Laser melt-brazing method for steel-aluminum dissimilar metal

Abstract

The invention discloses a laser melt-brazing method for steel-aluminum dissimilar metal. The laser melt-brazing method comprises the steps that a steel part and an aluminum part are in lap joint to form a connector; an aluminum-based welding wire is used, laser melt-brazing welding is adopted for welding the joint, an adopted laser spot is circular, and the first light intensity I1 in a first circular range with the center of the spot as the circle center and the radius R1 is equal to (45%-65%) * I0; the second light intensity I2 in a second circle range with the light spot center as the circle center and the radius R2 is larger than or equal to 90% * I0; r1 ranges from 0.5 mm to 0.8 mm, R2 ranges from 1.5 mm to 2.0 mm, and I0 represents the total light intensity of the laser beam. According to the method, the spreading width of the weld metal on the surface of the steel plate and the thickness of the intermetallic compound layer on the surface of the steel plate can be synchronously controlled in the laser melt-brazing process of the steel-aluminum dissimilar metal, so that the steel-aluminum dissimilar metal component with excellent joint performance is prepared.

Description

Technical Field

[0001] The invention relates to a welding method, in particular to a welding method for dissimilar metals of steel and aluminum. Background Art

[0002] Aluminum alloy has low density, high specific strength and specific stiffness. On the other hand, although aluminum alloy has more potential than steel materials in terms of lightweight, its collision performance in some key safety parts cannot match that of advanced high-strength steel. Therefore, taking lightweight and safety into consideration, steel-aluminum hybrid construction is being widely adopted.

[0003] An unavoidable problem in steel-aluminum hybrid is the joining of dissimilar metals. Steel and aluminum have completely different physical properties. The huge difference in thermal properties, especially the difference in thermal expansion coefficient, makes it difficult to join steel and aluminum together using traditional fusion welding technology.

[0004] The laser brazing method uses laser as a heat source and has the advantages of high energy density, precise control of melting position, high degree of automation and high production efficiency. During the steel-aluminum laser brazing process, the steel plate does not melt, the aluminum alloy and filler metal melt to form liquid weld metal, and spread a certain width on the surface of the steel plate. During the subsequent cooling and solidification process, a Fe-Al intermetallic compound layer with a certain thickness is formed between the weld metal and the surface of the steel plate, thereby realizing the metallurgical connection of steel and aluminum dissimilar metals.

[0005] Generally, a good steel-aluminum fusion brazing joint meets two basic conditions: (1) the thickness of the intermetallic compound layer should be controlled within 5-20 μm, and (2) the spreading width of the weld metal should not be less than 5 mm. To achieve these two conditions, the welding heat input must be carefully controlled. On the one hand, the formation of the intermetallic compound layer is controlled by the diffusion of elements. Therefore, to control the thickness of the intermetallic compound layer within 5-20 μm, it is necessary to ensure that the peak temperature of the liquid metal is not too high and the liquid state time is not too long, that is, the welding heat input should be controlled at a low level; on the other hand, the spreading width of the weld metal on the steel plate surface is directly determined by the surface temperature of the steel plate. The higher the temperature, the more conducive to the spreading of the weld metal. Therefore, to achieve a spreading width of more than 5 mm, the steel plate surface must reach a sufficiently high temperature, which means that the heat input needs to be controlled at a higher level.

[0006] It can be seen that the requirements for welding heat input under conditions (1) and (2) are opposite, so the conventional laser melting brazing process cannot achieve the synchronous control of the spreading width and the thickness of the intermetallic compound layer, and it is difficult to obtain a steel-aluminum joint with excellent performance.

[0007] A Chinese patent document with publication number CN103447647A and publication date December 18, 2013, entitled “A laser melting-brazing process for connecting galvanized steel to aluminum”, discloses a method for controlling the position of a laser spot, where 1 / 3 of the laser spot is irradiated on an aluminum plate and 2 / 3 of the spot is irradiated on a steel plate. This method focuses on concentrating heat on the surface of the steel plate, which is beneficial to the spreading of the weld metal, but cannot achieve control of the thickness of the intermetallic compound layer.

