Control Method of α-AlFe(Mn / Cr)Si Dispersed Phase in 6 Series Aluminum Alloys

Abstract

The invention discloses a method for regulating an α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy. The method comprises the following steps: a first-stage homogenization treatment: heating a 6-series aluminum alloy ingot containing Mn / Cr from room temperature to between 200°C and 330°C at a heating rate of 40°C / h-300°C / h, and keeping the temperature for 0.5h-18h; a second-stage homogenization treatment: continuously heating the 6-series aluminum alloy ingot subjected to the first-stage homogenization treatment to between 350°C and 500°C at a heating rate of 40°C / h-300°C / h, and keeping the temperature for 2h-24h; a third-stage homogenization treatment: continuously heating the 6-series aluminum alloy ingot subjected to the second-stage homogenization treatment to between 520°C and 580°C at a heating rate of 40°C / h-180°C / h, and keeping the temperature for 2h-12h; and cooling the 6-series aluminum alloy ingot subjected to the third-stage homogenization treatment to room temperature. The α-AlFe(Mn / Cr)Si dispersed phase control method in the 6-series aluminum alloy can eliminate or reduce the dispersion-free phase precipitation zone and the dispersed phase coarse area, thereby improving the distribution of the dispersed phase in the α-AlFe(Mn / Cr)Si and achieving high number density, small size and uniform dispersed distribution of the dispersed phase.

Description

Technical Field

[0001] The present invention relates to the field of aluminum alloy materials, in particular to a method for regulating α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy. Background Art

[0002] 6 series aluminum alloys are widely used in rail transportation, new energy vehicles, ships and other fields due to their medium strength, good forming properties, welding properties and corrosion resistance. However, due to their strength, toughness, corrosion properties and forming properties, the further application of 6 series Al-Mg-Si-Cu alloys is limited. At present, the research on improving the strength, toughness and corrosion properties of 6 series aluminum alloys is mainly focused on microalloying by adding transition elements such as Mn, Cr, Zr, Mo, V, Er, Sc and Hf. Through microalloying, dispersed phases such as Al(MnFe)Si, Al6Mn, Al7Cr, Al3Zr, Al3Sc and Al3Er are formed in the alloy. These dispersed phases have good stability at high temperatures, and due to the strong interaction between the dispersed phase grain boundaries, substructures and dislocations, they can effectively inhibit the dynamic / static softening mechanism, increase the recrystallization temperature of the alloy, limit the growth of grain size, and improve the toughness and strength of the alloy. However, their applications all have certain limitations. For example, Al(MnFe)Si, Al6Mn, and Al7Cr have poor thermal stability and are prone to coarsening during high-temperature homogenization. Although Al3Zr has high thermal stability, the introduction of Si atoms in 6-series aluminum alloys will "poison" Zr atoms, making it difficult to play an effective role. Elements such as Er, Sc, and Hf are the most effective rare earth elements to inhibit the recrystallization of aluminum alloys, but their high composition limits their industrial application in aluminum alloys.

[0003] Therefore, Mn / Cr elements are still the most widely used transition elements in 6-series aluminum alloys. However, Mn / Cr elements show obvious segregation behavior during the solidification process of the alloy, which makes the nucleation and precipitation of the dispersed phase in the subsequent heat treatment process also show obvious segregation behavior, such as the formation of a dispersoids free zone (DFZ) near the grain boundary, and the formation of a coarse dispersoids zone (CDZ) inside the grain, and the potential of the dispersed phase to inhibit recrystallization behavior cannot be fully released.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The object of the present invention is to provide a method for regulating α-AlFe(Mn / Cr)Si dispersed phase in 6 series aluminum alloy, which can eliminate or reduce the precipitation zone without dispersed phase and the coarse dispersed phase area, thereby improving the distribution of dispersed phase in α-AlFe(Mn / Cr)Si and achieving high number density, small size and uniform dispersed distribution of dispersed phase.

