CN113201672B - A kind of Al-Mg-Si-Cu-Zn alloy with high baking paint hardening increment and preparation method thereof - Google Patents

Abstract

An Al-Mg-Si-Cu-Zn alloy with high baking varnish hardening increment and a preparation method thereof, belonging to the field of aluminum alloy and preparation thereof. The alloy comprises the following chemical components, by mass, 1.2-1.6 wt% of Mg, 1.2-1.6 wt% of Si, 0.1-0.3 wt% of Cu, 2.0-4.0 wt% of Zn, 0.1-0.5 wt% of Fe, 0.5-0.8 wt% of Mn, less than or equal to 0.03 wt% of Ti, less than or equal to 0.04 wt% of Ni, and the balance of Al. The main elements of the alloy exceed the range of the traditional alloy system, and further, after the pre-aging process is optimized, the deterioration effect of natural aging is effectively inhibited, the hardening increment of baking finish is greatly improved, and the hardening increment of the alloy baking finish reaches 180MPa. Through high baking varnish hardening increment, the yield strength of the alloy after baking varnish is improved, so that the dent resistance is enhanced, meanwhile, the T4P alloy has good plasticity, the elongation of the alloy in the T4P state reaches 25%, and the strength is greatly improved on the basis of high formability.

Description

A kind of Al-Mg-Si-Cu-Zn alloy with high baking paint hardening increment and preparation method thereof

technical field

The invention belongs to the field of aluminum alloys and preparations thereof, and relates to an Al-Mg-Si-Cu-Zn alloy with high hardening increment of baking paint for automobiles and a preparation method.

Background technique

With people's emphasis on energy saving, vehicle lightweighting has become a global trend. Aluminum alloys have received extensive attention as an important lightweight material. In particular, the 6xxx (Al-Mg-Si) alloy has excellent formability (to meet the requirements of stamping forming) before varnishing (T4P state), and during the varnishing process, the yield strength increases significantly, which meets the resistance of the subsequent use process. It is widely used due to the requirements of indentation. However, the low temperature (160～185℃) and short time (20～30min) of the paint baking process cannot fully exert the potential paint hardening ability, resulting in the yield strength of the paint baking hardened alloy is much lower than that of the peak aging alloy. 6xxx (Al-Mg-Si) alloys are currently widely used in the automotive field are 6016 and 6111 alloys, but after the simulated baking process of 185 ° C for 20 minutes, the baking hardening increments of these two alloys are 85 and 90 MPa, respectively. The yield strength of the two alloys in the paint state is only about 300MPa, which is much lower than that of steel. Therefore, increasing the hardening increment of baking paint has become a research hotspot.

Alloys must be transported and stored for a period of time before use, and natural aging during this period will significantly reduce the bake hardening increment. This is because the clusters formed at room temperature after solution treatment will not act as the core of β″ phase precipitation during the paint baking process, but will dissolve back and waste paint baking time. In order to weaken the deterioration effect of natural aging, the researchers The pre-aging process was introduced and a lot of research was carried out, and it was concluded that adding the pre-aging process immediately after solution quenching can effectively suppress the deterioration effect of natural aging and increase the hardening increment of baking paint.

In addition, the study found that the addition of Cu can improve the aging response speed of the alloy, and the addition of Zn can increase the hardening increment of the alloy's baking paint, so the Al-Mg-Si-Cu-Zn alloy system was developed. However, due to the serious influence of the relative plasticity of the grid-like micron-scale precipitations, solution treatment is often carried out in the Al single-phase region to achieve the purpose of all the micron-scale precipitations resolubilizing, but this also limits the content of the alloy, Mg and Si. The element content is strictly limited within 1.2wt%. Even after baking paint treatment, the yield strength of the alloy still does not meet the application requirements, and it is difficult to meet the requirements of dent resistance during use. The hardening increment of baking paint still needs to be further improved. And the heat treatment process solves the serious influence of the relative plasticity of the grid-like micron-scale precipitation, and is expected to greatly improve the hardening increment and yield strength of the alloy baking paint on the basis of maintaining the high formability of the alloy to meet the application requirements. However, this strategy is far from fully understood, and related work is rarely reported.

