CN113234978A - Extruded magnesium-yttrium alloy and preparation method thereof - Google Patents
Extruded magnesium-yttrium alloy and preparation method thereof Download PDFInfo
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- MIOQWPPQVGUZFD-UHFFFAOYSA-N magnesium yttrium Chemical compound [Mg].[Y] MIOQWPPQVGUZFD-UHFFFAOYSA-N 0.000 title claims abstract description 36
- 229910000946 Y alloy Inorganic materials 0.000 title claims abstract description 33
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
- 238000000265 homogenisation Methods 0.000 claims abstract description 75
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims abstract description 43
- 229910052727 yttrium Inorganic materials 0.000 claims abstract description 39
- 239000011777 magnesium Substances 0.000 claims abstract description 34
- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 25
- 238000000034 method Methods 0.000 claims abstract description 25
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims abstract description 23
- 230000008569 process Effects 0.000 claims abstract description 14
- 238000005266 casting Methods 0.000 claims abstract description 8
- 230000001681 protective effect Effects 0.000 claims abstract description 6
- 238000002844 melting Methods 0.000 claims abstract description 5
- 230000008018 melting Effects 0.000 claims abstract description 5
- 239000002994 raw material Substances 0.000 claims abstract description 4
- 238000001125 extrusion Methods 0.000 claims description 19
- 239000000203 mixture Substances 0.000 claims description 8
- 238000005260 corrosion Methods 0.000 abstract description 58
- 230000007797 corrosion Effects 0.000 abstract description 58
- 239000011159 matrix material Substances 0.000 abstract description 19
- 238000004090 dissolution Methods 0.000 abstract description 3
- 238000002474 experimental method Methods 0.000 abstract description 3
- 230000002829 reductive effect Effects 0.000 abstract description 3
- 239000000956 alloy Substances 0.000 description 78
- 229910045601 alloy Inorganic materials 0.000 description 77
- 239000012071 phase Substances 0.000 description 31
- 229910052739 hydrogen Inorganic materials 0.000 description 22
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 18
- 239000001257 hydrogen Substances 0.000 description 18
- 239000000047 product Substances 0.000 description 16
- 230000000694 effects Effects 0.000 description 14
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 13
- 239000000243 solution Substances 0.000 description 10
- 238000012360 testing method Methods 0.000 description 9
- 229910052761 rare earth metal Inorganic materials 0.000 description 8
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- 238000002791 soaking Methods 0.000 description 6
- 239000011780 sodium chloride Substances 0.000 description 6
- 239000007789 gas Substances 0.000 description 5
- 229910000861 Mg alloy Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000007654 immersion Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
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- 238000005275 alloying Methods 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 2
- 230000002860 competitive effect Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000005315 distribution function Methods 0.000 description 2
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- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 2
- 230000000670 limiting effect Effects 0.000 description 2
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- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 2
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- RALJREMKCFCVCV-UHFFFAOYSA-N CC(O)=O.OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O Chemical compound CC(O)=O.OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O RALJREMKCFCVCV-UHFFFAOYSA-N 0.000 description 1
- PDMMFKSKQVNJMI-BLQWBTBKSA-N Testosterone propionate Chemical compound C1CC2=CC(=O)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H](OC(=O)CC)[C@@]1(C)CC2 PDMMFKSKQVNJMI-BLQWBTBKSA-N 0.000 description 1
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 229910000905 alloy phase Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000012267 brine Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000010835 comparative analysis Methods 0.000 description 1
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- 239000010432 diamond Substances 0.000 description 1
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- 238000011068 loading method Methods 0.000 description 1
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 1
- 239000000347 magnesium hydroxide Substances 0.000 description 1
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000002040 relaxant effect Effects 0.000 description 1
- 230000000979 retarding effect Effects 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910001961 silver nitrate Inorganic materials 0.000 description 1
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000004506 ultrasonic cleaning Methods 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
