Composite treatment method for modifying Fe-rich phase of 6016 secondary aluminum alloy and enhancing baking varnish hardening response

Abstract

The invention belongs to the technical field of regenerated aluminum alloys, and discloses a composite treatment method for modifying a Fe-rich phase of a 6016 regenerated aluminum alloy and enhancing baking varnish hardening response. The composite treatment method comprises the following steps: S1) carrying out Sr, Cr and Sn multi-element microalloying treatment on the remelted 6016 aluminum alloy; then, the microalloyed melt is prepared into a cast ingot; and (S2) the cast ingot is subjected to heat preservation homogenization treatment, hot rolling, cold rolling, solution treatment, natural aging and baking finish treatment, and the regenerated aluminum alloy is obtained. According to the method, conversion from a beta-Fe phase to an alpha-Fe phase in the 6016 secondary aluminum alloy is achieved, the rich form is effectively deteriorated into a small Chinese character shape from a thick long needle shape, in addition, the negative influence of natural aging is effectively restrained, and the baking varnish hardening increment is enhanced. The mechanical property of the regenerated aluminum alloy subjected to multi-element microalloying treatment is excellent, the harm of the impurity element Fe to the 6016 regenerated aluminum alloy is remarkably reduced, and high-quality utilization of the regenerated aluminum alloy is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of recycled aluminum alloys for automobiles, and particularly relates to a composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response. Background Art

[0002] With the development of the automotive industry and the increase in vehicle ownership, energy, environmental, and safety issues have become increasingly prominent. Energy scarcity and environmental pollution have become the main factors hindering the sustainable development of the automotive industry. Vehicle lightweighting has become an effective way to reduce energy consumption. Aluminum alloys are widely used in automotive components due to their excellent mechanical properties, recyclability, and low cost. For example, heat-treatable 6xxx series aluminum alloys, due to their low density, high specific strength, excellent formability, and excellent paint-hardening properties, have been widely used in structural components such as automotive body panels, becoming one of the key materials for achieving vehicle lightweighting.

[0003] In the context of dual carbon, the lifecycle of aluminum products is closely linked to the carbon emissions from their production and use. To improve product lifecycles, more aluminum products will be processed using recycled aluminum in the future. However, the recycling process inevitably introduces impurities such as Fe, Cr, Mn, V, and Ti, with Fe being the most common. Because Fe is an unavoidable impurity in aluminum alloys, the 6xxx series alloy system can be considered an Al-Mg-Si-Fe alloy system. During solidification, multiple Fe-rich phases form, and these phases undergo interconversion. α-Fe and β-Fe are the most common Fe-rich phases in 6xxx series aluminum alloys. The α-Fe phase has a hexagonal structure and is either Chinese character-shaped or blocky, with a relatively minimal impact on the overall material properties. The β-Fe phase has a monoclinic structure and is acicular or flaky. This phase poorly bonds with the matrix and is prone to stress concentration-induced fracture. Increasing the Fe content promotes the formation of coarse, acicular β-Fe phases, which reduces the alloy's mechanical properties, particularly its plasticity.

[0004] In response to the deterioration of mechanical properties caused by the needle-shaped β-Fe phase, application number CN202410080959.4 discloses a method for regulating the Fe-rich phase in recycled aluminum alloys. This patent application successfully achieved the transformation of β-Fe phase to α-Fe phase by regulating the mass ratio of Mn element to Fe element to 1:1 and optimizing the homogenization and hot deformation process. After regulation, the strength of the recycled aluminum alloy can reach 279.90MPa and the elongation can reach 11.75%, and its comprehensive performance is close to the level of original aluminum. When using Mn to modify the Fe phase in recycled aluminum, the Mn / Fe ratio must be close to 1:1 or even higher to achieve good results. When the Mn content is high, the alloy phase content increases significantly, which will significantly reduce the plasticity of the alloy, increase the difficulty of plastic forming, and also reduce the paint hardening response capability.

