TWI852413B - Aluminum alloy plate, method of forming the same and aluminum component for car structure - Google Patents

Abstract

An aluminum alloy plate, a method of forming the same and an aluminum component for car structure are provided. The method includes providing an aluminum blank, in which the aluminum blank has specific amounts of copper (Cu) and manganese (Mn); performing a rolling operation to the aluminum blank to obtain a cold rolled aluminum coil; performing a high-temperature forming operation to the cold rolled aluminum coil to obtain a formed aluminum plate; and performing a pre-treatment operation to the formed aluminum plate to obtain the aluminum alloy plate with great aging stability.

Description

Aluminum alloy sheet, manufacturing method thereof and aluminum component for automobile structure

The present invention relates to an aluminum alloy sheet and a method for manufacturing the same, and in particular to an aluminum alloy sheet, a method for manufacturing the same, and an aluminum component for automobile structure.

In recent years, the demand for lightweight automobiles has continued to increase, so the application of aluminum alloys has extended from exterior parts to internal components. Compared with 15B22 hot stamping steel, 7xxx series AlZnMgCu aviation aluminum alloys have considerable strength, so they can be used to replace steel to achieve the goal of lightweight automobiles. However, generally speaking, the room temperature formability of the aforementioned aluminum alloys is poor, and structural sheets with large strokes and complex shapes are prone to cracking, so this problem is generally overcome by increasing the forming temperature.

The conventional method is to subject the formed components to high-temperature solution treatment and quenching treatment according to the AMS-2772 specification, and then to lengthy artificial aging heat treatment, for example, at a temperature of about 121°C for 24 hours. This process is not only time-consuming and energy-consuming, but also not conducive to production. Furthermore, components are prone to deformation and residual stress problems during the quenching process, which results in the inability to ship the components smoothly.

To solve the problem of quenching deformation, the known method is to transfer the high-temperature plate to the mold for forming and quenching at the same time by integrating the high-temperature solid solution and processing forming process. Although this method solves the problems of cold punch cracking, large rebound, poor ductility and residual stress, the disadvantage is that the strength of the plate after forming is insufficient, and it still needs to be artificially aged for up to 24 hours to improve the strength. However, the obtained aluminum alloy sheet may have a problem of reduced strength after subsequent paint treatment in the car factory, and it is not enough for use.

In addition, aluminum alloy sheets usually need to be stored for a period of time (such as storage and transportation time) before being treated with paint. However, if the nuclei in the aluminum alloy sheet are not fully developed and/or mixed with poor atomic groups, there is a problem of storage hardening, that is, if the storage time is long, it will cause the strength after the paint treatment to drop sharply and fail to meet the specifications.

In view of this, it is urgent to provide an aluminum alloy sheet and a manufacturing method thereof to improve material stability, extend storage time and take strength into consideration.

One aspect of the present invention is to provide a method for manufacturing an aluminum alloy sheet, which improves material stability by controlling the composition of the aluminum blank and pre-treatment operations.

Another aspect of the present invention is to provide an aluminum alloy sheet, which is made using the above aspect.

Another aspect of the present invention is to provide an aluminum component for automobile structure.

According to one aspect of the present invention, a method for manufacturing an aluminum alloy sheet is provided, which includes providing an aluminum blank; performing a rolling operation on the aluminum blank to obtain a cold-rolled aluminum coil; performing a high-temperature forming operation on the cold-rolled aluminum coil to obtain a formed aluminum sheet; and performing a pre-treatment operation on the formed aluminum sheet to obtain an aluminum alloy sheet, wherein the pre-treatment temperature of the pre-treatment operation is 100°C to 300°C, and the pre-treatment time of the pre-treatment operation is 1 hour to 3 hours. Based on 100wt% of the aluminum billet, the aluminum billet contains 4.0wt% to 8.0wt% of zinc, 1.5wt% to 3.2wt% of magnesium, 1.0wt% to 3.0wt% of copper, no more than 0.5wt% of silicon, no more than 0.5wt% of iron, no more than 0.3wt% of titanium, no more than 0.5wt% of manganese, no more than 1.5wt% of impurities and a balance of aluminum, and the copper (Cu) and manganese (Mn) in the aluminum billet satisfy the following formula.

According to one embodiment of the present invention, before the rolling operation, the above method further comprises a two-stage homogenization treatment of the aluminum blank. The two-stage homogenization treatment comprises a first stage homogenization treatment, wherein the treatment temperature of the first stage homogenization treatment is 455°C to 475°C, and the treatment time of the first stage homogenization treatment is 12 hours to 24 hours; and a second stage homogenization treatment, wherein the treatment temperature of the second stage homogenization treatment is 475°C to 490°C, and the treatment time of the second stage homogenization treatment is 12 hours to 48 hours.