- C22C23/06—Alloys based on magnesium with a rare earth metal as the next major constituent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C23/00—Extruding metal; Impact extrusion
- B21C23/02—Making uncoated products
- B21C23/04—Making uncoated products by direct extrusion
- B21C23/08—Making wire, bars, tubes
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
- C22C1/03—Making non-ferrous alloys by melting using master alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Extrusion Of Metal (AREA)
Abstract
The invention discloses an extruded magnesium-yttrium alloy and a preparation method thereof, wherein the method comprises the following steps: (1) melting raw materials of magnesium and yttrium under the atmosphere of protective gas to obtain a casting blank with the yttrium content of 6.53-11.4% by weight; (2) homogenizing the casting blank at 400-500 ℃ for 2h to obtain a homogenized blank; (3) and extruding the blank to obtain the extruded magnesium-yttrium alloy. The invention has the advantages that: by controlling higher pre-homogenization degree and proper yttrium content, the short-time preparation of the extruded magnesium-yttrium alloy is realized, the energy loss in the preparation process is effectively reduced, the preparation efficiency is improved, and the prepared extruded magnesium-yttrium alloy has no obvious difference in performance compared with the traditional process (longer-time homogenization); in addition, the invention proves the influence of the dissolution of yttrium element and the generation of a large number of matrix textures on the mechanical property and the corrosion resistance of the extruded magnesium-yttrium alloy on the premise of short-time homogenization through experiments.
Description
Technical Field
The invention belongs to the technical field of magnesium alloy materials, and particularly relates to an extruded magnesium-yttrium alloy and a preparation method thereof.
Background
Magnesium and its alloys have a high strength to density ratio and are considered key structural materials for lightweight research and applications in the automotive and aerospace industries. In addition, because the elastic modulus of magnesium is close to that of a human body and has degradation behavior, magnesium and magnesium alloy are widely applied to biomedicine.
It is well known that alloying elements are also effective in increasing the strength of the matrix, especially the addition of rare earth elements to magnesium alloys. Recently, magnesium-rare earth (rare earth element) -based alloys have received much attention due to their excellent mechanical properties. According to previous reports, the strength of the magnesium-yttrium alloy is improved by increasing the yttrium content in the matrix, and the magnesium-yttrium alloy with higher addition of yttrium element needs longer homogenization time and higher homogenization temperature to achieve good homogenization effect. However, homogenization for a relatively long time increases energy consumption and reduces the production efficiency of the wrought alloy, but activates movement of grain boundaries to weaken the grain boundary strengthening effect. Therefore, it is necessary to study the effect of solid solution strengthening and precipitation hardening on the mechanical properties of the magnesium-rare earth alloy by homogenization in a short time.
In addition, rare earth elements with relatively low electronegativity are easy to form an active second phase, so that the potential difference between the rare earth elements and a magnesium matrix is reduced, and the occurrence of galvanic corrosion is delayed. The second phase containing rare earth plays an important role in improving the corrosion resistance of the matrix, and it serves as a barrier to separate grains, retarding the development of intergranular corrosion. However, there is a competitive behavior between alloying elements and homogenization due to the dual effect of the second phase on corrosion performance. Therefore, in order to obtain magnesium-rare earth alloys with excellent mechanical and corrosion properties, it is necessary to reveal the collective and competitive effects from precipitation and homogenization.
Disclosure of Invention
The invention aims to provide an extruded magnesium-yttrium alloy and a preparation method thereof, which solve the problems of high energy consumption and low preparation efficiency caused by adopting a long-time homogenization process in the prior art, and simultaneously disclose the influences of the pre-homogenization degree and the yttrium content on the mechanical property and the corrosion resistance of the extruded magnesium-yttrium alloy.
The invention realizes the purpose through the following technical scheme:
a preparation method of an extruded magnesium-yttrium alloy comprises the following steps:
(1) melting raw materials of magnesium and yttrium under the atmosphere of protective gas to obtain a casting blank with the yttrium content of 6.53-11.4% by weight;
(2) homogenizing the casting blank at 400-500 ℃ for 2h to obtain a homogenized blank;
(3) and extruding the blank to obtain the extruded magnesium-yttrium alloy.