[0006] To achieve the above object, an embodiment of the present invention provides a method for controlling α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy, which comprises the following steps:

[0007] The first stage homogenization treatment: the 6 series aluminum alloy ingot containing Mn / Cr is heated from room temperature to between 200°C and 330°C at a heating rate of 40°C / h-300°C / h, and kept at this temperature for 0.5h-18h; the first stage homogenization treatment causes the metastable phase in the 6 series aluminum alloy to precipitate and be evenly distributed;

[0008] Second stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the first stage homogenization treatment is further heated to between 350°C and 500°C at a heating rate of 40°C / h-300°C / h, and kept at this temperature for 2h-24h; the second stage homogenization treatment causes the precipitated metastable phase to dissolve back to form a Si-rich region, which is used to promote the nucleation and precipitation of the α-AlFe(Mn / Cr)Si dispersed phase;

[0009] The third stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the second stage homogenization treatment is further heated to between 520°C and 580°C at a heating rate of 40°C / h-180°C / h, and kept at this temperature for 2h-12h; the third stage homogenization treatment is used for the dissolution of the non-equilibrium eutectic structure, the elimination of dendrite segregation, and the stabilization of the α-AlFe(Mn / Cr)Si dispersed phase size; and

[0010] The 6 series aluminum alloy ingot subjected to the third stage homogenization treatment is cooled to room temperature.

[0011] In one or more embodiments of the present invention, in the first stage homogenization treatment, the 6-series aluminum alloy ingot containing Mn / Cr is heated from room temperature to 220°C at a heating rate of 120°C / h and kept at this temperature for 8h.

[0012] In one or more embodiments of the present invention, in the second stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the first stage homogenization treatment is further heated to 380°C at a heating rate of 150°C / h and kept at this temperature for 12h.

[0013] In one or more embodiments of the present invention, in the third stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the second stage homogenization treatment is further heated to 550° C. at a heating rate of 80° C. / h and kept at this temperature for 6 hours.

[0014] In one or more embodiments of the present invention, the components of the 6 series aluminum alloy ingot include, by weight percentage: Mg: 0.4%-1.4%, Si: 0.4%-1.6%, Mn: 0.15%-1.3%, Cr: 0%-0.6%; Cu: 0%-0.9%, Ti≤0.2%, Zn≤0.25%, Fe≤0.3%, and the balance is Al.

[0015] In one or more embodiments of the present invention, continuous or staged temperature increase is adopted among the first-stage homogenization treatment, the second-stage homogenization treatment and the third-stage homogenization treatment.

[0016] In one or more embodiments of the present invention, the area percentage of the region without dispersed phase precipitation of the 6-series aluminum alloy ingot subjected to the third-stage homogenization treatment is ≤5%.

[0017] In one or more embodiments of the present invention, the area percentage of the coarse low number density dispersed phase region of the 6 series aluminum alloy ingot subjected to the third stage homogenization treatment is ≤2%.

[0018] In one or more embodiments of the present invention, the average equivalent diameter of the α-AlFe(Mn / Cr)Si phase in the 6-series aluminum alloy ingot subjected to the third-stage homogenization treatment is ≤200 nm.

[0019] In one or more embodiments of the present invention, the number density of the α-AlFe(Mn / Cr)Si dispersed phase in the 6-series aluminum alloy ingot subjected to the third-stage homogenization treatment is ≥15 / μm 2 .

[0020] Compared with the prior art, the method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in the 6-series aluminum alloy according to the embodiment of the present invention combines the characteristics of the microstructure evolution of the 6-series aluminum alloy during the homogenization heat treatment, and adopts a multi-stage homogenization heat treatment method to effectively control the distribution, size and number density of the α-AlFe(Mn / Cr)Si dispersed phase, thereby improving the microstructure of the 6-series aluminum alloy, improving the strength, toughness and other properties, and further broadening the application of the 6-series aluminum alloy in modern industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is a schematic flow diagram of a method for controlling α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to an embodiment of the present invention;

[0022] Figure 2 are the diffuse phase dark field optical photograph and SEM photograph of Example 1;

[0023] Figure 3is a metallographic photograph of a cross section of an aluminum alloy extruded profile of Example 1;

[0024] Figure 4 are the diffuse phase dark field optical photograph and SEM photograph of Example 2;

[0025] Figure 5 is a metallographic photograph of a cross section of an aluminum alloy extruded profile coated in Example 2;

[0026] Figure 6 are the diffuse phase dark field optical photograph and SEM photograph of Example 3;

[0027] Figure 7 is a metallographic photograph of a cross section of an aluminum alloy extruded profile coated in Example 3;

[0028] Figure 8 These are the dark field optical photograph and SEM photograph of the diffuse phase of Comparative Example 1;

[0029] Fig. 9 This is a metallographic photograph of the cross section of the aluminum alloy extruded profile of Comparative Example 1;

