A composite treatment method for modifying fe-rich phases of 6016 recycled aluminum alloy and enhancing the response to stoving paint hardening

Abstract

The present application belongs to the technical field of recycled aluminum alloy, and discloses a composite treatment method for modifying Fe-rich phase of 6016 recycled aluminum alloy and enhancing paint-baking hardening response. The composite treatment method comprises the following steps: S1) performing Sr, Cr and Sn multi-element micro-alloying treatment on remelted 6016 aluminum alloy; then preparing the micro-alloyed melt into an ingot; S2) performing heat preservation homogenization treatment, hot rolling, cold rolling, solid solution treatment, natural aging, paint baking treatment on the ingot to obtain the recycled aluminum alloy. The method realizes the conversion of β-Fe phase to α-Fe phase in the 6016 recycled aluminum alloy, effectively modifies the coarse long needle-shaped Fe-rich phase into fine Chinese character-shaped Fe-rich phase, effectively suppresses the negative influence of natural aging, and enhances the paint-baking hardening increment. The recycled aluminum alloy after multi-element micro-alloying treatment has excellent mechanical properties, significantly reduces the harm of impurity element Fe to the 6016 recycled aluminum alloy, and realizes high-quality utilization of the recycled aluminum alloy.

Description

Technical Field

[0001] This invention belongs to the field of automotive recycled aluminum alloy technology, specifically relating to a composite treatment method for modified 6016 recycled aluminum alloy with Fe-rich phase and enhanced paint hardening response. Background Technology

[0002] With the development of the automotive industry and the increase in car ownership, the three major issues of energy, environment, and safety have become increasingly prominent. Energy scarcity and environmental pollution have become the main reasons affecting the sustainable development of the automotive industry. Lightweighting of automobiles has become one of the effective ways to reduce energy consumption. Aluminum alloys, due to their excellent mechanical properties, recyclability, and low cost, are widely used in automotive parts. For example, heat-treatable 6xxx series aluminum alloys, due to their low density, high specific strength, good 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 automotive lightweighting.

[0003] In the context of dual carbon emissions, the lifecycle of aluminum products is closely related to carbon emissions during their production and use. To improve product lifecycles, more aluminum products will be processed using recycled aluminum in the future. However, the recycling process of aluminum alloys inevitably introduces impurity elements such as Fe, Cr, Mn, V, and Ti, with Fe being the most common. Since Fe is an unavoidable impurity element in aluminum alloys, the 6xxx series alloy system can be considered an Al-Mg-Si-Fe alloy system. During solidification, various Fe-rich phases are formed, and different Fe-rich phases can inter-transform. α-Fe and β-Fe phases are the most common Fe-rich phases in 6xxx series aluminum alloys. The α-Fe phase has a hexagonal structure and is shaped like Chinese characters or in blocks, having a relatively small impact on the overall material properties. The β-Fe phase has a monoclinic structure and is needle-like or lamellar; this phase has poor bonding with the matrix and is prone to stress concentration and fracture. Increased Fe content promotes the formation of coarse needle-like β-Fe phases, thereby reducing the mechanical properties of the alloy, especially affecting its plasticity.

[0004] To address the deterioration of the mechanical properties of acicular β-Fe, patent application CN202410080959.4 discloses a method for controlling the Fe-rich phase in recycled aluminum alloys. This patent application successfully achieved the transformation of the β-Fe phase to the α-Fe phase by controlling the mass ratio of Mn to Fe to 1:1 and optimizing the homogenization and hot deformation processes. After this control, the recycled aluminum alloy achieved a strength of 279.90 MPa and an elongation of 11.75%, with overall performance approaching that of primary aluminum. When utilizing the Fe phase in Mn-modified recycled aluminum, a Mn / Fe ratio close to 1:1 or even higher is necessary to achieve good results. High Mn content significantly increases the alloy phase content, which significantly reduces alloy plasticity, increases the difficulty of plastic forming, and also reduces the paint hardening response.

