High-strength and high-toughness magnesium alloy and preparation method thereof

Abstract

A high-strength and high-toughness magnesium alloy includes a Mg—Al—Bi—Sb—Zn—Sr—Y—Mn alloy, prepared from the following components in percentage by mass: 7.0 to 10.0% of Al, 0.2 to 2.0% of Bi, 0.2 to 0.8% of Sb, 0.2 to 0.5% of Zn, 0.1 to 0.5% of Sr, 0.03 to 0.3% of Y, 0.05 to 0.1% of Mn and a balance of Mg.

Claims

1. A preparation method of a magnesium alloy, comprising: 1) performing mixing: mixing a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sb block, a pure Zn block, a Mg-Y intermediate alloy, a Mg-Sr intermediate alloy and a Mg-Mn intermediate alloy which serve as raw materials according to a magnesium alloy composition; 2) performing smelting: putting the pure Mg ingot into a crucible of a smelting furnace, setting a furnace temperature at 700 to 730° C., maintaining the temperature, and respectively adding the pure Bi block, the pure Sb block and the pure Zn block which are preheated to 50 to 100° C., the Mg-Sr intermediate alloy, the Mg-Y intermediate alloy and the Mg-Mn intermediate alloy which are preheated to 200 to 250° C. into the magnesium melt after the pure Mg ingot is melted; then increasing the smelting temperature by 20 to 40° C., and maintaining the temperature for 5 to 15 minutes, then stirring the mixture for 3 to 10 minutes, reducing the furnace temperature by 10 to 30° C. for refining and degassing treatment, and then standing for heat preservation for 3 to 15 minutes, wherein the whole process is performed under the protection of CO.sub.2/SF.sub.6 mixed gas; 3) performing casting: removing dross from the surface of the melt, and pouring the magnesium alloy melt into a corresponding mold to obtain an as-cast magnesium alloy, wherein no gas protection is performed during the casting; 4) performing solution treatment: performing solution treatment on the obtained as-cast magnesium alloy at a solution treatment temperature of 415 to 440° C. for 6 to 10 hours, and quenching the alloy with warm water of 30 to 80° C., wherein no gas protection is performed during the heating and heat preservation processes of the solution treatment; 5) performing aging treatment: performing aging treatment on the alloy subjected to the solution treatment, and maintaining the temperature at 175 to 200° C. for 8 to 15 hours; and 6) performing extrusion treatment: extruding the alloy obtained in the step 5) to deform: firstly, cutting a cast ingot into a corresponding blank, and peeling the blank, and then putting the obtained blank into the mold for extrusion deformation treatment at an extrusion deformation speed of 1 to 2.8 m/min, an extrusion ratio of 10 to 50 and an extrusion temperature of 250 to 400° C., wherein the deformed blank is heated to the required extrusion temperature within 30 minutes; and after the extrusion is ended, cooling the alloy at a room temperature.

2. The preparation method of claim 1, wherein the magnesium alloy composition comprises in percentage by mass: 7.0 to 10.0% of Al, 0.2 to 2.0% of Bi, 0.2 to 0.8% of Sb, 0.2 to 0.5% of Zn, 0.1 to 0.5% of Sr, 0.03 to 0.3% of Y, 0.05 to 0.1% of Mn and a balance of Mg.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to make the objectives, technical solutions and advantages of the present disclosure clearer, the present disclosure is further described below in combination with the accompanying drawings.

