A Y-shaped drawing composite forming method for magnesium and magnesium alloy wire

Abstract

The present invention proposes a magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method, which performs solid solution treatment on the magnesium alloy ingot, and prevents the precipitation of the second phase after water quenching. It is heated to above the recrystallization temperature, kept warm for a certain period of time, and then hot extruded in a horizontal extruder to extrude into a wire with a diameter of 3 mm; then the extruded wire is further heated, kept warm for a certain period of time, and transferred to a Y-type drawing die for drawing. The magnesium alloy wire extrusion Y-type drawing composite forming method provided by the present invention causes the magnesium alloy rod to first undergo severe plastic deformation at high temperature to obtain a 3mm fine-grained magnesium alloy wire, and then the 3mm wire is cooled and subjected to multiple Y-drawing passes, which solves the technical difficulties in the forming of magnesium alloy wires and realizes the precision forming of magnesium alloy wires with different compositions.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic processing of metal materials, and in particular relates to a method for extruding and drawing a magnesium and magnesium alloy wire composite forming method. Background Art

[0002] Magnesium is one of the light metals with abundant reserves on earth. In the context of increasingly serious global resource consumption, the development of magnesium alloy materials is of great strategic significance. As the metal structural material with the lowest density, magnesium alloy is known as the green engineering material of the 21st century. At the same time, magnesium alloy has the advantages of high specific strength, high specific stiffness, good impact resistance and energy absorption, and has been widely used in aerospace, automotive industry, electronic communications and biomedical fields.

[0003] The excellent performance of magnesium alloys makes magnesium alloy wires urgently needed in various fields. At present, magnesium alloy wires can be directly used to prepare medical devices such as surgical sutures, staples and vascular stents. They can also be combined with the matrix as a reinforcement phase to prepare artificial bones. Magnesium alloy wires can also be used as TIG welding wires for welding magnesium alloy parts such as aerospace and optical instruments, and for repairing cracks in magnesium alloy parts. In addition, magnesium alloy wires are also a raw material for metal 3D printing. For some magnesium alloy parts that are difficult to process, 3D printing is an excellent forming method. However, due to the poor plasticity and difficult deformation of magnesium alloys at room temperature, how to use a suitable process to prepare magnesium alloy wires with excellent performance has become a difficult problem that has been solved. Summary of the invention

[0004] The purpose of the present invention is to provide a magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method, which solves the fracture problem in the traditional magnesium alloy wire drawing process and realizes the precise forming of the magnesium alloy wire.

[0005] A magnesium and magnesium alloy wire extrusion Y-shaped drawing composite forming method specifically comprises the following steps:

[0006] Step S1: subjecting the magnesium alloy ingot to a solid solution treatment and then to water quenching to prevent the second phase from precipitating;

[0007] Then, it is heated to above the recrystallization temperature and kept warm for a certain period of time to prepare for hot extrusion;

[0008] Step S2: reaching the preset temperature and time for hot extrusion, that is, after preheating at 500° C. for 1 hour, cutting a cylinder with a diameter of 80 mm and a length of 100 mm from the magnesium alloy ingot as an extrusion blank, placing the magnesium alloy extrusion blank into the barrel of a horizontal extruder, and performing hot extrusion to extrude a 3 mm magnesium alloy wire;

[0009] Step S3: continue heating the 3 mm magnesium alloy wire and keep it warm for a period of time, that is, heating it to 350° C. and keeping it warm for 30 minutes;

[0010] Step S4: reaching the preset temperature and time, i.e. preheating at 500° C. for 1 hour, placing the magnesium alloy wire into a Y-shaped drawing module for drawing;

[0011] Step S5: During the drawing process, the position near the discharge end in the Y-shaped drawing die (or the triangular area, which is also close to the discharge end) is heated, and the heating temperature is slightly higher than the melting point of the magnesium alloy to form a semi-solid state.

[0012] In the step S1, the magnesium alloy ingot is heated to the solution temperature and kept at this temperature for more than 20 hours to eliminate the as-cast non-uniform structure, and then the precipitation of the second phase is suppressed by water cooling.

[0013] In the step S2, the extrusion temperature is above the recrystallization temperature and is kept at this temperature for a period of time so that the magnesium alloy undergoes dynamic recrystallization during the extrusion process.

