METHOD FOR CONTROLLING MICROSTRUCTURE OF RECYCLED ALUMINUM ALLOY

Abstract

A method for controlling a microstructure of a recycled aluminum alloy includes steps of: degassing and removing inclusions from the molten aluminum alloy, refining grains and controlling the deformed microstructure. Good microstructures of the deformed aluminum alloy can be obtained after degassing by gas flushing, removing the inclusions by filtering, refining the grains by adding a modifier, and extruding or rolling or forging. The present invention provides desirable results of degassing and impurity removal. Contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02-0.26 ml/100 g Al and 0.4-0.7 area % metallographic field respectively.

In an aluminum alloy billet, an average grain size is 25-50 m and a short rod-shaped or elliptical second phase is 10-100 nm. In the deformed aluminum alloy, a grain aspect ratio is 10:1-100:1 and short rod-shaped or elliptical particles are 5-80 nm.

Claims

1. A method for controlling a microstructure of a recycled aluminum alloy, comprising steps of: (1), adopting aluminum scrap as raw material, and obtaining a target molten aluminum alloy successively through smelting, slagging and composition adjustment; (2), refining the target molten aluminum alloy obtained in the step (1) with degassing and adding a modifier, so as to obtain a refined recycled molten aluminum alloy; wherein gas of the target molten aluminum alloy is removed by gas flushing, and the modifier is added to achieve grain refinement; (3), filtering the refined recycled molten aluminum alloy and casting into an aluminum alloy billet; wherein filtering is for removing inclusions; (4), heating the aluminum alloy billet for homogenization; and (5), processing the homogenized billet with extruding, rolling or forging, so as to obtain a deformed aluminum alloy.

2. The method, as recited in claim 1, wherein the step (1) particularly comprises steps of: adopting the aluminum scrap as the raw material, smelting at 650-900 C. for 30-300 minutes, removing slag from a molten aluminum alloy, and adjusting compositions of the molten aluminum alloy to target compositions, so as to obtain the target molten aluminum alloy with the target compositions.

3. The method, as recited in claim 1, wherein the step (2) particularly comprises steps of: refining the target molten aluminum alloy with the target compositions with degassing and modifying at 700-900 C. for 10-60 minutes; wherein: degassing is gas flushing by N.sub.2, Ar, or a mixed gas of N.sub.2 and Ar; for gas flushing, a flow rate is 1-15 L/min, and a pressure is 0.12-0.50 MPa; the modifier is added into the target molten aluminum alloy with an addition amount of 0.5-3.5 kg/t, and is at least one member selected from a group consisting of AlTiB alloy, AlTiC alloy, and AlTiC-RE (RE represents rare earths) alloy; and contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02-0.26 ml/100 g Al and 0.4-0.7 area % metallographic field respectively.

4. The method, as recited in claim 3, wherein: when gas flushing is made by the mixed gas of N.sub.2 and Ar, a volume ratio of N.sub.2 and Ar is 5:1 to 1:5.

5. The method, as recited in claim 1, wherein the step (3) particularly comprises steps of: filtering the refined recycled molten aluminum alloy with a ceramic filter of 10-60 meshes, and then casting into the aluminum alloy billet, wherein the aluminum alloy billet has an average grain size of 25-50 m and a short rod-shaped or elliptical second phase of 10-100 nm.

6. The method, as recited in claim 1, wherein the step (4) particularly comprises steps of: homogenizing at 350-500 C. for 8-40 hours.

7. The method, as recited in claim 1, wherein the step (5) particularly comprises steps of: extruding the homogenized billet into a profile at a temperature from room temperature to 500 C. with an extrusion ratio of 4-40 and a billet speed of 0.1-5.0 mm/s, wherein the profile has short rod-shaped or elliptical particles of 5-80 nm with a grain aspect ratio of 20:1-100:1.

8. The method, as recited in claim 1, wherein the step (5) particularly comprises steps of: rolling the homogenized billet into a profile at a temperature from room temperature to 500 C. with reduction of 5-50%, wherein the profile has short rod-shaped or elliptical particles of 5-80 nm with a grain aspect ratio of 10:1-100:1.