(2) FIG. 1 illustrate mechanical property curves of the materials, in which panel (a) is a T6-state mechanical property curve, and panel (b) is an extruded-state mechanical performance curve;

(3) FIG. 2 is a microstructure of an alloy of Embodiment 1, in which panel (a) is T6-state OM tissue; panel (b) is T6-state SEM tissue; panel (c) is extruded-state OM tissue; and panel (d) is extruded-state SEM tissue;

(4) FIG. 3 is a microstructure of an alloy of Embodiment 2, in which panel (a) is T6-state OM tissue; panel (b) is T6-state SEM tissue; panel (c) is extruded-state OM tissue; and (d) is extruded-state SEM tissue;

(5) FIG. 4 is a microstructure of an alloy of Embodiment 3, in which panel (a) is T6-state OM tissue, and panel (b) is extruded-state OM tissue; and

(6) FIG. 5 is a microstructure of an alloy of a reference example, in which panel (a) is T6-state OM tissue; panel (b) is T6-state SEM tissue; panel (c) is extruded-state OM tissue; and panel (d) is extruded-state SEM tissue.

DETAILED DESCRIPTION

(7) The present disclosure will be further described below with specific implementation modes. The following embodiments are all implemented on the premise of the technical solution of the present disclosure, and detailed implementation modes and specific operation processes are given, but the protection scope of the present disclosure is not limited to the following embodiments.

(8) Three alloy compositions are selected as typical examples:

(9) Mg-7Al-0.6Bi-0.3Sb-0.2Zn-0.1Sr-0.05Y-0.08Mn (wt %) (alloy 1),

(10) Mg-8Al-0.7Bi-0.35b-0.3Zn-0.1Sr-0.05Y-0.09Mn (wt %) (alloy 2), and

(11) Mg-8.5Al-0.8Bi-0.65b-0.4Zn-0.1Sr-0.04Y-0.08Mn (wt %) (alloy 3).

Embodiment 1

(12) 1) raw materials are weighed according to the mass percentage of the alloy Mg-7A1-0.6Bi-0.3Sb-0.2Zn-0.1Sr-0.05Y-0.08Mn (wt %): a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sb block, a pure Zn block, a Mg-30Y intermediate alloy, a Mg-20Sr intermediate alloy and a Mg-10Mn intermediate alloy are the raw materials, and surface treatment is performed on the raw materials;

(13) 2) the pure Mg ingot is put into a crucible of a smelting furnace; a furnace temperature is set at 715° C. and then maintained; the pure Al block, the pure Bi block, the pure Sb block, the pure Zn block, the Mg-30Y intermediate alloy, the Mg-20Sr intermediate alloy and the Mg-10Mn intermediate alloy are respectively added into the magnesium melt after the pure Mg ingot is melted; then the melting temperature is increased by 30° C. and maintained for 10 minutes; the mixture is stirred for 5 minutes; the furnace temperature is reduced by 20° C. for refining and degassing treatment; and then standing for heat preservation is performed for 15 minutes, in which the whole process is performed under the protection of CO2/SF6 mixed gas;

(14) 3) casting is performed: dross is removed from the surface of the melt, and the magnesium alloy melt is poured into a cylindrical mold having a diameter of 60 mm by adopting a gravity casting mode to obtain an as-cast magnesium alloy bar, in which the casting process requires no gas protection;

(15) 4) solution treatment is performed: solution treatment is performed on the obtained as-cast magnesium alloy at a solution treatment temperature of 420° C. for 8 hours, and the alloy is quenched with warm water of 50° C., in which the heating and heat preservation processes of the solution treatment require no gas protection;

(16) 5) aging treatment is performed: aging treatment is performed on the alloy subjected to the solution treatment, and the temperature is maintained at 200° C. for 8 hours; and

(17) 6) extrusion treatment is performed: the alloy obtained in the step 5) is extruded to deform: firstly, a cast ingot is cut into a corresponding blank, and the blank is peeled, and then the obtained blank is put into the mold for extrusion deformation treatment at an extrusion deformation speed of 2.3 m/min, an extrusion ratio of 36 and an extrusion temperature of 300° C., in which the deformed blank should be heated to the required extrusion temperature within 30 minutes; and after the extrusion is ended, the alloy is cooled at a room temperature.