[0005] However, as age-hardenable 6xxx aluminum alloys, not only the mechanical properties of the alloy sheet after solution quenching must be considered, but also the hardening response of the sheet after the paint treatment. Patent applications CN201910560443.9 and CN202110425080.5 both disclose methods for introducing pre-aging to enhance the paint hardening increment and natural aging stability of 6xxx alloys. The pre-aging process generates pre-aging clusters, which reduce the concentration of Mg and Si atoms in the matrix, thereby inhibiting the formation of natural aging clusters. During the subsequent paint treatment, the pre-aging clusters can directly serve as nucleation sites for the primary strengthening phase, β" phase, or directly grow into β" phase, achieving a rapid aging response. Whether based on pre-aging, pre-deformation, or a combination of pre-aging and pre-deformation, it will increase the process steps and is not conducive to actual production.

[0006] Currently, 6xxx series aluminum alloys used in automobiles suffer from anisotropic mechanical properties, poor stamping formability, poor resistance to natural aging, and insufficient bake hardening after painting. As an indispensable material for lightweighting vehicles, 6xxx series aluminum alloys are in huge demand for the future development of transportation. With the depletion of bauxite resources and rising environmental awareness, the concept of developing a circular economy has become a global consensus. Therefore, achieving the grade-preserving utilization of 6xxx series recycled aluminum alloys can generate significant economic, environmental, and social value. Summary of the Invention

[0007] To address the problem that the introduction of a high content of Fe into recycled 6016 aluminum alloy forms a coarse, needle-shaped β-Fe phase, which reduces the alloy's aging response and thus leads to reduced alloy performance, the present invention provides a composite treatment method for modifying the Fe-rich phase in 6016 recycled aluminum alloy and enhancing its paint-hardening response. The present invention regulates the Fe-rich phase and aging behavior in the 6016 recycled alloy through multi-component microalloying with Sr, Cr, and Sn. The present invention achieves the transformation of the harmful β-Fe phase in the recycled 6016 aluminum alloy into the α-Fe phase, realizes the beneficial utilization of the impurity element Fe, suppresses the harmful effects of natural aging, improves the aluminum alloy's mechanical properties before baking and the bake-hardening strength increment, and ultimately achieves the grade-preserving utilization of the 6016 recycled aluminum alloy.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response comprises the following steps:

[0010] S1) performing a multi-component microalloying treatment on a remelted 6016 aluminum alloy with Sr, Cr, and Sn; and then preparing an ingot from the microalloyed melt;

[0011] S2) performing heat preservation and homogenization treatment on the ingot, hot rolling, and cold rolling;

[0012] S3) performing a solution treatment on the cold-rolled plate to obtain a supersaturated solid solution plate;

[0013] S4) performing natural aging and baking varnish treatment on the supersaturated solid solution plate to obtain a recycled aluminum alloy.

[0014] By performing Sr, Cr and Sn multi-element microalloying treatment on remelted 6016 aluminum alloy, the product recycled aluminum alloy contains the following components: percentage by mass, Mg: 0.45-0.6%, Si: 1.0-1.2%, Fe: 0.1-0.6%, Cr: 0.1-0.25%, Sn: 0.03-0.1%, Sr: 0.03-0.1%, and the balance is Al and other inevitable impurity elements, and the total amount of impurity elements is ≤0.05%.

[0015] Preferably, Fe: 0.5-0.6%;

[0016] Preferably, Cr: 0.15-0.25%; Sr: 0.03-0.08%; Sn: 0.05-0.1%.

[0017] The microalloying process involves melting remelted 6016 aluminum alloy, adding a Cr-containing master alloy, cooling the mixture to 715-725°C and holding the temperature for 45-70 minutes, adding a Sr-containing master alloy and Sn, stirring, and allowing the mixture to stand. The remelted 6016 aluminum alloy is an aluminum alloy rich in Fe. The melting temperature is 725-750°C.

[0018] The melt is cleaned and slag removed before casting.

[0019] The temperature of the heat preservation and homogenization treatment in step S2) is 550-580°C and the time is 6-10 hours; after the heat preservation and homogenization treatment, the mixture is cooled to room temperature.