[0008] The Chinese patent document with publication number CN110899882A and publication date March 24, 2020, entitled "A process for laser brazing of dissimilar metals of aluminum and steel with filler wire", discloses a laser brazing method using specific brazing filler metals and flux. This method improves the performance of the joint by changing the composition of the intermetallic compound layer by adding alloying elements, but still fails to solve the problem of controlling the thickness of the intermetallic compound layer. Summary of the invention

[0009] One of the purposes of the present invention is to provide a method for laser brazing of steel and aluminum dissimilar metals, which can achieve synchronous control of the spreading width of the weld metal on the steel plate surface and the thickness of the intermetallic compound layer on the steel plate surface during the laser brazing process of steel and aluminum dissimilar metals, thereby preparing steel and aluminum dissimilar metal components with excellent joint performance.

[0010] In order to achieve the above object, the present invention provides a laser melting brazing method for steel and aluminum dissimilar metals, which comprises the following steps:

[0011] Overlap steel and aluminum parts to form joints;

[0012] Aluminum-based welding wire is used to weld the joints by laser brazing: the laser spot used is circular, and the first light intensity I1 in the first circular range with a radius of R1 and the center of the spot is equal to (45% to 65%)·I0; the second light intensity I2 in the second circular range with a radius of R2 and the center of the spot is equal to or greater than 90%·I0; R1 is 0.5 to 0.8 mm, R2 is 1.5 to 2.0 mm, and I0 represents the total light intensity of the laser beam.

[0013] Furthermore, during the welding process of the laser brazing method of the present invention, the laser is controlled to heat the upper surface of the steel part to 907-1350°C and the lower surface of the steel plate to 25-420°C.

[0014] In this preferred embodiment, the laser is controlled to heat the upper surface of the steel part to 907-1350°C and the lower surface of the steel plate to 25-420°C, which is more conducive to meeting the two control targets of the thickness of the intermetallic compound layer being between 5 and 20 μm and the spreading width of the weld metal being not less than 5 mm.

[0015] Furthermore, in the laser brazing method described in the present invention, the center of the laser spot coincides with the center of the end of the aluminum-based welding wire, and the minimum distance from the part where the laser spot coincides with the surface of the steel part to the center of the laser spot is equal to R1, and the maximum distance from the part where the laser spot coincides with the surface of the aluminum part to the center of the laser spot is equal to R1+R2.

[0016] Furthermore, in the laser brazing method described in the present invention, the diameter of the aluminum-based welding wire is 1.0 to 1.6 mm.

[0017] Furthermore, in the laser melting brazing method of the present invention, the thickness d of the aluminum part is 铝 and the thickness of the steel part d 钢 Satisfies: 0≤d 铝 -d 钢 ≤2.0mm.

[0018] In this embodiment, controlling the above parameters is beneficial to further avoid welding cracks caused by the difference in thermal expansion coefficients between the aluminum alloy and the steel.

[0019] Furthermore, in the laser melting brazing method of the present invention, the thickness d of the aluminum part is 铝 The value is 1 to 3 mm, and the thickness d of the steel part 钢 0.5~2.5mm.

[0020] In this embodiment, controlling the above parameters is beneficial to further avoid welding cracks caused by the difference in thermal expansion coefficients between the aluminum alloy and the steel.

[0021] Furthermore, in the laser melting and brazing method described in the present invention, the surface of the steel part has a galvanized layer.

[0022] In this embodiment, the galvanized layer on the surface of the steel part is beneficial to avoid the problem of poor spreading performance of liquid metal formed after the aluminum plate and the welding wire are melted due to oxidation of the steel plate surface before welding.

[0023] Furthermore, in the laser melting brazing method described in the present invention, the thickness of the zinc coating layer is 10 to 90 μm.

[0024] In a more specific embodiment, the galvanized layer may contain Al, Si, and Fe elements, for example, the mass percentage ω of each element satisfies: 85%≤ω Zn ≤100%, 0%≤ω Al ≤15%, 0%≤ω Si ≤5%, 0%≤ω Fe ≤1%.

[0025] In another more specific embodiment, the zinc coating may contain Al, Mg, Si, and Fe elements, for example, the mass percentage ω of each element satisfies: 85%≤ω Zn ≤100%, 0%≤ω Al ≤15%, 0%≤ω Mg ≤5%, 0%≤ω Si ≤5%, 0%≤ω Fe ≤1%.