(18) Finally, the alloy treated in the step 5) and the step 6) is tested for mechanical properties (a room temperature test method of Part 1 of GB/T 228.1-2010 Metal Material Tensile Test and a GB/T 7314-2005 metal material room temperature compression test method are adopted) until the alloy is broken by pulling (pressing), and a stress-strain curve is obtained, as shown in FIG. 1.

Embodiment 2

(19) 1) raw materials are weighed according to the mass percentage of the alloy Mg-8A1-0.7Bi-0.3Sb-0.3Zn-0.1Sr-0.05Y-0.09Mn (wt %): a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sb block, a pure Zn block, a Mg-30Y intermediate alloy, a Mg-20Sr intermediate alloy and a Mg-10Mn intermediate alloy are the raw materials, and surface treatment is performed on the raw materials;

(20) 2) the pure Mg ingot is put into a crucible of a smelting furnace; a furnace temperature is set at 715° C. and then maintained; the pure Al block, the pure Bi block, the pure Sb block, the pure Zn block, the Mg-30Y intermediate alloy, the Mg-20Sr intermediate alloy and the Mg-10Mn intermediate alloy are respectively added into the magnesium melt after the pure Mg ingot is melted; then the melting temperature is increased by 30° C. and maintained for 10 minutes; the mixture is stirred for 5 minutes; the furnace temperature is reduced by 20° C. for refining and degassing treatment; and then standing for heat preservation is performed for 15 minutes, in which the whole process is performed under the protection of CO2/SF6 mixed gas;

(21) 3) casting is performed: dross is removed from the surface of the melt, and the magnesium alloy melt is poured into a cylindrical mold having a diameter of 60 mm by adopting a gravity casting mode to obtain an as-cast magnesium alloy bar, in which the casting process requires no gas protection;

(22) 4) solution treatment is performed: solution treatment is performed on the obtained as-cast magnesium alloy at a solution treatment temperature of 420° C. for 8 hours, and the alloy is quenched with warm water of 50° C., in which the heating and heat preservation processes of the solution treatment require no gas protection;

(23) 5) aging treatment is performed: aging treatment is performed on the alloy subjected to the solution treatment, and the temperature is maintained at 200° C. for 8 hours; and

(24) 6) extrusion treatment is performed: the alloy obtained in the step 5) is extruded to deform: firstly, a cast ingot is cut into a corresponding blank, and the blank is peeled, and then the obtained blank is put into the mold for extrusion deformation treatment at an extrusion deformation speed of 2.3 m/min, an extrusion ratio of 36 and an extrusion temperature of 300° C., in which the deformed blank should be heated to the required extrusion temperature within 30 minutes; and after the extrusion is ended, the alloy is cooled at a room temperature.

(25) Finally, the alloy treated in the step 5) and the step 6) is tested for mechanical properties (a room temperature test method of Part 1 of GB/T 228.1-2010 Metal Material Tensile Test and a GB/T 7314-2005 metal material room temperature compression test method are adopted) until the alloy is broken by pulling (pressing), and a stress-strain curve is obtained, as shown in FIG. 1.

Embodiment 3

(26) 1) raw materials are weighed according to the mass percentage of the alloy Mg-8.5A1-0.8Bi-0.6Sb-0.4Zn-0.1Sr-0.04Y-0.08Mn (wt %): a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sb block, a pure Zn block, a Mg-30Y intermediate alloy, a Mg-20Sr intermediate alloy and a Mg-10Mn intermediate alloy are the raw materials, and surface treatment is performed on the raw materials;

(27) 2) the pure Mg ingot is put into a crucible of a smelting furnace; a furnace temperature is set at 715° C. and then maintained; the pure Al block, the pure Bi block, the pure Sb block, the pure Zn block, the Mg-30Y intermediate alloy, the Mg-20Sr intermediate alloy and the Mg-10Mn intermediate alloy are respectively added into the magnesium melt after the pure Mg ingot is melted; then the melting temperature is increased by 30° C. and maintained for 10 minutes; the mixture is stirred for 5 minutes; the furnace temperature is reduced by 20° C. for refining and degassing treatment; and then standing for heat preservation is performed for 15 minutes, in which the whole process is performed under the protection of CO2/SF6 mixed gas;