According to one embodiment of the present invention, the above-mentioned rolling operation includes hot rolling the aluminum billet to obtain a hot-rolled aluminum coil; and cold rolling the hot-rolled aluminum coil to obtain a cold-rolled aluminum coil.

According to one embodiment of the present invention, the high temperature forming operation includes heating the cold rolled aluminum coil to 350°C to 500°C.

According to one embodiment of the present invention, before performing the pre-treatment operation, the method further includes storing the formed aluminum sheet for a delay time, wherein the delay time is no more than 24 hours.

According to one embodiment of the present invention, before performing pre-treatment operations on the formed aluminum sheet, the above method further includes rapidly cooling the formed aluminum sheet to room temperature.

According to one embodiment of the present invention, the above method further includes performing a paint baking treatment on the aluminum alloy sheet, wherein the paint baking temperature of the paint baking treatment is 170°C to 205°C, and the paint baking time of the paint baking treatment is 20 minutes to 30 minutes.

According to one embodiment of the present invention, the above-mentioned aluminum alloy sheet has a storage time of no less than three months before being subjected to the paint treatment.

According to another aspect of the present invention, an aluminum alloy sheet is provided, which is produced by the aluminum alloy sheet manufacturing method described in the above aspect, wherein the aluminum alloy sheet has a tensile strength of not less than 550 MPa.

According to another aspect of the present invention, an aluminum component for automobile structure is provided, which comprises the aluminum alloy sheet described in the above aspect.

The aluminum alloy sheet, the manufacturing method thereof and the aluminum components for automobile structures containing the aluminum alloy sheet of the present invention are applied by controlling the composition ratio of the aluminum blank and specific pre-treatment operations to control the type and size of the crystal nucleus, thereby improving the material stability and increasing the storage time of the aluminum alloy sheet.

100:Methods

110,120,130,140: Operation

The following detailed description and accompanying drawings will provide a better understanding of the present disclosure. It should be noted that, as is standard practice in the industry, many features are not drawn to scale. In fact, for the sake of clarity of discussion, the dimensions of many features may be arbitrarily scaled.

[Figure 1] is a flow chart showing a method for manufacturing an aluminum alloy sheet according to some embodiments of the present invention.

As used in the present invention, "around", "about", "approximately" or "substantially" generally means within 20%, within 10%, or within 5% of the value or range described.

Aluminum alloys have become one of the main materials for lightweight electric vehicles and fuel vehicles due to their advantages of light weight, corrosion resistance and high strength. However, aluminum alloy materials have the disadvantage of natural aging hardening when stored at room temperature. However, car factories usually require a long time of transportation and concentration before assembly. The problem of natural aging hardening will lead to a decrease in strength after subsequent baking and painting, which does not meet safety regulations. Therefore, the present invention provides an aluminum alloy sheet, a manufacturing method thereof, and an aluminum component for automobile structure, which controls the composition ratio of the aluminum blank and a specific pre-treatment operation to change the type and size of the crystal nucleus, thereby improving the material stability and the storage time of the aluminum alloy sheet, and improving the problems caused by natural aging hardening.

若錳的含量過高，即上述比例關係小於2.5時，則後續製得之鋁合金片雖然可具有符合需求的強度，但會生成太多的粗大顆粒，反而不耐衝擊且容易破裂。反之，若銅的含量過高，即上述比例關係大於10時，則會因形成過多AlCuMg相，而消耗大量的強化原子，進而造成後續製得之鋁合金片的強度及安全性不足。 Please refer to FIG. 1, which is a flow chart of a method 100 for manufacturing an aluminum alloy sheet according to some embodiments of the present invention. First, an operation 110 is performed to provide an aluminum billet. In some embodiments, the composition of the aluminum billet is consistent with the composition of AA7075 aluminum alloy. Based on 100wt% of the aluminum billet, the aluminum billet comprises about 4.0wt% to about 8.0wt% of zinc, about 1.5wt% to about 3.2wt% of magnesium, about 1.0wt% to about 3.0wt% of copper, not more than about 0.5wt% of silicon, not more than about 0.5wt% of iron, not more than about 0.3wt% of titanium, not more than about 0.5wt% of manganese, not more than about 1.5wt% of impurities, and a balance of aluminum. The copper content in the aluminum billet is higher than the manganese content, and the ratio of copper (Cu) to manganese (Mn) must satisfy the following formula:

If the manganese content is too high, that is, the above ratio is less than 2.5, the aluminum alloy sheet produced subsequently may have the required strength, but too many coarse particles will be generated, which will be less impact-resistant and easy to break. On the contrary, if the copper content is too high, that is, the above ratio is greater than 10, too many AlCuMg phases will be formed, consuming a large amount of strengthening atoms, thereby causing the strength and safety of the aluminum alloy sheet produced subsequently to be insufficient.