[0026] Furthermore, in the laser melting brazing method described in the present invention, the mass percentage of Si element in the aluminum-based welding wire is 5-12%.

[0027] Of course, in addition to Al and Si elements, the aluminum-based welding wire may also contain other elements, such as Mg, Cu, and Fe, and the sum of the mass fractions of these other elements is not higher than 1%.

[0028] Furthermore, in the laser brazing method described in the present invention, when the aluminum part is a shell and the steel part is a cover, the flange width f1 of the aluminum part ≥ 15 mm, the length l2 of the steel part satisfies l2 ≥ l1 + f1 + 10, and the width w2 of the steel part ≥ w1 + f1 + 10, l1 and w1 are the bottom length and width of the aluminum part, respectively.

[0029] Furthermore, in the laser brazing method described in the present invention, when the steel part is a shell and the aluminum part is a cover, the flange width f4 of the steel part is ≥30 mm, and the length l5 of the aluminum part satisfies: l4+10≤l5≤l4+f4-10, and the width w5 of the aluminum part satisfies: w4+10≤w5≤w4+f4-10, l4 and w4 respectively represent the bottom length and width of the steel part.

[0030] The above two different implementation methods can be used to produce a sealed shell obtained by welding steel and aluminum dissimilar metals. Controlling the above parameters can prepare a steel and aluminum dissimilar metal laser brazing sealed shell with better joint appearance and performance than the conventional laser brazing method.

[0031] In the present invention, the aluminum part can be a spliced ​​aluminum plate or a non-spliced ​​aluminum plate, which can be cast or stamped in a mold, and the present invention is not limited to this. Similarly, the steel part can be a spliced ​​steel plate or a non-spliced ​​steel plate, which can be stamped in a mold.

[0032] In addition, in order to obtain a sealed shell with excellent overall performance, in some specific embodiments, the tensile strength of the aluminum part can be no less than 200 MPa, and the strength-plasticity product can be no less than 4000 MPa·%, and the material can be 5 series aluminum alloy or 6 series aluminum alloy.

[0033] For example, in a more specific embodiment, the chemical element composition of the aluminum part can be: Mg element content is between 0.3% and 5.5%, Si element content is between 0.4% and 1.5%, Mn element content is between 0.1% and 0.6%, Zn element content is between 0.05% and 0.3%, Cu element content is between 0.05% and 0.6%, Fe element content is between 0.05% and 0.5%, and the balance is Al.

[0034] In addition, the tensile strength of the steel parts may not be less than 600 MPa, and the strength-plasticity product may not be less than 10000 MPa·%.

[0035] For example, in a more specific embodiment, the chemical element composition of the steel part can be: C element is between 0.1% and 0.38%, Si element is between 0.1% and 2.5%, Mn element is between 0.55% and 3.0%, P element is between 0.001% and 0.05%, S element is between 0.001% and 0.015%, the sum of the contents of five elements Nb, Ti, Cr, Mo, and B is between 0.1% and 1.5%, and the balance is Fe.

[0036] The laser melting brazing method of steel and aluminum dissimilar metals of the present invention has the following advantages and beneficial effects:

[0037] The laser melting and brazing method for dissimilar metals of steel and aluminum described in the present invention can control the thickness of the intermetallic compound layer to be 5 to 20 μm, and at the same time control the spreading width of the weld metal to be no less than 5 mm, thereby making the weld joint have excellent performance. When the joint is subjected to a tensile shear performance test, the failure position occurs in the aluminum alloy base material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The welding arrangement diagram in the laser melting and brazing method of steel and aluminum dissimilar metals described in the present invention is schematically shown.

[0039] Figure 2 The range of the first circle and the second circle is schematically shown.

[0040] Figure 3 A light intensity distribution form of a laser spot is schematically shown.

[0041] Figure 4 Another form of light intensity distribution of the laser spot is schematically shown.

[0042] Figure 5 Another light intensity distribution form of the laser spot is schematically shown.

[0043] Figure 6 A schematic structural diagram of an aluminum part in one embodiment of the present invention is shown.

[0044] Figure 7 A schematic structural diagram of a steel component in one embodiment of the present invention is shown.