(28) 3) casting is performed: dross is removed from the surface of the melt, and the magnesium alloy melt is poured into a cylindrical mold having a diameter of 60 mm by adopting a gravity casting mode to obtain an as-cast magnesium alloy bar, in which the casting process requires no gas protection;

(29) 4) solution treatment is performed: solution treatment is performed on the obtained as-cast magnesium alloy at a solution treatment temperature of 420° C. for 8 hours, and the alloy is quenched with warm water of 50° C., in which the heating and heat preservation processes of the solution treatment require no gas protection;

(30) 5) aging treatment is performed: aging treatment is performed on the alloy subjected to the solution treatment, and the temperature is maintained at 200° C. for 8 hours; and

(31) 6) extrusion treatment is performed: the alloy obtained in the step 5) is extruded to deform: firstly, a cast ingot is cut into a corresponding blank, and the blank is peeled, and then the obtained blank is put into the mold for extrusion deformation treatment at an extrusion deformation speed of 2.3 m/min, an extrusion ratio of 36 and an extrusion temperature of 300° C., in which the deformed blank should be heated to the required extrusion temperature within 30 minutes; and after the extrusion is ended, the alloy is cooled at a room temperature.

(32) Finally, the alloy treated in the step 5) and the step 6) is tested for mechanical properties by adopting a room temperature test method of Part 1 of GB/T 228.1-2010 Metal Material Tensile Test and a GB/T 7314-2005 metal material room temperature compression test method until the alloy is broken by pulling (pressing), and a stress-strain curve is obtained, as shown in FIG. 1.

(33) Reference example: an existing commercial magnesium alloy AZ80 is selected in the reference example and is obtained under the same processing conditions of the Embodiment 2.

(34) The raw materials and equipment which are used in the aforementioned embodiments are all obtained by publicly known ways, and operation processes used are familiar to those skilled in the art.

(35) FIG. 1 shows test results of relevant mechanical properties of the Examples 1, 2, 3 and reference example AZ80. The relevant mechanical properties are summarized in Table 1. The alloy of the present disclosure has the tensile strength of about 220 MPa, the yield strength of about 120 MPa and the elongation rate up to 10% in the T6 state, and has the tensile strength of about 370 MPa, the yield strength of about 205 MPa and the elongation rate of about 24% in the extruded state. The reference alloy has the tensile strength of 146 MPa, the yield strength of 93 MPa and the elongation rate of 3.54% in the T6 state, and has the tensile strength of 355 MPa, the yield strength of 184 MPa and the elongation rate of 17.3% in the extruded state. It can be seen from the comparison that the magnesium alloy of the present disclosure has an obvious improvement on yield strength, tensile strength and elongation rate in both T6 state and extruded state, and is a high-strength and high-toughness magnesium alloy material having market competitiveness.

(36) FIGS. 2-4 respectively show microstructures in different states of the Embodiment 1, Embodiment 2 and Embodiment 3, and FIG. 5 shows microstructures in different states of the reference example. It can be seen from comparison diagrams of 2a, 3a, 4a and 5a that after the composite microalloying, grains of the embodiments are remarkably refined, and the continuous coarse second phases in the as-cast microstructure of the reference example are converted into dispersion distribution, which weakens the splitting action on the matrix. This is also the reason for the improvement of the mechanical properties of the alloy of the present disclosure. Analysis of FIG. 2, panel (b), FIG. 3, panel (b) and FIG. 5, panel (b) shows that after being subjected to the T6 treatment, the alloys all have been subjected to aging precipitation; and the aged structure of the reference example shows that the aging precipitation second phases of the alloys of the embodiments are finer, indicating that the composite microalloying improves the aging precipitation behaviors of the alloys, which is consistent with the improvement of the properties of the T6-state alloy.