[0030] Fig.10 These are the dark field optical photograph and SEM photograph of the diffuse phase of Comparative Example 2;

[0031] Fig.11 This is a metallographic photograph of the cross section of the aluminum alloy extruded profile of Comparative Example 2;

[0032] Fig.12 These are the dark field optical photograph and SEM photograph of the diffuse phase of Comparative Example 3;

[0033] Fig.13 This is a metallographic photograph of the cross section of the aluminum alloy extruded profile of Comparative Example 3;

[0034] Fig.14 It is a statistical chart of the percentage of dispersed phase CDZ zone and DFZ zone in the aluminum alloys of Comparative Examples 1-3 and Examples 1-3;

[0035] Fig.15 It is a statistical graph of the number density of dispersed phases and the width of the coarse-grained layer of the profiles in the aluminum alloys of Comparative Examples 1-3 and Examples 1-3. DETAILED DESCRIPTION

[0036] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

[0037] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0038] like Figures 1 to 15 As shown, a method for controlling α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to a preferred embodiment of the present invention includes steps S1-S4.

[0039] Step S1: First stage homogenization treatment: heating the 6 series aluminum alloy ingot containing Mn / Cr from room temperature to between 200°C and 330°C at a heating rate of 40°C / h-300°C / h, and keeping the temperature for 0.5h-18h.

[0040] Specifically, in step S1, the 6 series aluminum alloy ingot containing Mn / Cr is heated from room temperature to between 200°C and 330°C in a heat treatment furnace at a heating rate of 40°C / h-300°C / h, and kept warm for 0.5h-18h. Preferably, the 6 series aluminum alloy ingot is heated from room temperature to between 220°C at a heating rate of 120°C / h, and kept warm for 8h. The first stage homogenization treatment allows the 6 series aluminum alloy to precipitate metastable phases such as β′ / β″, Q′ / Q″, L′ / L″ or μ during the low-temperature insulation process, and the metastable phases are kept warm for a period of time to allow sufficient nucleation, precipitation and uniform distribution.

[0041] Step S2: Second stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the first stage homogenization treatment is further heated to between 350°C and 500°C at a heating rate of 40°C / h-300°C / h, and kept at this temperature for 2h-24h.

[0042] Specifically, in step S2, the 6-series aluminum alloy ingot subjected to the first-stage homogenization treatment is further heated to between 350°C and 500°C at a heating rate of 40°C / h-300°C / h, and is kept warm for 2h-24h. Preferably, the 6-series aluminum alloy ingot subjected to the first-stage homogenization treatment is further heated to 380°C at a heating rate of 150°C / h, and is kept warm for 12h. The 6-series aluminum alloy ingot is heated from the first-stage homogenization treatment to the second-stage homogenization treatment at the above-mentioned heating rate. During the process, the metastable phase pre-nucleated and precipitated during the first-stage homogenization treatment gradually dissolves back, and the Mg atoms dissolve back into the aluminum alloy matrix, and the "Si" skeleton is retained to form a Si-rich region. During the insulation process of the second-stage homogenization treatment, the Si-rich region serves as a heterogeneous nucleation point of the α-AlFe(Mn / Cr)Si dispersed phase, promoting the full nucleation and precipitation of the α-AlFe(Mn / Cr)Si dispersed phase.

[0043] Step S3: third-stage homogenization treatment: the 6-series aluminum alloy ingot subjected to the second-stage homogenization treatment is further heated to between 520°C and 580°C at a heating rate of 40°C / h-180°C / h, and kept at this temperature for 2h-12h.

[0044] Specifically, in step S3, the 6-series aluminum alloy ingot subjected to the second-stage homogenization treatment is further heated to between 520°C and 580°C at a heating rate of 40°C / h-180°C / h, and is kept warm for 2h-12h. Preferably, the 6-series aluminum alloy ingot subjected to the second-stage homogenization treatment is further heated to between 550°C at a heating rate of 80°C / h, and is kept warm for 6h. The 6-series aluminum alloy ingot is heated from the second-stage homogenization treatment to the third-stage homogenization treatment at the above-mentioned heating rate. During the heating process, the non-equilibrium eutectic structure in the 6-series aluminum alloy ingot begins to gradually dissolve back into the aluminum alloy matrix, which can effectively reduce the temperature and holding time of the third-stage homogenization treatment. On the basis of achieving full dissolution of the non-equilibrium eutectic structure, the α-AlFe(Mn / Cr)Si dispersed phase precipitated in the low-temperature stage is avoided from staying in the high-temperature stage for a long time and coarsening.

