Plastic wrought magnesium alloy and preparation method thereof

Abstract

A plastic wrought magnesium alloy includes a Mg—Al—Bi—Sn—Ca—Y alloy, prepared from the following chemical components in percentage by mass: 3 to 6.0% of Al, 1 to 3.0% of Bi, 0.5 to 2.0% of Sn, 0.02 to 0.05% of Ca, 0.02 to 0.05% of Y and the balance of Mg, in which the percentage sum of Ca and Y elements is more than 0.05% and less than 0.1%.

Claims

1. A preparation method of a plastic wrought magnesium alloy, comprising the following steps: 1) performing mixing: mixing a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sn block, a Mg—Ca intermediate alloy and a Mg—Y 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 and the pure Sn block which are preheated to 50 to 80° C., and the pure Al block, the Mg—Ca intermediate alloy and the Mg—Y 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 to 750° C., and maintaining the temperature for 5 to 15 minutes, then stirring the mixture for 3 to 10 minutes, feeding Ar gas for refining and degassing treatment, and adjusting and controlling the temperature at 710 to 730° C. and maintaining the temperature for 2 to 10 minutes, wherein the smelting 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 a solution treatment process by maintaining a temperature of 400 to 415° C. for 16 to 36 hours, then maintaining a temperature of 440 to 460° C. for 6 to 12 hours, and quenching the alloy with warm water of 40 to 80° C., wherein no gas protection is performed during the heating and heat preservation processes of the solution treatment; 5) cutting a cast ingot subjected to the solution treatment in the previous step into a corresponding blank, and peeling the blank; and 6) performing extrusion deformation: heating the blank obtained in the previous step to 250 to 300° C. within 30 minutes, putting the blank into the mold for deformation processing at an extrusion speed of 0.01 to 2 m/min, and cooling the deformed blank in air to finally obtain the plastic magnesium alloy material.

2. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the mold is a mold for forming a bar, a plate, a pipe, a line or a profile.

3. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the stirring in the step 2) is mechanical stirring.

4. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the stirring in the step 2) is stirring via argon blowing.

5. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the Mg—Ca intermediate alloy is a Mg-20Ca intermediate alloy.

6. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the Mg—Y intermediate alloy is a Mg-30Y intermediate alloy.

7. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the volume ratio of components of the CO.sub.2/SF.sub.6 mixed gas is CO.sub.2: SF.sub.6=(50-100):1.

8. The preparation method of the plastic wrought magnesium alloy according to claim 1, wherein the magnesium alloy composition comprises in percentage by mass: 3 to 6.0% of Al, 1 to 3.0% of Bi, 0.5 to 2.0% of Sn, 0.02 to 0.05% of Ca, 0.02 to 0.05% of Y and a balance of Mg; and the percentage sum of Ca and Y elements is more than 0.05% and less than 0.1%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows room-temperature tensile test stress-strain curves of magnesium alloys of Embodiments 1, 2 and 3 and a reference example;

(3) FIG. 2 is a microstructure parallel to an extrusion direction of Embodiment 1;

(4) FIG. 3 is a microstructure parallel to an extrusion direction of Embodiment 2;

(5) FIG. 4 is a microstructure parallel to an extrusion direction of Embodiment 3;

(6) FIG. 5 is a TEM structure of the alloy of Embodiment 3; and

(7) FIG. 6 is an inverse pole diagram of the alloy of Embodiment 3.

DETAILED DESCRIPTION

(8) The present disclosure is further described below by the specific embodiments and the accompanying drawings. 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.

(9) Three alloy compositions Mg-3Al-3Bi-1Sn-0.04Ca-0.02Y (wt %) (alloy 1), Mg-4Al-2Bi-1Sn-0.03Ca-0.03Y (wt %) (alloy 2) and Mg-6Al-3Bi-1Sn-0.03Ca-0.05Y (wt %) (alloy 3) are selected as typical examples.