(37) It can be seen from FIG. 2, panel (c), FIG. 3, panel (c), FIG. 4, panel (b) and FIG. 5, panel (c) that after being subjected to the extrusion treatment, the alloys all have undergone dynamic recrystallization, the recrystallized grains of the alloys of the present disclosure are finer, and the undissolved second phases are distributed along the extrusion direction. The presence of these undissolved phases may hinder the growth of alpha-Mg grains during the dynamic recrystallization. To determine the composition of the second phases, the Embodiments 1 and 2 and the reference example are selected for further EDS analysis. Results are shown in Table 2, Table 3 and Table 4. The EDS test results show that the second phases in stripe distribution in the alloy of the Embodiment 1 may include a phase rich in Al, Bi and Sb, a phase rich in Al and Sb and a phase rich in Al, Y and Mn, in addition to the Mg17A112 phase. In the Embodiment 2, a phase rich in Mg, Al and Y, a phase rich in Mg, Al and Mn and a phase rich in Mg, Al, Y and Mn appear, and meanwhile, there are Al and Sn elements dissolved in the matrix. These micron-sized second phases have a higher melting point and are difficultly dissolved into the matrix during the solution treatment, which may promote the dynamic recrystallization in the subsequent deformation process by means of particle-excited nucleation, thereby improving the comprehensive mechanical properties of the deformed alloy. The alloy of the reference example mainly includes Mg17Al12 with low thermal stability and a small amount of relatively large Al—Mn phase. This is consistent with the improvement of the strength and plasticity of the alloy of the present disclosure.

(38) TABLE-US-00001 TABLE 1 Mechanical property test results of the Embodiments and the reference example at room temperature Item Yield Tensile Elongation Processing strength strength rate Example Alloy composition (wt %) state MPa MPa % Embodiment Mg—7Al—0.6Bi—0.3Sb—0.2Zn—0.1Sr—0.05Y—0.08Mn AE 201.4 361.4 24.7 1 T6 120 210 6.31 Embodiment Mg—8Al—0.7Bi—0.3Sb—0.3Zn—0.1Sr—0.05Y—0.09Mn AE 199.6 372.5 25.1 2 T6 121 228 7.9 Embodiment Mg—8.5Al—0.8Bi—0.6Sb—0.4Zn—0.1Sr—0.04Y—0.08Mn AE 209 359.5 24.6 3 T6 118 231 10.73 Reference AZ80 AE 184 335 17.3 example T6 93 146 3.54

(39) TABLE-US-00002 TABLE 2 EDS analysis results of the alloy of the Embodiment 1 Corresponding Position Mg Al Y Mn Bi Sb phase A 50.34 6.66 20.79 22.21 Al—Bi—Sb B 89.66 13.34 Mg.sub.17Al.sub.12 C 88.51 8.61 2.88 Al—Sb D 88.74 9.96 1.30 Al—Sb E 16.84 32.66 49.63 0.86 Al—Y—Mn

(40) TABLE-US-00003 TABLE 3 EDS analysis results of the alloy of the Embodiment 2 Correpsonding Position Mg Al Y Mn Sn phase A 55.14 23.26 21.29 0.28 Mg—Al—Y B 70.15 20.39 9.46 Mg—Al—Mn C 6.14 37.66 46.76 9.47 Mg—Al—Y—Mn D 89.81 9.10 1.09 Mg—Al—Sn E 89.51 8.91 1.58 Mg—Al—Sn

(41) TABLE-US-00004 TABLE 4 EDS analysis results of the AZ80 alloy Correpsonding Position Mg Al Mn phase A 91.07 8.93 Mg.sub.17Al.sub.12 B 90.64 9.36 Mg.sub.17Al.sub.12 C 23.02 48.49 28.49 Al—Mn D 49.94 30.19 19.87 Al—Mn