CN107974652B - Extrusion shear die and forming method for realizing grain refinement of magnesium alloy - Google Patents

Abstract

The invention belongs to the field of magnesium alloy deformation technology and mold design and manufacture, and relates to an extrusion shearing mold and a forming method for realizing grain refinement of magnesium alloy. The extrusion shearing mold includes a pressing block, a sleeve and an extrusion shearing insert; the half mold of the extrusion shearing insert includes an extrusion cup, an extrusion section, a shear section, a forming section and a discharge area. The invention overcomes the disadvantages of the prior art, such as high requirements on equipment extrusion force, mold structure and strength, complicated process, etc., and provides an extrusion shearing mold and forming method that can effectively realize magnesium alloy grain refinement, the mold structure Simple, convenient method, easy to operate and obvious effect.

Description

Extrusion shear die and forming method for realizing grain refinement of magnesium alloy

technical field

The invention relates to an extrusion shear die and a forming method for realizing grain refinement of magnesium alloys, and belongs to the fields of magnesium alloy deformation technology and die design and manufacture.

Background technique

Magnesium alloy is known as a green material for the sustainable development of resources and environment in the 21st century, and has become the focus of attention of various countries. Due to the close-packed hexagonal crystal structure of magnesium alloys, the plastic deformation ability of magnesium alloys is poor. At present, more than 90% of magnesium alloys are obtained in the form of castings. The low strength of magnesium alloys obtained under conventional casting conditions limits the wide application of magnesium alloys to a large extent. Compared with cast magnesium alloys, the grains of wrought magnesium alloys are finer, and casting defects are reduced or even eliminated, so that the comprehensive mechanical properties of the product are greatly improved, and magnesium alloy rods of various sizes and specifications can be produced through plastic deformation. Tubes, profiles, wires, plates and forgings to meet the performance requirements of magnesium alloy structural parts in different occasions, and have important practical significance for expanding the application range of magnesium alloys. According to the Hall-Petch formula, the alloy strength is mainly directly related to the grain size. In recent years, some studies have been carried out on the grain refinement of magnesium alloys, mainly through large plastic deformation methods such as equal channel extrusion, cross rolling, asynchronous rolling, reciprocating extrusion, high ratio extrusion, multi-directional forging and large Deformation and hot rolling are used to refine the grains. Although these methods have obvious effects on the grain refinement of magnesium alloys, these methods are complicated in process, cumbersome in operation, and the product size is limited, so they are not suitable for industrial applications. For example, Equal Channel Extrusion (ECAP) is a new type of metal strong plastic deformation process that has attracted much attention in recent years. Through this method, magnesium alloys can obtain obvious grain refinement effects, but the billets need to go through multiple passes. Shearing can achieve a better grain refinement effect, and the mechanical properties of magnesium alloys are greatly affected by grain size and deformation parameters, resulting in low production efficiency and complicated processes; in addition, equal channel extrusion cannot be applied to The preparation of larger-sized profiles is also limited in its application range. In "ZK60 Magnesium Alloy ECAP Deformation Microstructure and Mechanical Properties" (2013, Volume 42, Issue 1), Wu Baohong et al. found that the as-cast ZK60 alloy can obtain an average grain size of 20µm after 2 passes of equal channel extrusion, and its tensile mechanical properties Can reach: tensile strength 250MPa, elongation 17.7%, but continue to increase the number of passes of equal channel extrusion, but will cause grain growth (average grain size after 4 passes is 50µm) and tensile strength Strength reduction (242MPa). In "Microstructure and Mechanical Properties of Fine-grained ZK60 Magnesium Alloy Prepared by ECAP Method" (No. 6, 2011), He Yunbin et al. found that the average grain size of extruded ZK60 alloy is about 1- 2µm, its tensile mechanical properties reach the best: tensile strength 221MPa, elongation 28.1%. However, with the increase of the passes of equal channel extrusion, the grain refinement effect is not obvious, and the strength of the alloy increases slightly, but the elongation increases significantly (35.1%). At present, there are continuous angular shear dies, which achieve the purpose of fully refining the grains through two angular shears. The angle of the angular plays an important role in the alloy shear deformation process. When the test conditions permit, The smaller the angle, the greater the shear force and the more obvious the grain refinement of the alloy. But this method has high requirements on equipment extrusion force, mold structure and strength.

Contents of the invention

Purpose of the invention:

The object of the present invention is to overcome the deficiencies of the prior art and provide an extrusion shearing die and forming method for effectively realizing magnesium alloy grain refinement. The die has a simple structure, a simple method, is easy to operate and has obvious effects.

