CN109604359B

CN109604359B - Forming method for Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal-channel extrusion blank making

Info

Publication number: CN109604359B
Application number: CN201811647295.6A
Authority: CN
Inventors: 张治民; 闫钊鸣; 王强; 朱家萱; 张冠世; 任璐英
Original assignee: North University of China
Current assignee: North University of China
Priority date: 2018-12-30
Filing date: 2018-12-30
Publication date: 2020-05-26
Anticipated expiration: 2038-12-30
Also published as: CN109604359A

Abstract

The invention discloses a forming method of a Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank, which relates to a forming die of a Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank, the die comprises an upper die base, a convex die and a concave die, the concave die is arranged below the convex die, the concave die is in an inverted T shape and is formed by communicating a vertical cavity and a horizontal cavity with the same diameter, meanwhile, a spherical cabin is formed at the intersection of the vertical cavity and the horizontal cavity, small round corners are arranged at the connection parts of the spherical cabin and the vertical cavity and the horizontal cavity respectively, and the vertical cavity is used for the convex die to enter. The invention adopts a bidirectional equal-channel extrusion structure consisting of a vertical cavity and a horizontal cavity, a spherical cabin is arranged at the intersection of the channels, and a multi-pass deformation test is carried out, so that the shearing deformation at the corner of the cavity and the upsetting extrusion deformation in the spherical cabin are compositely superposed in the material extrusion process, the material accumulation plastic deformation process is achieved, the microstructure of the Mg-Gd-Y-Zn-Zr magnesium alloy blank is finally refined, and the mechanical property of the alloy is improved.

Description

Forming method for Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal-channel extrusion blank making

Technical Field

The invention belongs to the technical field of plastic processing and forming of metal materials, and particularly relates to a forming method for a Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal-channel extrusion blank.

Background

With the continuous consumption of natural energy and the increasing severity of the forms of near exhaustion, the development of weight reduction of equipment is inevitably oriented, and magnesium is the lightest metal, with a density of 1.74g/cm3, which is only two thirds of aluminum, one quarter of steel, and one third of titanium. Meanwhile, the magnesium alloy has high specific strength, specific rigidity, corrosion resistance and electromagnetic shielding property, so that the magnesium alloy becomes an important selection direction for aerospace and electronic materials. The alloy has higher performance than the traditional magnesium alloy due to the existence of an LPSO (Long period Stacking ordered) structure in the Mg-Gd-Y-Zn-Zr alloy, and researches find that the LPSO phase has two structures, namely a lamellar structure and a blocky structure, wherein the kinking deformation mechanism of the lamellar LPSO phase is one of important deformation mechanisms of the Mg-Gd-Y-Zn-Zr alloy, plays a role in coordinating deformation under the condition that a slippage system at lower temperature is difficult to start, and is an advantageous phase for improving the plasticity of the material; the other bulk LPSO phase is a hardening phase which is easily generated as a crack source during deformation and macroscopically shows that surface cracks appear on the alloy. Plastic deformation is a common method for improving material performance by alloy, and the traditional plastic deformation blank making method, such as a blank making method of upsetting, drawing and growing, is simple, convenient and easy to operate, but has the defect of small strain capacity and is difficult to achieve ultra-fining of materials; large Plastic Deformation (SPD) realizes the refinement of tissue grains by introducing large strain quantity, and large blocky LPSO phase is broken up, so that the tissue components become more compact and uniform, and the bidirectional promotion of material strength and plasticity is realized.

The blank making process is an important process for manufacturing the forge piece, and the quality of the forged blank directly influences the subsequent forming process. ECAE (Equal Channel Angular extrusion) technology has been widely researched as a mature large plastic deformation method, meanwhile, the improvement technology based on the ECAE technology is also deeply researched, ultra-fine grains (less than 1 μm) are observed after 9-pass test of pure aluminum by the double Equal Channel Angular extrusion technology researched by Talebanpour et al, and meanwhile, the extrusion force is reduced by the double Equal Channel Angular extrusion technology, so that the blank manufacturing efficiency is increased. The repeated upsetting RU (repaired assembling) technique studied by Zhou et al is applied to Mg-9.8Gd-2.7Y-0.4Zr magnesium alloy to obtain the grain size of 2.5-3.0 μm.

Based on the research results and the high performance requirements required by the current engineering materials, in order to break up the blocky second phase of the Mg-Gd-Y-Zn-Zn magnesium alloy, the tissue composition is more uniform, and the Dual expansion equal Channel Extrusion (DEECLE) is the new forming process provided by the scheme.