9. The method, as recited in claim 1, wherein the step (5) particularly comprises steps of: forging the homogenized billet into a profile at a temperature from room temperature to 500 C. with deformation of 10-50%, wherein the profile has short rod-shaped or elliptical particles of 5-80 nm with a grain aspect ratio of 10:1-100:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be explained in detail with reference to the accompanying drawings.

[0029] FIG. 1 shows a process flow diagram of a method for controlling a microstructure of a recycled aluminum alloy according to the present invention.

[0030] FIG. 2 shows an as-cast microstructure of a recycled 2024 aluminum alloy billet according to a first example of the present invention.

[0031] FIG. 3 shows an as-cast microstructure of a recycled 7075 aluminum alloy billet according to a sixteenth example of the present invention.

[0032] FIG. 4 shows a microstructure of a recycled 2024 aluminum alloy profile according to the first example of the present invention.

[0033] FIG. 5 shows a microstructure of a recycled 7075 aluminum alloy profile according to the sixteenth example of the present invention.

[0034] FIG. 6 shows a microstructure of a recycled 7075 aluminum alloy profile according to an eighteenth example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0035] The present invention will be further described in detail reference to the accompanying drawings and examples. Further, in order to provide a better understanding of the present invention, the specific details are described in the following detailed description of the present invention. The present invention may be fully understood by those skilled in the art without the description of these details.

[0036] The present invention provides a method for controlling a microstructure of a recycled aluminum alloy, and a process flow diagram thereof is showed in FIG. 1. Detailed examples are described as follows.

Example 1

[0037] Aluminum scrap is smelted at 650 C. for 300 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 2024 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 5:1. For gas flushing, a flow rate is 1 L/min, and a pressure is 0.12 MPa. The AlTiB alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 0.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 10 meshes and then casted into a billet, wherein the billet has an average grain size of 50 m (as shown in FIG. 2) and a short rod-shaped or elliptical second phase of 100 nm. After being homogenized at 350 C. for 40 hours, the billet is extruded at 500 C. into a profile with an extrusion ratio of 4 and a billet speed of 0.1 mm/s. The profile has short rod-shaped or elliptical particles of 80 nm with a grain aspect ratio of 20:1 (as shown in FIG. 4).

[0038] According to the first example, the aluminum scrap is selected from the group consisting of scrap aluminum of aircraft, cars, cans, doors and windows, etc.

Example 2

[0039] Aluminum scrap is smelted at 700 C. for 250 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 2024 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 2:1. For gas flushing, a flow rate is 3 L/min, and a pressure is 0.20 MPa. The AlTiC alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 1.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.05 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 20 meshes and then casted into a billet, wherein the billet has an average grain size of 45 m and a short rod-shaped or elliptical second phase of 80 nm. After being homogenized at 450 C. for 24 hours, the billet is rolled into a profile at 500 C. with reduction of 5%. The profile has short rod-shaped or elliptical particles of 70 nm with a grain aspect ratio of 10:1.

Example 3

[0040] Aluminum scrap is smelted at 750 C. for 200 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 2024 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:1. For gas flushing, a flow rate is 6 L/min, and a pressure is 0.25 MPa. The AlTiB alloy and the AlTiC alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 1.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.10 ml/100 g Al and 0.5 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 30 meshes and then casted into a billet, wherein the billet has an average grain size of 40 m and a short rod-shaped or elliptical second phase of 60 nm. After being homogenized at 500 C. for 8 hours, the billet is forged into a profile at 500 C. with deformation of 10%. The profile has short rod-shaped or elliptical particles of 50 nm with a grain aspect ratio of 10:1.

Example 4

[0041] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 3A21 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy (RE represents rare earths), as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 40 nm. After being homogenized at 350 C. for 40 hours, the billet is extruded at 450 C. into a profile with an extrusion ratio of 10 and a billet speed of 1.0 mm/s. The profile has short rod-shaped or elliptical particles of 30 nm with a grain aspect ratio of 40:1.

