Preparation method for a high-strength extruded profile of Mg—Zn—Sn—Mn alloy

Abstract

A method for preparing a high-strength extruded profile of an Mg—Zn—Sn—Mn alloy is composed of a solid solution treatment at two stages to a billet, a high-temperature pre-aging to the billet, a low-temperature rapid extrusion and a low-temperature aging treatment to a profile. The Mg—Zn—Sn—Mn alloy includes the following elements in mass percent: 5.8-6.2% of Zn, 3.0-3.5% of Sn, 0.25-0.45% of Mn, unavoidable impurities of 0.05% or less, and the balance magnesium. The Mg—Zn—Sn—Mn magnesium alloy profile has a fine grain size of about 10-20 μm and a dispersed second phase, so a high strength and a good elongation can be obtained therein, and a tensile strength of 350 MPa or more, a yield strength of 280 MPa or more, and the elongation of 12% or more. In addition, the profile has a high extrusion production efficiency and a high yield, and a low extrusion cost.

Claims

1. A Mg—Zn—Sn—Mn alloy, consisting of the following elements in mass percent: 5.8-6.2% of Zn, 3.0-3.5% of Sn, 0.25¬0.45% of Mn, unavoidable impurities of 0.05% or less, and the balance magnesium; and the grain size of the Mg—Zn—Sn—Mn alloy is from 10 μm to 20 μm; and the Mg—Zn—Sn—Mn alloy being produced by a method comprising: a solid solution treatment at two stages to a billet, a high-temperature pre-aging to the billet, a low-temperature rapid extrusion and a low-temperature aging treatment to a profile; wherein, the solid solution treatment at two stages comprises: a low-temperature solid solution, a high-temperature solid solution and a cooling; the low-temperature solid solution has a temperature of 330 to 350° C., and a low-temperature solid solution heat preservation duration of 2 to 4 hours; the high-temperature solid solution temperature has a temperature of 400-420° C., and a high-temperature solid solution heat preservation duration of 8-10 hours; and the temperature is increased at a rate of 0.8-2° C./min; the high-temperature pre-aging has a temperature of 320-340° C.; the low-temperature rapid extrusion treatment has a mold temperature and a extrusion cylinder temperature both of 320-340° C.; and the low temperature aging is performed at conditions of: the aging temperature being 150-160° C., the heat preservation duration being 16-64 hours, and the temperature being increased at a rate of 0.8-2° C./min.

2. The Mg—Zn—Sn—Mn alloy according to claim 1, wherein the high-temperature pre-aging treatment to the billet is performed at conditions of: the aging temperature being 320-340° C., and the aging heat preservation duration being 1-3 hours; and the temperature being increased at a rate of 0.8-2° C./min.

3. The Mg—Zn—Sn—Mn alloy according to claim 1, wherein the magnesium alloy is extruded into a profile using a split assembly mold during the low temperature rapid extrusion.

4. The Mg—Zn—Sn—Mn alloy according to claim 1, wherein in the low-temperature rapid extrusion process, the preheating temperature of the billet is 10 to 20° C. lower than the high-temperature pre-aging temperature, and is 300 to 330° C., the heat preservation duration is 0.5 to 1 hour, and the temperature is increased at a rate of 0.8 to 2° C./min; the temperature of the mold is equal to that of the extrusion cylinder and is 320-340° C.; the extrusion ratio is 10-40, and the extrusion speed is 1-5 mm/min.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanation of the present application. Unless defined otherwise, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

(2) It should be noted that the terminology used herein is only for describing a specific embodiment, and is not intended to limit the exemplary embodiments according to the present application. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise, and it should also be understood that when the terms “including” and/or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and/or combinations thereof.

(3) As described in the Background of the Invention, the technical problem directed in this application is the too high cost of the current ZK-based magnesium alloys and rare earth-containing magnesium alloys. Therefore, the present invention proposes a method for preparing a high-strength, low-cost Mg—Zn—Sn—Mn alloy extruded profile, and the preparation method consists of a solid solution treatment at two stages to a billet, a high-temperature pre-aging to the billet, a low-temperature rapid extrusion and a low-temperature aging treatment to a profile and other processes.

(4) During the solid solution treatment at two stages to the billet of the present invention, a low temperature solid solution temperature is 330 to 350° C., a low temperature solid solution heat preservation duration is 2-4 hours; a high temperature solid solution temperature is 400-420° C., a high temperature solid solution heat preservation duration is 8-10 hours; and the temperature is increased at a rate of 0.8 to 2° C./min; and after solid solution treatment, a water quenching is employed as cooling manner.