[0020] The hot rolling temperature in step S2) is 450-480°C, and the total hot rolling reduction is 40%-80%; the cold rolling is carried out after the plate cools to room temperature after the hot rolling, and the total cold rolling reduction is 45%-80%.

[0021] The hot rolling and cold rolling are multi-pass rolling, and the reduction amount of each hot rolling or cold rolling pass is 5-20%.

[0022] The temperature of the solution treatment in step S3) is 510-530°C, and the time of the solution treatment is 20-40 minutes.

[0023] After solution treatment, the plate is cooled to room temperature; the cooling is performed by water quenching, specifically by rapidly placing the plate in water for cooling or by spraying water on the plate.

[0024] The natural aging in step S4) is to place the product naturally at room temperature for 7-15 days.

[0025] The paint baking treatment in step S5) refers to baking at 175-185° C. for 25-40 minutes.

[0026] The alloy prepared by the present invention can be used for automobile engine hood cover plates.

[0027] The present invention adds three elements, Sr, Cr and Sn, to a recycled 6016 alloy with a high Fe content to perform a multi-element microalloying treatment. Sr and Cr can effectively modify the Fe element and transform the needle-shaped β-Fe phase into the Chinese character-shaped α-Fe. Sn atoms have stronger binding energy with vacancies. When Sn atoms are doped into Mg-Si clusters and β" (Mg5Al2Si) strengthening phases, the formation enthalpy of these precipitates is reduced, thereby promoting cluster formation and the precipitation of β" and Q' (Al4Cu2Mg8Si7) strengthening phases.

[0028] Compared with the existing preparation process of 6xxx series aluminum alloy for automobile body panels, it has the following outstanding advantages and beneficial effects:

[0029] (1) The present invention can not only effectively modify the Fe-rich phase in the deformed aluminum alloy, but also effectively inhibit natural aging and significantly enhance the paint hardening response.

[0030] (2) The performance of Fe-rich recycled deformed aluminum alloy prepared by the process of the present invention is even better than that of original aluminum alloy, and the maximum Fe element tolerance can reach 0.5% to 0.6%, realizing the recycled and grade-preserving utilization of aluminum alloy.

[0031] (3) The present invention prepares a high-Fe content 6016 aluminum alloy with a yield strength of 101.3 MPa and an elongation of 38.8% before painting. After being treated by the present invention, the paint hardening increment can reach 74.8 MPa, that is, the yield strength is 176.1 MPa, and the elongation is 28.7%.

[0032] (4) Compared with the pre-aging process or pre-deformation process introduced in the traditional production process, the present invention reduces the flow of the pretreatment process and has a significant advantage in reducing consumption in production.

[0033] (5) The process of the present invention does not require the addition of new equipment. Instead, it only requires adjustments to the production steps of the existing production line to produce high-Fe recycled 6016 aluminum alloy with mechanical properties comparable to those of the original 6016 aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the as-cast SEM microstructure of the high-Fe content 6016 aluminum alloy without microalloying treatment in Comparative Example 1;

[0035] Figure 2 SEM microstructure of the as-cast high-Fe 6016 aluminum alloy microalloyed in Example 1;

[0036] Figure 3 SEM microstructure of the as-cast high-Fe 6016 aluminum alloy microalloyed in Example 2;

[0037] Figure 4 SEM microstructure of the as-cast high-Fe 6016 aluminum alloy microalloyed in Example 3;

[0038] Figure 5 Artificial aging kinetic curves of Comparative Example 1, Example 3, Comparative Example 2, Comparative Example 5 and Comparative Example 6;

[0039] Figure 6 The natural aging hardness change curves of Example 3, Comparative Example 2, Comparative Example 3 and Comparative Example 4 are shown. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0041] In order to better illustrate the implementation effect of the present invention, the preparation process of the high-Fe content 6016 aluminum alloy deformed aluminum alloy that has not been micro-alloyed in actual production is used as comparative example 1.