Example 5

[0042] Aluminum scrap is smelted at 850 C. for 100 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 3A21 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 10 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:5. For gas flushing, a flow rate is 12 L/min, and a pressure is 0.40 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.20 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 50 meshes and then casted into a billet, wherein the billet has an average grain size of 30 m and a short rod-shaped or elliptical second phase of 20 nm. After being homogenized at 450 C. for 24 hours, the billet is rolled into a profile at 450 C. with reduction of 10%. The profile has short rod-shaped or elliptical particles of 10 nm with a grain aspect ratio of 40:1.

Example 6

[0043] Aluminum scrap is smelted at 900 C. for 30 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 3A21 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by Ar. For gas flushing, a flow rate is 15 L/min, and a pressure is 0.50 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 3.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.26 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 60 meshes and then is casted into a billet, wherein the billet has an average grain size of 25 m and a short rod-shaped or elliptical second phase of 10 nm. After being homogenized at 500 C. for 8 hours, the billet is forged into a profile at 450 C. with deformation of 20%. The profile has short rod-shaped or elliptical particles of 5 nm with a grain aspect ratio of 30:1.

Example 7

[0044] Aluminum scrap is smelted at 650 C. for 300 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 4032 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 5:1. For gas flushing, a flow rate is 1 L/min, and a pressure is 0.12 MPa. The AlTiB alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 0.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 10 meshes and then is casted into a billet, wherein the billet has an average grain size of 50 m and a short rod-shaped or elliptical second phase of 100 nm. After being homogenized at 350 C. for 40 hours, the billet is extruded at 400 C. into a profile with an extrusion ratio of 20 and a billet speed of 2.0 mm/s. The profile has short rod-shaped or elliptical particles of 80 nm with a grain aspect ratio of 60:1.

Example 8

[0045] Aluminum scrap is smelted at 700 C. for 250 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 4032 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 2:1. For gas flushing, a flow rate is 3 L/min, and a pressure is 0.20 MPa. The AlTiC alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 1.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.05 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 20 meshes and then is casted into a billet, wherein the billet has an average grain size of 45 m and a short rod-shaped or elliptical second phase of 80 nm. After being homogenized at 450 C. for 24 hours, the billet is rolled into a profile at 400 C. with reduction of 20%. The profile has short rod-shaped or elliptical particles of 70 nm with a grain aspect ratio of 60:1.

Example 9

[0046] Aluminum scrap is smelted at 750 C. for 200 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 4032 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:1. For gas flushing, a flow rate is 6 L/min, and a pressure is 0.25 MPa. The AlTiB alloy and the AlTiC alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 1.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.10 ml/100 g Al and 0.5 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 30 meshes and then is casted into a billet, wherein the billet has an average grain size of 40 m and a short rod-shaped or elliptical second phase of 60 nm. After being homogenized at 500 C. for 8 hours, the billet is forged into a profile at 400 C. with deformation of 30%. The profile has short rod-shaped or elliptical particles of 50 nm with a grain aspect ratio of 50:1.

Example 10

[0047] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 5052 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 10 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 40 nm. After being homogenized at 350 C. for 40 hours, the billet is extruded at 350 C. into a profile with an extrusion ratio of 30 and a billet speed of 3.0 mm/s. The profile has short rod-shaped or elliptical particles of 30 nm with a grain aspect ratio of 80:1.

Example 11

[0048] Aluminum scrap is smelted at 850 C. for 100 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 5052 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:5. For gas flushing, a flow rate is 12 L/min, and a pressure is 0.40 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.22 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 50 meshes and then is casted into a billet, wherein the billet has an average grain size of 30 m and a short rod-shaped or elliptical second phase of 20 nm. After being homogenized at 400 C. for 24 hours, the billet is forged into a profile at 350 C. with deformation of 30%. The profile has short rod-shaped or elliptical particles of 10 nm with a grain aspect ratio of 80:1.