Technical solutions:

The present invention is achieved through the following technical solutions:

An extrusion shearing die for realizing grain refinement of a magnesium alloy comprises a briquetting block, a sleeve and an extrusion shearing insert. The briquetting block and the extrusion shearing insert are assembled in the sleeve. The blank is placed between the press-shear inserts; the extrusion-shear insert is divided into two symmetrical half-molds by the axis, and the half-mold includes an extrusion cup, an extrusion section, a shear section, a forming section, and a discharge area; the blanks are sequentially After extrusion cup, extrusion section, shear section, forming section and discharge area.

The radius R1 of the inner circle of the sleeve is 18-95mm, and an empty slot corresponding to the discharge area of the extrusion shearing insert is provided at the lower end of the sleeve, the height L1 of the empty slot is 100-250mm, and the width L2 of the empty slot is 30-50mm; The inner side of the sleeve and the same height as the empty groove are provided with a draft angle β of 1°-1.5°.

The extrusion cup cone angle α is 85-95°, the extrusion section length L2 is 15-40mm, the extrusion section fillet radius r1 is 10-20mm, the shear section fillet radius r2 is 5-15mm, and the forming section radius R2 5-15mm, the length L3 of the working belt is 3-5mm, and the radius R3 of the exit area is the radius R2 of the forming section plus 1mm.

The extrusion ratio R1 ² /R2 ² of an extrusion shearing die for realizing magnesium alloy grain refinement is 12-40.

A forming method for realizing grain refinement of a magnesium alloy, the forming method comprising the following steps:

Step 1: Heating the cylindrical casting magnesium alloy billet to 300-550°C and keeping it warm for 5-20 hours to perform homogenization treatment;

Step 2: Assemble the sleeve and extrusion shearing insert together, and preheat to 300-450°C; preheat the compact to 200-250°C;

Step 3: Heat the homogenized billet to 300-550°C again, keep it warm for 2 hours, place it on the top of the extrusion shearing insert in the sleeve, put a briquetting block on the upper end of the billet for extrusion, and extrude The pressing speed is 1.5-2.5m/min, and the bar is air-cooled at the outer end of the hollow groove of the sleeve;

Step 4: After the extrusion is completed, pad the sleeve, and place the ejector rod above the pressing block to push out the pressing block, extrusion shearing insert and magnesium alloy rod from the lower end of the sleeve, and open the extrusion shearing insert A block of magnesium alloy rods is obtained.

Before extrusion, apply high-temperature lubricant on the inner surface of the sleeve, the surface of the briquette and the billet, and the inner and outer surfaces of the extrusion shear insert.

The material used in the forming method is a magnesium-zinc alloy.

Advantages and effects:

(1) The mold has simple structure, reasonable size, convenient installation and disassembly, simple forming method, stable forming process, and high forming quality of magnesium alloy;

(2) The die combines the extrusion process with the shearing process, which can obtain a large plastic deformation of the magnesium alloy at a small extrusion ratio, and effectively refine the grain size of the magnesium alloy (not greater than 20µm), And improve the mechanical properties of magnesium alloy;

(3) The mold can realize the preparation of fine-grained magnesium alloy rods on a small and medium-sized vertical hydraulic press, and magnesium alloy rods of different sizes can be obtained by changing the inner diameter of the sleeve and the diameter of the forming section of the extrusion die insert.

Description of drawings:

Figure 1 Schematic diagram of mold assembly;

Figure 2 Schematic diagram of the sleeve;

Fig. 3 Schematic diagram of half-mold of extrusion shearing insert;

Fig.4 Microstructure of Mg-6Zn-0.5Cu-0.6Zr alloy with an extrusion ratio of 12;

Fig.5 Microstructure of Mg-4Zn-1Y-0.6Zr alloy with an extrusion ratio of 40.

Fig.6 Microstructure of Mg-6Zn-0.5Zr alloy with an extrusion ratio of 25. Explanation of reference signs:

1. Briquetting block; 2. Billet; 3. Sleeve; 4. Extrusion shear insert; 5. Extrusion cup; 6. Extrusion section;

7. Shear section; 8. Forming section; 9. Discharge area; 10. Empty slot.

Detailed ways:

The present invention is further described below in conjunction with accompanying drawing:

As shown in Fig. 1, Fig. 2 and Fig. 3, an extrusion shearing die for realizing grain refinement of magnesium alloys includes a compact 1, a sleeve 3 and an extrusion shear insert 4, and the compact 1 and extrusion The press shear insert 4 is assembled in the sleeve 3, and the blank 2 is placed between the press block 1 and the extrusion shear insert 4; the extrusion shear insert 4 is divided into two symmetrical half molds by the axis, and the half mold It includes extrusion cup 5, extrusion section 6, shear section 7, forming section 8 and discharge area 9; billet 2 passes through extrusion cup 5, extrusion section 6, shear section 7, forming section 8 and discharge area in sequence. Material area 9. From top to bottom in the cavity of sleeve 3 are briquetting block 1, billet 2, extrusion cup 5, extrusion section 6, shearing section 7, forming section 8 and discharge area 9; the mold half is vertically divided into Extrusion cup 5, extrusion section 6 and shear section 7; horizontally divided into forming section 8 and discharge area 9.

An extrusion shearing die for realizing grain refinement of magnesium alloys, the radius R1 of the inner circle of the sleeve ranges from 18 to 95mm, and an empty groove 10 corresponding to the discharge area of the extrusion shearing insert is provided at the lower end of the sleeve, The range of the slot height L1 is 100-250mm, the range of the slot width L2 is 30-50mm; the inside of the sleeve and the same height as the slot 10 are provided with a draft angle β ranging from 1°-1.5°.

An extrusion shearing die for realizing grain refinement of magnesium alloy, the range of extrusion cup cone angle α is 85-95°, the length L2 of the extrusion section is 15-40mm, and the fillet radius r1 of the extrusion section is 10-20mm , The fillet radius r2 of the shearing section is 5-15mm, the radius R2 of the forming section is 5-15mm, the length L3 of the working belt is 3-5mm, and the radius R3 of the exit area is the radius R2 of the forming section plus 1mm.

The extrusion ratio R1 ² /R2 ² of an extrusion shearing die for realizing magnesium alloy grain refinement is 12-40, that is, the extrusion ratio is the square ratio of the radius of a billet to the radius of a formed bar.

A forming method for realizing grain refinement of magnesium alloy, characterized in that: the forming method comprises the following steps:

Step 1: Heating the cylindrical casting magnesium alloy billet to 300-550°C and keeping it warm for 5-20 hours to perform homogenization treatment;

Step 2: Assemble the sleeve 3 and the extrusion shear insert 4 together, and preheat to 300-450°C; preheat the briquetting block 1 to 200-250°C;

Step 3: Heat the homogenized billet to 300-550°C again, keep it warm for 2 hours, place it on the top of the extrusion shearing insert 4 in the sleeve 3, put the briquetting block 1 on the upper end of the billet 2 to carry out Extrusion, the extrusion speed is 1.5-2.5m/min, and the bar is air-cooled at the outer end of the hollow groove of the sleeve;

Step 4: After the extrusion is finished, pad the sleeve 3, and place the ejector pin above the briquetting block to eject the briquetting block 1, the extrusion shearing insert 4 and the magnesium alloy rod from the lower end of the sleeve 3, and open the extrusion Press and shear the insert 4 to obtain a magnesium alloy rod.

In the forming method for realizing magnesium alloy grain refinement, high-temperature lubricant is applied to the inner surface of the sleeve 3, the surface of the briquetting block 1 and the billet, and the inner and outer surfaces of the extrusion shearing insert 4 before extrusion.

Example 1

The material is Mg-6Zn-0.5Cu-0.6Zr alloy, and the extrusion ratio is set to 12. Firstly, the cylindrical billet with a radius of 17.4 mm is heated to 400° C. and kept for 10 hours for homogenization treatment. Then assemble the sleeve and the extrusion shear insert together, and preheat to 400°C; preheat the compact to 200°C. Heat the homogenized billet to 400°C again, keep it warm for 2 hours, place it on the top of the extrusion shearing insert in the sleeve, put a briquetting block on the upper end of the billet for extrusion, and the extrusion speed is 2.5m /min, and the bar is air-cooled at the outer end of the hollow slot of the sleeve. Before extrusion, apply high-temperature lubricant MoS ₂ on the inner surface of the sleeve, the surface of the briquetting block and the blank, and the inner and outer surfaces of the extrusion shear insert. After the extrusion is finished, the sleeve is cushioned, and the ejector rod is placed above the pressing block to push out the pressing block, extrusion shearing insert and magnesium alloy rod from the lower end of the sleeve, and the extrusion shearing insert is opened to obtain magnesium Alloy bars. The main structural dimensions of the mold are sleeve inner circle radius R118mm, slot height L1 is 100mm, slot width L2 is 30mm; draft angle β is 1°; extrusion cup cone angle α is 90°, extrusion section length L2 The fillet radius r1 of the extrusion section is 10mm, the fillet radius r2 of the shear section is 5mm, the radius R2 of the forming section is 5mm, the length L3 of the working belt is 5mm, and the radius R3 of the exit area is 6mm.