[0014] In step S3, the heating furnace used is a tubular furnace, and the wire is passed through the furnace for heating. The wire with a diameter of 3 mm is heated to a recrystallization temperature of 350 degrees Celsius and kept warm for 30 minutes.

[0015] In the step S4, the magnesium alloy is placed in a Y-shaped drawing die set for drawing.

[0016] In the step S4, the wire is reduced in diameter by Y-type drawing, and the mold of the Y-type drawing is a roller mold;

[0017] The main body of the mold is composed of three roller molds, which are at an angle of 120° to each other, and the wire passes through the pore formed in the center.

[0018] In the step S4, the hole shape of the selected Y-type drawing method is an arc-edged triangle. After one Y-type drawing, the cross section of the wire changes from a circle to an arc-edged triangle;

[0019] The pore shape of the next Y-type drawing is circular, and the cross-section of the wire after two Y-type drawing changes to "circle-arc-edge triangle-circle".

[0020] In step S4, the Y-shaped drawing die is divided into two groups, and the first Y-shaped drawing die group and the second Y-shaped drawing die group form an angle of 60°.

[0021] In the step S4, semi-solid heating is performed at the arc-edge triangle position of the drawing die.

[0022] The positive effects of the present invention are as follows:

[0023] (1) The present invention provides a method for preparing a magnesium alloy wire, which adopts a process route combining extrusion and Y-type drawing. Compared with the traditional drawing, this method first performs a large plastic deformation (extrusion) on the magnesium alloy rod in the early stage. The severe plastic deformation causes the magnesium alloy to undergo dynamic recrystallization, refine the grains, and obtain a 3mm diameter magnesium wire with very good plasticity, so that it is not easy to break in the subsequent drawing process, and obtain an ultra-long magnesium alloy wire that is not easy to break;

[0024] (2) The present invention provides a Y-type drawing method for magnesium alloy wire, which uses a roller die instead of a fixed die. Compared with traditional drawing, this method has low friction, high wire diameter reduction rate, and energy saving. In addition, the processing of the wire can be regulated by changing the pore shape of the Y-type drawing die. This drawing method is particularly important for the preparation of magnesium alloy wire with a high rare earth content, and avoids wire breakage during the drawing process.

[0025] (3) In this solution, semi-solid heating is performed at the arc-edge triangle position of the roller mold, which has the following two technical effects:

[0026] First, the introduction of semi-solid technology into extrusion-drawing composite molding helps to give full play to the advantages of semi-solid and reduce the resistance of drawing;

[0027] Second, because both ends of the arc-edge triangular area of ​​the roller die are circular in cross-section, that is, sandwiched between two circular cross-sections, a closed process is achieved, which helps prevent the entry of external oxygen and solves the problem of easy oxidation that often exists in semi-solid technology;

[0028] Third, the movement of the semi-solid slurry on the inner wall of the roller die is conducive to the shear friction of the semi-solid slurry, which promotes the fracture of dendrites, realizes grain refinement, avoids internal tissue defects, and improves the mechanical properties of magnesium alloy wire;

[0029] Fourth, the semi-solid heating area is close to the discharge end of the roller die, so that the heat can be taken away by the extruded material, avoiding damage to the roller die caused by thermal expansion;

[0030] (4) In this scheme, extrusion + semi-solid forming + drawing are combined for composite forming, which produces unexpected technical effects and has good organizational structure and mechanical properties, which helps to save production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the Y-type drawing process.

[0032] Figure 2 This is the distribution of rollers in Y-type drawing.

[0033] Figure 3 It is the change of wire cross section during drawing process.

[0034] Figure 4 This is the initial organization diagram of Mg-Gd-Y alloy.

[0035] Figure 5 This is the streamlined structure diagram of Mg-Gd-Y alloy after extrusion.

[0036] Figure 6 This is the microstructure diagram of Mg-Gd-Y alloy after extrusion with wires of different diameters.

[0037] Figure 7 This is the microstructure diagram of Mg-Gd-Y alloy after extrusion + drawing.

[0038] Figure 8 This is the microstructure diagram of Mg-Gd-Y alloy after extrusion + semi-solid forming + drawing.