Example 12

[0049] Aluminum scrap is smelted at 900 C. for 30 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 5052 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by Ar. For gas flushing, a flow rate is 15 L/min, and a pressure is 0.50 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 3.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.24 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 60 meshes and then is casted into a billet, wherein the billet has an average grain size of 25 m and a short rod-shaped or elliptical second phase of 10 nm. After being homogenized at 450 C. for 10 hours, the billet is forged into a profile at 350 C. with deformation of 40%. The profile has short rod-shaped or elliptical particles of 5 nm with a grain aspect ratio of 80:1.

Example 13

[0050] Aluminum scrap is smelted at 650 C. for 300 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 6063 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 5:1. For gas flushing, a flow rate is 1 L/min, and a pressure is 0.12 MPa. The AlTiB alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 0.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 10 meshes and then is casted into a billet, wherein the billet has an average grain size of 50 m and a short rod-shaped or elliptical second phase of 100 nm. After being homogenized at 350 C. for 40 hours, the billet is extruded at a room temperature into a profile with an extrusion ratio of 40 and a billet speed of 4.0 mm/s. The profile has short rod-shaped or elliptical particles of 80 nm with a grain aspect ratio of 100:1.

Example 14

[0051] Aluminum scrap is smelted at 700 C. for 250 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 6063 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 2:1. For gas flushing, a flow rate is 3 L/min, and a pressure is 0.20 MPa. The AlTiC alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 1.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.05 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 20 meshes and then is casted into a billet, wherein the billet has an average grain size of 45 m and a short rod-shaped or elliptical second phase of 80 nm. After being homogenized at 400 C. for 24 hours, the billet is rolled into a profile at a room temperature with reduction of 40%. The profile has short rod-shaped or elliptical particles of 70 nm with a grain aspect ratio of 90:1.

Example 15

[0052] Aluminum scrap is smelted at 750 C. for 200 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 6063 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 20 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:1. For gas flushing, a flow rate is 6 L/min, and a pressure is 0.25 MPa. The AlTiB alloy and the AlTiC alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 1.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.10 ml/100 g Al and 0.5 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 30 meshes and then is casted into a billet, wherein the billet has an average grain size of 40 m and a short rod-shaped or elliptical second phase of 60 nm. After being homogenized at 450 C. for 10 hours, the billet is forged into a profile at a room temperature with deformation of 50%. The profile has short rod-shaped or elliptical particles of 50 nm with a grain aspect ratio of 100:1.

Example 16

[0053] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 7075 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m (as shown in FIG. 3) and a short rod-shaped or elliptical second phase of 40 nm. After being homogenized at 350 C. for 40 hours, the billet is extruded at 430 C. into a profile with an extrusion ratio of 40 and a billet speed of 5.0 mm/s. The profile has short rod-shaped or elliptical particles of 30 nm with a grain aspect ratio of 80:1 (as shown in FIG. 5).

Example 17

[0054] Aluminum scrap is smelted at 850 C. for 100 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 7075 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:5. For gas flushing, a flow rate is 12 L/min, and a pressure is 0.40 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.18 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 50 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 20 nm. After being homogenized at 400 C. for 24 hours, the billet is rolled into a profile at 430 C. with reduction of 50%. The profile has short rod-shaped or elliptical particles of 10 nm with a grain aspect ratio of 100:1.

Example 18

[0055] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 7075 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 40 nm. After being homogenized at 400 C. for 24 hours, the billet is extruded at 400 C. into a profile with an extrusion ratio of 20 and a billet speed of 2.0 mm/s. The profile has short rod-shaped or elliptical particles of 30 nm with a grain aspect ratio of 50:1 (as shown in FIG. 6).

Example 19

[0056] Aluminum scrap is smelted at 900 C. for 30 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a 7075 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by Ar. For gas flushing, a flow rate is 15 L/min, and a pressure is 0.50 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 3.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.20 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 60 meshes and then is casted into a billet, wherein the billet has an average grain size of 25 m and a short rod-shaped or elliptical second phase of 10 nm. After being homogenized at 450 C. for 10 hours, the billet is forged into a profile at 430 C. with deformation of 10%. The profile has short rod-shaped or elliptical particles of 5 nm with a grain aspect ratio of 20:1.

