Method for synergistically improving mechanical property and corrosion resistance of AZ91 magnesium alloy

Abstract

The invention provides a method for synergistically improving mechanical properties and corrosion resistance of an AZ91 magnesium alloy, which comprises the following steps: S1, carrying out homogenizing annealing treatment on an as-cast AZ91 magnesium alloy, and carrying out air cooling to room temperature; s2, the AZ91 magnesium alloy treated in the step S1 is subjected to hot extrusion forming; s3, the AZ91 magnesium alloy subjected to hot extrusion forming is subjected to solution treatment; and S4, aging treatment is conducted on the AZ91 magnesium alloy subjected to solution treatment. According to the invention, through a hot extrusion process, dynamic recrystallization can be carried out to significantly refine matrix grains, subsequent aging treatment can induce precipitation of a fine and dispersed beta-Mg17Al12 phase, a synergistic effect of refined grain strengthening and precipitation strengthening is realized, and good plasticity and corrosion resistance are maintained while the strength is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnesium alloy processing, and particularly relates to a method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy. BACKGROUND

[0002] Magnesium and magnesium alloy are widely used in the fields of aerospace, automobile lightweight and 3C electronic products due to their light weight, high specific strength, good shock absorption and other characteristics, and are known as "green engineering materials in the 21st century". However, as a widely used magnesium alloy, the close-packed hexagonal crystal structure of AZ91 magnesium alloy leads to fewer slip systems and poor plastic deformation capacity, which limits the further improvement of its mechanical properties. In addition, the low electrode potential (-2.37V) of magnesium makes it exhibit a high corrosion rate in most environments, and poor corrosion resistance becomes the main bottleneck limiting its wide application. Therefore, how to simultaneously improve the mechanical properties and corrosion resistance of AZ91 magnesium alloy has become one of the key problems in current research.

[0003] In recent years, researches have shown that the performance short board of magnesium alloy can be effectively made up by introducing high plasticity and high corrosion resistance metals or alloys into magnesium alloy. For example, aluminum alloy is often used for compounding with magnesium alloy to improve the overall performance due to its good plasticity and corrosion resistance. However, the traditional compounding processes such as vacuum hot pressing, explosive welding and rolling have certain limitations: the vacuum hot pressing has high cost and limited product size; the explosive welding process has poor controllability and serious pollution; and the rolling process easily leads to edge cracks, affecting the material utilization. Therefore, it is necessary to study a method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy. SUMMARY

[0004] The purpose of the present application is to overcome the defects of the prior art, and to provide a method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy in view of the problems of low strength, poor plastic deformation capacity and poor corrosion resistance of magnesium alloy.

[0005] The present application provides the following technical solutions:

[0006] The present application provides a method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy, comprising the following steps:

[0007] S1, homogenizing annealing treatment is performed on the as-cast AZ91 magnesium alloy, and air cooling is performed to room temperature;

[0008] S2, hot extrusion forming is performed on the AZ91 magnesium alloy treated in step S1;

[0009] S3, solid solution treatment is performed on the AZ91 magnesium alloy after hot extrusion forming;

[0010] S4, aging treatment is performed on the AZ91 magnesium alloy after solid solution treatment.

[0011] The process of the application first carries out homogenization annealing treatment to eliminate internal stress and improve the uniformity of the structure, and then obtains AZ91 magnesium alloy with different grain sizes through hot extrusion and subsequent aging treatment at different temperatures to obtain different amounts and morphologies of precipitated phases. Compared with traditional processes, the hot extrusion process can cause severe plastic deformation of the material under high pressure, effectively refining the grain size and improving the uniformity of the grains. The fine and uniform grain structure can significantly improve the strength and toughness of the material, and improve its fatigue resistance.

[0012] Through aging treatment at different temperatures, the number, size and distribution of precipitated phases can be precisely controlled. Optimized precipitated phases can further strengthen the matrix, improve the tensile strength and yield strength of the material, and maintain good ductility. The synergistic effect of hot extrusion and aging treatment can improve the surface state of AZ91 magnesium alloy, reduce surface defects and microcracks, thereby significantly improving its corrosion resistance. In addition, the presence of precipitated phases can form a protective film, further enhancing the corrosion resistance of the material.