SUMMARY OF THE INVENTION

The invention provides an improved 6xxx (Al-Mg-Si) alloy material. On the basis of Al-Mg-Si, Cu and Zn are added to form an Al-Mg-Si-Cu-Zn alloy system. Based on the concept of high alloying, the The content of main elements (Mg, Si and Zn) is beyond the range of 6xxx alloys. The deformation and heat treatment process are used to improve the shape and size of micron-scale precipitates, solve their deterioration effect on plasticity, and simultaneously form multi-scale particles (micron and nanoscale) ), through the coarse particles to promote the nucleation of fine particles to hinder the grain growth principle to refine the grains. Compared with the standard 6016 and 6111 alloys, the mechanical properties of the alloys are greatly improved on the premise that the forming properties of the alloys are basically unchanged, thereby solving the problems of insufficient paint hardening and dent resistance of the 6xxx alloys.

The composition range of the alloy of the present invention is Mg: 1.2-1.6 wt%, Si: 1.2-1.6 wt%, Cu: 0.1-0.3 wt%, Zn: 2.0-4.0 wt%, Fe: 0.1-0.5 wt% , Mn: 0.5～0.8wt%, Ti≤0.03wt%, Ni≤0.04wt%, and the rest are Al.

The preferred composition range of the alloy of the present invention is Mg: 1.2-1.4wt%, Si: 1.4-1.6wt%, Cu: 0.1-0.2wt%, Zn: 2.0-3.0wt%, Fe: 0.2-0.4wt% %, Mn: 0.5～0.6wt%, Ti: 0.01～0.02wt%, Ni: 0.02～0.03wt%, and the rest are Al.

The preparation process of the alloy of the invention is as follows: the Al-Mg-Si-Cu-Zn alloy is smelted according to the above alloy composition range, and then the obtained ingot is subjected to two-stage homogenization treatment, and then hot rolling, cooling and annealing treatment are carried out, The annealed cold-rolled sheet is first subjected to solution treatment and water quenching, and then pre-aging treatment is carried out immediately, that is, the cold-rolled sheet is placed in an isothermal aging furnace at 80 to 185 °C for 4 min to 15 hours to obtain Al with high baking paint hardening increment -Mg-Si-Cu-Zn alloy.

The two-stage homogenization treatment is to heat up to 510-520°C for 6-10 hours at a rate of 20-40°C/h, and then heat up to 540-560°C for 15-20h at a rate of 20-40°C/h. .

The hot rolling, cold rolling and annealing treatment process is that the hot rolling rolling temperature is 520-540 ° C, the total deformation is 90-93%, and then cold rolling with a total deformation of 40-60% is performed, and after cold rolling, 380 is performed. Intermediate annealing at ~420°C for 0.5~1.5h, and after annealing, the sheet is cold rolled with a total deformation of 50~70%.

The solution treatment is to carry out the cold-rolled sheet in a salt bath furnace at 540-560° C. for 1-10 minutes.

The preferred pre-aging process is 140-180°C for 4-8 minutes.

The baking paint hardening increment of the prepared Al-Mg-Si-Cu-Zn alloy is 130-180Mpa. The elongation of T4P state after 14 days of natural placement is 23-26%, and the 14-day natural placement and aging treatment (simulated baking paint) The post-yield strength is 330-370MPa, and the tensile strength is 380-410MPa.

The invention adds Cu and Zn on the basis of 6xxx (Al-Mg-Si) alloy, increases the content of main elements, optimizes the pre-aging process, effectively suppresses the deterioration effect of natural aging, and greatly improves the hardening increment of baking paint. Through the high baking paint hardening increment, the yield strength of the alloy after baking paint is improved, thereby enhancing the dent resistance. At the same time, the T4P alloy has good plasticity. But the hardening increment of baking paint is as high as 180Mpa, which is more than twice that of 6016 and 6111 alloys. Therefore, the alloy of the present invention not only has the advantage of high plasticity of 6xxx (Al-Mg-Si) alloy and can be integrally stamped, but also greatly improves the hardening increment of baking paint, thereby solving the problem of excessive yield strength of 6xxx (Al-Mg-Si) alloy. Low can not meet the problem of dent resistance. The alloy of the invention has great industrial application value and can be applied to the outer panel of automobiles.

Description of drawings

Fig.1 Natural age hardening curves of 5# alloy treated with different pre-aging processes.

Fig. 2 Schematic diagram of grain size of 5# alloy in solution quenched state.

Detailed ways

The present invention is further supplemented and explained below in conjunction with specific implementation cases.

The raw materials used in the present invention are 99.9wt% pure metals (Al, Mg and Zn) and master alloys (Al-20wt%Si, Al-50wt%Cu, Al-10wt%Mn, and Al-20wt%Fe). The specific chemical composition of the implemented alloy is shown in Table 1. 1# is commercial alloy 6016, 2# is commercial alloy 6111, 1# and 2# alloys are reference alloys; 3#, 4#, 5#, 6#, 7# are alloy compositions designed by the present invention.

