A high-uniformity semi-solid alloy and its forming process

Abstract

The present invention relates to a semi-solid alloy forming process with high uniformity, comprising the following steps: obtaining a semi-solid temperature range of an alloy material to be formed; preheating the temperature of a lower mold of the mold to a preset temperature, the preset temperature being 50-100°C lower than the lower limit of the semi-solid temperature range, and preheating an upper mold to a forming temperature, wherein the forming temperature is lower than the preset temperature; preparing a semi-solid alloy billet using the material to be formed as a raw material, wherein the semi-solid alloy billet comprises a first region and a second region, and the liquid phase volume fraction of the first region is greater than the liquid phase volume fraction of the second region; placing the semi-solid alloy billet in the mold for die casting, wherein the first region is arranged corresponding to the upper mold, and the second region is arranged corresponding to the lower mold, and the second region and the first region of the semi-solid alloy billet are better matched by setting the upper mold and the lower mold at different temperatures, thereby improving the uniformity of the semi-solid alloy.

Description

Technical Field

[0001] The invention relates to the technical field of semi-solid alloy materials, and in particular to a highly uniform semi-solid alloy and a forming process thereof. Background Art

[0002] Semi-solid thixotropic processing technology utilizes the thixotropic fluidity of alloys or metal-based composite materials after being kept at semi-solid temperature for a certain period of time, and processes parts with complex shapes and high mechanical properties by forging, extrusion, etc. Since the heating and conveying process of semi-solid billets is relatively simple and easy to achieve mass production, semi-solid thixotropic forming technology has received widespread attention.

[0003] However, there are some difficult-to-solve problems in semi-solid processing technology, such as the uneven structure of semi-solid parts caused by segregation. Segregation is the solid-liquid separation phenomenon caused by the different deformation and flow behaviors of the solid and liquid phases in the billet under the forming load. Because the liquid phase contains a large amount of alloy elements, it eventually leads to uneven structure, which seriously affects the performance of semiconductor parts and hinders the industrialization of semi-solid technology.

[0004] CN107199321A discloses a time-varying controlled semi-solid forming process, which shortens the time of liquid outflow through a faster strain rate in the first step of forming, thereby suppressing the segregation of liquid while completing partial forming. By cooling before the second step of forming, the liquid volume ratio of each part is reduced, so that during the second step of forming, on the one hand, the small amount of liquid is not enough to form an outflow path to ensure the uniformity of the workpiece structure; on the other hand, the microstructural evolution such as recrystallization of the larger solid phase during the plastic deformation process realizes further refinement of the grains, which helps to improve the mechanical properties of the workpiece. The above process flow is too complicated, and it is particularly necessary to strictly control the parameters of the first step of forming to prevent serious liquid segregation during the first step of forming. Summary of the invention

[0005] Based on this, it is necessary to provide a semi-solid alloy forming process with high uniformity.

[0006] A high uniformity semi-solid alloy forming process comprises the following steps:

[0007] Obtaining a semi-solid temperature range of the alloy material to be formed;

[0008] The temperature of the lower mold of the mold is preheated to a preset temperature, which is 50-100° C. lower than the lower limit of the semi-solid temperature range, and the upper mold of the mold is preheated to a forming temperature, wherein the forming temperature is lower than the preset temperature; specifically, the forming temperature is the forming temperature of the semi-solid alloy in the prior art, for example, 350-400° C. The lower limit of the semi-solid temperature range refers to the minimum value within the semi-solid temperature range.

[0009] Using the material to be formed as a raw material to prepare a semi-solid alloy billet, wherein the semi-solid alloy billet comprises a first region and a second region, and the liquid phase volume fraction of the first region is greater than the liquid phase volume fraction of the second region;

[0010] The semi-solid alloy blank is placed in the mold for die casting, wherein the first area is arranged corresponding to the upper mold, and the second area is arranged corresponding to the lower mold.