[0013] Further, in step S1, the annealing temperature is 410℃ and the treatment time is 12h.

[0014] Further, in step S2, the hot extrusion temperature is 350℃-450℃ and the extrusion ratio is 20.3:1.

[0015] Further, in step S3, after hot extrusion molding, the AZ91 magnesium alloy is cut into multiple cubic samples, and the sample surface is polished.

[0016] Further, in step S3, the solid solution treatment is water cooling after holding at 415℃ for 12h.

[0017] Further, in step S4, the aging treatment temperature is 140℃-200℃ and the treatment time is 22h-26h.

[0018] The present application has the following advantages:

[0019] 1. In the method of the present application, no other alloying elements are added, and the as-cast AZ91 is subjected to aging treatment after hot extrusion, which can well improve its mechanical properties and corrosion resistance;

[0020] 2. The hot extrusion process of the present application can dynamically recrystallize the matrix grains, and the subsequent aging treatment can induce the precipitation of fine and dispersed β-Mg17Al12 phases, realizing the synergistic effect of fine-grain strengthening and precipitation strengthening, improving the strength while maintaining good strength and corrosion resistance;

[0021] 3、The process has strong controllability, and parameters such as hot extrusion deformation, aging temperature and time can be accurately controlled, so that the customized design of the organization and performance is facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0023] Figure 1 is a process schematic diagram of the method of the embodiments of the present application;

[0024] Figure 2 is a metallographic structure and grain size diagram after single extrusion;

[0025] Figure 3 is a hardness diagram after single extrusion;

[0026] Figure 4 is an electrochemical test diagram after single extrusion;

[0027] Figure 5 is a post-surface morphology of the polarization curve after single extrusion;

[0028] Figure 6 is a hardness exploration diagram of single aging state;

[0029] Figure 7 is an electrochemical test diagram of single aging state;

[0030] Figure 8 is a post-surface morphology of the polarization curve of single aging state;

[0031] Figure 9 is a metallographic diagram of AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application;

[0032] Figure 10 is a SEM diagram of AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application;

[0033] Figure 11 is a hardness diagram of AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application;

[0034] Figure 12 is a tensile curve diagram of AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application;

[0035] Figure 13 is an electrochemical test diagram of AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application;

[0036] Figure 14 is the surface corrosion graph of the polarization curve test of the AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application;

[0037] Figure 15 is the surface corrosion graph of the AZ91 magnesium alloy after extrusion and aging in the embodiments of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0039] The embodiments of the present application provide a method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy, comprising the following steps:

[0040] S1, homogenizing annealing treatment is performed on the as-cast AZ91 magnesium alloy, and air cooling is performed to room temperature;

[0041] S2, the AZ91 magnesium alloy after step S1 is processed is subjected to hot extrusion forming;

[0042] S3, the AZ91 magnesium alloy after hot extrusion forming is subjected to solid solution treatment;

[0043] S4, the AZ91 magnesium alloy after solid solution treatment is subjected to aging treatment.

[0044] Reference is made to Figure 1 is a process schematic diagram of the method of the embodiments of the present application;

[0045] Single extrusion treatment: linear cutting is performed on the AZ91 magnesium alloy, and then the as-cast AZ91 magnesium alloy is subjected to homogenizing annealing treatment at 410 DEG C for 12 hours, and air cooling is performed to room temperature;

[0046] The homogenizing annealed AZ91 magnesium alloy is subjected to extrusion forming at three different temperatures of 350 DEG C, 400 DEG C and 450 DEG C, and the extrusion ratio is fixed at 20.3:1, and the final plate thickness is 5mm;

[0047] After forming, the sample was cut into a 5mm x 10mm x 15mm (extrusion direction) cuboid along the extrusion direction, with a surface area of 150mm2. Finally, using 400# to 3000# SiC sandpaper, the surface was polished step by step (avoiding overheating to cause crystal) to ensure that the surface finish met the experimental requirements. When observing the extruded magnesium alloy sample by metallographic observation, pure acetic acid solution was used for etching for 15-20 seconds to clearly show the microstructure. In order to avoid the formation of a blurred layer on the magnesium alloy during polishing, alcohol was used throughout the polishing process.