[0042] Comparative Example 1

[0043] 6016 aluminum alloy is a common wrought aluminum alloy used in automobiles. Its preparation process includes alloy melting, billet casting, homogenization annealing, high-temperature hot rolling, cold rolling, solution quenching, and artificial aging. The high-Fe 6016 aluminum alloy produced in Comparative Example 1 has a composition of 0.5% Mg, 1.2% Si, and 0.6% Fe, with the remainder being Al and other impurities. The total amount of impurities is ≤ 0.05%. All figures are by weight. The preparation process and related process parameters are as follows:

[0044] 1) 6016 hot-rolled plate was remelted and Al-20Fe master alloy was added. The mass percentage of Fe in the product was 0.6%. The alloy was smelted at 740°C. After being completely melted, it was kept warm for 1 hour. After ventilation, impurity removal, and slag removal, it was cast into a steel mold preheated to 200°C to obtain a plate-shaped ingot.

[0045] 2) The as-cast ingot is homogenized to reduce component segregation; the homogenization temperature is 560°C, the holding time is 8 hours, and the ingot is cooled with the furnace.

[0046] 3) heating the homogenized billet to 460° C., hot-rolling the billet in multiple passes to a plate having a thickness of 7.5 to 8 mm with a total hot-rolling reduction of 50%, and then cold-rolling the billet to a plate having a thickness of 2 mm with a single-pass reduction of 10 to 20%; and finally rolling the billet to a total deformation of 90%.

[0047] 4) The cold-rolled plate was subjected to solution quenching treatment at a solution temperature of 520°C for 30 minutes; then water quenched to room temperature to obtain a supersaturated solid solution.

[0048] 5) The supersaturated solid solution plate is placed at room temperature for natural aging for 14 days, and then artificial aging treatment is performed (baking paint treatment is part of the artificial aging treatment, and the baking paint treatment is performed first for 30 minutes). The aging temperature is 180°C and the aging time is 0 to 36 hours.

[0049] In order to characterize the microstructure and mechanical properties of the above alloys, high-resolution field emission scanning electron microscopy was used for characterization. The hardness of the alloy samples was measured using a Vickers hardness tester with a load of 500 g and a holding time of 10 s. Seven microindentations were measured for each condition sample, and the average value was taken as the final hardness to minimize experimental error. In order to better evaluate the mechanical properties of the alloy plate, a tensile test was performed on the plate using a universal testing machine at room temperature with an initial strain rate of 1.0×10 -3 s -1 The tensile test was repeated at least three times for each set of samples to ensure the repeatability of the tensile response.

[0050] Figure 1 This is a SEM microstructure image of the as-cast, unmicroalloyed, high-Fe 6016 aluminum alloy from Comparative Example 1. The Fe-rich phase is primarily composed of coarse, acicular β-Fe phases. These acicular / plate-like β-Fe phases are potential sites for crack initiation and propagation, severely impairing the alloy's tensile properties, particularly its plasticity.

[0051] The yield strength, tensile strength, and elongation of the alloy in T4 and T4+PB states in Comparative Example 1 were tested. The yield strength of the T4 state was 89.6 MPa, that of the T4+PB state was 146.9 MPa, and the paint bake increase was 57.3 MPa; the elongation of the T4 state was 28.1%.

[0052] To further illustrate the implementation effect of the present invention, the present invention is described below in conjunction with embodiments.

[0053] Example 1

[0054] The aluminum alloy produced in this embodiment contains the following components: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.1% Cr, 0.05% Sr, 0.1% Sn, and the remainder is Al and other impurities. The above ratios are all by mass.

[0055] The microalloying method of the high-Fe content 6016 aluminum alloy in this embodiment specifically includes the following steps:

[0056] Step 1: Microalloying and Casting of the Melt

[0057] 1.1) Remelt a pre-calculated weight of raw 6016 alloy plate and add an Al-20Fe master alloy to a Fe content of 0.6% by mass. Maintain the alloy melting temperature at 740°C. Then, add an Al-20Cr master alloy to a Cr content of 0.1% by mass. Gradually cool the mixture to 720°C and hold for 1 hour.

