CN102732760B - Aluminum alloy plate for automobile bodies - Google Patents

Abstract

The invention belongs to the technical field of aluminium alloy plates, and specifically provides an aluminum alloy plate for automobile bodies. An aluminum alloy comprises the following components in percentage by mass: 0.5-0.8 wt. % of Si, 0.6-1.2 wt. % of Mg, 0.6-1.1 wt. % of Cu, 0.15-0.3 wt. % of Mn, and the balance being Al and trace impurities, wherein the trace impurities are composed of Fe (0.3 wt. %), Zn (0.2 wt. %), Ti (0.1 wt. %) and Cr (0.2 wt. %); and the mass ratio of Mg to Si is 1-2; and after being subjected to solution hardening treatment, the aluminum alloy is subjected to heat treatment in 20 minutes, wherein the heat treatment temperature is 100-150 DEG C, and the heat treatment time is 10 minutes-2 hours. The aluminum alloy plate (subjected to baking varnish coating) for automobile bodies is high in strength and stable in performance under the condition of thermal exposure; meanwhile, the aluminum alloy plate for automobile bodies, before being subjected to baking varnish coating, also has a good machining forming performance.

Description

A kind of aluminum alloy sheet material for vehicle body

technical field

The invention belongs to the field of aluminum alloy plates and relates to a novel aluminum alloy plate for automobile bodies with good stamping formability and baking hardening performance.

technical background

Due to the key role of lightweight in energy saving and emission reduction of transportation vehicles, lightweight materials have been widely used in the automotive field in recent years. Compared with traditional steel, aluminum alloy has low density, excellent corrosion resistance and easy recycling, so the application of aluminum alloy in automobiles is increasing year by year. At present, the aluminum alloy sheets used for stamping and forming of automobile bodies are mainly three grades of aluminum alloys: AA6016, AA6022 and AA6111. These alloys are mainly formed by adding magnesium and silicon to aluminum. Copper is also added to the AA6111 alloy to increase the strength of the alloy. Another important feature is that the content ratio of magnesium to silicon in these alloys is less than 1, or even less than 0.5. For example, the domestic invention patent with the publication number of CN 102031431A "6000 series high-performance aluminum alloy plate for automobile cover parts and its manufacturing method", and the invention patent with the authorized patent number of ZL200910043311.5 "improve the processing and forming of 6××× aluminum alloy sheet Heat treatment method for hardening and baking hardenability", authorized patent No. ZL 200610046027.X invention patent "preheating process for improving formability and bake hardenability of 6111 aluminum alloy automotive sheet" and patent No. WO published in 2000 00/70115 and Patent No. WO 2005/071127 published in 2005 and other invention patents related to the heat treatment of automobile body panels, the content of silicon in the implemented aluminum alloys is much greater than that of magnesium. The above alloy composition design is related to the manufacturing process of the aluminum alloy body. Generally, aluminum alloys are cast, homogenized, hot-rolled, annealed and cold-rolled in the factory to prepare thin sheets, and then preheated (T4P) and then coiled and transported to the automobile factory. These panels are stamped and painted in the car factory, and then transferred to the oven for baking. The above production process requires that the aluminum alloy thin plate is easy to stamp and the strength is greatly improved during the baking process to obtain good anti-dent performance. Generally, the paint temperature is between 160-190 degrees and the time is within 30 minutes. Therefore, this requires that the selected aluminum alloy can be rapidly strengthened during the baking process, and the 6××× aluminum alloy with excess silicon content just has this characteristic. As a typical precipitation-strengthened aluminum alloy, the 6××× aluminum alloy with excess silicon content (magnesium-silicon content ratio less than 1) has faster precipitation kinetics and can form a large number of monoclinic GP regions in a short time and β" precursor phase. After solid solution and quenching treatment, this type of alloy is stabilized. The strength of the alloy increases slightly after being placed at room temperature for more than two weeks, and it can still be strengthened rapidly during the baking process. Aluminum alloys manufactured by different heat treatment processes Board, the performance of the advantages and disadvantages vary greatly.

The development of the automobile industry now puts forward higher requirements for aluminum alloy sheets for body, especially compared with the new generation of steel, aluminum alloy sheets have more disadvantages. First of all, the customer's emphasis on collision safety requires the car body to have higher strength, and the strength of the currently used aluminum materials is mostly lower than 250Mpa or lower after baking paint treatment. Secondly, although the high-silicon content 6××× aluminum alloys currently used have faster precipitation kinetics, the high silicon content is also easy to cause these alloys to be exposed to heat during use (especially radiators, water tanks, and exhausts). The strengthening phase inside the pipe) is easy to coarsen and the strength is reduced. In addition, alloys with high silicon content are prone to precipitate larger silicon particles at the grain boundary under heat exposure, resulting in a decrease in corrosion resistance and fracture toughness. These factors will reduce service safety and life coefficient. Based on the above analysis, it is very important to develop a new type of aluminum alloy that has the same rapid baking paint strengthening performance but higher strength after baking paint, better anti-sinking performance, and more stable under heat exposure. In this way, we can not only obtain a new aluminum alloy body plate for automobile factories to choose, but also enhance the competitiveness of lightweight aluminum alloy plate and traditional steel, and promote the wide application of aluminum alloy in automobile body. Moreover, cars made of this new material are more advantageous in regions with higher ambient temperatures (such as the Middle East).