[0045] Step S4: Cooling the 6-series aluminum alloy ingot after the third-stage homogenization treatment to room temperature.

[0046] In the above-mentioned dispersed phase control method, continuous heating or segmented heating can be used between the first-stage homogenization treatment, the second-stage homogenization treatment and the third-stage homogenization treatment. Continuous heating means that there is no interval time between the three-stage homogenization treatment, so that continuous heating is performed. Segmented heating means that there can be an interval time between the three-stage homogenization treatment. Through the three-stage homogenization treatment, the uneven distribution of the α-AlFe(Mn / Cr)Si dispersed phase and the rapid coarsening at high temperature under the traditional homogenization treatment method can be effectively improved, so that the alloy can obtain more excellent comprehensive performance.

[0047] In one embodiment, the components of the 6-series aluminum alloy ingot include, by weight percentage: Mg: 0.4%-1.4%, Si: 0.4%-1.6%, Mn: 0.15%-1.3%, Cr: 0%-0.6%; Cu: 0%-0.9%, Ti≤0.2%, Zn≤0.25%, Fe≤0.3%, and the balance is Al. The dispersed phase control method has a good control effect on the above-mentioned 6-series aluminum alloy ingot.

[0048] In one embodiment, the area percentage of the non-dispersed phase precipitation region of the 6-series aluminum alloy ingot after the third-stage homogenization treatment is ≤5%. The area percentage of the coarse low-number-density dispersed phase region is ≤2%. The average equivalent diameter of the α-AlFe(Mn / Cr)Si phase in the 6-series aluminum alloy ingot after the third-stage homogenization treatment is ≤200nm; the number density of the α-AlFe(Mn / Cr)Si dispersed phase is ≥15 / μm 2 .

[0049] The present invention will be further described below in conjunction with specific embodiments and comparative examples.

[0050] Example 1

[0051] The mass percentage of the aluminum alloy is: Mg: 0.45%, Si: 0.5%, Mn: 0.2%, Cr: 0.1%; Cu: 0.1%, Ti≤0.2%, Zn≤0.2%, Fe≤0.3%, and the rest is Al.

[0052] The first stage homogenization treatment: the 6 series aluminum alloy ingot is heated from room temperature to 220°C at a heating rate of 120°C / h and kept at this temperature for 8h.

[0053] Second stage homogenization treatment: The 6 series aluminum alloy ingot that has undergone the first stage homogenization treatment is heated to 380°C at a heating rate of 300°C / h and kept at this temperature for 6h.

[0054] The third stage homogenization treatment: the 6 series aluminum alloy ingot which has undergone the second stage homogenization treatment is heated to 550°C at a heating rate of 180°C / h and kept at this temperature for 10 hours.

[0055] The 6 series aluminum alloy ingot after the third stage homogenization treatment is cooled to room temperature.

[0056] After the aluminum alloy ingot is homogenized, hot extrusion is performed. The preheating temperature of the aluminum alloy ingot is 480℃, the extrusion speed is 4mm / s, and the extrusion ratio is 20. After the extrusion, T6 artificial aging treatment is performed immediately. The aging process is heating to 180℃ and keeping warm for 8h. The mechanical properties and intergranular corrosion properties of the T6 state samples are tested.

[0057] Figure 2 Figures a) and b) are respectively the dark field optical photograph and SEM photograph of the dispersed phase of the aluminum alloy after multi-stage homogenization. Figure 3 This is a metallographic photograph of the cross section of an aluminum alloy extruded profile. Figure 2 and Figure 3 As shown in the figure, after homogenization treatment, the CDZ zone is almost not observed in the center of the grain of the 6 series aluminum alloy, the area percentage of the DFZ zone near the grain boundary is reduced, and the α-AlFe(Mn / Cr)Si dispersed phase is evenly distributed, with a small size and a high number density.

[0058] The thickness of the coarse-grained layer of the profile is 120-130μm.

[0059] Room temperature tensile properties: Rm = 246MPa, Rp0.2 = 210MPa, elongation after fracture 16%. Average intergranular corrosion depth 120μm.

[0060] Example 2

[0061] The mass percentage of the aluminum alloy is: Mg: 0.8%, Si: 1.0%, Mn: 0.6%, Cr: 0.3%; Cu: 0.4%, Ti≤0.2%, Zn≤0.2%, Fe≤0.3%, and the rest is Al.