The further improvement is that the yttrium content in the casting blank is 11.4 weight percent, the homogenization treatment temperature is 450 ℃, and under the parameter, the comprehensive mechanical properties of the obtained extruded magnesium-yttrium alloy reach the optimum, including tensile, compressive yield strength, plasticity and the like.
The further improvement is that the yttrium content in the casting blank is 6.53 weight percent, the homogenization temperature is 500 ℃, and under the parameter, the corrosion resistance of the obtained extruded magnesium-yttrium alloy is optimal.
The further improvement is that the extrusion processing operation is specifically used for extruding the homogenized billet into an extrusion rod with a set specification at the extrusion ratio of 25 at 400 ℃.
In a further improvement, the raw materials magnesium and yttrium refer to 99.9% pure Mg and Mg-40Y.
In a further improvement, the shielding gas is 99 volume percent CO2With 1% by volume of SF6The mixed protective gas of the composition.
The invention also provides the extruded magnesium-yttrium alloy prepared by the method.
The invention has the beneficial effects that:
(1) according to the invention, by controlling the higher pre-homogenization degree and the proper yttrium content, the short-time preparation of the extruded magnesium-yttrium alloy is realized, the energy loss in the preparation process is effectively reduced, the preparation efficiency is improved, and the prepared extruded magnesium-yttrium alloy has no obvious difference in performance compared with the traditional process (longer-time homogenization);
(2) the invention proves the influence of the dissolution of yttrium element and the generation of a large number of matrix textures on the mechanical property and the corrosion resistance of the extruded magnesium-yttrium alloy on the premise of short-time homogenization through experiments, provides reference for the production of alloy products, controls process parameters according to performance requirements, and prepares a proper product, particularly the mechanical property of the alloy is optimal when the yttrium content is 11.4 weight percent and the homogenization temperature is 450 ℃, and the corrosion resistance of the alloy is optimal when the yttrium content is 6.53 weight percent and the homogenization temperature is 500 ℃.
Drawings
FIG. 1 is a reference diagram of a process for preparing a magnesium-yttrium alloy, wherein: (a) the phase diagram of the binary magnesium-rich magnesium-yttrium alloy is shown, (b) the solidification behavior diagram of the W7 alloy is shown, (c) the solidification behavior diagram of the W11 alloy is shown;
FIG. 2 is an optical micrograph and scanning electron micrograph of the as-cast and homogenized W7 and W11 alloys, in which: (a, i) as-cast W7; (b, j) homogenizing W7H 4002H; (c, k) homogenizing W7H 4502H; (d, l) homogenizing W7H 5002H; (e, m) as-cast W11; (f, n) homogenizing W11H 4002H; (g, o) homogenizing W11H 4502H; (H, p) homogenizing W11H 5002H;
FIG. 3 is a graphical representation of the yttrium content in the magnesium matrix for different degrees of homogenization of the as-cast and homogenized W7 and W11 alloys;
FIG. 4 is an as-cast and homogenized XRD pattern of the W7 and W11 alloys;
FIG. 5 is a schematic diagram of the phase composition and texture evolution of the W7 and W11 alloys in extruded form, wherein: (a) is XRD pattern, (b) is texture evolution diagram;
FIG. 6 is an optical microstructure and scanning electron microscope image of the W7 and W11 alloys in the as-extruded state at different pre-homogenization temperatures, in which: (a, g) W7H400E400, (b, H) W7H450E400, (c, i) W7H500E400, (d, j) W11H400E400, (E, k) W11H450E400, (f, l) W11H500E 400;
FIG. 7 is a graph of microstructure statistics and Cumulative Distribution Function (CDF) of grain size, where: (a) as microstructure statistics, (b) as a function of the cumulative distribution of grain sizes of the extruded W7 and W11 alloys at different pre-homogenization temperatures;
FIG. 8 is a graph showing the amount of yttrium in the magnesium matrix in the extruded W7 and W11 alloys with varying degrees of homogenization;