(10) According to the technical solution of the present disclosure, a pure Mg (99.8 wt %) ingot, a pure Al (99.9 wt %) block, a pure Bi (99 wt %) block, a pure Mg (99.5 wt %) block, a Mg-20Ca (actually detected content of Ca is 20.01 wt %) intermediate alloy and a Mg-30Y (actually detected content of Y is 30.02 wt %) intermediate alloy are used as alloying raw materials. The raw materials are smelted into a low-cost magnesium alloy ingot; a blank subjected to solution treatment and peeling treatment is placed in an induction heating furnace and rapidly heated to an extrusion temperature of 260° C.; then, the magnesium alloy blank is deformed into a bar by extrusion processing at an extrusion speed of 1 m/min and an extrusion ratio of 36, and the extruded bar is cooled in air. Meanwhile, the extruded bar is tested for mechanical properties. Test results of the room-temperature mechanical properties of the embodiments and Reference example AZ31 are shown in Table 1.

(11) Embodiment 1: the Mg-3Al-3Bi-1Sn-0.04Ca-0.02Y (wt %) alloy composition is selected and proportioned into a magnesium alloy. The preparation method includes the following steps:

(12) 1) mixing is performed: a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sn block, a Mg—Ca intermediate alloy and a Mg—Y intermediate alloy which serve as raw materials are mixed according to the aforementioned target composition;

(13) 2) smelting is performed: the pure Mg ingot is put into a crucible of a smelting furnace, a furnace temperature is set at 720° C. and then maintained, and the pure Bi block and the pure Sn block which are preheated to 50° C. and the pure Al block, the Mg-20Ca intermediate alloy and the Mg-30Y intermediate alloy which are preheated to 200° C. are respectively added into the magnesium melt after the pure Mg ingot is melted; then the smelting temperature is increased to 750° C. and maintained for 15 minutes; the mixture is stirred for 5 minutes; high-purity Ar gas is fed for refining and degassing treatment; and the temperature is adjusted and controlled at 720° C. and maintained for 8 minutes, in which the smelting process is performed under the protection of CO.sub.2/SF.sub.6 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 corresponding mold to obtain an as-cast magnesium alloy, in which the casting process requires no gas protection;

(15) 4) solution treatment is performed: a solution treatment process is performed by maintaining a temperature of 415° C. for 20 hours, then maintaining a temperature of 440° C. for 8 hours, and quenching the alloy with warm water of 50° C., in which the heating and heat preservation processes of the solution treatment require no gas protection;

(16) 5) a cast ingot subjected to the solution treatment in the previous step is cut into a corresponding blank, and the blank is peeled;

(17) 6) extrusion deformation is formed: the blank obtained in the previous step is heated to 260° C. within 30 minutes and is put into the mold for deformation processing at an extrusion speed of 1 m/min, and the deformed blank is cooled in air to finally obtain the plastic magnesium alloy material.

(18) A test sample having a length of 70 mm is cut off from the extruded magnesium alloy bar obtained in Embodiment 1 and then is processed into a round bar-shaped tensile test sample having a diameter of 5 mm and a gauge length of 32 mm for tensile test, and the axial direction of the test sample round bar is the same as an extrusion flow direction of the material. It is measured that the magnesium alloy of the present disclosure has a tensile strength of 243.5 MPa, a yield strength of 153.7 MPa and an elongation rate of 38.2% as shown in Table 1. The magnesium alloy obtained in this embodiment has both high strength and high elongation rate. The typical tensile curve of the magnesium alloy obtained in this embodiment is shown in FIG. 1. FIG. 2 is a microstructure morphology, parallel to the extrusion direction, of the Mg-3Al-3Bi-1Sn-0.04Ca-0.02Y (wt %) magnesium alloy prepared in the present embodiment. It also can be seen from the metallographic diagram that the alloy undergoes complete dynamic recrystallization during the extrusion, and the grain size is about 15 μm.