[0005] However, for 6xxx series aluminum alloys that can be age-strengthened, it is necessary to consider not only the mechanical properties of the alloy sheet after solution quenching but also the hardening response capability of the sheet after baking paint treatment. Invention patents with application numbers CN201910560443.9 and CN202110425080.5 both disclose the introduction of pre-aging methods to enhance the baking paint hardening increment and resistance to natural aging of 6xxx series alloys. Pre-aging processes generate pre-aged clusters, which reduce the concentration of Mg and Si atoms in the matrix, thereby inhibiting the formation of naturally aged clusters. In the subsequent baking paint treatment, these pre-aged clusters can directly serve as nucleation sites for the main strengthening phase β" phase or directly grow into the β" phase, achieving a rapid aging response. Whether based on pre-aging, pre-deformation, or a combination of pre-aging and pre-deformation, all processes increase, which is detrimental to actual production.

[0006] Currently, 6xxx series aluminum alloys used in automobiles exhibit anisotropic mechanical properties, poor stamping formability, poor resistance to natural aging, and insufficient bake hardening after painting. As an indispensable material for automotive lightweighting, 6xxx series aluminum alloys will be in huge demand in the future development of transportation. With the depletion of bauxite resources and increasing environmental awareness, the concept of developing a circular economy has become a global consensus. Therefore, realizing the sustainable 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 high Fe content into recycled 6016 aluminum alloys leads to the formation of coarse, needle-like β-Fe phases, reducing the alloy's aging response and thus degrading its properties, this invention provides a composite treatment method for modifying 6016 recycled aluminum alloys to enrich the Fe phase and enhance the bake-hardening response. This invention regulates the Fe-rich phase and aging behavior in the 6016 recycled alloy through Sr, Cr, and Sn multi-element microalloying. This invention achieves the transformation of the harmful β-Fe phase into the α-Fe phase in the recycled 6016 aluminum alloy, realizing the beneficial utilization of the impurity element Fe, suppressing the harmful effects of natural aging, improving the mechanical properties before baking and the increase in bake-hardening strength, ultimately achieving the preservation and utilization of 6016 recycled aluminum alloys.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

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

[0010] S1) The remelted 6016 aluminum alloy is subjected to Sr, Cr and Sn multi-element microalloying treatment; then the microalloyed melt is prepared into an ingot.

[0011] S2) The ingot is subjected to heat preservation and homogenization treatment, followed by hot rolling and cold rolling;

[0012] S3) The cold-rolled sheet is subjected to solution treatment to obtain a supersaturated solution-treated sheet.

[0013] S4) Natural aging and baking paint treatment are carried out on supersaturated solid solution plates to obtain recycled aluminum alloy.

[0014] By subjecting remelted 6016 aluminum alloy to Sr, Cr, and Sn multi-element microalloying treatment, the resulting recycled aluminum alloy contains the following components: percentages are 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%, with the balance being Al and other unavoidable impurity elements, the total amount of impurity elements ≤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 treatment refers to melting remelted 6016 aluminum alloy, adding a Cr-containing master alloy, then cooling to 715–725°C and holding for 45–70 minutes; adding an Sr-containing master alloy and Sn, stirring and letting stand; remelted 6016 aluminum alloy refers to an aluminum alloy rich in Fe. The melting temperature is 725–750°C.

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

[0019] The temperature for the heat preservation and homogenization treatment in step S2) is 550-580℃, and the time is 6-10h; after the heat preservation and homogenization treatment, it 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 has cooled to room temperature after hot rolling, and the total reduction is 45%-80%.

[0021] The hot rolling and cold rolling processes are multi-pass rolling, with a reduction of 5 to 20% per pass in hot rolling or cold rolling.

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

[0023] After solution treatment, the material is cooled to room temperature; this cooling refers to water quenching. Specifically, this means rapidly immersing the solution-treated sheet in water for cooling or spraying water mist to cool the sheet.

[0024] The natural aging process described in step S4) involves placing the object at room temperature for 7-15 days.

[0025] The baking process described in step S5) refers to baking at 175–185°C for 25–40 minutes.

[0026] The alloy prepared by this invention can be used for automotive engine hood covers.

[0027] This invention involves adding Sr, Cr, and Sn to a high-Fe-content recycled 6016 alloy for multi-element microalloying. Sr and Cr effectively modify Fe, transforming the needle-like β-Fe phase into the Chinese character-shaped α-Fe. Sn atoms have a stronger binding energy with vacancies. When Sn atoms are doped into Mg-Si clusters and β”(Mg5Al2Si) strengthening phases, they reduce the formation enthalpy of these precipitates, thereby promoting cluster formation and the precipitation of β” and Q’(Al4Cu2Mg8Si7) strengthening phases.