FIG. 9 is a graph of the engineered tensile stress-strain curves and compressive stress-strain curves of W7 and W11 alloys at different pre-homogenization temperatures, in which: (a) is an extruded W7 alloy, (b) is an extruded W11 alloy;
FIG. 10 is a schematic fracture diagram of tensile tests of extruded W7 and W11 alloys at different pre-homogenization temperatures, in which: (a) W7H400E400, (b) W7H450E400, (c) W7H500E400, (d) W11H400E400, (E) W11H450E400, (f) W11H500E 400;
FIG. 11 is a graphical representation of the corrosion behavior of the W7 and W11 alloys, wherein: (a) hydrogen amount as a function of immersion time, (b) average corrosion rates of W7 and W11 alloys at different pre-homogenization temperatures in 3.5% aqueous sodium chloride solution for 24 hours;
FIG. 12 is a graph of the corrosion surface morphology of the extruded W7 and W11 alloys in a 3.5% aqueous sodium chloride solution at different pre-homogenization temperatures for 1 hour, in which: (a, g) W7H400E400, (b, H) W7H450E400, (c, i) W7H500E400, (d, j) W11H400E400, (E, k) W11H450E400, (f, l) W11H500E 400;
FIG. 13 is a cross-sectional corrosion morphology of the corrosion-free products of the extruded W7 and W11 alloys in a 3.5% aqueous sodium chloride solution at different pre-homogenization temperatures for 1 hour, in which: (a) W7H400E400, (b) W7H450E400, (c) W7H500E400, (d) W11H400E400, (E) W11H450E400, (f) W11H500E 400;
FIG. 14 is a graph of the corrosion profile in longitudinal section of the extruded W7 and W11 alloys at different prehomogenization temperatures, after 24 hours in an aqueous solution of sodium chloride with a concentration of 3.5%, showing the absence of corrosion products: (a) W7H400E400, (b) W7H450E400, (c) W7H500E400, (d) W11H400E400, (E) W11H450E400, and (f) W11H500E 400.
Detailed Description
The present application will now be described in further detail with reference to the drawings, it should be noted that the following detailed description is given for illustrative purposes only and is not to be construed as limiting the scope of the present application, as those skilled in the art will be able to make numerous insubstantial modifications and adaptations to the present application based on the above disclosure.
1. Preparation of materials
As shown in FIG. 1, magnesium was produced according to the phase diagram and solidification behavior calculated from JmatPro-6.5 yttrium and magnesium-11 yttrium alloy, the preparation process is as follows: pure magnesium (99.9%) and Mg-40 yttrium at 99% content in CO2And SF in an amount of 1%6(vol%) of a mixed shielding gas. After melting, the billets were homogenized at 400 ℃, 450 ℃ and 500 ℃ for 2 hours, respectively, and then the homogenized billets were extruded at 400 ℃ into 12 mm diameter bars at an extrusion ratio of 25 (although different extrusion parameters, such as 380 ℃ and 20 extrusion ratios, may be used in other embodiments).
In order to study the combined and competing effects of precipitation and homogenization on the mechanical and corrosion properties of magnesium substrates, magnesium-6.5 yttrium and magnesium-11 yttrium alloys (wt.%, hereinafter referred to as W7 and W11, respectively) were studied, designed from the solubility curve of yttrium in magnesium, as shown in fig. 1 a. Furthermore, the predicted solidification behavior of the W7 and W11 alloys calculated from JmatPro are shown in fig. 1b and c, respectively, clearly showing the solidification order and second phase fraction of the W7 and W11 alloys predicted from temperature. Table 1 shows the chemical composition of the as-cast W7 and W11 alloys.
Table 1: chemical composition of as-cast W7 and W11 alloys
The homogenization temperature does not accord with the typical principle, the homogenization temperature is 5-10 ℃ lower than the solidus, and the higher homogenization temperature can shorten the homogenization time, thereby improving the preparation efficiency and achieving good homogenization effect. According to the phase diagram, the homogenization temperature was designed to study the effect of short time homogenization on dendrite segregation and mechanical and corrosion behavior of the extruded W7 and W11 alloys.
