Production process of high-energy-absorption 6-series aluminum alloy plate for automobile

Abstract

The invention discloses a production process of a high-energy-absorption 6-series aluminum alloy plate for an automobile, which takes a 6014A aluminum alloy as a raw material and is prepared by smelting and casting, saw cutting and surface milling, homogenizing treatment, hot rolling, cold rolling and intermediate annealing, solid solution and pre-aging, and back rolling and finishing. The Si content in the alloy components is controlled, solution treatment and a pre-aging system are carried out, and meanwhile work hardening is controlled to prevent dislocation proliferation from affecting aging. The process inhibits a large-size GP region and promotes formation of a small-size GP region and a beta ''precursor phase, so that the PB strength is effectively improved at any time, the T4 strength increase is reduced, the service life of the material is prolonged to more than one year, and the process can be widely used for improving the lateral rigidity of a vehicle body.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy processing and manufacturing technology, specifically relating to a production process for high energy absorption 6-series aluminum alloy sheets for automobiles. Background Technology

[0002] With the rapid development of China's economy, the transportation system has become increasingly sophisticated. The construction of highways, urban roads, and other transportation facilities has progressed rapidly, improving road safety and traffic efficiency. Currently, most energy-absorbing components used for automotive protection are applied to the front and rear bumper systems, leaving lateral protection weak. To address this shortcoming, higher requirements are placed on the strength of the door panels. The outer door panels, in particular, have numerous and stringent requirements for raw material specifications, and the balance between various performance parameters is constrained by the process parameters. It is difficult to improve a single indicator without affecting others; therefore, the task of improving lateral stiffness falls on the inner door panels. For common 6-series aluminum alloy sheet products, the aging trend shows that the tensile strength in the natural state (T4) continuously increases with time after solution treatment, while the tensile strength continuously decreases after paint treatment (PB). OEMs need to complete stamping within 6 months; otherwise, the material's stamping formability deteriorates, easily causing cracking, resulting in lower tensile strength after paint treatment (PB) that fails to meet usage requirements. Summary of the Invention

[0003] In view of this, the present invention discloses a manufacturing process for high energy absorption 6-series aluminum alloy sheets for automobiles, specifically including the following steps:

[0004] S1. 6014A aluminum alloy raw material is put into a melting furnace for melting, and then cast to obtain 6014A aluminum alloy flat ingot;

[0005] S2. Sawing the ingot derrick and gate of the 6014A aluminum alloy flat ingot and milling the solidified shell layer on its surface.

[0006] S3. The sawed and milled 6014A aluminum alloy flat ingots are sent into a heating furnace for homogenization treatment.

[0007] S4. Hot rolling is performed on the homogenized 6014A aluminum alloy flat ingot to obtain 6014A aluminum alloy hot-rolled plate.

[0008] S5. Cold rolling and intermediate annealing of 6014A aluminum alloy hot-rolled sheet to obtain 6014A aluminum alloy cold-rolled sheet;

[0009] S6. Solution treatment and pre-aging treatment of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, the 6014A aluminum alloy cold-rolled sheet is solution treated to a minimum. The target temperature is heated to 500±3℃ and then immediately quenched by air cooling. When the 6014A aluminum alloy cold-rolled sheet is cooled to 105℃~145℃, the air cooling is stopped and it is over-coiled. The residual heat is used for pre-aging to obtain 6-series aluminum alloy sheet.

[0010] S7. The 6-series aluminum alloy sheet rolled in step S6 is re-rolled and finished.

[0011] The precipitation sequence of strengthening phases in 6-series aluminum alloys during the heating process is: solid solution → solute atomic groups and vacancies → GP zone → β'' phase → β' phase → excess solute → β phase.

[0012] The strengthening phase of 6014A aluminum alloy in its natural aging state is the GP zone, while the strengthening phase after baking paint treatment is the β'' phase.

[0013] The GP regions precipitated under natural aging are relatively large and cannot be directly converted to the β'' phase. During the baking process, they need to be re-dissolved into the substrate first, and then re-precipitated into smaller GP regions, which then convert to the β'' phase. Therefore, the longer the natural aging, the more large GP regions are formed, and the higher the strength. However, the time for the re-dissolution and re-precipitation process during baking will also be longer, resulting in fewer newly precipitated small GP regions and fewer subsequently precipitated β'' phases, thus lowering the strength of the baking process.