[0045] Figure 8 A schematic structural diagram of a sealing housing in one embodiment of the present invention is shown.

[0046] Fig. 9 A schematic structural diagram of an aluminum part in another embodiment of the present invention is shown.

[0047] Fig.10 A schematic structural diagram of a steel component in another embodiment of the present invention is shown.

[0048] Fig.11 A schematic structural diagram of a sealing housing in another embodiment of the present invention is shown.

[0049] Fig.12 The microstructure of the intermetallic compound layer at the interface of the steel-aluminum dissimilar metal joint obtained in Example 2 of the present invention is shown.

[0050] Fig.13 The macroscopic morphology of the steel-aluminum dissimilar metal joint obtained in Example 2 of the present invention is shown. DETAILED DESCRIPTION

[0051] The laser brazing method for dissimilar metals of steel and aluminum described in the present invention will be further explained and illustrated below in conjunction with specific embodiments and the accompanying drawings of the specification. However, such explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0052] Figure 1 The welding arrangement diagram in the laser melting and brazing method of steel and aluminum dissimilar metals described in the present invention is schematically shown.

[0053] like Figure 1 As shown, in some embodiments, when laser brazing of dissimilar metals of steel and aluminum is performed, the aluminum part 1 and the steel part 2 are first overlapped to form a joint; then an aluminum-based welding wire 3 is used and a laser beam 4 is used to perform laser brazing.

[0054] When laser brazing is performed, the laser spot used is circular, and Figure 2 As shown, the first light intensity I1 in the first circular range with the center of the light spot as the center and the radius R1 is equal to (45% to 65%)·I0; the second light intensity I2 in the second circular range with the center of the light spot as the center and the radius R2 is equal to or greater than 90%·I0; R1 is 0.5 to 0.8 mm, R2 is 1.5 to 2.0 mm, and I0 represents the total light intensity of the laser beam. In a specific example, I0 is 3.5×10 4 W / cm2 .

[0055] It should be noted that the present invention only needs the above-mentioned limitations to implement the present technical solution, and there is no specific limitation on the specific distribution of light intensity in the area. Figure 3 , Figure 4 and Figure 5 Therefore, as long as the laser spot area division method and the percentage of the light intensity in each area to the total light intensity of the laser beam fall within the scope of this method, only changing the specific distribution method of the laser intensity in each area should be considered to fall within the protection scope of this method.

[0056] During welding, the center of the laser spot coincides with the center of the end of the aluminum-based welding wire 3, and the minimum distance from the part where the laser spot coincides with the surface of the steel part to the center of the laser spot is equal to R1, and the maximum distance from the part where the laser spot coincides with the surface of the aluminum part to the center of the laser spot is equal to R1+R2.

[0057] In some preferred embodiments, the upper surface 21 of the steel part is heated to 907-1350°C, and the lower surface 22 of the steel plate is heated to 25-420°C by using the laser beam 4.

[0058] In some preferred embodiments, the diameter of the aluminum-based welding wire is 1.0-1.6 mm, and the mass percentage of Si element in the aluminum-based welding wire is 5-12%. Of course, in addition to Al and Si elements, the aluminum-based welding wire may also contain other elements, such as Mg, Cu, Fe, and the sum of the mass fractions of these other elements is not higher than 1%.

[0059] In some preferred embodiments, the thickness d of the aluminum part 铝 and the thickness of the steel part d 钢 Satisfies: 0≤d 铝 -d 钢 ≤2.0mm, and the thickness of the aluminum part d 铝 The thickness d of the steel part is 1 to 3 mm. 钢 0.5~2.5mm.

[0060] In some preferred embodiments, the surface of the steel part has a galvanized layer, and the thickness of the galvanized layer may be 10 to 90 μm.

[0061] In some more specific embodiments, the galvanized layer may contain Al, Si, and Fe elements, for example, the mass percentage ω of each element satisfies: 85%≤ω Zn ≤100%, 0%≤ω Al ≤15%, 0%≤ω Si ≤5%, 0%≤ω Fe ≤1%.

[0062] In some other more specific embodiments, the zinc coating may contain Al, Mg, Si, and Fe elements, for example, the mass percentage ω of each element satisfies: 85%≤ω Zn ≤100%, 0%≤ω Al ≤15%, 0%≤ω Mg ≤5%, 0%≤ω Si ≤5%, 0%≤ω Fe ≤1%.