2. Experimental testing
2.1. Microstructural characterisation
The microstructure of the grains and the second phase was observed with an optical microscope and a scanning electron microscope. Cast and homogenized samples were cut from the billet in the cooling direction, while extruded samples were cut from the extrusion bar in the extrusion direction. Phase fraction and texture evolution of samples in different states were measured by 600-2500 mesh sandpaper polishing using Smart lab X-ray diffraction at a scan angle of 10-90 degrees and a scan speed of 12 degrees/min, and the results were analyzed with Jade 6.5. Then polishing with 3-micron, 1-micron and 0.5-micron diamond polishing agents respectively, corroding with acetic acid-picric acid solution, and observing the shapes of crystal grains and a second phase of the sample by using an optical microstructure and a scanning electron microscope. The particle size and volume fraction of the second phase in all samples were estimated based on optical and scanning electron micrographs using image analysis software (ImageJ).
2.2. Mechanical Property test
The samples were processed from the ingot and the extrusion bar in the cooling direction and the extrusion direction. The tensile test specimen had a gauge length of 36 mm and a diameter of 5 mm, and the compression cylindrical specimen had a processed diameter of 8 mm and a length of 12 mm. A strain rate of 1x 10^ at room temperature according to ASTM standard B557M-3s-1The alloys in pressed state W7 and W11 were subjected to tensile and compression tests with the loading axis parallel to the pressing direction, and the tensile fracture of the pressed samples was observed by a scanning electron microscope.
2.3. Immersion test
Weight loss and hydrogen evolution tests were carried out in 3.5% by weight sodium chloride solution at 25 ℃. + -. 1 ℃. The sample was processed longitudinally from an extruded rod with an exposed area of 1cm2. Samples soaked in saline solution were removed after 1 hour and 24 hours. Samples soaked for 1 hour were divided into two groups. One of them is left on the corrosion surface to observe the morphology of the corrosion product, and the other is removed from the corrosion product, and the degree of homogenization of corrosion is observed from the longitudinal section and the cross section. After 24 hours immersion in the salt solution, the samples were removed from the corrosion products with chromic acid, followed by ultrasonic cleaning and mass loss measurements. All samples were treated with a chromic acid solution mixture of 200 g/l chromic oxide and 10 g/l silver nitrate to remove surface corrosion products.
During hydrogen evolution measurement, hydrogen in the sample soaking process is collected by adopting a volume method, so that the sample is covered in an inverted burette by using a funnel, and a hydrogen volume value is recorded every 1 hour.
The average corrosion rate was estimated by weight loss and hydrogen collection according to U.S. material test standard G1-03. Dissolution of the magnesium alloy resulted in hydrogen evolution, indicating that the recorded hydrogen volume can be converted to a weight loss of magnesium (0.001083 grams of magnesium consumed at 1 milliliter of H2 gas). The corrosion rate based on weight loss and volume method was calculated using the following formula:
wherein, the delta W refers to weight loss (g) and is respectively obtained by weight loss test and hydrogen collection. A is the surface area (cm) of the exposed sample-2) T is total soaking time (h), rho is actually measured alloy density and the unit is g/cm3. The density of the alloy was calculated from JmatPro.