Disclosure of Invention

Aiming at the current situation of the prior processing technology, the invention provides a forming method for a Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal-channel extrusion blank, which achieves the purposes of refining the microstructure of a Mg-Gd-Y-Zn-Zr magnesium alloy blank and improving the mechanical property of the alloy.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a forming method of Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank making relates to a forming die of Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank making, the die comprises an upper die base, a convex die and a concave die, the convex die is a cylinder and is vertically arranged on the upper die base, the concave die is arranged below the convex die, the concave die is in an inverted T shape and is formed by communicating a vertical cavity and a horizontal cavity with the same diameter, meanwhile, a spherical cabin is formed at the intersection of the vertical cavity and the horizontal cavity, small fillets are respectively arranged at the connection parts of the spherical cabin and the vertical cavity and the horizontal cavity, and the vertical cavity is used for the convex die to enter, the method specifically comprises the following steps:

s1: blanking in a rod shape;

s2: homogenizing at 415 ℃ for 16 h;

s3: assembling a mould;

s4: the rod-shaped blank after homogenization treatment is placed into the female die from the vertical cavity, then the male die is placed into the vertical cavity from the upper part, finally, the die and the rod-shaped blank are placed into the heating furnace together for heating and heat preservation, and after the heat preservation is finished, a constant-temperature multi-pass deformation test is carried out on a universal material testing machine: controlling the male die to descend to the bottom surface of the male die and the horizontal cavity at a constant speed to ensure that the upper surface of the blank is relatively flat, wherein the step is a one-time deformation test, after the one-time deformation test is finished, taking out the blank, putting the blank into water to protect a deformed tissue, after cooling, grinding the extruded blank to form a hemispherical structure, putting the blank into a female die, and adding the blank to a preset temperature to perform a two-time deformation test;

s5: before the second-pass deformation test, the ground blank is aligned to the position vertical to the cavity and placed, the second-pass deformation test is carried out after the position is placed, and after the second-pass deformation test is completed, the blank is cooled, ground and placed into a female die in the same way to prepare for the third-pass deformation;

s6: and during the three-pass deformation test, the placing position of the blank is the placing position of the step S5, the three-pass deformation test is carried out after the blank is placed, and the blank is cooled and polished in the same way after the test is finished, so that the finished product is finally obtained.

Preferably, the multi-pass deformation test comprises more than three deformation tests, and the test is continuously carried out along the route deformation rule until the test is finished to the expected set target.

Preferably, the female die is provided with fastening screws, the female die is divided into an upper layer and a lower layer, the upper layer and the lower layer are fixed together by the fastening screws, and the layered surfaces are arranged on the parallel plane where the diameter of the horizontal cavity is located.

After the scheme is adopted, compared with the traditional blank manufacturing method by upsetting and drawing, the method has the beneficial effects that: (1) the accumulated strain is large. The traditional blank making method has the strain which is difficult to exceed 1 and has limited deformation effect. The blank manufacturing method is based on the SPD large plastic deformation technology, and the strain is far larger than that of the traditional upsetting and drawing method. (2) Various stresses combine. The traditional method generally suffers from single stress, tensile stress or compressive stress. According to the blank manufacturing method, multiple stresses are combined, the design of the spherical cavity realizes the upsetting and extruding processes of the Mg-Gd-Y-Zn-Zr alloy, and meanwhile, the shearing stress deformation of metal is realized at the joint of the spherical cabin, the vertical cavity and the horizontal cavity. (3) The deformation uniformity is good. The traditional upsetting method is generally an open blank making method, a large deformation area of a material is concentrated in an easy deformation area in metal, and a hard deformation area in contact with a male die and a female die is basically not deformed, so that the material is deformed unevenly. The design of the spherical cabin realizes the upsetting extrusion composite deformation of metal and enhances the uniformity of materials.

Compared with the ECAE method, the method has the following beneficial effects: (1) the deformation force is small. Compared with ECAE, the design of the bidirectional extrusion structure greatly reduces the forming force, prolongs the service life of the machine and reduces the cost. (2) The spherical capsule design is more deformable. The ECAE technology has positive promotion effect on grain refinement and material performance improvement as a widely researched large plastic deformation method. Compared with an ECAE technology, the spherical cabin is designed, the shearing deformation is the same as that of the ECAE technology, large-plasticity high-stress deformation occurs in a deformation area under the action of shearing force, crystal grains are refined, large second phases are broken, tissues are uniform and compact, alloy materials with good performance are obtained, in addition, upsetting extrusion composite deformation of metal in the spherical cabin is increased, more efficient blank making efficiency can be obtained, the flow of the material in the spherical cavity at a channel connection part is changed into a more complex mixed flow mode of upsetting and extrusion, and the novel large-plasticity deformation blank making method with diversified metal flow modes and large accumulated strain is provided.