Next, operation 120 is performed to perform a rolling operation on the aluminum blank to obtain a cold-rolled aluminum coil. In some embodiments, the rolling operation includes first performing a hot rolling operation on the aluminum blank to obtain a hot-rolled aluminum coil; and performing a cold rolling operation on the hot-rolled aluminum coil to obtain a cold-rolled aluminum coil. In some embodiments, the finished rolled thickness of the cold-rolled aluminum coil is about 0.4 mm to about 4 mm, but the finished rolled thickness still depends on the product requirements, so the present invention is not limited thereto.

In some embodiments, before operation 120, the aluminum blank may be selectively subjected to a two-stage homogenization treatment to eliminate the low melting point phase and further increase the content of the solid solution atoms. Furthermore, the two-stage homogenization treatment can spheroidize the coarse crystal phase, thereby avoiding cracks or fractures during the rolling operation, and also avoiding the occurrence of cracks due to excessive coarse particles during subsequent forming.

In some embodiments, the two-stage homogenization process includes a first stage homogenization process and a second stage homogenization process, wherein the processing temperature of the first stage homogenization process is about 455°C to about 475°C, and the processing time is about 12 hours to about 24 hours; and the processing temperature of the second stage homogenization process is about 475°C to about 490°C, and the processing time is about 12 hours to about 48 hours.

Next, operation 130 is performed to perform a high temperature forming operation on the cold rolled aluminum coil to obtain a formed aluminum sheet. In some embodiments, the high temperature forming operation is to heat the cold rolled aluminum coil to about 350°C to about 500°C. The heating temperature in the aforementioned range is a preferred forming temperature, which can make the resulting formed aluminum sheet have better ductility and not easy to become brittle, so it is not easy to break and can be formed smoothly. In some embodiments, after the aforementioned heating and forming, the formed aluminum sheet can be quickly cooled to room temperature to shorten the forming time. In a specific example, the aforementioned rapid cooling method is to use mold cooling instead of quenching, which can make the formed aluminum sheet less likely to deform.

Then, operation 140 is performed to perform a pre-treatment operation on the formed aluminum sheet to obtain an aluminum alloy sheet. In some embodiments, the formed aluminum sheet can be stored for a delay time before the pre-treatment operation, and the delay time is not more than about 24 hours. Too long a delay time may lead to the generation of undesirable atomic groups, and the pre-treatment operation will lose its effect, thereby making the strength of the obtained aluminum alloy sheet insufficient. It is to be noted that the aforementioned "undesirable atomic groups" refer to the crystal nucleus composition that is not conducive to strength improvement.

In some embodiments, the pre-treatment temperature of the pre-treatment operation is about 100°C to about 300°C. If the pre-treatment temperature is too low (e.g., below about 100°C), although smaller nuclei can be obtained, the precipitation of undesirable atomic groups cannot be effectively suppressed due to insufficient driving force; on the contrary, if the pre-treatment temperature is too high (e.g., above about 300°C), it will directly react into coarse grains, making the obtained aluminum alloy sheet easy to break or deform.

In some embodiments, the pre-treatment time of the pre-treatment operation is about 1 hour to about 3 hours. If the pre-treatment time is too short (e.g., less than about 1 hour), the undesirable atomic groups will continue to precipitate, which may lead to insufficient strength of the obtained aluminum alloy sheet; on the contrary, if the pre-treatment time is too long (e.g., greater than about 3 hours), the crystal nucleus is easy to transform into a strengthening phase, and in subsequent operations, the grain size will continue to coarsen, thereby causing a decrease in strength.

In some embodiments, the aluminum alloy sheet can be selectively subjected to a paint treatment. In one embodiment, the paint temperature of the paint treatment is about 170°C to about 205°C, and the paint time is about 20 minutes to about 30 minutes. It should be understood that the present invention can improve the strength of the aluminum alloy sheet to meet safety standards by paint treatment without performing the known artificial aging heat treatment. In some embodiments, the aluminum alloy sheet produced by method 100 has a tensile strength of not less than 550 MPa. In some embodiments, the aluminum alloy sheet can be stored at room temperature for not less than three months before the paint treatment. In other words, the aluminum alloy sheet produced has good aging stability.