3. Results of the experiment
3.1 Observation of As-cast and homogenized microstructures
As shown in fig. 2, the as-cast and homogenized microstructure along the cooling direction. It was found that the needle phase (A, B, D, F, H, J, L) and the cubic particles (C, E, G, I, K) were distributed along dendrites and grain boundaries in the as-cast and homogenized states, respectively. According to the results of the energy spectrum shown in Table 2, the needle-like phase was Mg24Y5Phase, cubic particles are pure Y phase or Y-rich phase. Further, by homogenization, the as-cast dendrites gradually turn into grain boundaries. In addition, the second phase is homogenized out at 400 ℃ and dissolves into the magnesium matrix as the homogenization temperature increases. Further, the volume fraction of the second phase in the as-cast and homogenized W11 alloy is greater than W7. Referring to the magnesium-yttrium binary phase diagram, the solid solubility of yttrium atoms in the magnesium matrix is about 12.47%. This indicates that melting of W7 and W11 occurred during the unbalanced solidification. Undercooling-driven diffusion separation of isolated yttrium atoms at the liquidus-solidus interface. They are partially dissolved in the magnesium matrix and form a magnesium-yttrium binary phase on the solidification solution during solidification. During the subsequent homogenization process, the yttrium atoms are activated at high temperature, dissociated from the magnesium-yttrium binary phase, and dissolved in the magnesium matrix, resulting in a decrease in the volume fraction of the magnesium-yttrium second phase. The results are consistent with the results of the spectroscopy on the amount of yttrium in the matrix and the XRD results of the as-cast and homogenized W7 and W11 alloys shown in fig. 3 and 4, respectively.
Table 2: EDS results for as-cast and homogenization indicating phases of W7 and W11 alloys in FIG. 2
3.2. Microstructure observation after extrusion
The phase composition and texture evolution of the extruded W7 and W11 alloys are shown in FIG. 5. In FIG. 5a, it is shown that the W7 and W11 alloys in the as-extruded state consist primarily of a-Mg and Mg24Y5Phase composition. Further, Mg24Y5The relative strength of (A) decreases with increasing homogenization temperature, indicating Mg24Y5The volume fraction of (a) differs depending on the homogenization process. According to (0002) shown in FIG. 5b and
the relative strength index of the facets, as the homogenization temperature increases, the basal texture of the extruded W7 alloy becomes substantially stronger. Whereas for the extruded W11 alloy, the matrix texture begins to weaken and then strengthens. This is probably due to the weak effect of yttrium and the competing effect of extrusion strengthening on the matrix texture.
FIG. 6 shows the microstructure of the extruded W7 and W11 alloys, both extruded W7 and W11 alloys exhibiting bimodal microstructures according to the microstructure statistics and cumulative grain size distribution function (CDF) shown in FIG. 7, and the bimodal microstructures becoming more pronounced with increasing pre-homogenization temperature. In addition, the second phase breaks, orients and elongates along the extrusion direction. Its morphology and distribution of the second phase effectively impede the movement of dislocations to refine the grains. Furthermore, as the pre-homogenization temperature increases, the volume fraction of the second phase in the as-extruded W7 and W11 alloys decreases. Therefore, during the extrusion process, the dynamically recrystallized grains grow and coarsen at a higher pre-homogenization temperature due to the weaker dislocation hindering effect of the precipitates.
In addition, fig. 6 shows sem images of the as-extruded W7 and W11 alloys, the corresponding energy spectrum results are shown in table 3. Obviously, the micron-scale and the nano-scale are verticalThe square and spherical particles form thermomechanical streamlines distributed at the grain boundaries and oriented in the direction of extrusion. The cubic particles are pure yttrium particles. The spherical particles being particles of a magnesium-yttrium binary phase, e.g. MgY or Mg2And (4) Y phase. The main second phase in the alloy was investigated as discrete bulk Mg distributed along the extrusion direction24Y5And (4) phase(s). Furthermore, according to the results of the energy spectrum analysis shown in FIG. 8, the content of yttrium in a-Mg increased with the increase of the pre-homogenization.
Table 3: FIG. 6 shows the results of the energy spectrum analysis of the alloy phase in the extruded state
Fig. 9 shows tensile and compressive stress-strain curves of the as-extruded W7 and W11 alloys along with their mechanical parameters at room temperature, as shown in table 4. The tensile and compressive yield strengths of the extruded W11 alloy were higher for the different degrees of pre-homogenization than for the extruded W7 alloy. This indicates that more yttrium content will improve mechanical properties. Furthermore, as the pre-homogenization temperature increases, the tensile yield strength, compressive yield strength, and yield strength symmetry ratio of the as-extruded W7 and W11 alloys extrema. Interestingly, a prehomogenisation temperature of 450 ℃ increases the plasticity of the extruded W7 and W11 alloys, so that at a temperature of 450 ℃ the overall mechanical properties are optimal. The result may be a competing effect and the impact of pre-homogenization on the thermo-mechanical streamline formation and Dynamic Recrystallization (DRX) behavior of solution effects of yttrium atoms.