[0014] The purpose of pre-aging is to rapidly heat the material to the precipitation temperature of the GP region (above 90~100℃) and the precipitation temperature of the β'' phase (below 150~160℃) and hold it at that temperature. This can suppress the precipitation of large-sized GP regions and instead use solute atoms to form small-sized GP regions → β'' precursor phase. In this way, under the baking paint conditions of 180~185℃, the precursor phase can grow rapidly to form the β'' phase, which suppresses the improvement of T4 strength while improving the strength of the baking paint treatment (PB).

[0015] The greater the solid solubility, the greater the driving force for precipitation during aging. As a result, more large-size GP regions will precipitate during the pre-aging heating process, and the smaller the effect of pre-aging will be.

[0016] The core of this patented technology is to control the solid solubility to a minimum, thereby reducing the size of the GP region. This further weakens the large GP region, increasing the T4 strength while simultaneously forming numerous small GP regions. This promotes the rapid nucleation and growth of the β'' precursor phase, improving the tensile strength of the paint coating. The principle of work hardening is dislocation multiplication. Another effect of dislocation multiplication is accelerating the aging precipitation process, which counteracts the effect of the core technology of this patent; therefore, strict control is necessary. In this paper, work hardening refers to the work hardening process after solution treatment and subsequent finishing, including methods such as roll straightening, roll box straightening, and tensile straightening. The hardening effect of this process is confirmed by measuring the tensile properties before and after straightening. The same process has different hardening effects on finished products of different thicknesses; ultimately, a T4 yield strength of no more than 5 MPa is acceptable.

[0017] As a supplement to the technical solution of the present invention, the homogenization process is as follows: heat to 560°C and hold for 6 hours, then cool with the furnace to 500°C and hold at 500°C for 2 hours.

[0018] As a supplement to the technical solution of the present invention, the hot rolling process specifically involves first performing rough rolling, and then performing four consecutive finish rolling to obtain hot-rolled aluminum alloy sheets.

[0019] As a supplement to the technical solution of the present invention, in step S5, the aluminum alloy hot-rolled plate obtained in step S4 is first subjected to intermediate annealing cold rolling, the intermediate annealing cold rolling processing rate is 59%~64%, and then the plate after intermediate annealing cold rolling is subjected to intermediate annealing treatment; the plate after intermediate annealing treatment is subjected to intermediate annealing cold rolling, the intermediate annealing cold rolling processing rate is 60%.

[0020] As a supplement to the technical solution of this invention, the Si content in the 6014A aluminum alloy raw material is 0.60~0.70%. Optimizing the Si content ensures smooth solid solution formation. When the Si content exceeds 0.70%, the solid solubility is higher than the minimum required solid solution.

[0021] As a supplement to the technical solution of the present invention, the finishing process in step S7 includes one or more of the following: roller straightening, roller box straightening, and stretch straightening.

[0022] As a supplement to the technical solution of the present invention, the difference in yield strength of the 6-absorption aluminum alloy sheet before and after the finishing process in step S7 is less than or equal to 5MPa.

[0023] Beneficial effects: This invention changes the traditional variation law of PB strength after aging of 6-series materials, transforming the PB strength from decreasing with aging to increasing with aging, while reducing the increase in T4 strength. This removes the restriction that OEMs must use the material within six months from both the perspectives of finished product quality and processability, extending it to one year or even longer. In another aspect of this invention, because its PB tensile properties do not decrease, it can be more widely used in designs to improve the lateral stiffness of the vehicle body. Attached Figure Description

[0024] Figure 1 The above is a statistical chart of the T4 yield strength over one year for embodiments and comparative examples of the present invention.

[0025] Figure 2 The above is a statistical chart of the yield strength of PB over one year for embodiments and comparative examples of the present invention. Detailed Implementation

[0026] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0027] Example 1:

[0028] A manufacturing process for high-energy-absorbing 6-series aluminum alloy sheets for automotive applications includes the following steps:

[0029] S1. 6014A aluminum alloy raw material is put into a melting furnace for melting, wherein the Si element content in the 6014A aluminum alloy raw material is 0.60%, and 6014A aluminum alloy flat ingot is obtained by casting.

[0030] S2. Sawing the ingot derrick and gate of the 6014A aluminum alloy flat ingot and milling the solidified shell layer on its surface.