[0058] 1.2) adding Al-10Sr master alloy and pure Sn particles to aluminum melt for microalloying, with the mass percentages of Sr and Sn in the product being 0.05% and 0.1%, respectively;

[0059] 1.3) After the Sr / Sn elements are added, stir and let stand for 5 to 10 minutes, ventilate the melt to remove impurities and slag, and then cast it. The casting temperature is 720°C, and the mold needs to be preheated to 200°C in advance.

[0060] Step 2: Homogenization and rolling of ingots

[0061] 2.1) Homogenizing annealing the as-cast ingot at a temperature of 560°C, heating and holding the ingot for 8 hours, and finally cooling the ingot to room temperature.

[0062] 2.2) The rolling process is divided into two parts: hot rolling and cold rolling. First, the upper and lower surfaces of the homogenized ingot are cut to remove the surface oxide layer, and then hot rolling is carried out at a temperature of 460°C. After multiple rolling passes, the thickness is reduced from 20mm to about 7.5mm. After the hot-rolled plate cools to room temperature, it is cold-rolled to about 2mm, with a single pass reduction of 10% to 20%.

[0063] Step 3: Solution quenching and artificial aging treatment

[0064] 3.1) Solution treatment of the cold-rolled plate, followed by water quenching to room temperature, to obtain a supersaturated solid solution plate; the solution temperature is 520°C and the holding time is 30 minutes;

[0065] 3.2) The supersaturated solid solution plate was naturally aged at room temperature for 14 days, and then artificially aged at a temperature of 180°C for 0 to 36 hours (including a 30-minute paint treatment).

[0066] Figure 2 This is a SEM microstructure image of the as-cast, high-Fe regenerated 6016 aluminum alloy subjected to the 0.1% Cr-0.05% Sr-0.1% Sn multi-component microalloying treatment in Example 1. Part of the coarse, needle-like β-Fe-rich phase is transformed into a Chinese character-shaped α-Fe phase. This indicates that the control of β-Fe is incomplete.

[0067] Similarly, the mechanical properties of Example 1 were tested. Its tensile strength in the T4 state was 91.2 MPa, its elongation was 36.1%, and its yield strength increase after paint baking was 66.9 MPa. Compared with Comparative Example 1, Example 1 showed an increase in paint bake hardening performance, as well as an increase in elongation in the T4+PB state. This demonstrates that multi-component microalloying can effectively control the Fe-rich phase and improve paint bake hardening performance.

[0068] Example 2

[0069] The smelting and subsequent mechanical heat treatment processes involved in this embodiment are the same as those in the above-mentioned embodiment 1. The difference from embodiment 1 is the specific composition of the alloy, which is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.2% Cr, 0.05% Sr, 0.05% Sn, and the balance is Al. The above are all mass ratios.

[0070] The microalloying method of the high-Fe content 6016 aluminum alloy in Example 2 specifically includes the following steps:

[0071] Step 1: Microalloying and Casting of the Melt

[0072] 1.1) Remelt a pre-calculated weight of raw 6016 alloy plate, add an Al-20Fe master alloy (Fe content is 0.6% by mass) and maintain the alloy melting temperature at 740°C. Add an Al-20Cr master alloy (Cr content is 0.2% by mass), then gradually cool to 720°C and hold for 1 hour.

[0073] 1.2) adding Al-10Sr master alloy and pure Sn particles to aluminum melt for microalloying, with the mass percentages of Sr and Sn being 0.05% and 0.05% respectively;

[0074] 1.3) After the Sr / Sn elements are added, stir and let stand for 5 to 10 minutes, ventilate the melt to remove impurities and slag, and then cast it. The casting temperature is 720°C, and the mold needs to be preheated to 200°C in advance.

[0075] Step 2: Homogenization and rolling of ingots

[0076] 2.1) Homogenizing annealing the as-cast ingot at a temperature of 560°C, heating and holding the ingot for 8 hours, and finally cooling the ingot to room temperature.

[0077] 2.2) The rolling process is divided into two parts: hot rolling and cold rolling. First, the upper and lower surfaces of the homogenized ingot are cut to remove the surface photooxidation layer, and then hot rolling is carried out at a temperature of 460°C. After multiple rolling passes, the thickness is reduced from 20mm to 7.5mm. After the hot-rolled plate cools to room temperature, it is cold rolled to about 2mm, with a single pass reduction of 10% to 20%.