[0048] The microstructure was observed by metallographic microscope, and the grain size was observed by EBSD. It was found that the smaller the extrusion temperature, the smaller the grain size, as shown in Figure 2 . Using a microhardness tester, a load of 100g, and a 15s parameter setting, the hardness was tested, with 10 random points, the maximum and minimum values were removed, and the average value was taken as Figure 3 . From Figure 3 it can be found that after different extrusion temperatures, although the grain size changes, the smaller the grain size, the smaller the hardness, although the grain size is smallest at 350℃, the hardness value is only 66HV.

[0049] The sample was encapsulated with epoxy resin after sandpaper water polishing, and the sample and lead were treated after solidification. Electrochemical test (CHI660E type electrochemical workstation), using a three-electrode system, the working electrode was AZ91 magnesium alloy under different extrusion temperatures, the auxiliary electrode was platinum electrode, and the reference electrode was saturated calomel electrode. Before impedance test, open circuit test for 300s to ensure system stability; the frequency range of impedance measurement is 100kHz-10mHz, the results are as follows Figure 4 ; Tafel polarization curve measurement scan speed is 1mV / s, and the scan range is relative open circuit potential-0.1V-0.5V as Figure 4 , and the surface morphology after polarization curve test is as Figure 5 .

[0050] Among them, Figure 2 shows the microstructure evolution process of AZ91 magnesium alloy under different extrusion temperatures. With the temperature rising from 350℃ to 450℃, the grain size increases significantly. Metallographic structure Figure 2 a, d, g) shows that the grain size difference between 350℃ and 400℃ is small, while the grain size at 450℃ is significantly larger than that at low temperature. The inverse pole figure (IPF) image Figure 2 b, e, h) further reveals the change rule of grain size. Although the extrusion temperature is different, the grain morphology remains basically stable. The corresponding grain size distribution graph Figure 2c、f、i) indicates that the average grain size increases from 8.9 pm at 350 °C to 14.7 pm at 450 °C. This significant grain growth is closely related to the enhanced atomic diffusion and accelerated grain boundary migration under high temperature environment. Therefore, the extrusion temperature has an important influence on the grain size regulation of AZ91 magnesium alloy.

[0051] Figure 3 The hardness test of the samples under three extrusion temperatures by using a microhardness tester shows that the hardness gradually decreases (66.7 HV at 350 °C, 63.8 HV at 400 °C, and 62.3 HV at 450 °C) with the increase of the extrusion temperature. This is because the fine-grained structure can increase the dislocation density and hinder the dislocation movement, thereby improving the hardness of the material.

[0052] Figure 4 (a) shows the polarization curves of the materials under different extrusion temperatures, which reveals the influence of the microstructure induced by the extrusion temperature on the electrochemical performance. The corrosion potential, as a key parameter for measuring the difficulty of the corrosion process, is larger, the smaller the thermodynamic tendency of corrosion, and the lower the possibility of material corrosion. With the increase of the extrusion temperature from 350 °C to 450 °C, the corrosion potential shows a significant negative shift trend (350 °C: -1.476 V, 400 °C: -1.492 V, 450 °C: -1.502 V), indicating that the material has higher thermodynamic stability at a lower extrusion temperature. Figure 4 (b) Nyquist plot shows that the impedance spectrum of the material under different extrusion temperatures is composed of the electrochemical polarization zone in the high-frequency region and the diffusion zone in the low-frequency region. The larger the radius of the semicircle in the high-frequency region, the greater the charge transfer resistance, and the better the corrosion resistance. The low-frequency region corresponds to the ion diffusion process. It is found that the smaller the grain size, the larger the capacitive arc radius, the larger the impedance value, the better the stability of the passivation film, and the best corrosion resistance.