[0039] The parts represented by the reference numerals in the accompanying drawings are listed as follows: 1. Drawing clamp; 2-1. Drawing roller die one; 2-2. Drawing roller die two; 2-3. Drawing roller die three; 3-1. Wire with arc-shaped triangular cross section; 3-2. Wire with circular cross section. DETAILED DESCRIPTION

[0040] In order to more clearly illustrate the technical features of this solution, this solution is described below through specific implementation methods.

[0041] See also Figure 1-Figure 3 The Y-shaped roller die structure in this scheme includes three drawing roller dies, namely, drawing roller die 1 2-1, drawing roller die 2-2, and drawing roller die 3 2-3. Under the action of the drawing clamp 1, the circular cross-section wire 3-2 is transformed into the arc triangular cross-section wire 3-1.

[0042] Example 1

[0043] ZM6 magnesium alloy wire forming method:

[0044] Step S1: Place the ZM6 magnesium alloy rod in a hot air circulation furnace for solution treatment at a heating rate of 10°C / min, perform homogenization annealing at 530°C, and keep the temperature for 8 hours to eliminate the inhomogeneous structure such as component segregation in the casting state, and water quench to prevent the precipitation of the second phase.

[0045] Step S2: The water-cooled billet is heated to 480° C. and kept warm for 2 hours. After reaching the preset temperature and time, the magnesium alloy rod is placed in the barrel of a horizontal extruder for hot extrusion to extrude a 3 mm magnesium alloy wire.

[0046] Step S3: Continue to heat the 3 mm wire to 480°C and keep it warm for 0.5 h;

[0047] Step S4: After reaching the preset temperature and time, the magnesium alloy wire is placed in the Y-type drawing die for drawing. The cross section of the wire first changes from a circle to an arc-edged triangle, and then from an arc-edged triangle to a circle. The central angle of each arc edge of the arc-edged triangle is 60°, and the cross-sectional area of ​​the wire after the first drawing is 4.76mm2; the second drawing forms an angle of 60° with the roller die space position of the first drawing, and the diameter of the wire after the second drawing is 2.20mm in diameter and 3.79mm2 in cross-sectional area.

[0048] Example 2

[0049] ZM6 magnesium alloy wire forming method:

[0050] Step S1: Based on the first embodiment, the diameter of the ZM6 magnesium alloy wire is further reduced, and the central angle of each side of the arc-edge triangle is still 60°;

[0051] Step S2: heating the wire to 480°C and keeping the temperature for 0.5h;

[0052] Step S3: The cross section after the first drawing is an arc-edged triangle with a cross-sectional area of ​​2.56 mm2. The roller die space position of the second drawing forms an angle of 60° with the first drawing. The wire diameter after the second drawing is 1.61 mm and the cross-sectional area is 2.04 mm2.

[0053] Example 3

[0054] High rare earth content magnesium alloy wire forming method:

[0055] Step S1: Put the Mg-Gd-Y-Zn-Zr magnesium alloy rod into a resistance furnace, heat it up at a rate of 10°C / min, perform solution treatment at 515°C, and keep it warm for 24 hours to eliminate the uneven structure such as component segregation in the casting state, and water quench to prevent the precipitation of the second phase.

[0056] Step S2: The water-cooled billet is heated to 500°C and kept warm for 2 hours. After reaching the preset temperature and time, the magnesium alloy rod is placed in the barrel of a horizontal extruder for hot extrusion to extrude 3 mm Mg-Gd-Y-Zn-Zr magnesium alloy wire.

[0057] Step S3: Continue to heat the 3 mm wire to 500°C and keep it warm for 0.5 h;

[0058] Step S4: After reaching the preset temperature and time, the Mg-Gd-Y-Zn-Zr magnesium alloy wire is placed in the Y-type drawing die for drawing. The wire cross section first changes from a circle to an arc-edged triangle, and then from an arc-edged triangle to a circle. The center angle of each arc edge of the arc-edged triangle is 90°; the second drawing and the roller die space position of the first drawing form an angle of 60°, and the wire diameter after the second drawing is 2.58mm in diameter;

[0059] Step S5: Repeat the drawing method of step S5 for the Mg-Gd-Y-Zn-Zr wire with a diameter of 2.58 mm, and finally obtain a wire with a diameter of 2.19 mm.