[0078] Step 3: Solution quenching and artificial aging treatment

[0079] 3.1) Solution treatment of the cold-rolled plate, followed by water quenching to room temperature, to obtain a supersaturated solid solution plate; the solution temperature is 520°C and the holding time is 30 minutes;

[0080] 3.2) The supersaturated solid solution plate was naturally aged at room temperature for 14 days, and then artificially aged at a temperature of 180°C for 0 to 36 hours (including a 30-minute paint treatment).

[0081] Figure 3 This is a microscopic SEM image of the cast state of the high-Fe 6016 alloy after 0.2% Cr-0.05% Sr-0.05% Sn multi-component microalloying in Example 2. It can be found that the Fe-rich phase in the high-Fe 6016 aluminum alloy modified by multi-component microalloying is almost transformed from a coarse needle-shaped β-Fe phase to a fishbone-shaped α-Fe phase. Similarly, the mechanical properties of the alloy were tested. Its yield strength in the T4 state is 95.6 MPa, the tensile strength is 206.7 MPa, and the elongation is 37.1%. Compared with Comparative Example 1, both the strength and elongation are improved. The yield strength increase after baking paint is 64.54 MPa, and the elongation can reach 30.6%.

[0082] Example 3

[0083] The smelting and subsequent mechanical heat treatment processes involved in this embodiment are the same as those in the above-mentioned embodiment 2. The difference from embodiment 2 is the specific composition of the alloy, which is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.2% Cr, 0.05% Sr, 0.1% Sn, and the balance is Al. The above are all mass ratios.

[0084] The microalloying method of the high-Fe content 6016 aluminum alloy in this embodiment specifically includes the following steps:

[0085] Step 1: Microalloying and Casting of the Melt

[0086] 1.1) Remelt a pre-calculated weight of raw 6016 alloy plate, add an Al-20Fe master alloy (Fe content is 0.6% by mass) and maintain the alloy melting temperature at 740°C. Add an Al-20Cr master alloy (Cr content is 0.2% by mass), then gradually cool to 720°C and hold for 1 hour.

[0087] 1.2) adding Al-10Sr master alloy and pure Sn particles to aluminum melt for microalloying, with the mass percentages of Sr and Sn being 0.05% and 0.1% respectively;

[0088] 1.3) After the Sr / Sn elements are added, stir and let stand for 5 to 10 minutes, ventilate the melt to remove impurities and slag, and then cast it. The casting temperature is 720°C, and the mold needs to be preheated to 200°C in advance.

[0089] Step 2: Homogenization and rolling of ingots

[0090] 2.1) Homogenization annealing is performed on the as-cast ingot to reduce composition segregation. The homogenization annealing temperature is 560°C, and the furnace is heated and held for 8 hours, and finally cooled to room temperature.

[0091] 2.2) The rolling process is divided into two steps: hot rolling and cold rolling. First, the upper and lower surfaces of the homogenized ingot are milled to remove the surface oxide layer. The hot rolling temperature is 460°C, and after multiple passes, the thickness is reduced from 20mm to approximately 7.5mm. After the hot-rolled plate cools to room temperature, it is cold-rolled to approximately 2mm, with a reduction of 10% to 20% per pass.

[0092] Step 3: Solution quenching and artificial aging treatment

[0093] 3.1) Solution treatment of the cold-rolled plate was performed, followed by water quenching to room temperature to obtain a supersaturated solid solution plate. The solution temperature was 520°C and the holding time was 30 minutes.

[0094] 3.2) The supersaturated solid solution plate was naturally aged at room temperature for 14 days, and then artificially aged at a temperature of 180°C for 0 to 36 hours (including a 30-minute paint treatment).

[0095] Figure 4 This is a SEM image of the as-cast high-Fe 6016 alloy subjected to 0.2% Cr-0.05% Sr-0.1% Sn multicomponent microalloying in Example 3. It can be seen that the Fe-rich phase in the high-Fe 6016 aluminum alloy modified by multicomponent microalloying is completely transformed from the coarse, needle-like β-Fe phase to the fishbone-like α-Fe phase, effectively controlling the Fe-rich phase.