The present invention provides an aluminum component for automobile structure, which comprises an aluminum alloy sheet produced by the above method 100. This aluminum component for automobile structure can have both safety and lightness, and meet the needs of automobile manufacturers.

Several embodiments are used below to illustrate the application of the present invention, but they are not intended to limit the present invention. Those with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention.

Implementation Example 1

Embodiment 1 uses an aluminum billet that complies with the international standard AA7075 and controls the ratio of Cu/2Mn to 4.51. The aluminum billet undergoes a two-stage homogenization treatment, wherein the treatment temperature of the first stage of homogenization treatment is 455°C to 475°C and the treatment time is 12 hours to 24 hours; and the treatment temperature of the second stage of homogenization treatment is 475°C to 490°C and the treatment time is 12 hours to 48 hours. Then, the aluminum billet after the two-stage homogenization treatment is sequentially hot-rolled and cold-rolled to obtain a cold-rolled aluminum coil with a thickness of 0.4mm to 4mm.

Then, the cold-rolled aluminum coil is subjected to high-temperature forming operation, which is heated to 350℃ to 500℃ and then quickly cooled to room temperature to obtain a formed aluminum sheet. After a 20-hour delay, the formed aluminum sheet is subjected to a pre-treatment operation to obtain an aluminum alloy sheet, wherein the pre-treatment temperature of the pre-treatment operation is 125℃ and the pre-treatment time is 1.5 hours. The aluminum alloy sheet is placed at room temperature and after three months of storage time, it is painted by the car factory, wherein the paint temperature of the paint treatment is 170℃ to 205℃ and the paint time is 20 minutes to 30 minutes. Finally, the finished product after the paint treatment is tested for strength and three-point bending crash resistance. The test results are shown in Table 1 below. The crash resistance that meets the standards is indicated by V, and the crash resistance that does not meet the standards is indicated by X.

Example 2 and Comparative Examples 1 to 10

Example 2 and Comparative Examples 1 to 10 use a process similar to Example 1 to manufacture aluminum alloy sheets. The only differences are the Cu/2Mn ratio of the aluminum billet, the delay time before the pretreatment operation, the pretreatment temperature and the pretreatment time of the pretreatment operation. In addition, the heating temperature of the high-temperature forming operation of Comparative Example 8 is lower than 350°C; the heating temperature of the high-temperature forming operation of Comparative Example 9 is higher than 500°C; and Comparative Example 10 does not perform a two-stage homogenization treatment. The rolling operation, storage time and baking varnish treatment conditions of Example 2 and Comparative Examples 1 to 10 are the same as those of Example 1. The process conditions of Example 2 and Comparative Examples 1 to 10 are shown in Table 1 below.

As shown in Table 1, the finished aluminum alloy sheets obtained in Example 1 and Example 2 have a tensile strength greater than 550MPa, and the impact resistance meets the standard. In contrast, the manganese content of Example 1 is too high. Although the strength of the finished product meets the requirements, it is not impact-resistant and easy to break due to the generation of too many coarse grains; the copper content of Example 2 is too high, so too many AlCuMg phases will be formed, thereby consuming a large amount of strengthening atoms, resulting in insufficient strength and safety of the finished product.

In comparison example 3, a too low pre-treatment temperature is used. Although a smaller crystal nucleus can be obtained, the driving force is insufficient, so the precipitation of bad atomic groups cannot be effectively suppressed, resulting in the finished product having too low strength and poor impact resistance. In comparison example 4, a too high pre-treatment temperature is used, so it is easy to directly react into a coarse phase, which also results in the finished product having too low strength and poor impact resistance. In comparison example 5, the pre-treatment time is too short, so bad atomic groups will continue to precipitate, resulting in insufficient strength of the finished product. In comparison example 6, the pre-treatment time is too long, so the crystal nucleus is transformed into a strengthening phase. After the subsequent paint treatment, the grain size is further coarsened, resulting in a decrease in the strength of the finished product.