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

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

[0030] (2) The performance of Fe-rich recycled wrought aluminum alloys prepared by the process of this invention is even better than that of primary aluminum alloys. The maximum Fe element tolerance can reach 0.5% to 0.6%, realizing the recycling and preservation of aluminum alloys.

[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 baking paint. 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 reaches 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 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. It only requires adjusting the production steps of the existing production line to produce high Fe content recycled 6016 aluminum alloy with mechanical properties comparable to those of virgin 6016 aluminum alloy. Attached Figure Description

[0034] Figure 1 The image shows the as-cast SEM microstructure of the high-Fe-content 6016 aluminum alloy in Comparative Example 1 without microalloying treatment.

[0035] Figure 2 As-cast SEM microstructure of the high-Fe-content 6016 aluminum alloy with microalloying treatment in Example 1;

[0036] Figure 3 As-cast SEM microstructure of the high-Fe-content 6016 aluminum alloy with microalloying treatment in Example 2;

[0037] Figure 4 As-cast SEM microstructure of the high-Fe-content 6016 aluminum alloy with microalloying treatment in Example 3;

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

[0039] Figure 6 The curves showing the change in hardness over natural aging for Examples 3, 2, 3 and 4 are shown. Detailed Implementation

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

[0041] To better illustrate the implementation effect of the present invention, a comparative example 1 is based on the preparation process of high Fe content 6016 aluminum alloy wrought aluminum alloy that has not undergone microalloying in actual production.

[0042] Comparative Example 1

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

[0044] 1) Remelt 6016 hot-rolled plate, add Al-20Fe master alloy, the mass percentage of Fe in the product is 0.6%, the melting temperature of the alloy is 740℃, after complete melting, keep it at the temperature for 1 hour, after aeration to remove impurities and slag, cast it into a steel mold preheated to 200℃ to obtain plate billet.

[0045] 2) Homogenize the cast billet to reduce compositional segregation; the homogenization temperature is 560℃, the holding time is 8h, and it is cooled with the furnace.

[0046] 3) The homogenized billet is heated to 460°C and hot-rolled in multiple passes to a plate with a thickness of 7.5-8 mm. The total reduction in hot rolling is 50%. Then it is cold-rolled to a plate with a thickness of 2 mm. The reduction in a single pass is 10-20%. The final total deformation of rolling is 90%.

[0047] 4) The cold-rolled sheet is subjected to solution quenching at a temperature of 520℃ for 30 minutes; then it is water quenched to room temperature to obtain a supersaturated solid solution.

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

[0049] To characterize the microstructure and mechanical properties of the above alloys, high-resolution field emission scanning electron microscopy was used. The hardness of all 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 sample under each condition, and the average value was taken as the final hardness to minimize experimental error. To better evaluate the mechanical properties of the alloy plates, tensile tests were performed on the plates at room temperature using a universal testing machine with an initial strain rate of 1.0 × 10⁻⁶. -3 s -1 The tensile test was repeated at least three times for each group of samples to ensure the repeatability of the tensile response.

[0050] Figure 1 The image shows the as-cast SEM microstructure of the high-Fe-content 6016 aluminum alloy in Comparative Example 1, which was not microalloyed. The Fe-rich phase is predominantly coarse acicular β-Fe phase. These coarse acicular / plate-like β-Fe phases are potential areas for crack initiation and propagation, severely impairing the alloy's tensile properties, especially its ductility.

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

[0052] To further illustrate the effects of the present invention, the present invention will be described below in conjunction with embodiments.

[0053] Example 1

[0054] In this embodiment, the aluminum alloy contains the following components: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.1% Cr, 0.05% Sr, 0.1% Sn, with the balance being Al and other impurities. All of the above are mass ratios.

[0055] The microalloying treatment method for 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 the pre-calculated weight of the original 6016 alloy plate, add Al-20Fe master alloy, with Fe content in the product being 0.6% by mass, and maintain the alloy melting temperature at 740℃; then add Al-20Cr master alloy, with Cr content in the product being 0.1% by mass, gradually cool down to 720℃, and hold for 1 hour.