Compared with the method for repeatedly extruding RU, the method has the following beneficial effects: (1) more suitable for use are Mg-Gd-Y-Zn-Zr magnesium alloys and the like which contain lumpy and hard second phase metals. According to the repeated extrusion design of Shanghai traffic university, no round corner is designed at the vertical channel and the horizontal channel, on one hand, the shear stress is enhanced, but for the massive LPSO phase contained in the Mg-Gd-Y-Zn-Zr magnesium alloy species, the shear crack is easy to generate during deformation. The small radius of the present design solves this problem. (2) The spherical tank design deforms more fully. The spherical bin design realizes the upsetting extrusion composite deformation of metal in the cavity, so that the deformation of the material is more sufficient.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings.

Drawings

FIG. 1 is a cross-sectional elevation view of a blank after one pass of the deformation test of the present invention;

FIG. 2 is a cross-sectional view taken along Y-Y of FIG. 1;

FIG. 3 is a schematic view of a workpiece completed after a multi-pass deformation test according to the present invention;

FIG. 4 is a cross-sectional view taken along Z-Z of FIG. 3;

FIG. 5 is an assembly view of the present invention;

FIG. 6 is a schematic structural view of the male mold of the present invention;

FIG. 7 is a schematic structural view of a fastening screw fixing female die according to the present invention;

FIG. 8 is a top view of the female mold of the present invention;

FIG. 9 is a cross-sectional view taken along L-L of FIG. 7;

FIG. 10 is an exploded view of FIG. 7;

FIG. 11 is a schematic view of an upper die base of the present invention;

FIG. 12 is a first schematic view illustrating the operation state of the present invention;

FIG. 13 is a second schematic view of the working state of the present invention;

FIG. 14 is a third schematic view of the working state of the present invention;

fig. 15 is an enlarged view at G in fig. 12.

Description of reference numerals:

1-upper die holder, 11-square groove, 12-conical hole, 2-male die, 21-fixing part, 3-fastening nut, 4-fastening screw, 5-female die, 51-vertical cavity, 52-horizontal cavity, 53-spherical cabin, 54-upper female die layer, 541-positioning groove, 55-lower female die layer, 551 positioning protrusion, 6-blank and 61-hemisphere.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The invention discloses a forming method of a Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank, and relates to a forming die of the Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank, and the die comprises an upper die holder 1, a male die 2 and a female die 5, and the reference is made to figures 1-15.

As shown in fig. 6, the male die 2 is a cylinder, a radially extending fixing portion 21 is formed at the upper end of the male die 2, the fixing portion 21 is square, as shown in fig. 11, a square groove 11 is formed in the upper die base 1 for the fixing portion 21 to be placed in, after the placing is completed, a fastening nut 3 is arranged at the lower end of the upper die base 1 and forms an external thread matched with the fastening nut 3, and the fastening nut 3 penetrates through the male die 2 to clamp the fixing portion 21, so that the male die 2 is coaxially and vertically fixed on the upper die base 1. The male thread is matched with the fastening nut 3 to achieve the purposes of fastening the male die 2 and preventing falling off, and the requirement on the bearing capacity of the die is not high due to small forming force and the assembly and disassembly are convenient; meanwhile, tapered holes 12 which are convenient for loading and unloading the die are uniformly distributed on the surface of the upper die holder 1.

The upper die holder 1 is further provided with a sliding groove (not shown in the figure), the sliding groove is communicated with the square groove 11, and the fixing part 21 is slidably arranged in the square groove 11 through the sliding groove. The sliding groove is used for replacing the male die 2, and when the male die 2 is replaced, the fastening nut 3 is unscrewed, the old male die 2 is pushed out, and the new male die 2 is placed; because the extrusion mode is forward extrusion, the convex die 2 is not provided with a round angle and a working band, and the aim is to prevent backward extrusion to the maximum extent.