Example 20

[0057] Aluminum scrap is smelted at 650 C. for 300 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL102 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 10 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 5:1. For gas flushing, a flow rate is 1 L/min, and a pressure is 0.12 MPa. The AlTiB alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 0.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 10 meshes and then is casted into a billet, wherein the billet has an average grain size of 50 m and a short rod-shaped or elliptical second phase of 100 nm.

Example 21

[0058] Aluminum scrap is smelted at 700 C. for 250 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL102 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 2:1. For gas flushing, a flow rate is 3 L/min, and a pressure is 0.20 MPa. The AlTiC alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 1.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.05 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 20 meshes and then is casted into a billet, wherein the billet has an average grain size of 45 m and a short rod-shaped or elliptical second phase of 80 nm.

Example 22

[0059] Aluminum scrap is smelted at 750 C. for 200 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL102 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:1. For gas flushing, a flow rate is 6 L/min, and a pressure is 0.25 MPa. The AlTiB alloy and the AlTiC alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 1.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.10 ml/100 g Al and 0.5 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 30 meshes and then is casted into a billet, wherein the billet has an average grain size of 40 m and a short rod-shaped or elliptical second phase of 60 nm.

Example 23

[0060] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL103 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 40 nm.

Example 24

[0061] Aluminum scrap is smelted at 850 C. for 100 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL103 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:5. For gas flushing, a flow rate is 12 L/min, and a pressure is 0.40 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.23 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 50 meshes and then is casted into a billet, wherein the billet has an average grain size of 30 m and a short rod-shaped or elliptical second phase of 20 nm.

Example 25

[0062] Aluminum scrap is smelted at 900 C. for 30 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL103 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 20 minutes. Degassing is gas flushing by Ar. For gas flushing, a flow rate is 15 L/min, and a pressure is 0.50 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 3.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.25 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 60 meshes and then is casted into a billet, wherein the billet has an average grain size of 25 m and a short rod-shaped or elliptical second phase of 10 nm.

Example 26

[0063] Aluminum scrap is smelted at 650 C. for 300 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL107 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 5:1. For gas flushing, a flow rate is 1 L/min, and a pressure is 0.12 MPa. The AlTiB alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 0.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 10 meshes and then is casted into a billet, wherein the billet has an average grain size of 50 m and a short rod-shaped or elliptical second phase of 100 nm.

Example 27

[0064] Aluminum scrap is smelted at 700 C. for 250 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL107 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 2:1. For gas flushing, a flow rate is 3 L/min, and a pressure is 0.20 MPa. The AlTiC alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 1.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.05 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 20 meshes and then is casted into a billet, wherein the billet has an average grain size of 45 m and a short rod-shaped or elliptical second phase of 80 nm.

Example 28

[0065] Aluminum scrap is smelted at 750 C. for 200 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL107 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:1. For gas flushing, a flow rate is 6 L/min, and a pressure is 0.25 MPa. The AlTiB alloy and the AlTiC alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 1.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.10 ml/100 g Al and 0.5 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 30 meshes and then is casted into a billet, wherein the billet has an average grain size of 40 m and a short rod-shaped or elliptical second phase of 60 nm.

Example 29

[0066] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL110 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 40 nm.

Example 30

[0067] Aluminum scrap is smelted at 850 C. for 100 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL110 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 10 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:5. For gas flushing, a flow rate is 12 L/min, and a pressure is 0.40 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.18 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 50 meshes and then is casted into a billet, wherein the billet has an average grain size of 30 m and a short rod-shaped or elliptical second phase of 20 nm.

Example 31

[0068] Aluminum scrap is smelted at 900 C. for 30 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL110 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 700 C. for 60 minutes. Degassing is gas flushing by Ar. For gas flushing, a flow rate is 15 L/min, and a pressure is 0.50 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 3.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.20 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 60 meshes and then is casted into a billet, wherein the billet has an average grain size of 25 m and a short rod-shaped or elliptical second phase of 10 nm.