(5) During the high temperature pre-aging to the billet of the present invention, the aging temperature is 320 to 340° C., aging heat preservation duration is 1 to 3 h; and the temperature is increased at a rate of 0.8 to 2° C./min; a water quenching is employed as cooling manner.

(6) During the low temperature rapid extrusion of the present invention, the magnesium alloy is extruded into a profile using a split assembly mold during the low temperature rapid extrusion. The preheating temperature of the billet is 10 to 20° C. lower than the high-temperature pre-aging temperature, and is 300 to 330° C., the heat preservation duration is 0.5 to 1 hour, and the temperature is increased at a rate of 0.8 to 2° C./min; the temperature of the mold is equal to that of the extrusion cylinder and is 320-340° C.; the extrusion ratio is 10-40, and the extrusion speed is 1-5 mm/min. An air cooling is employed as cooling manner.

(7) During the low temperature aging to the billet of the present invention, the aging temperature is 150 to 160° C., heat preservation duration is 16-64 h, and the temperature is increased at a rate of 0.8 to 2° C./min.

(8) Preferably, a solid solution treatment at two stages and the high temperature pre-aging processes to the billet can be performed continuously to save the intermediate temperature reduction and the temperature increase from room temperature. The temperature can be directly reduced from a high temperature solid solution temperature to a high temperature pre-aging temperature of the billet, using oil bath or salt bath.

(9) Preferably, a high temperature pre-aging and a low temperature rapid extrusion processes to the billet can be performed continuously to save the intermediate temperature reduction and the temperature increase from room temperature. The temperature can be directly reduced from a high temperature pre-aging temperature to the preheating temperature of the billet, and a furnace cooling is employed as cooling manner.

(10) The Mg—Zn—Sn—Mn magnesium alloy ingot according to the present invention has a composition in weight percentage of: 5.8-6.2% of Zn, 3.0-3.5% of Sn, 0.25-0.45% of Mn, unavoidable impurities of 0.05% or less, and the balance magnesium.

(11) Preferably, Mg—Zn—Sn—Mn magnesium alloy ingot according to the present invention has a composition in weight percentage of: 6.0% of Zn, 3.5% of Sn, 0.30% of Mn, unavoidable impurities of 0.05% or less, and the balance magnesium.

(12) The Mg—Zn—Sn—Mn alloy extruded profile prepared by the present invention has a tensile strength of 350 MPa or more, a yield strength of 280 MPa or more, and the elongation of 12% or more.

(13) The specific Examples are described as follows:

(14) The mechanical performances and average grain size of the alloy of the examples of the present invention and comparative examples are shown in Table 1. The test method of mechanical performances is performed according to GB T 228.1-2010; the measurement method of average grain size is performed according to GB T 6394-2002.

Example 1

(15) A high-strength extruded profile of Mg-6.00 wt % Zn-3.50 wt % Sn-0.30 wt % Mn alloy is prepared by a preparation method comprising: a solid solution treatment at two stages to a billet, a high-temperature pre-aging to the billet, a low-temperature rapid extrusion and a low-temperature aging treatment to a profile etc.

(16) The process of solid solution treatment at two stages to a billet: 340° C. was kept for 4 hours; 420° C. was kept for 10 hours; and the temperature was increased at a rate of 1° C./min; and a water quench was employed after the solid solution treatment.

(17) The process of high temperature pre-aging to the billet: 320° C. was kept for 2 hours; and the temperature was increased at a rate of 0.8° C./min; and a water quench was employed after the pre-aging finishes.

(18) The process of low temperature rapid extrusion: the billet was preheated at a temperature of 300° C., maintained at the temperature for 1 hour, and the temperature was increased at a rate of 2° C./min; the temperature of the mold was equal to that of the extrusion cylinder, being 320° C.; the extrusion ratio was 40, and the extrusion speed was 1 mm/min. An air cooling was employed as cooling manner for the extruded profile.

(19) The process of low temperature aging for the profile: 150° C. was kept for 64 hours; and the temperature was increased at a rate of 1° C./min.

Example 2

(20) A high-strength extruded profile of Mg-6.20 wt % Zn-3.00 wt % Sn-0.45 wt % Mn alloy is prepared by a preparation method comprising: a solid solution treatment at two stages to a billet, a high-temperature pre-aging to the billet, a low-temperature rapid extrusion and a low-temperature aging treatment to a profile etc.

(21) The process of solid solution treatment at two stages to a billet: 350° C. was kept for 2 hours; 400° C. was kept for 8 hours; and the temperature was increased at a rate of 0.8° C./min; and a water quench was employed after the solid solution treatment.