The metallographic structure of the bar after forming is shown in Figure 4. The grains are fine and the average grain size is about 15 μm. The tensile mechanical properties of the alloy can reach: tensile strength 320.2MPa, yield strength 240.6MPa, elongation 11.8 %

Example 2

The material is Mg-4Zn-1Y-0.5Zr alloy, and the extrusion ratio is 40. First, the cylindrical billet with a radius of 94.5 mm is heated to 450° C. and kept for 15 hours for homogenization. Then assemble the sleeve and the extrusion shear insert together, and preheat to 450°C; preheat the compact to 250°C. Heat the homogenized billet to 450°C again, keep it warm for 2 hours, place it on the top of the extrusion shearing insert in the sleeve, put a briquetting block on the upper end of the billet for extrusion, and the extrusion speed is 1.5m /min, and the bar is air-cooled at the outer end of the hollow slot of the sleeve. Before extrusion, apply high-temperature lubricant MoS ₂ on the inner surface of the sleeve, the surface of the briquetting block and the blank, and the inner and outer surfaces of the extrusion shear insert. After the extrusion is finished, the sleeve is cushioned, and the ejector rod is placed above the pressing block to push out the pressing block, extrusion shearing insert and magnesium alloy rod from the lower end of the sleeve, and the extrusion shearing insert is opened to obtain magnesium Alloy bars. The main structural dimensions of the mold are that the radius R1 of the inner circle of the sleeve is 95mm, the height of the cavity L1 is 250mm, and the width L2 of the cavity is 50mm; the draft angle β is 1.5°; the extrusion cup cone angle α is 95°; The length L2 is 15mm, the fillet radius r1 of the extrusion section is 20mm, the fillet radius r2 of the shear section is 15mm, the radius R2 of the forming section is 15mm, the length L3 of the working belt is 3mm, and the radius R3 of the exit zone is 16mm.

The metallographic structure of the bar after forming is shown in Figure 5. Its grains are fine and the average grain size is about 20 μm. The tensile mechanical properties of the alloy can reach: tensile strength 386.7MPa, yield strength 279.2MPa, elongation 19.5 %.

Example 3

The material is Mg-6Zn-0.5Zr alloy, and the extrusion ratio is 25. Firstly, the cylindrical billet with a radius of 49.5 mm is heated to 350° C. and kept for 20 hours for homogenization. Then assemble the sleeve and the extrusion shear insert together, and preheat to 350°C; preheat the compact to 220°C. Heat the homogenized billet to 350°C again, keep it warm for 2 hours, place it above the extrusion shearing insert in the sleeve, put a briquetting block on the upper end of the billet for extrusion, and the extrusion speed is 2m/ min, and the bar is air-cooled at the outer end of the hollow slot of the sleeve. Before extrusion, apply high-temperature lubricant MoS ₂ on the inner surface of the sleeve, the surface of the briquetting block and the blank, and the inner and outer surfaces of the extrusion shear insert. After the extrusion is finished, the sleeve is cushioned, and the ejector rod is placed above the pressing block to push out the pressing block, extrusion shearing insert and magnesium alloy rod from the lower end of the sleeve, and the extrusion shearing insert is opened to obtain magnesium Alloy bars. The main structural dimensions of the mold are that the radius R1 of the inner circle of the sleeve is 50mm, the height of the cavity L1 is 150mm, and the width L2 of the cavity is 40mm; the draft angle β is 1.2°; the extrusion cup cone angle α is 85°; The length L2 is 20mm, the fillet radius r1 of the extrusion section is 15mm, the fillet radius r2 of the shear section is 10mm, the radius R2 of the forming section is 10mm, the length L3 of the working belt is 4mm, and the radius R3 of the exit zone is 11mm.

The metallographic structure of the bar after forming is shown in Figure 6. The grains are fine and the average grain size is about 15 μm. The tensile mechanical properties of the alloy can reach: tensile strength 359.2 MPa, yield strength 258.7 MPa, and elongation 16.5 %.

