Si alloy of the present disclosure, Sifree=Si—0.3×(Mn+Fe+Cr), the mass ratio of Mg/Sifree is controlled to be 0.72-1.40, and the percentage by mass of Mg+2Sifree still satisfies 1.40%-2.40%.
In the Al—Mg—Si alloy, the percentage by mass of Mn+2Cr is 0.40%-1.0%. Further preferably, the percentage by mass of Cr is 0.10%-0.20%. Production and processing are a deformation process of external working material. With the continuous input of energy and the increase of deformation, a large amount of energy will be accumulated in the material. When the energy reaches a certain critical value (≥recrystallization activation energy), the material will be recrystallized. Recrystallization will first occur on the surface in direct contact with the work die and form a surface coarse-grained layer, and the formation of coarse-grained layer will seriously affect the uniformity and consistency of material properties. Mn/Cr and Al can form submicron dispersed precipitated phases with Al, such as Al6Mn(Fe), Al(CrFe)Si and the like, which can effectively refine the grain structure to inhibit recrystallization during processing, stabilize the deformation structure in the product and reduce the thickness of coarse grain layer on the surface of the product, on the other hand, the plasticity of the alloy can also be improved. 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. The Cr element is stronger than the Mn element in terms of overall performance, so the percentage by mass of Mn+2Cr in the Al—Mg—Si alloy of the present disclosure needs to satisfy 0.40%-1.0%, and the percentage by mass of Cr is preferably 0.10%-0.20%.
The Al—Mg—Si alloy further includes V, V≤0.20% in percentage by mass. Further preferably, the percentage by mass of V is 0.05%-0.15%. V can form peritectic dispersion phase with Al and other related elements in the melting and casting process, and distribute uniformly in the grains, which can effectively improve the dislocation movement channel in the deformation process and improve the impact toughness of the alloy; however, when too much V is added, the AlV phase tends to aggregate, which affects the uniformity of the alloy and deteriorates the toughness of the alloy. In addition, the V-containing phase can effectively improve the high temperature properties and thermal stability of the alloy. Thus for the Al—Mg—Si alloy of the present disclosure V≤0.20%, preferably 0.05%-0.15%.
The Al—Mg—Si alloy further includes Cu, Cu≤0.25% in percentage by mass.
The Al—Mg—Si alloy further includes Ti, Ti≤0.10% in percentage by mass.
The other unavoidable impurity elements in the Al—Mg—Si alloy are each ≤0.05%, and in total≤0.15%.
In the above-mentioned high-strength and high-toughness impact-resistant energy-absorbing Al—Mg—Si alloy, the Al—Mg—Si alloy has a multilayer structure of “macrocrystalline layer/fibrous tissue/macrocrystalline layer”, and a thickness of a single-sided macrocrystalline layer≤0.3× wall thickness. The core fibrous tissue of the middle layer of the multilayer 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 some extent.
Preferably, the resulting aluminum alloy article of the present disclosure has a wall thickness of ≤10 mm, and the properties may be low if the wall thickness is too thick to meet the yield strength requirement of 240 MPa.
The method for processing the high-strength and high-toughness impact-resistant energy-absorbing Al—Mg—Si alloy of the present disclosure includes an ageing treatment, the ageing treatment being a T6 treatment or a T7 treatment.
The high-strength and high-toughness impact-resistant energy-absorbing Al—Mg—Si alloy of the present disclosure may be processed using conventional aluminum alloys, including melting, casting, heat treatment, extrusion, and the like.
In the smelting process, the raw materials are added as aluminum ingots, magnesium ingots, and intermediate alloy ingots such as Al—Si, Al—Mn, Al—Cr and Al—V.
Prior to extrusion, the aluminum rod is preheated at 480-530° C.
The high-strength and high-toughness impact-resistant energy-absorbing Al—Mg—Si alloy of the present disclosure has a yield strength of ≥240 MPa and a good thermal stability. After the final alloy is annealed at 150° C./1000 h, the yield strength of the final alloy is ≥230 MPa and the bending toughness is excellent. The bending angle of the alloy is ≥75° in the transverse direction (perpendicular to the extrusion direction) and ≥650 in the longitudinal direction (parallel to the extrusion direction).
The present disclosure has the following advantageous effects compared to the prior art:
The technical solution of the present disclosure is further described below by means of specific examples. Unless otherwise specified, the raw materials used in the examples of the present disclosure are all common raw materials in the art, and the methods used in the examples are all conventional methods in the art. It should be understood that the particular Examples described herein are merely illustrative of the present disclosure and are not intended to limit the present disclosure in any way.
The Al—Mg—Si alloys of the present disclosure are amenable to various other conventional aluminum alloy processing methods such as melting, casting, heat treatment, extrusion, etc.