[0062] The first stage homogenization treatment: the 6 series aluminum alloy ingot is heated from room temperature to 280°C at a heating rate of 300°C / h and kept at this temperature for 4h.

[0063] Second stage homogenization treatment: The 6 series aluminum alloy ingot that has undergone the first stage homogenization treatment is heated to 420°C at a heating rate of 260°C / h and kept at this temperature for 24h.

[0064] The third stage homogenization treatment: the 6 series aluminum alloy ingot which has undergone the second stage homogenization treatment is heated to 550°C at a heating rate of 80°C / h and kept at this temperature for 6h.

[0065] The 6 series aluminum alloy ingot after the third stage homogenization treatment is cooled to room temperature.

[0066] After the aluminum alloy ingot is homogenized, hot extrusion is performed. The preheating temperature of the aluminum alloy ingot is 480℃, the extrusion speed is 4mm / s, and the extrusion ratio is 20. After the extrusion, T6 artificial aging treatment is performed immediately. The aging process is heating to 180℃ and keeping warm for 8h. The mechanical properties and intergranular corrosion properties of the T6 state samples are tested.

[0067] Figure 4 Figures a) and b) are respectively the dark field optical photograph and SEM photograph of the dispersed phase of the aluminum alloy after multi-stage homogenization. Figure 5 This is a metallographic photograph of the cross section of an aluminum alloy extruded profile. Figure 4 and Figure 5 As shown in the figure, after homogenization treatment, the CDZ zone is almost not observed in the center of the grain of the 6 series aluminum alloy, the area percentage of the DFZ zone near the grain boundary is reduced, and the α-AlFe(Mn / Cr)Si dispersed phase is evenly distributed with small size and high number density.

[0068] The thickness of the coarse-grained layer of the profile is 103-124μm.

[0069] Room temperature tensile properties: Rm = 351 MPa, Rp0.2 = 331 MPa, elongation after fracture 15%. Average intergranular corrosion depth 130 μm.

[0070] Example 3

[0071] The mass percentage of the aluminum alloy is: Mg: 1.1%, Si: 1.2%, Mn: 1.0%, Cr: 0.6%; Cu: 0.5%, Ti≤0.2%, Zn≤0.2%, Fe≤0.3%, and the rest is Al.

[0072] The first stage homogenization treatment: the 6 series aluminum alloy ingot is heated from room temperature to 320°C at a heating rate of 260°C / h and kept at this temperature for 4h.

[0073] Second stage homogenization treatment: The 6 series aluminum alloy ingot that has undergone the first stage homogenization treatment is heated to 380°C at a heating rate of 150°C / h and kept at this temperature for 12h.

[0074] The third stage homogenization treatment: the 6 series aluminum alloy ingot which has undergone the second stage homogenization treatment is heated to 540°C at a heating rate of 120°C / h and kept at this temperature for 12h.

[0075] The 6 series aluminum alloy ingot after the third stage homogenization treatment is cooled to room temperature.

[0076] After the aluminum alloy ingot is homogenized, hot extrusion is performed. The preheating temperature of the aluminum alloy ingot is 480℃, the extrusion speed is 4mm / s, and the extrusion ratio is 20. After the extrusion, T6 artificial aging treatment is performed immediately. The aging process is heating to 180℃ and keeping warm for 8h. The mechanical properties and intergranular corrosion properties of the T6 state samples are tested.

[0077] Figure 6 Figures a) and b) are respectively the dark field optical photograph and SEM photograph of the dispersed phase of the aluminum alloy after multi-stage homogenization. Figure 7 This is a metallographic photograph of the cross section of an aluminum alloy extruded profile. Figure 6 and Figure 7 As shown in the figure, after homogenization treatment, the CDZ zone is almost not observed in the center of the grain of the 6 series aluminum alloy, the area percentage of the DFZ zone near the grain boundary is reduced, and the fine and high number density α-AlFe(Mn / Cr)Si dispersed phase is evenly distributed.

[0078] The thickness of the coarse-grained layer of the profile is 97-105μm.

[0079] Room temperature tensile properties: Rm = 420 MPa, Rp0.2 = 391 MPa, elongation after fracture 13%. Average intergranular corrosion depth 146 μm.

[0080] Comparative Example 1

[0081] The aluminum alloy composition in Comparative Example 1 is the same as that in Example 1.