Table 1 The specific chemical composition of the alloy (mass percentage, wt%)

Mg Si Cu Zn Fe Mn Ti Ni Al 1# 0.6 1.1 0.2 0.2 0.4 0.2 0.02 / margin 2# 0.9 0.7 0.6 0.15 0.4 0.5 0.02 / margin 3# 1.2 1.2 0.2 3.0 0.4 0.5 0.02 0.03 margin 4# 1.2 1.4 0.2 3.0 0.4 0.5 0.02 0.03 margin 5# 1.2 1.6 0.2 3.0 0.4 0.5 0.02 0.03 margin 6# 1.4 1.2 0.2 3.0 0.4 0.5 0.02 0.03 margin 7# 1.6 1.2 0.2 3.0 0.4 0.5 0.02 0.03 margin

The above-mentioned Al-Mg-Si-Cu-Zn alloy is smelted; the obtained ingot is subjected to two-stage homogenization treatment, that is, the temperature is raised to 520 °C for 8 hours at a speed of 30 °C/h, and then the temperature is 30 °C/h. The temperature is raised to 550℃ for 16h; after homogenization, hot rolling is carried out, the rolling temperature is 540℃, and the total deformation is 90-93%; after that, cold rolling with a total deformation of 50% is carried out; Annealing; after annealing, the sheet is cold rolled with a total deformation of 67%. Finally, a 1mm cold-rolled sheet of 1#-7# alloy is obtained.

Comparative Example 1

The 1mm cold-rolled sheet of the 1# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 80°C/12h. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Comparative Example 2

The 1mm cold-rolled sheet of the 2# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 80°C/12h. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Comparative Example 3

The 1mm cold-rolled sheet of the 5# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. It was then left at room temperature for 14 days (T4 state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 1

The 1mm cold-rolled sheet of the 5# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 80°C/12h. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 2

The 1mm cold-rolled sheet of the 5# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 140°C/0.5h. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 3

The 1mm cold-rolled sheet of the 5# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 160°C/6min. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 4

The 1mm cold-rolled sheet of the 5# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 185°C/6min. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 5

The 1mm cold-rolled sheet of the 3# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 160°C/6min. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation in the T4P state and the increase in bake hardening are obtained.

Example 6

The 1mm cold-rolled sheet of the 4# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550° C. for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 160°C/6min. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 7

The 1mm cold-rolled sheet of the 6# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 160°C/6min. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Example 8

The 1mm cold-rolled sheet of the 7# alloy obtained by the above method was sampled, put into a salt bath furnace for solution treatment at 550°C for 8 minutes, and then rapidly water quenched. The quenched samples were placed in an aging furnace for pre-aging treatment at 160°C/6min. It was then left at room temperature for 14 days (T4P state). One group was directly stretched; the other group was pre-stretched by 2% (simulating stamping forming), and then subjected to aging treatment at 185° C./20min (simulating baking paint treatment). Thus, the elongation of the T4P state and the increase in bake hardening are obtained.

Table 2 Mechanical properties of alloy samples with different compositions and states before and after treatment at 185℃/20min (simulated baking paint)

It can be seen from Table 2 that on the basis of the 1# (6016) and 2# (6111) comparative alloys, based on the concept of high alloying, the content of Mg, Si and Zn elements is increased to exceed the element range of traditional 6xxx series aluminum alloys, from baking paint. In terms of post-strength and paint-hardening increments, the 3#-7# alloys are significantly higher than those of the comparative alloys; and the elongation in the T4P state does not decrease, even higher than that of the 2# (6111) alloy. Comparing Comparative Example 1 and Examples 1 to 4, it can be seen that the pre-aging process can effectively suppress the deterioration effect of natural aging and significantly increase the hardening increment of the baking paint. In particular, the baking paint hardening increase of Example 5 is more than twice that of Comparative Example 1 and Comparative Example 2, and the T4P state elongation is the same as that of Comparative Example 1 and higher than that of Comparative Example 2. It can be seen from Figure 1 that the pre-aging process at 160°C/6min has the most obvious inhibition on the deterioration effect of natural aging. Therefore, the other alloy embodiments adopt this process. It can be seen from Figure 2 that the grain size of the alloy is small, and the average grain size is only 12um. This is due to the multi-scale (nano-micron) precipitates in the alloy, which promote nucleation through coarse particles, and the fine example hinders the recrystallization growth effect. The grains are refined and the grains are strengthened.