[0096] To better compare the effects of the present invention, the key performance parameters of the alloys prepared in Comparative Example 1 and Examples 1-3 are summarized in Table 1. It should be noted that the comparative improvement values in this table are based on the tensile mechanical properties data of Comparative Example 1 after 14 days of natural aging.

[0097] Clearly, the alloy prepared in Example 3 of the present invention exhibits a relatively small increase in T4 yield strength during 14 days of natural aging, at only 11.7 MPa, while the yield strength increment after baking increases from 57.3 MPa to 74.8 MPa, and the tensile elongation also increases. Furthermore, the SEM images show that Example 3 effectively achieves the transformation of the β-Fe phase to the α-Fe phase in the high-Fe content 6016 alloy, effectively transforming the morphology from a coarse, long needle to a fine, Chinese character-like shape.

[0098] Table 1 Performance parameters of alloys prepared in Comparative Example 1 and Examples 1 to 3

[0099]

[0100]

[0101] Based on the above examples, the key to the multi-component microalloying method of the present invention lies in the regulation of the Fe-rich phase through Cr-Sr-Sn multi-component microalloying, which effectively reduces the adverse effects of the impurity element Fe in the recycled aluminum alloy on the mechanical properties, modifies the Fe phase, and improves the alloy's response to artificial aging. While having a high aging response, the alloy also maintains excellent ductility and yield strength at all stages of artificial aging.

[0102] In order to more conveniently illustrate the implementation effect of the present invention, the present invention also supplements the modification effect of single elements Cr, Sr, and Sn, as well as the modification effect of dual elements Cr+Sn and Cr+Sr, performs alloying treatment on high Fe content 6016 aluminum alloy, and provides supplementary comparative explanation.

[0103] Comparative Example 2

[0104] The composition of the alloy produced in this comparative example is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.2% Cr, and the balance is Al, all of which are by mass ratios.

[0105] Except for the difference in ingredients, the rest of the preparation process and its process parameters are consistent with those in Example 1.

[0106] Comparative Example 3

[0107] The composition of the product alloy in this comparative example is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.05% Sr, and the balance is Al, all of the above are by mass ratios.

[0108] Except for the difference in ingredients, the rest of the preparation process and its process parameters are consistent with those in Example 1.

[0109] Comparative Example 4

[0110] The composition of the product alloy in this comparative example is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.1% Sn, and the balance is Al, all of the above ratios are by mass.

[0111] Except for the difference in ingredients, the rest of the preparation process and its process parameters are consistent with those in Example 1.

[0112] Comparative Example 5

[0113] The composition of the product alloy in this comparative example is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.2% Cr, 0.05% Sr, and the balance is Al, all of the above are by mass ratios.

[0114] Except for the difference in ingredients, the rest of the preparation process and its process parameters are consistent with those in Example 1.

[0115] Comparative Example 6

[0116] The chemical composition of the alloy in this comparative example is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.2% Cr, 0.1% Sn, and the balance is Al, all of the above are by mass ratios.

[0117] Except for the difference in ingredients, the rest of the preparation process and its process parameters are consistent with those in Example 1.

[0118] For comparative examples 2 to 6, the artificial aging kinetic curves after different microalloying processes were tested, such as Figure 5 As shown in Figure 2. And the change trend of alloy hardness during natural aging process, as shown in Figure 2. Figure 6 shown. Figure 5 Artificial aging kinetic curves of Comparative Example 1 (0.6Fe), Example 3 (0.2Cr+0.1Sn+0.05Sr), Comparative Example 2 (0.2Cr), Comparative Example 5 (0.2Cr+0.05Sr) and Comparative Example 6 (0.2Cr+0.1Sn); Figure 6 These are the natural aging hardness change curves of Example 3 (0.2Cr+0.1Sn+0.05Sr), Comparative Example 2 (0.2Cr), Comparative Example 3 (0.05Sr) and Comparative Example 4 (0.1Sn).