Contents of the invention

In view of the above problems, the present invention provides an aluminum alloy plate for car body. The plate prepared by using this type of aluminum alloy has higher strength after baking paint and stable performance under heat exposure, and at the same time, it still has good processing and forming performance before baking paint .

In order to realize the purpose of the foregoing invention, the present invention adopts the following technical solutions:

An aluminum alloy plate for a vehicle body, the composition and mass percentage of the aluminum alloy are: Si0.5~0.8wt.%, Mg0.6~1.2wt.%, Cu0.6~1.1wt.%, Mn0. 15~0.3wt.%, the rest is Al and trace impurities, the composition of the trace impurities is: Fe<0.3wt.%, Zn<0.2wt.%, Ti<0.1wt.%, Cr<0.2wt.%; And the mass ratio of Mg and Si is between 1 and 2;

After the above-mentioned aluminum alloy is solution quenched, heat treatment is carried out within 20 minutes, the heat treatment temperature is 100° C. to 150° C., and the heat treatment time is 10 minutes to 2 hours.

The total mass percentage of Mg, Si and Cu in the aluminum alloy is preferably lower than 2.5wt.%.

The mass ratio of Si and Cu to Mg in the aluminum alloy [(Si+0.5×Cu)/Mg] is preferably greater than 0.8.

The heat treatment temperature is preferably 120° C. to 150° C., and the heat treatment time is preferably 5 minutes to 30 minutes.

The present invention is further explained and illustrated below:

The technical solution of the above solution quenching treatment means that the alloy is heated to 560°C and kept at a constant temperature for 10min-60min, preferably 30min, so that the excess phase is fully dissolved into the solid solution and then transferred to water for rapid cooling to obtain a supersaturated solid solution. (The solution quenching process is a very common prior art, and the 6xxx series aluminum alloys are the same).

Magnesium, silicon and copper are the main alloying elements added to 6××× series aluminum alloys for automobile body panels. The age hardening characteristics of this type of alloy are related to the segregation and precipitation of these elements during heat treatment. For copper-free alloys, alloys with a high magnesium/silicon content ratio do not have rapid age hardening properties, so they cannot be used as automotive body aluminum sheet materials for paint reinforcement. The strength of the paint is increased after the addition of copper elements, but copper, like silicon elements, tends to segregate at the grain boundaries during heat treatment, resulting in a decrease in stamping formability and corrosion resistance. The inventor systematically studied the effect of copper on the precipitation of magnesium and silicon during the aging process, and designed the above alloy composition. Within the above alloy composition range, the added alloy elements are mainly precipitated in the grain, and the tendency of grain boundary segregation is significantly reduced. In addition, the above-mentioned alloys will form a large number of lath-shaped Q" phases under long-term heat exposure during the use of automobile body panels.

What's more important is that the above-mentioned alloy has undergone a certain stabilization treatment, and it still has an obvious baking paint strengthening effect after being placed at room temperature for more than two months. At present, the stabilization treatment of aluminum alloys for automobile body panels is mainly divided into two categories: one is to perform low-temperature long-term treatment immediately after quenching (temperature 60-80℃ for 5-20 hours), called pre-aging treatment or T4P The other type is not to treat immediately after quenching, but to treat it at a higher temperature for a short time after natural aging at room temperature for a certain period of time (the natural residence time is from a few minutes to two weeks and then treated at 180-300°C for 1 minutes to 20 minutes), known as regression treatment or T4R. The key to T4P treatment is to obtain very small nucleation sites in the GP region that are stable at room temperature, and these nucleation sites can grow rapidly during the baking process. T4R is to make the clusters formed by quenching vacancies and solute atoms during the natural aging process redissolve into the aluminum matrix after high temperature and short-term treatment. At this time, the structure is more stable than the supersaturated solid solution vacancy concentration after quenching. These two methods have their own advantages and disadvantages. The inventor systematically studied the stability and rapid growth effect of the precipitated phase at various temperatures in the invented aluminum alloy sheet, and proposed a heat treatment method suitable for the above-mentioned aluminum alloy sheet for automobile body (heat treatment of the present invention) method). It is possible to improve the formability, bake hardening properties and retention time of the above-mentioned aluminum alloy for automobile bodies.