[0063] In addition, in order to obtain a sealed shell with excellent overall performance, in some specific embodiments, the tensile strength of the aluminum part can be no less than 200 MPa, and the strength-plasticity product can be no less than 4000 MPa·%, and the material can be 5 series aluminum alloy or 6 series aluminum alloy.

[0064] For example, in a more specific embodiment, the chemical element composition of the aluminum part can be: Mg element content is between 0.3% and 5.5%, Si element content is between 0.4% and 1.5%, Mn element content is between 0.1% and 0.6%, Zn element content is between 0.05% and 0.3%, Cu element content is between 0.05% and 0.6%, Fe element content is between 0.05% and 0.5%, and the balance is Al.

[0065] In addition, the tensile strength of the steel parts may not be less than 600 MPa, and the strength-plasticity product may not be less than 10000 MPa·%.

[0066] For example, in a more specific embodiment, the chemical element composition of the steel part can be: C element is between 0.1% and 0.38%, Si element is between 0.1% and 2.5%, Mn element is between 0.55% and 3.0%, P element is between 0.001% and 0.05%, S element is between 0.001% and 0.015%, the sum of the contents of five elements Nb, Ti, Cr, Mo, and B is between 0.1% and 1.5%, and the balance is Fe.

[0067] Table 1 lists the specific parameters used in preferred embodiments 1-6 of the present invention.

[0068] Table 1.

[0069]

[0070]

[0071] Figure 6 A schematic structural diagram of an aluminum part in one embodiment of the present invention is shown. Figure 7 A schematic structural diagram of a steel component in one embodiment of the present invention is shown. Figure 8A schematic structural diagram of a sealing housing in one embodiment of the present invention is shown.

[0072] The above examples 1-3 are all prepared as Figure 6-Figure 8 The aluminum part shown is a shell, and the steel part is a steel-aluminum dissimilar metal sealing shell of the cover. In this case, in order to obtain a better joint appearance and performance, the flange width f1 of the aluminum part can also be controlled to be ≥15mm, the length l2 of the steel part satisfies l2≥l1+f1+10, the width w2 of the steel part is ≥w1+f1+10, l1 and w1 are the bottom length and width of the aluminum part respectively, and the unit parameters of these parameters are all mm. Table 2 lists the specific parameters of Examples 1-3.

[0073] Table 2.

[0074] serial number <![CDATA[f1(mm)]]> <![CDATA[l1(mm)]]> <![CDATA[w1(mm)]]> <![CDATA[l2(mm)]]> <![CDATA[w2(mm)]]> Example 1 15 800 500 825 525 Example 2 30 1000 600 1050 650 Example 3 80 1500 800 1600 900

[0075] Fig. 9 A schematic structural diagram of an aluminum part in another embodiment of the present invention is shown. Fig.10 A schematic structural diagram of a steel component in another embodiment of the present invention is shown. Fig.11 A schematic structural diagram of a sealing housing in another embodiment of the present invention is shown.

[0076] The above-mentioned examples 4-6 are all prepared as Figure 9-11 The steel part is a shell, and the aluminum part is a steel-aluminum dissimilar metal sealing shell. In this case, in order to obtain a better joint appearance and performance, the flange width f4 of the steel part can also be controlled to be ≥ 30 mm, and the length l5 of the aluminum part satisfies: l4+10≤l5≤l4+f4-10, and the width w5 of the aluminum part satisfies: w4+10≤w5≤w4+f4-10, where l4 and w4 represent the bottom length and width of the steel part, respectively. Table 3 lists the specific parameters of Examples 4-6.

[0077] Table 3.

[0078] serial number <![CDATA[f4(mm)]]> <![CDATA[l4(mm)]]> <![CDATA[w4(mm)]]> <![CDATA[l5(mm)]]> <![CDATA[w5(mm)]]> Example 4 30 700 400 715 415 Example 5 50 1000 600 1020 620 Example 6 100 1300 800 1350 850

[0079] In addition, in order to demonstrate the implementation effect of the preferred embodiment, Table 4 lists the measured values ​​of the thickness of the intermetallic compound layer and the spreading width of the weld metal in the steel-aluminum laser brazing joints prepared in Examples 1-6.