[0119] The results show that the addition of Cr and Sr alone in Comparative Examples 2 and 3 can modify the Fe-rich phase, but the modification is incomplete and cannot effectively suppress the negative effects of the natural aging phase or enhance the natural aging response of the alloy. In Comparative Example 4, Sn alone can only suppress the negative effects of natural aging and enhance the artificial aging response, but cannot control the Fe-rich phase. In Comparative Example 5, the addition of Cr and Sr can completely modify the Fe-rich phase, but has no effect on suppressing natural aging or enhancing aging kinetics. In Comparative Example 6, the addition of Cr and Sn can modify the Fe phase to a certain extent, suppress the negative effects of natural aging, and enhance the artificial aging response.

[0120] In summary, Example 3 of the present invention, i.e., 0.2% Cr + 0.05% Sr + 0.1% Sn, can perfectly control the Fe-rich phase in the 6016 alloy with a high Fe content, suppress the negative effects of natural aging, and enhance the artificial aging response.

[0121] The implementation methods of the present invention are not limited to the embodiments described. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response, characterized by: The following steps are involved: S1) performing a multi-component microalloying treatment on a remelted 6016 aluminum alloy with Sr, Cr, and Sn; and then preparing an ingot from the microalloyed melt; S2) performing heat preservation and homogenization treatment on the ingot, hot rolling, and cold rolling; S3) performing a solution treatment on the cold-rolled plate to obtain a supersaturated solid solution plate; S4) subjecting the supersaturated solid solution plate to natural aging and baking varnish treatment to obtain a recycled aluminum alloy; By performing Sr, Cr and Sn multi-element microalloying treatment on remelted 6016 aluminum alloy, the product recycled aluminum alloy contains the following components: Mg: 0.45-0.6%, Si: 1.0-1.2%, Fe: 0.1-0.6%, Cr: 0.1-0.25%, Sn: 0.03-0.1%, Sr: 0.03-0.1%, and the balance is Al and other impurity elements. The total amount of impurity elements is ≤0.05%, and the percentages are mass percentages.

2. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 1, characterized in that: The Fe content: 0.5-0.6%; The Cr: 0.15-0.25%; Sr: 0.03-0.08%; Sn: 0.05-0.1%.

3. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 1, characterized in that: The microalloying treatment in step S1) is to melt the remelted 6016 aluminum alloy, add the Cr-containing master alloy, then cool to 715-725° C. and keep warm for 45-70 minutes; add the Sr-containing master alloy and Sn, stir and let stand.

4. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 3, characterized in that: The Cr-containing master alloy is Al-20Cr, and the Sr-containing master alloy is Al-10Sr master alloy.

5. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 1, characterized in that: The temperature of the heat preservation and homogenization treatment in step S2) is 550-580°C and the time is 6-10 hours; after the heat preservation and homogenization treatment, the mixture is cooled to room temperature.

6. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 1, characterized in that: The hot rolling temperature in step S2) is 450-480°C, and the total hot rolling reduction is 40%-80%; the cold rolling is performed after the plate cools to room temperature after the hot rolling, and the total cold rolling reduction is 45%-80%; The hot rolling and cold rolling are multi-pass rolling, and the reduction amount of each hot rolling or cold rolling pass is 5-20%.

7. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 1, characterized in that: The temperature of the solution treatment in step S3) is 510-530°C, and the time of the solution treatment is 20-40 minutes.

8. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 1, characterized in that: After solution treatment, cooling to room temperature; the cooling refers to cooling by water quenching; The natural aging in step S4) is carried out by placing the mixture at room temperature for 7-15 days. The paint baking treatment in step S5) refers to baking at 175-185° C. for 25-35 minutes.

9. The composite treatment method for modifying 6016 recycled aluminum alloy to enrich the Fe phase and enhance the paint hardening response according to claim 8, characterized in that: Specifically, it refers to quickly placing the plate after solid solution into water for cooling or spraying water atomization cooling on the plate.

10. An application of recycled aluminum alloy obtained by the method according to any one of claims 1 to 9, characterized in that: The recycled aluminum alloy is used in the field of automobile plates.

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