Table 4: tensile and yield mechanical parameters of room temperature engineering
FIG. 10 shows the fracture surfaces of the tensile tests of the alloys W7 and W11 in the as-pressed state. The fracture of these alloys studied consisted primarily of many dimples, few torn edges and cracks. As the pre-homogenization temperature increases, the number of equiaxed dimples and cracks in the alloy decreases. The local stress concentration caused by the particles is shown, and the fine particle synergistic effect is combined to have an influence on the plasticity of the matrix. Thus, as shown in table 4, the plastic strain of these investigated alloys showed irregularities as the pre-homogenization temperature was increased.
3.3. Corrosion behavior of extruded alloys
FIG. 11 shows the hydrogen volume change of the alloy in a 3.5% sodium chloride aqueous solution for 24 hours as a function of soak time and average corrosion rate, with the hydrogen volume change comprising two components, initially relaxing over a short period of time, increasing linearly with soak time. For relaxation, it is clear that the relaxation time becomes longer with increasing pre-homogenization temperature. This indicates that the uniformization temperature may affect the formation of an oxide film, which provides the substrate with corrosion resistance. After soaking in the brine solution for a period of time, the change in hydrogen volume was approximately linear with soaking time, indicating that the rate of hydrogen generation was nearly equal at each specified time. At the same time, the hydrogen evolution rates of the extruded W7 and W11 alloys were higher with lower pre-homogenization temperatures, indicating that the galvanic corrosion was more severe than the other alloys. The corrosion rate obtained from the weight loss measurement was slightly higher than the rate calculated from the hydrogen evolution test, as shown in fig. 11 b. This may be due to the remaining hydrogen bubbles accumulating on the funnel resulting in a decrease in the recorded amount. The corrosion rate of the as-extruded W11 alloy was higher than that of the pre-homogenized same as-extruded W7 alloy. Furthermore, the corrosion rate of the extruded W7 and W11 alloys with higher pre-homogenization temperatures is significantly lower than the lower pre-homogenization temperature alloys. The results show that the yttrium content and the pre-homogenization temperature play a crucial role in the corrosion rate of the as-extruded alloy.
Interestingly, however, the corrosion rate of the as-extruded W11 alloy with a pre-homogenization temperature of 450 ℃ was nearly the same as the lower pre-homogenization temperature, indicating that in addition to the volume fraction of the second phase and the fixed grain size, other factors also affect the corrosion resistance of the magnesium matrix, the result being attributed to the relatively high volume fraction and grain boundary energy of the second phase.
To compare the relaxation times of hydrogen generation in the W7 and W11 alloys, fig. 12 provides the corrosion surface morphology with and without corrosion products of the alloys after 1 hour of soaking, respectively. As shown in fig. 12(a-f), the etched surface is filled with a magnesium hydroxide oxide film and a product film having a tight sheet or porous band. Furthermore, it is clear that a large number of cracks appear on the product film, which indicates that the film has a weak corrosion resistance. Interestingly, however, the extruded W7 alloy, pre-homogenized by 450 ℃ was filled with sheet-like sheets, exhibiting a product film different from other products. The results show that the corrosion resistance of the product film is superior to that of the porous film.
After removal of the corrosion products, as shown in fig. 12(g-l), no corrosion was seen to occur along the hot process flow lines and started in pitting mode. Further, the higher the volume fraction, the more severe the corrosion. But all of these extruded alloys remain un-corroded surfaces and their area increases with increasing pre-homogenization.
FIG. 13 shows the cross-sectional corrosion morphology of the as-extruded alloy. As the yttrium content increased, the extruded W11 alloy had deeper corrosion pits than the W7 alloy, and localized corrosion was more severe as the pre-homogenization temperature increased. This is attributed to Mg24Y5As a discontinuous network of corrosion barriers, and the protective effect diminishes as its volume fraction decreases. The results are consistent with those observed in hydrogen evolution.