[0080] Table 4.

[0081] serial number Intermetallic compound layer thickness (μm) Weld metal spread width (mm) Example 1 19.9 6.9 Example 2 12.6 5.7 Example 3 7.4 5.5 Example 4 15.2 6.3 Example 5 11.2 5.4 Example 6 5.5 5.2

[0082] As can be seen from Table 4, by using the present invention, the thickness of the intermetallic compound layer in the steel-aluminum laser brazing joint can be controlled to 5-20 μm, while achieving a weld metal spreading width of not less than 5 mm. Therefore, it meets the basic conditions that a good steel-aluminum laser brazing joint needs to meet.

[0083] Fig.12 The microstructure of the intermetallic compound layer at the interface of the steel-aluminum dissimilar metal joint obtained in Example 2 of the present invention is shown.

[0084] from Fig.12 It can be seen that the thickness of the intermetallic compound layer in the steel-aluminum laser welding brazing joint obtained in this embodiment is 12.6 μm.

[0085] Fig.13 The macroscopic morphology of the steel-aluminum dissimilar metal joint obtained in Example 2 of the present invention is shown.

[0086] from Fig.13 It can be seen that the spread width of the weld metal of the steel-aluminum laser brazing joint obtained in this embodiment is 5.7 mm.

[0087] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0088] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A laser brazing method for steel and aluminum dissimilar metals, characterized in that: Includes steps: Overlap steel and aluminum parts to form joints; The joint is welded by laser brazing using aluminum-based welding wire: the laser spot used is circular, and the first light intensity I1 in the first circular range with a radius R1 and a center of the spot is equal to (45% to 65%)·I0; The second light intensity I2 within the second circular range with a radius R2 and the center of the light spot as the circle center is ≥90%·I0; R1 is 0.5-0.8 mm, R2 is 1.5-2.0 mm, and I0 represents the total light intensity of the laser beam.

2. The laser melting brazing method according to claim 1, characterized in that: During the welding process, the laser is controlled to heat the upper surface of the steel part to 907-1350°C and the lower surface of the steel plate to 25-420°C.

3. The laser brazing method according to claim 1, characterized in that: The center of the laser spot coincides with the center of the end of the aluminum-based welding wire, and the minimum distance from the part where the laser spot coincides with the surface of the steel part to the center of the laser spot is equal to R1, and the maximum distance from the part where the laser spot coincides with the surface of the aluminum part to the center of the laser spot is equal to R1+R2.

4. The laser brazing method according to claim 1, characterized in that: The diameter of the aluminum-based welding wire is 1.0-1.6 mm.

5. The laser brazing method according to claim 1, characterized in that: The thickness d of the aluminum part 铝 and the thickness of the steel part d 钢 Satisfies: 0≤d 铝 -d 钢 ≤2.0mm.

6. The laser brazing method according to claim 5, characterized in that: The thickness d of the aluminum part 铝 The value is 1 to 3 mm, and the thickness d of the steel part 钢 0.5~2.5mm.

7. The laser melting brazing method according to claim 1, characterized in that: The surface of the steel part has a galvanized layer.

8. The laser melting brazing method according to claim 7, characterized in that: The thickness of the zinc coating is 10 to 90 μm.

9. The laser melting brazing method according to claim 1, characterized in that: The mass percentage of Si element in the aluminum-based welding wire is 5-12%.

10. The laser brazing method according to claim 1, characterized in that: When the aluminum part is a shell and the steel part is a cover, the flange width f1 of the aluminum part ≥ 15 mm, the length l2 of the steel part satisfies l2 ≥ l1 + f1 + 10, the width w2 of the steel part ≥ w1 + f1 + 10, and l1 and w1 are the bottom length and width of the aluminum part respectively.

11. The laser brazing method according to claim 1, characterized in that: When the steel part is a shell and the aluminum part is a cover, the flange width f4 of the steel part is ≥30 mm, and the length l5 of the aluminum part satisfies: l4+10≤l5≤l4+f4-10, and the width w5 of the aluminum part satisfies: w4+10≤w5≤w4+f4-10, where l4 and w4 respectively represent the bottom length and width of the steel part.

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