[0058] 1.2) Al-10Sr master alloy and pure Sn particles were added to the aluminum melt for microalloying treatment, with Sr and Sn accounting for 0.05% and 0.1% of the product by mass, respectively.

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

[0060] Step 2: Homogenization and rolling of the ingot

[0061] 2.1) The cast billet is subjected to homogenization annealing at a temperature of 560℃, heated in the furnace and held for 8 hours, and finally cooled to room temperature in the furnace.

[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 billet are cut to remove the surface oxide layer. Then, hot rolling is carried out at a temperature of 460℃. After multiple rolling passes, the thickness is reduced from 20mm to about 7.5mm. After the hot-rolled plate is cooled to room temperature, it is further cold-rolled to about 2mm. The reduction in thickness per pass is 10% to 20%.

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

[0064] 3.1) The cold-rolled sheet is solution treated and then quenched in water to room temperature to obtain a supersaturated solid solution sheet; the solution treatment temperature is 520℃ and the holding time is 30 minutes.

[0065] 3.2) The supersaturated solid solution board was placed at room temperature for natural aging for 14 days, and then artificially aged at 180℃ for 0 to 36 hours (including 30 minutes for paint baking).

[0066] Figure 2 This is a SEM microstructure of the as-cast high-Fe content regenerated 6016 aluminum alloy treated with 0.1% Cr-0.05% Sr-0.1% Sn multi-element microalloying in Example 1. Some of the coarse needle-like β-Fe-rich phases have partially transformed into Chinese character-shaped α-Fe phases. This indicates that the control over β-Fe is not complete.

[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 the increase in yield strength after baking was 66.9 MPa. Compared with Comparative Example 1, Example 1 showed an improved increase in baking hardening and an increased elongation in the T4+PB state, indicating that multi-component microalloying can effectively regulate the Fe-rich phase and improve the baking hardening performance.

[0068] Example 2

[0069] The smelting and subsequent mechanical heat treatment processes involved in this embodiment are the same as those in Embodiment 1 above. 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, with the balance being Al. All of the above are mass ratios.

[0070] The microalloying treatment method for 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 the pre-calculated weight of the original 6016 alloy plate, add Al-20Fe master alloy, with Fe content in the product being 0.6% by mass, and maintain the alloy melting temperature at 740℃; add Al-20Cr master alloy, with Cr content in the product being 0.2% by mass, and then gradually cool down to 720℃ and hold for 1 hour.

[0073] 1.2) Add Al-10Sr master alloy and pure Sn particles to the aluminum melt for microalloying treatment, with Sr and Sn having a mass percentage of 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. Then, ventilate the melt to remove impurities and slag, and then cast it. The casting temperature is 720℃, and the mold needs to be preheated to 200℃ in advance.

[0075] Step 2: Homogenization and rolling of the ingot

[0076] 2.1) The cast billet is subjected to homogenization annealing at a temperature of 560℃, heated in the furnace and held for 8 hours, and finally cooled to room temperature in the furnace.

[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 billet are cut to remove the surface oxide layer. Then, hot rolling is carried out at a temperature of 460℃. After multiple rolling passes, the thickness is reduced from 20mm to 7.5mm. After the hot-rolled plate is cooled to room temperature, it is further cold-rolled to about 2mm. The reduction in thickness per pass is 10% to 20%.

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

[0079] 3.1) The cold-rolled sheet is solution treated and then quenched in water to room temperature to obtain a supersaturated solid solution sheet; the solution treatment temperature is 520℃ and the holding time is 30 minutes.

[0080] 3.2) The supersaturated solid solution board was placed at room temperature for natural aging for 14 days, and then artificially aged at 180℃ for 0 to 36 hours (including 30 minutes for paint baking).

[0081] Figure 3 This is a cast-state SEM image of the high-Fe content 6016 alloy from Example 2, which underwent multi-element microalloying with 0.2% Cr, 0.05% Sr, and 0.05% Sn. It can be observed that the Fe-rich phase in the high-Fe content 6016 aluminum alloy modified by multi-element microalloying almost completely transforms from a coarse needle-like β-Fe phase to a fishbone-like α-Fe phase. Similarly, the mechanical properties of the alloy were tested. In the T4 state, its yield strength was 95.6 MPa, tensile strength was 206.7 MPa, and elongation was 37.1%, showing improvements in both strength and elongation compared to Comparative Example 1. After baking paint, the yield strength increase was 64.54 MPa, and the elongation reached 30.6%.