[0031] S3. The sawed and milled 6014A aluminum alloy flat ingots are sent into a heating furnace for homogenization treatment. The homogenization treatment process involves heating the flat ingots to 560°C and holding them at that temperature for 6 hours, then cooling them to 500°C in the furnace and holding them at 500°C for 2 hours.

[0032] S4. The homogenized 6014A aluminum alloy flat ingot is subjected to reciprocating rough rolling and 4-time continuous finish rolling to obtain a 6.3mm thick hot-rolled coil.

[0033] S5. The 6014A aluminum alloy hot-rolled sheet is cold-rolled and intermediate annealed to obtain the 6014A aluminum alloy cold-rolled sheet; first, the 6.3mm thick hot-rolled coil is cold-rolled to 2.5mm, and then intermediate annealing is performed. The intermediate annealing process is to hold at 350℃ for 2 hours, and then cold-rolled to 1.0mm.

[0034] S6. Solution treatment and pre-aging of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, heat the 6014A aluminum alloy cold-rolled sheet to 503℃ and then immediately quench it by air cooling. When the 6014A aluminum alloy cold-rolled sheet cools to 126℃, stop the air cooling and over-coil it. Use the residual heat to pre-age it to obtain 6-series aluminum alloy sheet.

[0035] S7. The 6-series aluminum alloy sheet rolled in step S6 is re-rolled and finished.

[0036] Example 2:

[0037] A manufacturing process for high-energy-absorbing 6-series aluminum alloy sheets for automotive applications includes the following steps:

[0038] S1. 6014A aluminum alloy raw material is put into a melting furnace for melting, wherein the Si element content in the 6014A aluminum alloy raw material is 0.70%, and 6014A aluminum alloy flat ingot is obtained by casting.

[0039] S2. Sawing the ingot derrick and gate of the 6014A aluminum alloy flat ingot and milling the solidified shell layer on its surface.

[0040] S3. The sawed and milled 6014A aluminum alloy flat ingots are sent into a heating furnace for homogenization treatment. The homogenization treatment process involves heating the flat ingots to 560°C and holding them at that temperature for 6 hours, then cooling them to 500°C in the furnace and holding them at 500°C for 2 hours.

[0041] S4. The homogenized 6014A aluminum alloy flat ingot is subjected to reciprocating rough rolling and 4-time continuous finish rolling to obtain a 6.0mm thick hot-rolled coil.

[0042] S5. The 6014A aluminum alloy hot-rolled sheet is cold-rolled and intermediate annealed to obtain the 6014A aluminum alloy cold-rolled sheet; first, the 6.0mm thick hot-rolled coil is cold-rolled to 2.25mm, and then intermediate annealing is performed. The intermediate annealing process is to hold at 350℃ for 2 hours, and then cold-rolled to 0.9mm.

[0043] S6. Solution treatment and pre-aging of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, heat the 6014A aluminum alloy cold-rolled sheet to 497℃ and then immediately quench it by air cooling. When the 6014A aluminum alloy cold-rolled sheet cools to 32℃, stop the air cooling and over-coil it. Use the residual heat to pre-age it to obtain 6-series aluminum alloy sheet.

[0044] S7. The 6-series aluminum alloy sheet rolled in step S6 is re-rolled and finished.

[0045] Comparative Example 1:

[0046] The difference between Comparative Example 1 and Example 1 lies in steps S4 to S7, specifically:

[0047] S4. The homogenized 6014A aluminum alloy flat ingot is subjected to reciprocating rough rolling and 4-time continuous finish rolling to obtain a 7.5mm thick hot-rolled coil.

[0048] S5. The 6014A aluminum alloy hot-rolled sheet is cold-rolled and intermediate annealed to obtain the 6014A aluminum alloy cold-rolled sheet; first, the 7.5mm thick hot-rolled coil is cold-rolled to 3.0mm, and then intermediate annealing is performed. The intermediate annealing process is to hold at 350℃ for 2 hours, and then cold-rolled to 1.2mm.

[0049] S6. Solution treatment and pre-aging of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, heat the 6014A aluminum alloy cold-rolled sheet to 505℃ and then immediately quench it by air cooling. When the 6014A aluminum alloy cold-rolled sheet cools to 132℃, stop the air cooling and over-coil it. Use the residual heat to pre-age it to obtain 6-series aluminum alloy sheet.