Although the embodiments of the present invention have been presented and described, it should be noted that various changes and modifications to these embodiments can be made by those skilled in the art without departing from the principles and concepts of the present invention , alternatives and modifications, the scope of the invention is defined by the appended claims and equivalents.

Claims (8)

1. The Al-Mg-Si-Cu-Zn alloy with high baking varnish hardening increment is characterized in that the alloy comprises 1.2-1.6 wt% of Mg, 1.2-1.6 wt% of Si, 0.1-0.3 wt% of Cu, 3.0 wt% of Zn, 0.4 wt% of Fe, 0.5-0.8 wt% of Mn, less than or equal to 0.03 wt% of Ti, less than or equal to 0.04 wt% of Ni and the balance of Al in percentage by weight;

the preparation method of the Al-Mg-Si-Cu-Zn alloy with the high baking varnish hardening increment comprises the steps of smelting the Al-Mg-Si-Cu-Zn alloy, carrying out two-stage homogenization treatment on the obtained cast ingot, then carrying out hot rolling, cold rolling and annealing treatment, carrying out solution treatment and water quenching on the annealed cold-rolled sheet, and then immediately carrying out pre-aging treatment, namely putting the cold-rolled sheet into an isothermal aging furnace at the temperature of 80-185 ℃ for heat preservation for 4 min-15 h to prepare the Al-Mg-Si-Cu-Zn alloy with the high baking varnish hardening increment.

2. The Al-Mg-Si-Cu-Zn alloy with high baking varnish hardening increment as recited in claim 1, wherein the alloy comprises, in weight percent, 1.2 to 1.4 wt% of Mg, 1.4 to 1.6 wt% of Si, 0.1 to 0.2 wt% of Cu, 3.0 wt% of Zn, 0.4 wt% of Fe, 0.5 to 0.6 wt% of Mn, 0.01 to 0.02 wt% of Ti, 0.02 to 0.03 wt% of Ni, and the balance of Al.

3. The preparation method of the Al-Mg-Si-Cu-Zn alloy with the high baking finish hardening increment as recited in claim 1 or 2, characterized in that the Al-Mg-Si-Cu-Zn alloy is smelted, the obtained cast ingot is subjected to two-stage homogenization treatment, then hot rolling, cold rolling and annealing treatment are carried out, the annealed cold-rolled plate is subjected to solution treatment and water quenching, and then is subjected to pre-aging treatment immediately, namely the cold-rolled plate is placed into an isothermal aging furnace at 80-185 ℃ for heat preservation for 4 min-15 h, so that the Al-Mg-Si-Cu-Zn alloy with the high baking finish hardening increment is prepared.

4. The method for preparing the Al-Mg-Si-Cu-Zn alloy with high baking varnish hardening increment according to claim 3, wherein the two-stage homogenization treatment comprises the steps of heating to 510-520 ℃ at a speed of 20-40 ℃/h and preserving heat for 6-10 h, and then heating to 540-560 ℃ at a speed of 20-40 ℃/h and preserving heat for 15-20 h.

5. The method for preparing Al-Mg-Si-Cu-Zn alloy with high baking finish hardening increment according to claim 3, wherein the hot rolling, the cold rolling and the annealing treatment process comprise the steps of carrying out cold rolling at the hot rolling start rolling temperature of 520-540 ℃ and the total deformation of 90-93%, then carrying out cold rolling with the total deformation of 40-60%, carrying out intermediate annealing at the temperature of 380-420 ℃ for 0.5-1.5 h, and carrying out cold rolling with the total deformation of 50-70% after annealing.

6. The method for preparing the Al-Mg-Si-Cu-Zn alloy with high baking finish hardening increment according to claim 3, wherein the solution treatment is carried out on the cold-rolled sheet in a salt bath furnace at 540-560 ℃ for 1-10 min.

7. The method for preparing the Al-Mg-Si-Cu-Zn alloy with high baking finish hardening increment according to claim 3, wherein the pre-aging process is carried out at 140-180 ℃ for 4-8 min.

8. The method for preparing the Al-Mg-Si-Cu-Zn alloy with high baking finish hardening increment according to claim 3, wherein the baking finish hardening increment of the prepared Al-Mg-Si-Cu-Zn alloy is 130-180 Mpa, the elongation at T4P state is 23-26% after the Al-Mg-Si-Cu-Zn alloy is naturally placed for 14 days, the yield strength is 330-370 MPa after the Al-Mg-Si-Cu-Zn alloy is naturally placed for 14 days and subjected to aging treatment by adding simulated baking finish, and the tensile strength is 380-410M Pa.

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