FIG. 14 shows the corrosion surface morphology of the alloy after 24 hours soaking without corrosion products. It was found that the higher corrosion rate groups (W7H400E400, W11H450E400) all exhibited severe corrosion surfaces along the hot process flow line due to severe micro-couple corrosion. In contrast, the groups (W7H450E400, W7H500E400, W11H500E400) having relatively low corrosion rates exhibited corrosion along the grain boundaries. The effect of yttrium content and pre-homogenization temperature on hot working streamline formation on corrosion performance was demonstrated.
4. Comparative analysis of Performance with conventional Process
Taking mechanical properties as an example, table 8 summarizes previous reports on mechanical properties of magnesium-yttrium alloys. A comparison of the mechanical properties of these alloys can lead to the conclusion that: solid solution strengthening and grain boundary strengthening are effective methods for improving tensile properties of a matrix according to previous reports, the strength of magnesium-yttrium alloys will be increased by increasing the amount of yttrium in the matrix. However, magnesium-yttrium alloys with higher addition of yttrium element require longer homogenization time and higher homogenization temperature to achieve good homogenization effect, and although studies report that the retention time of homogenization does not significantly promote grain growth, higher homogenization temperature will effectively activate grain boundary migration, thereby weakening grain boundary strengthening through solid phase diffusion.
Table 5: comparison of the mechanical Properties of the magnesium-Yttrium alloy with corresponding extruded specimens
a) The value is the true tensile stress
More importantly, as can be seen from the results in table 5, the long-time solid solution adopted in the conventional process flow does not significantly improve the performance of the alloy, and has no obvious difference from the research, but the advantages of energy consumption reduction and efficiency improvement are brought due to the reduction of the homogenization time of the research. In addition, the invention can improve certain performance of the material by adjusting the pre-homogenization temperature and the yttrium content, is superior to the traditional preparation process, and meets the requirement of being applied to specific environments.
5. Conclusion
(1) The short-time preparation of the extruded magnesium-yttrium alloy is realized through the higher pre-homogenization temperature and the proper yttrium content, and the prepared extruded magnesium-yttrium alloy has no obvious difference in performance compared with the traditional process (longer-time homogenization).
(2) Higher pre-homogenization temperatures will improve mechanical and corrosion resistance due to their effect on the formation of bimodal grain microstructure, precipitation strengthening and solution hardening. Tensile and compressive tests prove that the W11 alloy with the pre-homogenizing temperature of 450 ℃ shows the best comprehensive mechanical property. Whereas the immersion test and corrosion morphology demonstrate that the W7 alloy pre-homogenized at 500 ℃ has the best corrosion resistance.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
Claims (7)
1. The preparation method of the extruded magnesium-yttrium alloy is characterized by comprising the following steps of:
(1) melting raw materials of magnesium and yttrium under the atmosphere of protective gas to obtain a casting blank with the yttrium content of 6.53-11.4% by weight;
(2) homogenizing the casting blank at 400-500 ℃ for 2h to obtain a homogenized blank;
(3) and extruding the blank to obtain the extruded magnesium-yttrium alloy.
2. The method of claim 1, wherein the billet has 11.4 wt% yttrium and the homogenization temperature is 450 ℃.
3. The method of claim 1, wherein the billet has an yttrium content of 6.53 wt% and the homogenization temperature is 500 ℃.
4. The method of claim 1, wherein the extrusion process is specifically operated to extrude the homogenized billet into an extrusion bar of a predetermined specification at an extrusion ratio of 25 at 400 ℃.
5. The method of claim 1, wherein the raw magnesium and yttrium are 99.9% pure Mg and Mg-40Y.
6. The method of claim 1, wherein the shielding gas is 99 vol% CO2With 1% by volume of SF6The mixed protective gas of the composition.
7. An extruded magnesium yttrium alloy produced by the method of any one of claims 1 to 6.
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