In Comparative Example 7, extending the delay time before the pre-treatment operation will cause the generation of undesirable atomic groups, and the subsequent pre-treatment operation will lose its effect, so the finished product strength is insufficient. The heating temperature of the high-temperature forming operation in Comparative Example 8 is too low, so the ductility is insufficient and it is easy to break during the forming process; the heating temperature of the high-temperature forming operation in Comparative Example 9 is too high, which will lead to the phenomenon of grain boundary liquefaction and cause the material to become brittle, so it cannot be formed smoothly. In Comparative Example 10, if no homogenization treatment is performed, the coarse crystal phase derived during casting cannot be spheroidized, resulting in serious cracking or fracture problems during the rolling operation. In the subsequent high-temperature forming operation, cracks will frequently occur due to excessive coarse particles, so it cannot be formed smoothly.

According to the above-mentioned embodiments, the aluminum alloy sheet and its manufacturing method provided by the present invention control the specific ratio of copper and manganese in the aluminum blank and perform pre-treatment operations under specific conditions to control the type and size of crystal nuclei, thereby improving the material stability and increasing the storage time of the aluminum alloy sheet. Furthermore, the aluminum alloy sheet produced can have sufficient strength and safety to be used as an aluminum component for automobile structure.

Although the present invention has been disclosed as above with several embodiments, they are not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of the patent application attached hereto.

100:Methods

110,120,130,140: Operation

Claims (10)

A method for manufacturing an aluminum alloy sheet comprises: providing an aluminum billet, wherein based on 100wt% of the aluminum billet, the aluminum billet comprises: 4.0wt% to 8.0wt% of zinc; 1.5wt% to 3.2wt% of magnesium; 1.0wt% to 3.0wt% of copper; not more than 0.5wt% of silicon; not more than 0.5wt% of iron; not more than 0.3wt% of titanium; not more than 0.5wt% of manganese; not more than 1.5wt% of impurities; and a balance of aluminum, and copper (Cu) and manganese (Mn) in the aluminum billet satisfy the following formula:

The aluminum blank is subjected to a rolling operation to obtain a cold-rolled aluminum coil; the cold-rolled aluminum coil is subjected to a high-temperature forming operation to obtain a formed aluminum sheet; and after the high-temperature forming operation, the formed aluminum sheet is subjected to a pre-treatment operation to obtain the aluminum alloy sheet, wherein a pre-treatment temperature of the pre-treatment operation is 100° C. to 300° C., and a pre-treatment time of the pre-treatment operation is 1 hour to 3 hours. The manufacturing method of the aluminum alloy sheet as described in claim 1 further includes: before the rolling operation, the aluminum blank is subjected to a two-stage homogenization treatment, wherein the two-stage homogenization treatment includes: a first stage homogenization treatment, wherein a treatment temperature of the first stage homogenization treatment is 455°C to 475°C, and a treatment time of the first stage homogenization treatment is 12 hours to 24 hours; and a second stage homogenization treatment, wherein a treatment temperature of the second stage homogenization treatment is 475°C to 490°C, and a treatment time of the second stage homogenization treatment is 12 hours to 48 hours. The manufacturing method of the aluminum alloy sheet as described in claim 1, wherein the rolling operation includes: performing a hot rolling operation on the aluminum blank to obtain a hot-rolled aluminum coil; and performing a cold rolling operation on the hot-rolled aluminum coil to obtain the cold-rolled aluminum coil. The method for manufacturing an aluminum alloy sheet as described in claim 1, wherein the high temperature forming operation includes heating the cold rolled aluminum coil to 350°C to 500°C. The method for manufacturing an aluminum alloy sheet as described in claim 4, wherein before the pre-treatment operation is performed on the formed aluminum sheet, it further comprises: after the step of heating the cold-rolled aluminum roll, the formed aluminum sheet is rapidly cooled to room temperature. The method for manufacturing an aluminum alloy sheet as described in claim 1, wherein before performing the pre-treatment operation, it further comprises: storing the formed aluminum sheet for a delay time, wherein the delay time is no more than 24 hours. The manufacturing method of the aluminum alloy sheet as described in claim 1 further comprises: performing a paint baking treatment on the aluminum alloy sheet, wherein a paint baking temperature of the paint baking treatment is 170°C to 205°C, and a paint baking time of the paint baking treatment is 20 minutes to 30 minutes. The manufacturing method of the aluminum alloy sheet as described in claim 7, wherein the aluminum alloy sheet has a storage time of not less than three months before the baking paint treatment. An aluminum alloy sheet is produced by the method for producing an aluminum alloy sheet as described in any one of claims 1 to 8, wherein the aluminum alloy sheet has a tensile strength of not less than 550 MPa. An aluminum component for automobile structure, comprising the aluminum alloy sheet described in claim 9.

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