Compared with the prior art, the present invention has the advantages of:

1. By optimizing the distribution ratio of alloy components, the present invention can effectively control the segregation of alloy elements at grain boundaries, and at the same time, can precipitate strengthening phases that are not easy to coarsen under high-temperature service environments, which not only improves the processing formability of aluminum alloys And the strength after baking, and ensure the stability and corrosion resistance of its performance during use.

2. The heat treatment method of the present invention can be carried out in the existing pre-aging equipment for automobile body panels, without adding new heat treatment equipment; the dwell time between different heat treatments is long, which is convenient for actual operation in accordance with the actual situation of the factory, and has Wide temperature window, easy to ensure stable product quality, can save energy and equipment investment.

3. The aluminum alloy plate for car body provided by the present invention has excellent formability and bake hardening properties, and the plate has high strength after baking paint, and excellent heat exposure stability and corrosion resistance. The invention can improve the tendency of cracking during stamping of the body of the automobile factory, and improve the machining accuracy and surface quality. More importantly, the baking hardening performance of the aluminum alloy sheet provided by the invention can last for several months, and the strength of the alloy sheet after baking paint can be kept for a long time under heat exposure, and the service safety and service life are improved.

4. The aluminum alloy sheet provided by the present invention can enhance the comprehensive competitiveness of the aluminum alloy sheet relative to steel, promote the replacement of the steel sheet by the aluminum alloy sheet and reduce the weight of the car body, which is beneficial to energy saving and pollution reduction. Since the present invention adopts an alloy with a mass ratio of magnesium to silicon greater than or equal to 1, compared with the existing alloy plate with a mass ratio of magnesium to silicon less than 1, the comprehensive performance is better, the product features are more distinct, and it is beneficial to develop the product market.

Description of drawings

Fig. 1 is the stress-strain curve of embodiment 2 sample before and after simulating baking paint in 2 weeks;

Fig. 2 is the stress-strain curve of embodiment 2 sample before and after simulating baking paint in 1 week;

Fig. 3 is the stress-strain curve of embodiment 6 sample before and after simulating baking paint in 2 weeks;

Fig. 4 is the stress-strain curve before and after simulating baking paint of embodiment 6 samples in 1 month;

Fig. 5 is the stress-strain curve of comparative example 2 sample before and after simulating baking paint in 2 weeks;

Fig. 6 is the stress-strain curve of the sample of Comparative Example 2 before and after simulating paint baking in one month.

Detailed ways

The method of the present invention is further explained and illustrated with data below in conjunction with examples, but the present invention is not limited to these examples. The room temperature in the present invention is generally between 0°C and 30°C.

The sample used in the embodiment is divided into A and B, and the chemical composition of A (magnesium to silicon mass ratio is 1) is: Mg 0.75wt.%, Si 0.75wt.%, Cu 0.8wt.%, Mn 0.15wt.%, Cr 0.15 wt.%, Ti 0.12wt.%, Fe0.20wt.%, the rest is aluminum; the chemical composition of B (mass ratio of magnesium to silicon is 2): Mg1.0wt.%, Si0.5wt.%, Cu0.8wt. %, Mn0.15wt.%, Cr0.15wt.%, Ti0.12wt.%, Fe0.20wt.%, the rest is aluminum. The chemical composition of Comparative Example C (magnesium to silicon mass ratio is 0.5, aluminum alloy for traditional body panels) is: Mg0.5wt.%, Si1.0wt.%, Cu0.8wt.%, Mn0.15wt.%, Cr0. 15wt.%, Ti0.12wt.%, Fe0.20wt.%, the rest is aluminum. The alloy hardness test was carried out on the HXD-1000T Vickers hardness testing machine, the experimental load was 4.9N, and the duration was 10s. Tensile test adopts standard: GB228-87. The cupping value is measured on the GBW-60Z cupping machine produced by Jinan Huaxing Company, and the GB/T4156-2007 standard is used to evaluate the stamping performance. There is no simulated processing strain before simulating paint baking (in fact, if processing strain is added, the strength after baking paint is usually 8-10HV higher (about 30Mpa).