(19) Embodiment 2: the Mg-4Al-2Bi-1Sn-0.03Ca-0.03Y (wt %) alloy composition is selected and proportioned into a magnesium alloy. The preparation method includes the following steps:

(20) 1) mixing is performed: a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sn block, a Mg—Ca intermediate alloy and a Mg—Y intermediate alloy which serve as raw materials are mixed according to the aforementioned target composition;

(21) 2) smelting is performed: the pure Mg ingot is put into a crucible of a smelting furnace, a furnace temperature is set at 720° C. and then maintained, and the pure Bi block and the pure Sn block which are preheated to 50° C. and the pure Al block, the Mg-20Ca intermediate alloy and the Mg-30Y intermediate alloy which are preheated to 200° C. are respectively added into the magnesium melt after the pure Mg ingot is melted; then the smelting temperature is increased to 750° C. and maintained for 15 minutes; the mixture is stirred for 5 minutes; high-purity Ar gas is fed for refining and degassing treatment; and the temperature is adjusted and controlled at 720° C. and maintained for 8 minutes, in which the smelting process is performed under the protection of CO.sub.2/SF.sub.6 mixed gas;

(22) 3) casting is performed: dross is removed from the surface of the melt, and the magnesium alloy melt is poured into a corresponding mold to obtain an as-cast magnesium alloy, in which the casting process requires no gas protection;

(23) 4) solution treatment is performed: a solution treatment process is performed by maintaining a temperature of 415° C. for 20 hours, then maintaining a temperature of 440° C. for 8 hours, and quenching the alloy with warm water of 50° C., in which the heating and heat preservation processes of the solution treatment require no gas protection;

(24) 5) a cast ingot subjected to the solution treatment in the previous step is cut into a corresponding blank, and the blank is peeled;

(25) 6) extrusion deformation is formed: the blank obtained in the previous step is heated to 260° C. within 30 minutes and is put into the mold for deformation processing at an extrusion speed of 1 m/min, and the deformed blank is cooled in air to finally obtain the plastic magnesium alloy material.

(26) A test sample having a length of 70 mm is cut off from the extruded magnesium alloy bar obtained in Embodiment 2 and then is processed into a round bar-shaped tensile test sample having a diameter of 5 mm and a gauge length of 32 mm for tensile test, and the axial direction of the test sample round bar is the same as an extrusion flow direction of the material. It is measured that the magnesium alloy of the present disclosure has a tensile strength of 255.3 MPa, a yield strength of 172.4 MPa and an elongation rate of 32.8% (Table 1). The magnesium alloy obtained in this embodiment has both relatively high strength and relatively high elongation rate. The typical tensile curve of the magnesium alloy obtained in this embodiment is shown in FIG. 1. FIG. 3 is a microstructure morphology, parallel to the extrusion direction, of the Mg-4Al-2Bi-1Sn-0.03Ca-0.03Y (wt %) magnesium alloy prepared in the present embodiment. It also can be seen from the metallographic diagram that the alloy undergoes complete dynamic recrystallization during the extrusion, and the grain size is about 10 μm.

(27) Embodiment 3: the Mg-6Al-3Bi-1Sn-0.03Ca-0.05Y (wt %) alloy composition is selected and proportioned into a magnesium alloy. The preparation method includes the following steps:

(28) 1) mixing is performed: a pure Mg ingot, a pure Al block, a pure Bi block, a pure Sn block, a Mg—Ca intermediate alloy and a Mg—Y intermediate alloy which serve as raw materials are mixed according to the aforementioned target composition;

(29) 2) smelting is performed: the pure Mg ingot is put into a crucible of a smelting furnace, a furnace temperature is set at 720° C. and then maintained, and the pure Bi block and the pure Sn block which are preheated to 50° C. and the pure Al block, the Mg-20Ca intermediate alloy and the Mg-30Y intermediate alloy which are preheated to 200° C. are respectively added into the magnesium melt after the pure Mg ingot is melted; then the melting temperature is increased to 750° C. and maintained for 15 minutes; the mixture is stirred for 5 minutes; high-purity Ar gas is fed for refining and degassing treatment; and the temperature is adjusted and controlled at 720° C. and maintained for 8 minutes, in which the smelting process is performed under the protection of CO.sub.2/SF.sub.6 mixed gas;

(30) 3) casting is performed: dross is removed from the surface of the melt, and the magnesium alloy melt is poured into a corresponding mold to obtain an as-cast magnesium alloy, in which the casting process requires no gas protection;