Example 32

[0069] Aluminum scrap is smelted at 650 C. for 300 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL104 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 750 C. for 50 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 5:1. For gas flushing, a flow rate is 1 L/min, and a pressure is 0.12 MPa. The AlTiB alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 0.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 10 meshes and then is casted into a billet, wherein the billet has an average grain size of 50 m and a short rod-shaped or elliptical second phase of 100 nm.

Example 33

[0070] Aluminum scrap is smelted at 700 C. for 250 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL104 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 2:1. For gas flushing, a flow rate is 3 L/min, and a pressure is 0.20 MPa. The AlTiC alloy, as the modifier, is added to the target molten aluminum alloy with an addition amount of 1.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.05 ml/100 g Al and 0.4 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 20 meshes and then is casted into a billet, wherein the billet has an average grain size of 45 m and a short rod-shaped or elliptical second phase of 80 nm.

Example 34

[0071] Aluminum scrap is smelted at 750 C. for 200 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL104 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:1. For gas flushing, a flow rate is 6 L/min, and a pressure is 0.25 MPa. The AlTiB alloy and the AlTiC alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 1.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.10 ml/100 g Al and 0.5 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 30 meshes and then is casted into a billet, wherein the billet has an average grain size of 40 m and a short rod-shaped or elliptical second phase of 60 nm.

Example 35

[0072] Aluminum scrap is smelted at 800 C. for 150 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL305 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 900 C. for 20 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:2. For gas flushing, a flow rate is 9 L/min, and a pressure is 0.30 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.0 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.15 ml/100 g Al and 0.6 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 40 meshes and then is casted into a billet, wherein the billet has an average grain size of 35 m and a short rod-shaped or elliptical second phase of 40 nm.

Example 36

[0073] Aluminum scrap is smelted at 850 C. for 100 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL305 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 850 C. for 30 minutes. Degassing is gas flushing by a mixed gas of N.sub.2 and Ar with a volume ratio of 1:5. For gas flushing, a flow rate is 12 L/min, and a pressure is 0.40 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 2.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.18 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 50 meshes and then is casted into a billet, wherein the billet has an average grain size of 30 m and a short rod-shaped or elliptical second phase of 20 nm.

Example 37

[0074] Aluminum scrap is smelted at 900 C. for 30 minutes. Slag is removed from the molten aluminum alloy. The compositions of the molten aluminum alloy are adjusted to compositions of a ZL305 aluminum alloy. Then the target molten aluminum alloy is refined with degassing and modifying at 800 C. for 40 minutes. Degassing is gas flushing by Ar. For gas flushing, a flow rate is 15 L/min, and a pressure is 0.50 MPa. The AlTiB alloy and the AlTiC-RE alloy, as the modifier, are added to the target molten aluminum alloy with an addition amount of 3.5 kg/t. The contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.20 ml/100 g Al and 0.7 area % metallographic field respectively. The refined recycled molten aluminum alloy is filtered with a ceramic filter of 60 meshes and then is casted into a billet, wherein the billet has an average grain size of 25 m and a short rod-shaped or elliptical second phase of 10 nm.

[0075] The present invention discloses a method for controlling a microstructure of a recycled aluminum alloy, comprising steps of: degassing and removing inclusions from the molten aluminum alloy, refining grains and controlling the deformed microstructure. Good microstructures of the deformed aluminum alloy can be obtained after degassing by gas flushing, removing the inclusions by filtering, refining the grains by adding a modifier, and extruding or rolling or forging. The present invention provides very desirable results of degassing and impurity removal. Contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02-0.26 ml/100 g Al and 0.4-0.7 area % metallographic field respectively. In the aluminum alloy billet, the average grain size is 25-50 m and the short rod-shaped or elliptical second phase is 10-100 nm. In the deformed aluminum alloy, the grain aspect ratio is 10:1-100:1 and the short rod-shaped or elliptical particles are 5-80 nm. The present invention can control the microstructure of the recycled aluminum alloy, and eliminate defects such as pores and inclusions.

[0076] It is to be understood that the specific examples described herein are merely illustrative and are not intended to limit the present invention. All alterations, modifications, equivalent method and scheme within the spirit and scope defined by the claims are encompassed by the present invention.