In the smelting process, the raw materials are added as aluminum ingots, magnesium ingots, and intermediate alloy ingots such as Al—Si, Al—Mn, Al—Cr and Al—V. The refining agent is added during melting.
It is extruded, the aluminum rod is first preheated at 480-530° C.
The composition of the Al—Mg—Si alloy as described in Examples 1 to 11 of table 2 was melted, semi-continuously cast into an ingot, the ingot was homogenized after cutting and tailing, extruded and cooled using a die with a corresponding section, and finally the extruded profile was subjected to ageing treatment using a T7 treatment.
Example 12 differs from Example 3 only in the ageing process, the ageing in Example 12 being a T6 treatment.
Comparative examples 1 to 4 differ from Example 1 only in the composition of the aluminum alloy, see Table 2 for details, and the preparation method is the same as that of Example 1.
Comparative examples 5 and 6 differ from Example 3 only in the ageing process, using natural ageing T4 and under-ageing T6X treatments, respectively. The alloy samples with under-aging T6X showed only partial precipitation of solid solution alloy atoms, and had lower impact properties.
The product made of the Al—Mg—Si alloy of Example 1 was compared with the alloy product of Comparative example 1 in terms of crushing and cracking. The comparative effect is shown in
A high-speed impact test was performed on the product made of the Al—Mg—Si alloy of Example 3, and the test results are shown in
The aluminum alloy articles of Examples 1-12 and Comparative examples 1-6 were tested for mechanical properties, flexural toughness, and crushing performance. The bending toughness test standard is VDA238-100, the test sample size is 60 mm×60 mm, the test direction is parallel (longitudinal direction)/perpendicular (transverse direction) to the extrusion direction, when the maximum load of indenter decreases by 60 N, the test ends, and the specific test diagram is shown in
the crushing performance evaluation of aluminum alloys was done by quasi-static compression testing (in the direction of profile extrusion). The crushing sample had an original length of 300 mm and was compressed to 100 mm at a speed of 100 mm/min. The crushing performance of the alloy was evaluated by measuring the crack length on the sample after the test, with no through-crack being class A, the through-crack≤10 mm being class B and the through-crack>100 mm being class C. The crushing ratings A and B indicate excellent crushing performance.
The alloys of the present disclosure, as compared with Comparative examples 1-2 and 4, has a great improvement in longitudinal bending toughness and crushing performance, in which the longitudinal bending angle is increased from 50° to more than 65°, and the crushing performance grade is increased from grade C to grade B and more. Meanwhile, the impact-resistant energy-absorbing Al—Mg—Si alloy of the present disclosure was also significantly improved in conventional mechanical properties (tensile strength, yield strength, elongation) compared to Comparative examples 3, 5 and 6, with an average tensile strength of ≥265 MPa, an average yield strength of ≥240 MPa, and an average elongation after fracture of ≥11%. The alloy of Comparative example 5 has excellent elongation, bending toughness and crushing properties, but the overall strength is too low, with a yield strength of only 115 MPa, less than 50% of the alloy of Example 1, indicating that the T4 process treatment does not achieve the desired strength effect. The elongation and bending properties of the alloy of Comparative example 6 were good, but the crushing properties were very poor, and the alloy was difficult to form when crushed.
In summary, the aluminum alloy provided by the present disclosure not only has excellent conventional mechanical properties, with a yield strength of ≥240 MPa and an elongation after fracture of ≥10%; at the same time, the alloy has good bending toughness, the bending angle of the alloy in transverse direction (perpendicular to extrusion direction) is ≥75°, and the bending angle of the alloy in longitudinal direction (parallel to extrusion direction) is ≥65°; and the outstanding crushing and impact-resistant energy-absorbing properties, and the overall crushing properties of the alloy are all ≥B grade.
The above examples are not exhaustive of the point values within the parameters of the claimed technical solutions of the present disclosure, as well as the new technical solutions formed by the equivalent replacement of single or multiple technical features in the technical solutions of the examples, are also within the scope of the claimed disclosure, and all the parameters involved in the technical solutions of the present disclosure, if not specifically stated, do not have an irreplaceable unique combination with each other.
The specific examples described herein are merely illustrative of the spirit of the present disclosure and are not intended to limit the scope of the present disclosure. A person skilled in the art to which the present disclosure pertains may obtain similar or analogous technical solutions to the present disclosure by using equivalent substitution or equivalent transformation, all falling within the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110757516.0 | Jul 2021 | CN | national |
This Application is a national stage application of PCT/CN201/113975. This application claims priorities from PCT Application No. PCT/CN201/113975, filed Aug. 23, 2021, and from the Chinese patent application 202110757516.0 filed Jul. 5, 2021, the content of which are incorporated herein in the entirety by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/113975 | 8/23/2021 | WO |