[0082] Comparative Example 1 adopts the traditional single-stage homogenization system, and the aluminum alloy ingot is heated to 560° C. at a heating rate of 300° C. / h and kept at this temperature for 10 h.

[0083] After the aluminum alloy ingot is homogenized, hot extrusion is performed. The preheating temperature of the aluminum alloy ingot is 480℃, the extrusion speed is 4mm / s, and the extrusion ratio is 20. After the extrusion, T6 artificial aging treatment is performed immediately. The aging process is heating to 180℃ and keeping warm for 8h. The mechanical properties and intergranular corrosion properties of the T6 state samples are tested.

[0084] Figure 8Figures a) and b) are respectively the dark field optical photograph and SEM photograph of the dispersed phase of the aluminum alloy after multi-stage homogenization. Fig. 9 This is a metallographic photograph of the cross section of an aluminum alloy extruded profile. Figure 8 and Fig. 9 As shown in the figure, after homogenization treatment, there is a CDZ zone in the center of the grain of the 6 series aluminum alloy, and a DFZ zone near the grain boundary. The α-AlFe(Mn / Cr)Si dispersed phase is unevenly distributed, coarse in size, and low in number density.

[0085] The thickness of the coarse-grained layer of the profile is 162-175μm.

[0086] Room temperature tensile properties: Rm = 420 MPa, Rp0.2 = 391 MPa, elongation after fracture 13%. Average intergranular corrosion depth 146 μm.

[0087] Comparative Example 2

[0088] The aluminum alloy composition in Comparative Example 2 is the same as that in Example 2.

[0089] Comparative Example 2 adopts the traditional single-stage homogenization system, and the aluminum alloy ingot is heated to 520° C. at a heating rate of 240° C. / h and kept warm for 24 hours.

[0090] After the aluminum alloy ingot is homogenized, hot extrusion is performed. The preheating temperature of the aluminum alloy ingot is 480℃, the extrusion speed is 4mm / s, and the extrusion ratio is 20. After the extrusion, T6 artificial aging treatment is performed immediately. The aging process is heating to 180℃ and keeping warm for 8h. The mechanical properties and intergranular corrosion properties of the T6 state samples are tested.

[0091] Fig.10 Figures a) and b) are respectively the dark field optical photograph and SEM photograph of the dispersed phase of the aluminum alloy after multi-stage homogenization. Fig.11 This is a metallographic photograph of the cross section of an aluminum alloy extruded profile. Fig.10 and Fig.11 As shown in the figure, after homogenization treatment, there is a CDZ zone in the center of the grain of the 6 series aluminum alloy, and a DFZ zone near the grain boundary. The α-AlFe(Mn / Cr)Si dispersed phase is unevenly distributed, coarse in size, and low in number density.

[0092] The thickness of the coarse-grained layer of the profile is 147-167μm.

[0093] Room temperature tensile properties: Rm = 338MPa, Rp0.2 = 315MPa, elongation after fracture 13%. Average intergranular corrosion depth 180μm.

[0094] Comparative Example 3

[0095] The aluminum alloy composition in Comparative Example 3 is the same as that in Example 3.

[0096] Comparative Example 3 adopts a two-stage homogenization system, heating the aluminum alloy ingot to 420°C at a heating rate of 120°C / h and keeping it warm for 24 hours, and then heating to 550°C at a heating rate of 120°C / h and keeping it warm for 10 hours.

[0097] After the aluminum alloy ingot is homogenized, hot extrusion is performed. The preheating temperature of the aluminum alloy ingot is 480℃, the extrusion speed is 4mm / s, and the extrusion ratio is 20. After the extrusion, T6 artificial aging treatment is performed immediately. The aging process is heating to 180℃ and keeping warm for 8h. The mechanical properties and intergranular corrosion properties of the T6 state samples are tested.

[0098] Fig.12 Figures a) and b) are respectively the dark field optical photograph and SEM photograph of the dispersed phase of the aluminum alloy after multi-stage homogenization. Fig.13 This is a metallographic photograph of the cross section of an aluminum alloy extruded profile. Fig.12 and Fig.13 As shown in the figure, after homogenization treatment, there is a CDZ zone in the center of the grain of the 6 series aluminum alloy, and a DFZ zone near the grain boundary. The α-AlFe(Mn / Cr)Si dispersed phase is unevenly distributed, coarse in size, and low in number density.