The female die 5 is arranged below the male die 2, as shown in fig. 7 and 8, the female die 5 is in an inverted 'T' shape and is formed by communicating a vertical cavity 51 and a horizontal cavity 52 with the same diameter, and similar to the ECAE technology, the angle of rotation is 90 degrees, except that the channel is bidirectional, the vertical cavity 51 is used for the male die 2 to enter, and a spherical cabin 53 is formed at the intersection of the vertical cavity 51 and the horizontal cavity 52. The spherical chamber 53 is coaxial with the vertical cavity 51 and with the horizontal cavity 52. The joints of the spherical cabin 53 and the vertical cavity 51 and the horizontal cavity 52 are provided with small round corners, so that the cracking of the deformed blank 6 caused by an excessively strong shearing force is prevented while the shearing force is ensured.

As shown in fig. 10, in order to facilitate material taking, the female die 5 is designed in a layered manner, the female die 5 is divided into an upper layer 54 and a lower layer 55, the upper layer and the lower layer are fixed together by using the fastening screws 4, and the layered surfaces are arranged on a parallel plane where the diameter of the horizontal cavity 52 is located. As shown in fig. 9, in order to ensure the accurate butt joint of the female die 5, the lower die layer 55 is provided with a positioning protrusion 551, the upper die layer 54 is provided with a positioning groove 541 corresponding to the positioning protrusion 551, the positioning protrusion 551 is matched with the positioning groove 541, and finally, the female die is fixed by a fastening screw 4.

In this embodiment, the movement and the method steps of the die are explained by taking the deformation of the Mg-Gd-Y-Zn-Zr rod-shaped blank 6 with the diameter of phi 10mm multiplied by 30mm as an example, and FIGS. 12, 13 and 14 are the deformation states of the die in operation, and the male die 2 and the vertical cavity 51 are provided with a single-side interval h of 0.1mm for the convenience of forward extrusion, and refer to FIG. 15. Fig. 12 shows a first deformed state of the metal blank 6, in which the blank 6 is deformed in the spherical chamber 53; fig. 13 shows a second deformation state of the metal blank 6, in which the blank 6 is extruded into the horizontal cavity 52 after upsetting, and the blank 6 is subjected to multi-directional stress including compressive stress and shear stress, and the deformation of the metal blank 6 is most severe; fig. 14 shows a third deformed state of the metal blank 6, in which the deformation of the blank 6 is completed.

As shown in fig. 5, the vertical cavity 51 and the horizontal cavity 52 in the female die 5 have the same diameter, so that the extruded workpiece can be deformed for many times by using the original die only by slight processing.

A forming method for Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank making comprises the following steps:

s1: blanking in a rod shape;

s2: homogenizing at 415 ℃ for 16 h;

s3: assembling a mould;

s4: the rod-shaped blank 6 after homogenization treatment is placed into the female die 5 from the vertical cavity 51, then the male die 2 is placed into the vertical cavity 51 from the upper part, finally the die and the rod-shaped blank 6 are placed into a heating furnace together for heating and heat preservation, after the heat preservation is finished, the forming process is carried out on a universal material testing machine, and a constant temperature three-time deformation test is carried out by taking the experimental temperature of 480 ℃ as an example: controlling the male die 2 to descend to the position of the bottom surface of the male die 2 and the horizontal cavity 52 at a constant speed to ensure that the upper surface of the blank 6 is relatively flat, wherein the step is a primary deformation test, after the primary deformation test is finished, loosening the fastening screw 4, taking out the blank 6, putting the blank into water to protect a deformed tissue, after cooling, grinding the extruded blank 6 to form a hemispherical structure 61, putting the hemispherical structure into the female die 5, and performing a secondary deformation test at a preset temperature;

s5: the ground blank 6 is placed in alignment with the vertical cavity 51 prior to the two pass deformation test. And (3) carrying out a two-pass deformation experiment after the position is placed, and after the two-pass deformation experiment is finished, similarly cooling, polishing and placing the product into the female die 5 to prepare for three-pass deformation.

It should be noted that if the expected set target is not reached, the multi-pass deformation test can be performed, the four-pass deformation test and the five-pass deformation test … continue to perform the tests according to the above-mentioned route deformation rule until the expected set target is completed, as shown in fig. 3 and 4, the present embodiment can be realized by three passes. In addition, during the test, samples need to be reserved for each pass, so that the observation and the detection of the microstructure and the mechanical property are convenient.

The parameter design of the multi-pass deformation test comprises extrusion speed, temperature and lubrication selection, and the design temperature of the isothermal test comprises 380 ℃, 440 ℃, 480 ℃ and 500 ℃; the extrusion speed is selected from 0.8mm/s, 1.0mm/s and 1.5 mm/s; the lubricating selection is oil-based graphite and dry graphite powder, and after the test conditions are prepared, a one-time extrusion test of the Mg-Gd-Y-Zn-Zr magnesium alloy rod is carried out.