[0050] S7. The 6-series aluminum alloy sheet coiled in step S6 is re-coiled and finished. This results in no increase in yield strength before and after re-coiling.

[0051] This comparative example does not meet the minimum solid solution requirement.

[0052] Comparative Example 2:

[0053] The difference between Comparative Example 2 and Example 1 lies in steps S4 to S7, specifically:

[0054] S4. The homogenized 6014A aluminum alloy flat ingot is subjected to reciprocating rough rolling and 4-time continuous finish rolling to obtain a 6.9mm thick hot-rolled aluminum alloy coil.

[0055] S5. The 6014A aluminum alloy hot-rolled sheet is cold-rolled and intermediate annealed to obtain the 6014A aluminum alloy cold-rolled sheet; first, the 6.9mm thick hot-rolled coil is cold-rolled to 2.75mm, and then intermediate annealing is performed. The intermediate annealing process is to hold at 350℃ for 2 hours, and then cold-rolled to 1.1mm.

[0056] S6. Solution treatment and pre-aging of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, heat the 6014A aluminum alloy cold-rolled sheet to 495℃ and then immediately quench it by air cooling. When the 6014A aluminum alloy cold-rolled sheet cools to 124℃, stop the air cooling and over-coil it. Use the residual heat to pre-age it to obtain 6-series aluminum alloy sheet.

[0057] S7. The 6-series aluminum alloy sheet rolled in step S6 is re-rolled and finished. The yield strength increases by only 2 MPa before and after cutting.

[0058] The aluminum alloy sheet in this comparative example was not solution treated.

[0059] Comparative Example 3:

[0060] The difference between Comparative Example 3 and Example 1 lies in steps S4 to S7, specifically:

[0061] S4. The homogenized 6014A aluminum alloy flat ingot is subjected to reciprocating rough rolling and 4-time continuous finish rolling to obtain a 6.0mm thick hot-rolled coil.

[0062] S5. The 6014A aluminum alloy hot-rolled sheet is cold-rolled and intermediate annealed to obtain the 6014A aluminum alloy cold-rolled sheet; first, the 6.0mm thick hot-rolled coil is cold-rolled to 2.25mm, and then intermediate annealing is performed. The intermediate annealing process is to hold at 350℃ for 2 hours, and then cold-rolled to 0.9mm.

[0063] S6. Solution treatment and pre-aging of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, heat the 6014A aluminum alloy cold-rolled sheet to 501℃ and then immediately quench it by air cooling. When the 6014A aluminum alloy cold-rolled sheet cools to 105℃, stop the air cooling and over-coil it. Use the residual heat to pre-age it to obtain 6-series aluminum alloy sheet.

[0064] S7. The 6-series aluminum alloy sheet rolled in step S6 is re-rolled and finished. The yield strength increases by only 3 MPa before and after cutting.

[0065] The pre-aging temperature of this comparative example is low.

[0066] Comparative Example 4:

[0067] The difference between Comparative Example 4 and Example 1 lies in steps S4 to S7, specifically:

[0068] S4. The homogenized 6014A aluminum alloy flat ingot is subjected to reciprocating rough rolling and 4-time continuous finish rolling to obtain an 8.1mm thick hot-rolled coil.

[0069] S5. The 6014A aluminum alloy hot-rolled sheet is cold-rolled and intermediate annealed to obtain the 6014A aluminum alloy cold-rolled sheet; first, the 8.1mm thick hot-rolled coil is cold-rolled to 3.25mm, and then intermediate annealing is performed. The intermediate annealing process is to hold at 350℃ for 2 hours, and then cold-rolled to 1.3mm.

[0070] S6. Solution treatment and pre-aging of 6014A aluminum alloy cold-rolled sheet. The specific process is as follows: first, heat the 6014A aluminum alloy cold-rolled sheet to 502℃ and then immediately quench it by air cooling. When the 6014A aluminum alloy cold-rolled sheet cools to 120℃, stop the air cooling and over-coil it. Use the residual heat to pre-age it to obtain 6-series aluminum alloy sheet.

[0071] S7. The 6-series aluminum alloy sheet coiled in step S6 is re-coiled and finished. The yield strength increases by 7 MPa before and after cutting, resulting in overwork hardening.