[0060] Example 4

[0061] The initial structure of Mg-Gd-Y alloy is as follows Figure 4 As shown, these are coarse equiaxed grains with some second phases distributed at the grain boundaries.

[0062] See also Figure 5 After extrusion, the second phase at the grain boundary is broken and evenly distributed in the extrusion direction, presenting the form of extrusion streamlines.

[0063] Microstructure of drawn wires with different diameters Figure 6 As shown in the figure, the equiaxed grains after extrusion recrystallization are obviously elongated; there are two forms of the second phase. In addition to the second phase with streamline distribution after extrusion, a small amount of fine dispersed second phase precipitates at the grain boundaries.

[0064] See also Figure 7 and Figure 8 , respectively, are the organization diagrams after extrusion + drawing, and the organization diagrams after extrusion + semi-solid forming + drawing. From the organization diagram after extrusion + drawing, it can be seen that it is still a streamlined organization, with a fine grain area of ​​about 2-3 microns and a coarse grain area greater than 5 microns; while from the organization diagram after extrusion + semi-solid forming + drawing, it can be seen that the grain size is relatively round, with a grain diameter between 2-5 microns, and no subsequent annealing or tempering treatment is required. It can be seen that semi-solid forming plays an important role in this scheme.

[0065] Technical features not described in the present invention can be achieved through or by adopting existing technologies and will not be described in detail here. Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for extruding and drawing magnesium and magnesium alloy wires into a Y-shaped composite forming process, characterized in that: The specific steps include: Step S1: subjecting the magnesium alloy ingot to a solid solution treatment and then to water quenching to prevent the second phase from precipitating; Then heat it to above the recrystallization temperature and keep it warm for more than 20 hours to prepare for hot extrusion; Step S2: reaching the preset temperature and time for hot extrusion, that is, after preheating at 500° C. for 1 hour, cutting a cylinder with a diameter of 80 mm and a length of 100 mm from the magnesium alloy ingot as an extrusion blank, placing the magnesium alloy extrusion blank into the barrel of a horizontal extruder, and performing hot extrusion to extrude a 3 mm magnesium alloy wire; Step S3: continue heating the 3 mm magnesium alloy wire and keep it warm for a period of time, that is, heating it to 350° C. and keeping it warm for 30 minutes; Step S4: reaching the preset temperature and time, i.e. preheating at 500° C. for 1 hour, placing the magnesium alloy wire into a Y-shaped drawing module for drawing; Step S5: During the drawing process, the position near the discharge end of the Y-shaped drawing die is heated, and the heating temperature is slightly higher than the melting point of the magnesium alloy to form a semi-solid state.

2. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 1, characterized in that: In the step S1, the magnesium alloy ingot is heated to the solution temperature to eliminate the as-cast inhomogeneous structure, and then the precipitation of the second phase is suppressed by water cooling.

3. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 1, characterized in that: In the step S2, the extrusion temperature is above the recrystallization temperature and is kept at this temperature for a period of time so that the magnesium alloy undergoes dynamic recrystallization during the extrusion process.

4. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 1, characterized in that: In step S3, the heating furnace used is a tubular furnace, and the wire is passed through the furnace for heating. The wire with a diameter of 3 mm is heated to a recrystallization temperature of 350 degrees Celsius and kept warm for 30 minutes.

5. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 1, characterized in that: In the step S4, the wire is reduced in diameter by Y-type drawing, and the mold of the Y-type drawing is a roller mold; The main body of the mold is composed of three roller molds, which are at an angle of 120° to each other, and the wire passes through the pore formed in the center.

6. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 5, characterized in that: In the step S4, the hole shape of the selected Y-type drawing method is an arc-edged triangle. After one Y-type drawing, the cross section of the wire changes from a circle to an arc-edged triangle; The pore shape of the next Y-type drawing is circular, and the cross-section of the wire after two Y-type drawing changes to "circle-arc-edged triangle-circle".

7. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 6, characterized in that: In step S4, the Y-shaped drawing die is divided into two groups, and the first Y-shaped drawing die group and the second Y-shaped drawing die group form an angle of 60°.

8. The magnesium and magnesium alloy wire extrusion Y-type drawing composite forming method according to claim 6, characterized in that: In the step S4, semi-solid heating is performed at the arc-edge triangle position of the drawing die.

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