[0053] From Figure 5 The corrosion pit area on the surface of the sample after polarization test can be clearly seen that the corrosion pit area under 350 °C is the smallest, and the corrosion pit area under 450 °C is the largest. This indicates that the corrosion resistance is the best at 350 °C. This is mainly because with the increase of the extrusion temperature, the microstructure of the material changes significantly: the grain coarsening leads to the decrease of the grain boundary density, which weakens the physical hindrance of the grain boundary to the corrosion propagation; the texture weakening exacerbates the anisotropy of the microstructure, which promotes the increase of the local electrochemical activity difference; at the same time, the decrease of the dislocation density weakens the inhibition effect of the dislocation entanglement on the corrosion path. Under the synergistic action of the three, a more continuous corrosion channel is formed in the material, the diffusion rate of the corrosion medium is improved, and the active reaction site is increased, which eventually leads to the stepwise decrease of the electrochemical corrosion resistance.

[0054] Single aging treatment: AZ91 magnesium alloy was line-cut, and the as-cast alloy was processed into 10mm x 10mm x 10mm cubic samples using the line-cut method. The surface area was 100mm 2 , and then water polishing was performed using 400# to 3000# SiC sandpaper in sequence to avoid the generation of twin crystals. The samples were subjected to solid solution treatment in a heat treatment furnace at 415℃ for 12h and then water-cooled. Subsequently, aging treatment was performed at 140℃, 170℃ and 200℃ respectively. The peak aging time at each temperature was determined by microhardness testing, as shown in Figure 6 .

[0055] The samples were encapsulated with epoxy resin after sandpaper water polishing, and then treated after solidification. Electrochemical testing (CHI660E type electrochemical workstation) was performed using a three-electrode system, with the working electrode being AZ91 magnesium alloy under different aging treatments, the auxiliary electrode being a platinum electrode, and the reference electrode being a saturated calomel electrode. Open circuit test was performed for 300s before impedance test to ensure system stability; the impedance measurement frequency range was 100kHz-10mHz, and the results are shown in Figure 7 ; the Tafel polarization curve measurement scanning speed was 1mV / s, and the scanning range was relative open circuit potential-0.1V-0.5V, as shown in Figure 7 , and the surface morphology after polarization curve test was observed, as shown in Figure 8 .

[0056] Figure 6 The relationship between the aging time of AZ91 magnesium alloy and the hardness change at different temperatures is shown in the figure. As can be clearly seen from the figure, as the aging temperature rises, the hardness of AZ91 magnesium alloy increases significantly, and the time to reach peak aging also shortens accordingly. This fully demonstrates that the aging temperature has a significant impact on the mechanical properties of the material. During the aging process, the phase transformation and precipitation behavior inside the material directly affect the hardness. As the aging temperature rises, the atomic diffusion rate accelerates, and the nucleation and growth process of the precipitated phase becomes more rapid. These precipitated phases can effectively hinder the movement of dislocations, thereby enhancing the hardness of the material. At the same time, the shortening of the aging time also reflects the ability of the material to rapidly adjust its internal structure at high temperatures. Although the time required for the material to reach peak aging varies at different aging temperatures, at each temperature condition, the material in the peak aging state exhibits the best performance. Therefore, the peak aging state corresponding to each temperature is selected as the benchmark for performance comparison and analysis.

[0057] The influence of different heat treatment states on the corrosion behavior of AZ91 magnesium alloy is shown in Figure 7 . Corrosion potential is an important thermodynamic parameter for characterizing the corrosion tendency of materials, and the more positive the value, the higher the thermodynamic stability of the material. The polarization curve test results show that the corrosion potential of the material increases with the increase of the aging temperature, and the corrosion resistance of the material is improved.Figure 7 (a) shows that the corrosion potential of the 170℃ / 24h aging sample is optimal (-1.491V), which is significantly better than that of the 140℃ / 26h (-1.502V) and 200℃ / 22h (-1.494V) aging samples, indicating that the aging process can significantly improve the thermodynamic stability of the material. Electrochemical impedance spectroscopy analysis Figure 7 (b) shows that the Nyquist plots of AZ91 magnesium alloys in different states are composed of high-frequency capacitive arcs and low-frequency diffusion impedances. The radius of the high-frequency capacitive arc directly reflects the resistance of the charge transfer process. The larger the radius, the greater the resistance of the charge transfer on the surface of the material, and the better the corrosion resistance. The test results show that the capacitive arc radius of the 170℃ / 24h aging sample is the largest.