[0082] Example 3

[0083] The smelting and subsequent mechanical heat treatment processes involved in this embodiment are the same as those in Example 2. The difference from Example 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, with the balance being Al. All of the above are mass ratios.

[0084] The microalloying treatment method for 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 the pre-calculated weight of the original 6016 alloy plate, add Al-20Fe master alloy, with Fe content in the product being 0.6% by mass, and maintain the alloy melting temperature at 740℃; add Al-20Cr master alloy, with Cr content in the product being 0.2% by mass, and then gradually cool down to 720℃ and hold for 1 hour.

[0087] 1.2) Add Al-10Sr master alloy and pure Sn particles to the aluminum melt for microalloying treatment, with Sr and Sn having mass percentages of 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. Then, ventilate the melt to remove impurities and slag, and then cast it. The casting temperature is 720℃, and the mold needs to be preheated to 200℃ in advance.

[0089] Step 2: Homogenization and rolling of the ingot

[0090] 2.1) Homogenize the cast billet by annealing to reduce compositional segregation. The homogenization annealing temperature is 560℃, heated in the furnace and held for 8 hours, and finally cooled to room temperature in the furnace.

[0091] 2.2) The rolling process can be divided into two parts: hot rolling and cold rolling. First, the upper and lower surfaces of the homogenized billet are cut to remove the surface oxide layer. The hot rolling temperature is 460℃, and after multiple rolling passes, the thickness is reduced from 20mm to about 7.5mm. After the hot-rolled plate is cooled to room temperature, it is further cold-rolled to about 2mm, with a single-pass reduction of 10% to 20%.

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

[0093] 3.1) The cold-rolled sheet was solution treated and then water-quenched to room temperature to obtain a supersaturated solid solution sheet. The solution treatment temperature was 520℃ and the holding time was 30 minutes.

[0094] 3.2) The supersaturated solid solution board was placed at room temperature for natural aging for 14 days, and then artificially aged at 180℃ for 0 to 36 hours (including 30 minutes for paint baking).

[0095] Figure 4 The image shown is a cast-state SEM image of the high-Fe content 6016 alloy from Example 3, which underwent multi-element microalloying with 0.2% Cr, 0.05% Sr, and 0.1% Sn. It can be observed that the Fe-rich phase in the high-Fe content 6016 aluminum alloy modified by multi-element microalloying was completely transformed from coarse needle-like β-Fe phase to fishbone-like α-Fe phase, which effectively controlled the Fe-rich phase.

[0096] To better compare the implementation 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 also be noted that the comparative improvement values ​​in this table are based on the tensile mechanical properties data after 14 days of natural aging in Comparative Example 1.

[0097] Clearly, the alloy prepared according to Example 3 of this invention showed a relatively small increase in yield strength in the T4 state during natural aging for 14 days, only 11.7 MPa, while the yield strength increase after baking increased from 57.3 MPa to 74.8 MPa, and the tensile elongation also increased. Furthermore, SEM images show that Example 3 effectively achieved the transformation of the β-Fe phase to the α-Fe phase in the high-Fe content 6016 alloy, effectively changing the morphology from coarse, long needle-like structures to fine, Chinese character-like structures.

[0098] Table 1 Performance parameters of the alloys prepared in Comparative Examples 1 and Examples 1-3

[0099]

[0100]

[0101] Based on the above embodiments, the key to the multi-element microalloying treatment method of the present invention lies in the regulation of the Fe-rich phase by Cr-Sr-Sn multi-element microalloying, which effectively reduces the adverse effects of impurity element Fe on mechanical properties in recycled aluminum alloys, modifies the Fe phase, and improves the response capability of the alloy during artificial aging. While having a high aging response, the alloy also has excellent strength, plasticity and yield strength at each stage of artificial aging.

[0102] To better illustrate the effects of this invention, the invention also supplements the description of the modification effects of single elements Cr, Sr, and Sn, as well as the modification effects of dual elements Cr+Sn and Cr+Sr. Alloying treatment is performed on high Fe content 6016 aluminum alloy, and supplementary comparative explanations are provided.