[0072] Comparative Example 5:

[0073] The difference between Comparative Example 5 and Example 2 lies in step S1, specifically:

[0074] S1. 6014A aluminum alloy raw material is put into a melting furnace for melting, wherein the Si element content in the 6014A aluminum alloy raw material is 0.76%, and 6014A aluminum alloy flat ingot is obtained by casting.

[0075] The aluminum alloy sheet used in this comparative example exceeds the minimum solution treatment limit.

[0076] Comparative Example 6:

[0077] The difference between Comparative Example 6 and Example 2 lies in step S1, which is as follows:

[0078] S1. 6014A aluminum alloy raw material is put into a melting furnace for melting, wherein the Si element content in the 6014A aluminum alloy raw material is 0.54%, and 6014A aluminum alloy flat ingot is obtained by casting.

[0079] This comparative example does not meet the minimum solid solution requirement.

[0080] The yield strength of T4 and the yield strength of PB in each embodiment and comparative example within one year are shown in the figure. Figure 1 and Figure 2 .

[0081] As can be seen from Comparative Examples 2 and 6, when the solution is below the minimum limit, no solution is formed and the material only recrystallizes. The T4 yield strength and PB strength do not increase with aging, and the latter does not meet the requirements for use in stamped parts.

[0082] As can be seen from Comparative Examples 1, 3, 4, and 5, failure to use minimum solution treatment, pre-aging temperature close to the precipitation temperature of large-size GP regions, and excessive hardening after pre-aging all lead to the formation of more large-size GP regions, which in turn reduces the yield strength of PB with aging.

[0083] As can be seen from Examples 1 and 2, their T4 strength is lower than that of Comparative Examples 1, 3 and 4 which were aged at the same time, and they have better stamping formability. Moreover, the PB strength increases with aging, and there is no risk of finished product defects.

[0084] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A manufacturing process for high-energy-absorbing 6-series aluminum alloy sheets for automobiles, characterized in that, Includes the following steps: S1. 6014A aluminum alloy raw material is put into a melting furnace for melting, and then cast to obtain 6014A aluminum alloy flat ingot; S2. Sawing the ingot end and gate end of the 6014A aluminum alloy flat ingot, and milling the solidified shell layer on its surface; S3. The sawed and milled 6014A aluminum alloy flat ingots are sent into a heating furnace for homogenization treatment. S4. Hot rolling is performed on the homogenized 6014A aluminum alloy flat ingot to obtain 6014A aluminum alloy hot-rolled plate. S5. Cold rolling and intermediate annealing of 6014A aluminum alloy hot-rolled sheet to obtain 6014A aluminum alloy cold-rolled sheet; S6. Solution treatment and pre-aging treatment of 6014A aluminum alloy cold-rolled sheet: First, solution treatment of 6014A aluminum alloy cold-rolled sheet is carried out. After heating to 500±3℃, air cooling is immediately used for quenching. When the 6014A aluminum alloy cold-rolled sheet is cooled to 105℃~145℃, air cooling is stopped and over-coiling is performed. Pre-aging is carried out using the residual heat to obtain 6-series aluminum alloy sheet.

2. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 1, characterized in that, The homogenization process is as follows: heat to 560°C and hold for 6 hours, then cool to 500°C in the furnace and hold at 500°C for 2 hours.

3. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 1, characterized in that, In step S4, the hot rolling process specifically involves first performing rough rolling, followed by four consecutive precision rolling processes to obtain an aluminum alloy hot-rolled plate.

4. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 3, characterized in that, In step S5, the aluminum alloy hot-rolled plate obtained in step S4 is first subjected to pre-annealing cold rolling, with a processing rate of 59% to 64%. Then, the plate after pre-annealing cold rolling is subjected to intermediate annealing treatment. After intermediate annealing treatment, the plate is subjected to post-annealing cold rolling, with a processing rate of 60%.

5. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 1, characterized in that, The Si content in the 6014A aluminum alloy raw material is 0.60~0.70%.

6. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 1, characterized in that, It also includes step S7: rewinding and finishing the 6-series aluminum alloy sheet rolled in step S6.

7. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 6, characterized in that, The finishing process in step S7 includes one or more of the following: roller straightening, roller box straightening, and stretch straightening.

8. The manufacturing process for a high-energy-absorbing 6-series aluminum alloy sheet for automobiles according to claim 6, characterized in that, In step S7, the difference in yield strength between the six aluminum alloy plates before and after the finishing process is less than or equal to 5 MPa.

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