[0099] The thickness of the coarse-grained layer of the profile is 146-151μm.

[0100] Room temperature tensile properties: Rm = 400 MPa, Rp0.2 = 374 MPa, elongation after fracture 11%. Average intergranular corrosion depth 208 μm.

[0101] like Fig.13 and Fig.15 As shown, compared with Comparative Examples 1-3, Examples 1-3 have smaller percentages of dispersed phase precipitation bands and dispersed phase coarse regions, lower coarse grain layer widths, and higher number density of dispersed phases in α-AlFe(Mn / Cr)Si.

[0102] In summary, the method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in the 6 series aluminum alloy of the present invention combines the characteristics of the microstructure evolution of the 6 series aluminum alloy during the homogenization heat treatment process, and adopts a multi-stage homogenization heat treatment method to effectively control the distribution, size and number density of the α-AlFe(Mn / Cr)Si dispersed phase, thereby improving the microstructure of the 6 series aluminum alloy, improving the strength, toughness and other properties, and further broadening the application of the 6 series aluminum alloy in modern industry.

[0103] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A method for controlling α-AlFe(Mn / Cr)Si dispersed phase in 6 series aluminum alloy, characterized in that: The following steps are involved: The first stage homogenization treatment: the 6 series aluminum alloy ingot containing Mn / Cr is heated from room temperature to between 200°C and 330°C at a heating rate of 40°C / h-300°C / h, and kept at this temperature for 0.5h-18h; the first stage homogenization treatment causes the metastable phase in the 6 series aluminum alloy to precipitate and be evenly distributed; Second stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the first stage homogenization treatment is further heated to between 350°C and 500°C at a heating rate of 40°C / h-300°C / h, and kept at this temperature for 2h-24h; the second stage homogenization treatment causes the precipitated metastable phase to dissolve back to form a Si-rich region, which is used to promote the nucleation and precipitation of the α-AlFe(Mn / Cr)Si dispersed phase; The third stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the second stage homogenization treatment is further heated to between 520°C and 580°C at a heating rate of 40°C / h-180°C / h, and kept at this temperature for 2h-12h; the third stage homogenization treatment is used for the dissolution of the non-equilibrium eutectic structure, the elimination of dendrite segregation, and the stabilization of the α-AlFe(Mn / Cr)Si dispersed phase size; and The 6 series aluminum alloy ingot subjected to the third stage homogenization treatment is cooled to room temperature.

2. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: In the first stage homogenization treatment, the 6 series aluminum alloy ingot containing Mn / Cr is heated from room temperature to 220°C at a heating rate of 120°C / h and kept at this temperature for 8h.

3. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: In the second stage homogenization treatment: the 6 series aluminum alloy ingot subjected to the first stage homogenization treatment is further heated to 380° C. at a heating rate of 150° C. / h and kept at this temperature for 12 hours.

4. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: In the third stage homogenization treatment, the 6 series aluminum alloy ingot subjected to the second stage homogenization treatment is further heated to 550° C. at a heating rate of 80° C. / h and kept at this temperature for 6 hours.

5. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: The components of the 6 series aluminum alloy ingot include, by weight percentage: Mg: 0.4%-1.4%, Si: 0.4%-1.6%, Mn: 0.15%-1.3%, Cr: 0%-0.6%; Cu: 0%-0.9%, Ti≤0.2%, Zn≤0.25%, Fe≤0.3%, and the balance is Al.

6. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: Continuous or segmented heating is adopted between the first stage homogenization treatment, the second stage homogenization treatment and the third stage homogenization treatment.

7. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: The area percentage of the region without dispersed phase precipitation of the 6 series aluminum alloy ingot after the third stage homogenization treatment is ≤5%.

8. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: The area percentage of the coarse low number density dispersed phase region of the 6 series aluminum alloy ingot after the third stage homogenization treatment is ≤2%.

9. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: The average equivalent diameter of the α-AlFe(Mn / Cr)Si dispersed phase in the 6-series aluminum alloy ingot after the third-stage homogenization treatment is ≤200nm.

10. The method for controlling the α-AlFe(Mn / Cr)Si dispersed phase in a 6-series aluminum alloy according to claim 1, characterized in that: The number density of the α-AlFe(Mn / Cr)Si dispersed phase in the 6-series aluminum alloy ingot after the third-stage homogenization treatment is ≥15 / μm 2 .

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