Based on the above considerations, the following embodiments have been designed:

Comparative Example 1

C aluminum alloy ingots were homogenized in a circulating air resistance furnace at 550 °C for 24 h, then cut and face milled, hot rolled, intermittently annealed, and finally cold rolled into 1 mm thick sheets. After the thin plate is quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it is immediately treated in an oil bath furnace at 120°C×0.5h to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Comparative Example 2

C aluminum alloy ingots were homogenized in a circulating air resistance furnace at 550 °C for 24 h, then cut and face milled, hot rolled, intermittently annealed, and finally cold rolled into 1 mm thick sheets. After the thin plate is quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it is immediately treated in an oil bath furnace at 150°C×10min to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 1

A aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, then cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate is quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it is immediately treated in an oil bath furnace at 120°C×0.5h to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 2

A aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, then cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate was quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it was immediately treated at 120°C×1h in an oil bath furnace to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, and 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 3

A aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, then cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate is quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it is immediately treated in an oil bath furnace at 150°C×20min to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, and 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 4

A aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, then cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate was quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it was immediately treated in an oil bath furnace at 150°C×30min to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, and 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 5

After the B aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, it is cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate is quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it is immediately treated in an oil bath furnace at 120°C×0.5h to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 6

After the B aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, it is cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate was quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it was immediately treated at 120°C×1h in an oil bath furnace to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, and 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 7

After the B aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, it is cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate is quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it is immediately treated in an oil bath furnace at 150°C×20min to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, and 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 8

After the B aluminum alloy ingot is homogenized in a circulating air resistance furnace at 550°C for 24h, it is cut and face milled, hot rolled, intermittently annealed and finally cold rolled into a 1mm thick sheet. After the thin plate was quenched by solution treatment at 560°C×30min in an air circulation resistance furnace, it was immediately treated in an oil bath furnace at 150°C×30min to obtain an aluminum alloy plate; and then parked at room temperature for 1 day, 2 weeks, and 1 Hardness test and tensile test were carried out after 1 month and 2 months. The simulated paint baking is carried out in an oil bath furnace at a temperature of 180°C×30min. After the paint is baked, the hardness test and tensile test are carried out.

Example 9

In order to test the thermal cycle stability of the alloys A and B of the embodiments relative to the ratio C alloy, we respectively put the samples after the simulated baking paint of the comparative example 1, embodiment 1 and embodiment 5 in an oil bath furnace with a temperature of 180°C for a time of 1 week, 2 weeks, 3 weeks and 4 weeks heat treatment, and the microhardness of these samples were tested.

Tables 1-3 are the microhardness test values of each embodiment before and after simulating paint baking. The above examples have been repeated more than 3 times, so the microhardness values are the average value of a large number of experiments.

Table 1 embodiment 1-4 supply state and the hardness value after simulated baking paint treatment

Table 2 embodiment 5-8 delivery state and the hardness value after simulated baking paint treatment

Table 3 Comparative Example 1 and Examples 1 and 5 The cupping value (mm) of the sample delivery state

Table 4 takes a typical case for the measurement results of the tensile test

Table 5 Example 9 Hardness value after six kinds of samples thermal cycle

Compared with comparative examples, the results of Table 1-Table 5 show that the basic mechanical properties of the aluminum sheet for automobile body provided by the present invention are equivalent to those of traditional alloys, but the performance is more stable when stored at room temperature, and the baking paint performance lasts longer. The aluminum alloy sheet material with high magnesium-silicon ratio provided by the invention is easy to stamp before baking, and the strength after baking is also relatively large. Through the simulated heat exposure test, we found that the hardness value of the alloy plate of the present invention is much higher than that of the comparative example (traditional alloy) after a long time, which proves that the alloy plate provided by the present invention has higher service safety performance and longer service life life.

It can be clearly seen from Tables 1-5 and accompanying drawings 1-6 that the aluminum alloy and the heat treatment method of the present invention can prepare an aluminum alloy sheet for automobile bodies with excellent comprehensive properties, the sheet has excellent formability and bake hardening properties, and the strength after baking High, excellent thermal exposure stability and corrosion resistance.

Claims (2)

1. aluminium alloys for auto body sheet material, it is characterized in that, the composition of described aluminium alloy and mass percentage content thereof are: Si0.5～0.8wt.%, Mg0.6～1.2wt.%, Cu0.6～1.1wt.%, Mn0.15～0.3wt.%, all the other are Al and trace impurity, the consisting of of described trace impurity: Fe＜0.3wt.%, Zn＜0.2wt.%, Ti＜0.1wt.%, Cr＜0.2wt.%; And the mass ratio of Mg and Si is between 1～2, and the total percentage composition of quality that the mass ratio of Mg and Si is not equal to 1, Mg, Si and Cu is lower than 2.5wt.%, Si and Cu with respect to the mass ratio of Mg [(Si+0.5 * Cu)/Mg] greater than 0.8;

Heat-treated in 20 minutes after above-mentioned alloyed aluminum solution hardening is processed, thermal treatment temp is 100 ℃～150 ℃, heat treatment time 10 minutes～2 hours.

2. a kind of aluminium alloys for auto body sheet material according to claim 1, is characterized in that, described thermal treatment temp is 120 ℃～150 ℃, heat treatment time 5 minutes～30 minutes.

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