[0103] Comparative Example 2

[0104] The alloy composition of the product in this comparative example is: 0.5% Mg, 1.2% Si, 0.6% Fe, 0.2% Cr, with the balance being Al. All of the above are mass ratios.

[0105] Except for the difference in composition, the rest of the preparation process and its process parameters are the same as in Example 1.

[0106] Comparative Example 3

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

[0108] Except for the difference in composition, the rest of the preparation process and its process parameters are the same as in Example 1.

[0109] Comparative Example 4

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

[0111] Except for the difference in composition, the rest of the preparation process and its process parameters are the same as in Example 1.

[0112] Comparative Example 5

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

[0114] Except for the difference in composition, the rest of the preparation process and its process parameters are the same as in Example 1.

[0115] Comparative Example 6

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

[0117] Except for the difference in composition, the rest of the preparation process and its process parameters are the same as in Example 1.

[0118] For comparative examples 2–6, the artificial aging kinetic curves after different microalloying processes were tested, such as… Figure 5 As shown. And the trend of alloy hardness change during natural aging, such as... Figure 6 As shown. Figure 5 Artificial aging kinetic curves for 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 The curves showing the natural aging hardness changes 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 in Comparative Examples 2 and 3, Cr and Sr alone can modify the Fe-rich phase, but the modification is incomplete and cannot effectively suppress the negative effects of naturally aged phases, nor can it 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 regulate the Fe-rich phase. In Comparative Example 5, Cr+Sr can completely modify the Fe-rich phase, but has no effect on suppressing natural aging or enhancing aging kinetics. In Comparative Example 6, Cr+Sn can modify the Fe phase to a certain extent and suppress the negative effects of natural aging and enhance the artificial aging response.

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

[0121] The implementation of the present invention is not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope 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 in that: Includes the following steps: S1) The remelted 6016 aluminum alloy is subjected to Sr, Cr and Sn multi-element microalloying treatment; then the microalloyed melt is prepared into an ingot. S2) The ingot is subjected to heat preservation and homogenization treatment, followed by hot rolling and cold rolling; S3) The cold-rolled sheet is subjected to solution treatment to obtain a supersaturated solution sheet. S4) Natural aging and baking paint treatment are carried out on supersaturated solid solution plates to obtain recycled aluminum alloy; By performing Sr, Cr and Sn multi-element microalloying treatment on remelted 6016 aluminum alloy, the resulting recycled aluminum alloy contains the following components: Mg: 0.45~0.6%, Si: 1.0~1.2%, Fe: 0.5~0.6%, Cr: 0.15~0.25%, Sn: 0.05~0.1%, Sr: 0.03~0.08%, with the balance being Al and other impurity elements. The total amount of impurity elements is ≤0.05%, and the percentages are by mass. The microalloying treatment mentioned in step S1) refers to melting the remelted 6016 aluminum alloy, adding a Cr-containing master alloy, then cooling to 715~725℃ and holding for 45~70min; adding a Sr-containing master alloy and Sn, stirring and letting stand. The temperature for the heat preservation and homogenization treatment in step S2) is 550~580℃, and the time is 6~10h; after the heat preservation and homogenization treatment, cool to room temperature; The hot rolling temperature in step S2) is 450~480℃, and the total hot rolling reduction is 40%~80%; the cold rolling is carried out after the plate has cooled to room temperature after hot rolling, and the total reduction is 45%~80%. The hot rolling and cold rolling processes are multi-pass rolling, with a reduction of 5-20% per pass in hot rolling or cold rolling. The solution treatment temperature in step S3) is 510~530℃, and the solution treatment time is 20~40min.

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 Cr-containing master alloy is Al-20Cr, and the Sr-containing master alloy is Al-10Sr master alloy.

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: After solution treatment, cool to room temperature; the cooling refers to cooling by water quenching. The natural aging process mentioned in step S4) involves placing the object at room temperature naturally for 7-15 days. The baking process described in step S5) refers to baking at 175~185℃ for 25~35 minutes.

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: Specifically, this refers to rapidly immersing the solution-treated board in water for cooling or spraying water mist to cool the board.

5. An application of recycled aluminum alloy obtained by the method according to any one of claims 1 to 4, characterized in that: The recycled aluminum alloy is used in the automotive sheet metal industry.

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