[0058] Figure 8 ((a), (b), (c)) The corrosion pits on the surface of the AZ91 magnesium alloy in different states were observed by stereomicroscope after polarization curve test, and it was found that the corrosion morphology was different under different states. This is mainly related to the influence of precipitated phase on corrosion resistance under different states. The 140℃ / 26h aging treatment will make the second phase β phase in the alloy begin to precipitate, but the precipitation amount is relatively small. During the corrosion process, the existence of β phase will hinder the formation and expansion of corrosion pits to a certain extent, but due to its low content, the inhibition effect on corrosion pits is limited. Corrosion pits are mainly formed on α phase and gradually expand to the inside of the substrate, but the expansion speed is relatively slow. After 170℃ / 24h aging treatment, the β phase in the alloy further increases, which is in the form of fine needles and is uniformly distributed. During the corrosion process, the high electrode potential of β phase will protect α phase to a certain extent, so that the formation and expansion of corrosion pits are inhibited. The size of the corrosion pits is relatively small, and the number is relatively small. After 200℃ / 22h aging treatment, the coarse β phase leads to rapid corrosion along the grain boundary, forming deep and connected corrosion pits. This is also the main factor affecting the electrochemical data.

[0059] The application will be further described below through specific examples.

[0060] Example 1

[0061] In this embodiment, a method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy is provided, and the specific steps are as follows:

[0062] S1, linear cutting of AZ91 magnesium alloy, and then homogenizing annealing treatment of the as-cast AZ91 magnesium alloy at 410℃ for 12 hours, and air cooling to room temperature;

[0063] S2, extruding the homogenized annealed AZ91 magnesium alloy at a temperature of 350℃, with a fixed extrusion ratio of 20.3:1, and the final plate thickness is 5mm.

[0064] S3, cut the sample into a rectangular sample of 15 mm x 10 mm x 5 mm (ED x TD x ND) along the extrusion direction, wherein ED, TD and ND respectively refer to the extrusion direction, the transverse direction and the normal direction; the ED-TD plane of the sample is polished with 400# to 3000# silicon carbide sandpaper under water lubrication in turn to obtain a mirror effect; then the sample is subjected to a solid solution treatment of 415℃ for 12h and then water cooling;

[0065] S4, the material after the solid solution treatment of step S3 is subjected to an aging treatment of 140℃ / 26h.

[0066] Example 2

[0067] The method steps of this example are basically the same as those of example 1, except that step S4 is an aging treatment of 170℃ / 24h.

[0068] Example 3

[0069] The method steps of this example are basically the same as those of example 1, except that step S4 is an aging treatment of 200℃ / 22h.

[0070] Example 4

[0071] The method steps of this example are basically the same as those of example 1, except that step S2 is an extrusion molding at a temperature of 400℃.

[0072] Example 5

[0073] The method steps of this example are basically the same as those of example 4, except that step S4 is an aging treatment of 170℃ / 24h.

[0074] Example 6

[0075] The method steps of this example are basically the same as those of example 4, except that step S4 is an aging treatment of 200℃ / 22h.

[0076] Example 7

[0077] The method steps of this example are basically the same as those of example 1, except that step S2 is an extrusion molding at a temperature of 450℃.

[0078] Example 8

[0079] The method steps of this example are basically the same as those of example 7, except that step S4 is an aging treatment of 170℃ / 24h.

[0080] Example 9

[0081] The method steps of this example are basically the same as those of example 7, except that step S4 is an aging treatment of 200℃ / 22h.

[0082] The samples obtained by the final processing of each of the above embodiments were subjected to metallographic observation Figure 9 ) and scanning electron microscope observation Figure 10 ), and hardness testing was performed. Hardness testing was performed using a microhardness tester with a load of 100 g, a loading time of 15 s, and the following parameters: 10 random points were punched, the maximum and minimum values were removed, and the average value was taken, as shown in Figure 11 .

[0083] Figure 9 、 Figure 10 The metallographic and SEM images of the extrusion and aging state of AZ91 magnesium alloy can be found that after extrusion and aging, the precipitated phase will grow inward along the grain boundary, and the higher the aging temperature, the more the precipitated phase grows in the grain boundary.