(31) 4) solution treatment is performed: a solution treatment process is performed by maintaining a temperature of 415° C. for 20 hours, then maintaining a temperature of 440° C. for 8 hours, and quenching the alloy with warm water of 50° C., in which the heating and heat preservation processes of the solution treatment require no gas protection;

(32) 5) a cast ingot subjected to the solution treatment in the previous step is cut into a corresponding blank, and the blank is peeled;

(33) 6) extrusion deformation is formed: the blank obtained in the previous step is heated to 260° C. within 30 minutes and is put into the mold for deformation processing at an extrusion speed of 1 m/min, and the deformed blank is cooled in air to finally obtain the plastic magnesium alloy material.

(34) A test sample having a length of 70 mm is cut off from the extruded magnesium alloy bar obtained in Embodiment 3 and then is processed into a round bar-shaped tensile test sample having a diameter of 5 mm and a gauge length of 32 mm for tensile test, and the axial direction of the test sample round bar is the same as an extrusion flow direction of the material. It is measured that the magnesium alloy of the present disclosure has a tensile strength of 168.4 MPa, a yield strength of 187.8 MPa and an elongation rate of 32.3%, as shown in Table 1. The magnesium alloy obtained in this embodiment has both relatively high strength and moderate elongation rate. The typical tensile curve of the magnesium alloy obtained in this embodiment is shown in FIG. 1. FIG. 4 is a microstructure morphology, parallel to the extrusion direction, of the Mg-6Al-3Bi-1Sn-0.03Ca-0.05Y (wt %) magnesium alloy prepared in the present embodiment. It also can be seen from the metallographic diagram that the features are similar to those in Embodiment 1 and Embodiment 2, and the alloy undergoes complete dynamic recrystallization during the extrusion, and the grain size is about 8 μm. In addition to the trace micron-sized second phases remaining outside the matrix, a large amount of tiny nano-sized second phases are dispersed in the matrix. FIG. 5 is a TEM structure diagram of the alloy of the embodiment. It can be found that there are many nano-sized precipitated phases in the alloy. These precipitated phases include Mg.sub.17Al.sub.12 phase, Mg.sub.3Bi.sub.2 phase and Mg.sub.2Sn phase. These nano-sized precipitated phases may suppress early occurrence of delayed twinning during alloy deformation, thereby improving the room-temperature plasticity of the alloy. FIG. 6 is an inverse pole diagram of the alloy of the embodiment, from which it can be seen that the alloy exhibits a weak non-base texture, thus avoiding the strong base texture and significantly improving the room-temperature plasticity of the alloy.

(35) The reference example is a current commercial AZ31 magnesium alloy: Mg-2.8Al-0.9Zn-0.3Mn (wt %) magnesium alloy. The typical stress-strain curve of the reference example (obtained under the same processing conditions as in Embodiment 2) in the tensile test is shown in FIG. 1. The reference example has a tensile strength of 223.7 MPa, a yield strength of 203.5 MPa and an elongation rate of 20.2%, as shown in Table 1. It can be seen by comparison that the room-temperature strength and elongation rate of the novel magnesium alloy of the present disclosure are significantly improved compared to the alloy of the reference example, thereby achieving similar effects as an alloy subjected to adding of a large number of rare earth elements and large plastic deformation. The novel alloy is a novel low-cost, high-strength and high-toughness magnesium alloy material with extremely high market competitiveness.

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

(37) TABLE-US-00001 TABLE 1 Test results of room-temperature mechanical properties of the Embodiments and the reference example Item Tensile Yield Elongation strength strength rate Example Alloy composition (wt %) MPa MPa % Embodiment 1 Mg—3Al—3Bi—1Sn—0.04Ca—0.02Y 243.5 153.7 38.2 Embodiment 2 Mg—4Al—2Bi—1Sn—0.03Ca—0.03Y 255.3 172.4 32.8 Embodiment 3 Mg—6Al—3Bi—1Sn—0.03Ca—0.05Y 168.4 187.8 32.3 Reference AZ31 223.7 203.5 20.2 example