(22) The process of high temperature pre-aging to the billet: 340° C. was kept for 1 hour; and the temperature was increased at a rate of 2° C./min; and the temperature was changed to and kept at 330° C. after the pre-aging finishes.

(23) The process of low temperature rapid extrusion: the billet was preheated at a temperature of 330° C., maintained at the temperature for 1 hour; the temperature of the mold was equal to that of the extrusion cylinder, being 340° C.; the extrusion ratio was 30, and the extrusion speed was 5 mm/min. An air cooling was employed as cooling manner for the extruded profile.

(24) The process of low temperature aging for the profile: 160° C. was kept for 16 hours; and the temperature was increased at a rate of 0.8° C./min.

Example 3

(25) A high-strength extruded profile of Mg-5.80 wt % Zn-3.30 wt % Sn-0.25 wt % Mn alloy is prepared by a preparation method comprising: a solid solution treatment at two stages to a billet, a high-temperature pre-aging in oil bath method, a low-temperature rapid extrusion and a low-temperature aging treatment to a profile etc.

(26) The process of solid solution treatment at two stages to a billet: 330° C. was kept for 4 hours; 420° C. was kept for 10 hours; and the temperature was increased at a rate of 2° C./min; and in an oil bath.

(27) The process of high temperature pre-aging in an oil bath: 320° C. was kept for 2 hours; and a water quench was employed after the pre-aging finishes.

(28) The process of low temperature rapid extrusion: the billet was preheated at a temperature of 310° C., maintained at the temperature for 0.5 hours, and the temperature was increased at a rate of 1° C./min; the temperature of the mold was equal to that of the extrusion cylinder, being 320° C.; the extrusion ratio was 10, and the extrusion speed was 5 mm/min. An air cooling was employed as cooling manner for the extruded profile.

(29) The process of low temperature aging for the profile: 160° C. was kept for 32 hours; and the temperature was increased at a rate of 1.5° C./min.

Comparative Example 1

(30) It is similar to Example 1 except that the alloy had a composition of: Mg-5.50 wt % Zn-2.00 wt % Sn-0.03 wt % Mn.

Comparative Example 2

(31) It is similar to Example 1 except that the solid solution process in the preparation method is only kept at 420° C. for 10 hours.

Comparative Example 3

(32) It is similar to Example 1 except that the preparation method does not comprise a high temperature pre-aging process.

Comparative Example 4

(33) It is similar to Example 1 except that the extrusion process in the preparation method: the billet was preheated at a temperature of 400° C., maintained at the temperature for 0.5 hours, and the temperature was increased at a rate of 1° C./min; the temperature of the mold was equal to that of the extrusion cylinder, being 400° C.; the extrusion ratio was 10, and the extrusion speed was 1 mm/min. An air cooling was employed as cooling manner for the extruded profile.

Comparative Example 5

(34) It is similar to Example 1 except that the preparation method does not comprise a low-temperature aging treatment to a profile.

(35) TABLE-US-00001 TABLE 1 Mechanical performances and average grain size of the magnesium alloy profiles at room temperature Tensile Yield Strength Strength Average Grain (MPa) (MPa) Elongation Size (μm) Example 1 358 284 13% about 15 Example 2 366 295 14% about 18 Example 3 360 287 12% about 20 Comparative 320 260 12% about 20 example 1 Comparative 345 259  9% about 32 example 2 Comparative 337 240  8% about 34 example 3 Comparative 313 249  6% about 55 example 4 Comparative 286 226 14% about 15 example 5

(36) By comparing the Examples with Comparative examples, it can be seen that the average grain size of the Mg—Zn—Sn—Mn alloy extruded profile prepared by the present invention is significantly better than that of the Comparative example, and the mechanical performances of the examples of the present invention are also significantly better than those of the Comparative examples.

(37) Therefore, the mechanical performances of the low-cost and high-strength Mg—Zn—Sn—Mn alloy profiles prepared by the present invention can meet the requirements for the mechanical performances of profiles in such civil fields as electric vehicle and rail transit, and can further enlarge the application range of magnesium alloys.

(38) Finally, it should be noted that the above are only preferred examples of the present invention, and not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing Examples, those skilled in the art still can make modifications or portion equivalent replacements to the technical solutions described in the foregoing Examples. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. Although the above describes the specific embodiment of the present invention, it does not limit the protection scope of the present invention. Those skilled in the art should understand that based on the technical solution of the present invention, the various modifications or deformations made by those skilled in the art without any inventive labor are still within the protection scope of the present invention.