[0084] Figure 11 The hardness test graph of the extrusion and aging state of AZ91 magnesium alloy can be found that after extrusion and aging, the hardness is significantly improved, and the hardness at 350°C (the best extrusion temperature) / 170°C (the best aging temperature) is the highest, reaching 94HV, and the hardness at 450°C / 140°C is also 84HV. Compared with simple extrusion and aging, the hardness is greatly improved.

[0085] The samples obtained by the final processing of each of the above embodiments were subjected to tensile testing. The tensile sample size was in accordance with GB / T228.1-2021, and the room temperature tensile test was performed on a CMT6305-300 kN electronic universal testing machine with a tensile speed of 0.75 mm / min (nominal strain rate 1×10 -3 s -1 ). The stress-strain curve was recorded during the test. To ensure the repeatability of the results, each sample was subjected to three tensile tests, and the average value was taken as the result, as shown in Figure 12 .

[0086] Figure 12 The mechanical property test graph curve of the extrusion and aging state of AZ91 magnesium alloy can be found that 450°C / 140°C exhibits good strength and plasticity matching.

[0087] The samples for electrochemical testing were encapsulated with epoxy resin after sandpaper water milling. After the epoxy resin solidified, the samples were processed. The electrochemical test (CHI660E type electrochemical workstation) used a three-electrode system, the working electrode was AZ91 magnesium alloy after different extrusion and aging, the auxiliary electrode was a platinum electrode, and the reference electrode was a saturated calomel electrode. Before impedance testing, 300 s open circuit test was performed to ensure that the system remained stable; the impedance measurement frequency range was 100 kHz-10 mHz, and the results were as shown in Figure 13 ; the Tafel polarization curve measurement scanning speed was 1 mV / s, and the scanning range was relative open circuit potential-0.1 V-0.5 V, as shown inFigure 13 and the surface morphology after polarization curve test is observed as Figure 14 .

[0088] Figure 13 For electrochemical test, the 450℃ / 140℃ impedance arc radius is the largest and the corrosion potential is the highest.

[0089] Figure 14 From the corrosion of the surface after polarization, compared with Figure 5 and Figure 8 Compared with simple extrusion and aging, the 450℃ / 140℃ surface has few corrosion pits.

[0090] The different states are immersed in 3.5% sodium chloride, and the corrosion and weight loss changes are observed (the sample is immersed in a solution composed of 200g / L CrO3 and 2g / L AgNO3 (8-10 seconds), and the corrosion product is removed), and the results are shown in Figure 15 .

[0091] Figure 15 For further verification of corrosion resistance by immersion in 3.5% sodium chloride, it is found that the 450℃ / 140℃ surface has almost no corrosion pit phenomenon after immersion for 6 days.

[0092] In summary, the as-cast AZ91 magnesium alloy treated by the method of the present application can improve its mechanical properties and corrosion resistance, and the 450℃ / 140℃ exhibits the best mechanical properties and corrosion resistance.

[0093] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy, characterized in that, The method comprises the following steps: S1, homogenizing annealing treatment is performed on as-cast AZ91 magnesium alloy, and air cooling is performed to room temperature; S2, hot extrusion molding is performed on the AZ91 magnesium alloy after step S1; S3, solid solution treatment is performed on the hot extrusion molded AZ91 magnesium alloy; S4, aging treatment is performed on the solid solution treated AZ91 magnesium alloy.

2. The method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy according to claim 1, characterized in that: In step S1, the annealing temperature is 410 DEG C, and the treatment time is 12h.

3. The method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy according to claim 1, characterized in that: In step S2, the hot extrusion temperature is 350 DEG C-450 DEG C, and the extrusion ratio is 20.3:

1.

4. The method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy according to claim 1, characterized in that: In step S3, after hot extrusion molding, the AZ91 magnesium alloy is cut into multiple cubic samples, and the sample surface is polished.

5. The method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy according to claim 1, characterized in that: In step S3, the solid solution treatment is water cooling after being kept at 415 DEG C for 12h.

6. The method for synergistically improving the mechanical properties and corrosion resistance of AZ91 magnesium alloy according to claim 1, characterized in that: In step S4, the aging treatment temperature is 140 DEG C-200 DEG C, and the treatment time is 22h-26h.

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