Compared with the traditional blank manufacturing method by upsetting and drawing, the invention has the advantages that: (1) the accumulated strain is large. The traditional blank making method has the strain which is difficult to exceed 1 and has limited deformation effect. The blank manufacturing method is based on the SPD large plastic deformation technology, and the strain is far larger than that of the traditional upsetting and drawing method. (2) Various stresses combine. The traditional method generally suffers from single stress, tensile stress or compressive stress. According to the blank manufacturing method, various stresses are combined, the design of the spherical cabin 53 realizes the upsetting and extruding processes of Mg-Gd-Y-Zn-Zr alloy, and meanwhile, the shearing stress deformation of metal is realized at the connecting part of the spherical cabin 53 and the vertical cavity 51 as well as the horizontal cavity 52. (3) The deformation uniformity is good. The traditional upsetting method is generally an open blank making method, large deformation areas of materials are concentrated in an easy deformation area in metal, and a hard deformation area in contact with a male die 2 and a female die 5 is basically not deformed, so that the deformation of the materials is not uniform. The design of the spherical cabin 53 in the invention realizes the upsetting extrusion composite deformation of metal, and enhances the uniformity of materials.

Compared with the ECAE method, the method has the following beneficial effects: (1) the deformation force is small. Compared with ECAE, the design of the bidirectional extrusion structure greatly reduces the forming force, prolongs the service life of the machine and reduces the cost. (2) The spherical capsule 53 design is more deformable. The ECAE technology has positive promotion effect on grain refinement and material performance improvement as a widely researched large plastic deformation method. Compared with the ECAE technology, the spherical cabin 53 is designed, the shearing deformation is the same as that of the ECAE technology, the deformation area generates large-plasticity high-stress deformation under the action of shearing force, so that crystal grains are refined, large second phases are crushed, the tissue is uniform and compact, and alloy materials with good performance are obtained.

Compared with the method for repeatedly extruding RU, the method has the following beneficial effects: (1) more suitable for use are Mg-Gd-Y-Zn-Zr magnesium alloys and the like which contain lumpy and hard second phase metals. According to the repeated extrusion design of Shanghai university of transportation, the vertical cavity 51 and the horizontal cavity 52 are not designed with fillets, so that on one hand, the shear stress is enhanced, but the massive LPSO phase contained in the Mg-Gd-Y-Zn-Zr magnesium alloy species is easy to generate shear cracks during deformation. The small rounded corners designed by the present invention over-solve this problem. (2) The spherical chamber 53 design deforms more fully. The spherical bin design realizes the upsetting extrusion composite deformation of metal in the cavity, so that the deformation of the material is more sufficient.

The above description is only an embodiment of the present invention, and is not intended to limit the scope of the present invention, and is not limited to the single horizontal cavity mold structure, but also includes the multiple horizontal cavity mold structure. All equivalent changes made according to the design idea of the present application fall within the protection scope of the present application.

Claims

1. A forming method of Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank making relates to a forming die of Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank making, the die comprises an upper die base, a convex die and a concave die, the convex die is a cylinder and is vertically arranged on the upper die base, the concave die is arranged below the convex die, the concave die is in an inverted T shape and is formed by communicating a vertical cavity and a horizontal cavity with the same diameter, meanwhile, a spherical cabin is formed at the intersection of the vertical cavity and the horizontal cavity, small fillets are respectively arranged at the connection parts of the spherical cabin and the vertical cavity and the horizontal cavity, and the vertical cavity is used for the convex die to enter, the method specifically comprises the following steps:

s1: blanking in a rod shape;

s2: homogenizing at 415 ℃ for 16 h;

s3: assembling a mould;

2. The method for forming the Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank according to claim 1, wherein the method comprises the following steps: the multi-pass deformation test comprises more than three deformation tests, and the test is continuously carried out along the route deformation rule until the test is finished to the expected set target.

3. The method for forming the Mg-Gd-Y-Zn-Zr magnesium alloy bidirectional expansion equal channel extrusion blank according to claim 1, wherein the method comprises the following steps: the female die is provided with fastening screws, the female die is divided into an upper layer and a lower layer, the upper layer and the lower layer are fixed together by the fastening screws, and the layered surfaces are arranged on parallel planes where the diameters of the horizontal cavities are located.