Example 4

The material is Mg-6Zn-0.5Gd-0.4Zr alloy, and the extrusion ratio is set to 35. Firstly, the cylindrical billet with a radius of 47.3 mm is heated to 550° C. and kept for 5 hours for homogenization treatment. Then assemble the sleeve and the extrusion shear insert together, and preheat to 300°C; preheat the compact to 240°C. Heat the homogenized billet to 550°C again, keep it warm for 2 hours, place it on the top of the extrusion shearing insert in the sleeve, put a briquetting block on the upper end of the billet for extrusion, and the extrusion speed is 1.8m /min, and the bar is air-cooled at the outer end of the hollow slot of the sleeve. Before extrusion, apply high-temperature lubricant MoS ₂ on the inner surface of the sleeve, the surface of the briquetting block and the billet, and the inner and outer surfaces of the extrusion shear insert. After the extrusion is finished, pad the sleeve, and place the ejector rod above the briquetting block to push out the briquetting block, extrusion shearing insert and magnesium alloy rod from the lower end of the sleeve, and open the extrusion shearing insert to obtain magnesium Alloy bars. The main structural dimensions of the mold are that the radius R1 of the inner circle of the sleeve is 47.5mm, the height of the cavity L1 is 120mm, and the width L2 of the cavity is 30mm; The section length L2 is 25mm, the extrusion section fillet radius r1 is 10mm, the shearing section fillet radius r2 is 8mm, the forming section radius R2 is 8mm, the working belt length L3 is 5mm, and the exit zone radius R3 is 9mm.

The metallographic structure of the bar after forming is shown in Figure 4. The grains are fine and the average grain size is about 10 μm. The tensile mechanical properties of the alloy can reach: tensile strength 360.2MPa, yield strength 270.6MPa, and elongation 17.8 %.

Claims (5)

1. a kind of extrusion shearing mold for realizing magnesium alloy grains, including briquetting (1), sleeve (3) and extrusion shearing insert (4), it is characterised in that: briquetting (1) and extrusion shearing insert (4) are assemblied in sleeve (3), are inlayed in briquetting (1) and extrusion shearing Blank (2) are placed between block (4)；Extrusion shearing insert (4) is divided into two symmetrical half modules with axis, and half module includes extrusion cup (5), extruded segment (6), cut section (7), shaped segment (8) and discharge zone (9)；Blank (2) successively passes through extrusion cup (5), extruded segment (6), cut section (7), shaped segment (8) and discharge zone (9)；

Sleeve inner circle radius (R1) 18-95mm, end is equipped with empty slot (10) corresponding with extrusion shearing insert discharge zone under a bushing, Empty slot height (L1) 100-250mm, empty slot width (L2) 30-50mm；It is oblique equipped with depanning with empty slot (10) equal-height position on the inside of sleeve 1 ° -1.5 ° of degree (β)；

85-95 ° of extrusion cup cone angle (α) squeezes segment length (L2) 15 ~ 40mm, extruded segment radius of corner (r1) 10-20mm, shearing Section radius of corner (r2) 5-15mm, shaped segment radius (R2) 5-15mm, land length (L3) 3-5mm, outlet area radius (R3) For shaped segment radius (R2) plus 1mm.

2. a kind of extrusion shearing mold for realizing magnesium alloy grains according to claim 1, it is characterised in that: squeeze Pressure ratio R1²/R2²For 12-40.

3. a kind of manufacturing process of the realization magnesium alloy grains using extrusion shearing mold described in claim 1, special Sign is: the manufacturing process the following steps are included:

Step 1: by cylindrical cast magnesium alloy blank heating to 300-550 DEG C, and 5-20 hours are kept the temperature, carried out at homogenization Reason；

Step 2: sleeve (3) and extrusion shearing insert (4) are assembled together, and are preheated to 300-450 DEG C；Briquetting (1) is pre- Heat is to 200-250 DEG C；

Step 3: the blank (2) after Homogenization Treatments is again heated to 300-550 DEG C, and after heat preservation 2 hours, is placed in set The top of cylinder (3) interior extrusion shearing insert (4), is put into briquetting (1) in blank (2) upper end and is squeezed, extrusion speed 1.5- 2.5m/min, and it is air-cooled to bar progress in the outer end of sleeve empty slot；

Step 4: after extruding, sleeve (3) being paved, and is placed mandril above briquetting and inlayed briquetting (1), extrusion shearing Block (4) and magnesium alloy rod are ejected from sleeve (3) lower end, are opened extrusion shearing insert (4) and are obtained magnesium alloy rod.

4. the manufacturing process according to claim 3 for realizing magnesium alloy grains, it is characterised in that: before extruding, covering Cylinder (3) inner surface, briquetting (1) and blank surface and extrusion shearing insert (4) surfaces externally and internally smear high-temperature lubricant.

5. the manufacturing process according to claim 3 for realizing magnesium alloy grains, it is characterised in that: the manufacturing process is adopted Material is Mg-Zn based alloy.