[0011] In the above-mentioned high-uniformity semi-solid alloy forming process, the second region has a low liquid phase volume fraction and a high solid content, and can be mixed with the first region during the die-casting process. On the one hand, the low liquid phase content in the second region makes it difficult to produce a liquid phase flow channel inside, thereby avoiding liquid phase segregation in the second region, and more solid phases in the second region are mixed with the first region during the die-casting process, which hinders the liquid phase flow in the first region. On the other hand, solid particles with high liquid phase volume are easily gathered in the lower mold in the traditional forming process, while the second region of the present invention is equivalent to a deformable "lower mold", which can drive the solid phase particles in the first region to move, promote the uniform mixing and forming of liquid and solid phases, and avoid liquid phase segregation in the first region. Through the cooperation of the first region and the second region, the segregation phenomenon of the semi-solid alloy billet can be avoided, so that a highly uniform semi-solid magnesium alloy can be obtained. The high-uniformity semi-solid alloy forming process requires fewer parameters to be strictly controlled, mainly utilizing the physical properties of the materials at different temperatures, and cooperating with the mold to improve the uniformity of the semi-solid alloy. The operating space is large, which is conducive to the industrial production of semi-solid alloys.

[0012] In one embodiment, the alloy material to be formed is a magnesium alloy material. Through experiments conducted by the inventors, it was found that magnesium metal materials are particularly suitable for achieving high uniformity through a forming process. For example, the magnesium alloy material is AZ91D magnesium alloy. For another example, the magnesium alloy material is Mg-Y-Gd-Zn-Zr alloy. In one embodiment, the forming temperature is 300-450°C. Within this temperature range, a semi-solid magnesium alloy billet can achieve a good forming effect after being placed in a mold.

[0013] In one embodiment, the liquid phase volume fraction of the first region is 25-35%, and the liquid phase volume fraction of the second region is 10-15%. In this way, the first region and the second region have different liquid phase volume settings, the liquid phase volume fraction of the first region is high, and the liquid phase volume fraction of the second region is low. The second region with a higher solid phase volume fraction has a better pushing or extrusion effect, which can push the solid phase particles in the first region, and the less liquid phase itself is not easy to converge into a flow channel, avoiding liquid phase segregation, especially between 10-15% liquid phase volume fraction, which can better avoid liquid phase segregation. If the liquid phase content of the first region is too low, even close to the second region, it will affect the processing performance of the blank. If the liquid phase content of the first region is too high, the liquid phase flows too fast, and the setting of the second region is also difficult to improve the liquid phase segregation of the first region. If the liquid phase content of the second region is too high, it will itself undergo liquid phase segregation; if the liquid phase content of the second region is too low, it will affect the processing performance of the blank.

[0014] In one embodiment, in the step of placing the semi-solid alloy billet in the mold for die casting, the die casting extrusion rate is 50-150 mm / s. Within this extrusion range, the semi-solid alloy billet can be mixed and formed more uniformly.

[0015] In one embodiment, the weight fraction of the first region in the semi-solid alloy blank is 60-80%. The first region occupies a larger proportion of the semi-solid alloy blank, so when the first region is well formed, the finished semi-solid alloy also has better forming performance.

[0016] In one embodiment, the weight fraction of the first region in the semi-solid alloy billet is 65-70%. According to research, the first region with a weight fraction of 65-70% can better cooperate with the second region, thereby making the semi-solid alloy obtain higher uniformity.

[0017] In one embodiment, the method for preparing the semi-solid alloy blank comprises:

[0018] An initial alloy billet is prepared using the alloy material to be formed as raw material, wherein the initial alloy billet includes a first region and a second region; in this embodiment, the first region and the second region are distributed along the thickness direction of the initial alloy billet, and the first region and the second region are layered structures, thereby better matching the mold.

[0019] The first region is heated to a liquid phase volume fraction of 25-35%, and the second region is heated to a liquid phase volume fraction of 10-15%, to obtain the semi-solid alloy billet. For example, the first region or the second region is accurately heated by electromagnetic induction heating or infrared heating, and the first region and the second region can be penetrated to a certain extent for heating, so that the first region and the second region are uniformly heated to a preset liquid phase volume fraction.

[0020] In one embodiment, in the step of obtaining the semi-solid temperature range of the alloy material to be formed, the semi-solid temperature range of the alloy material to be formed is obtained by DSC differential thermal analysis. Differential scanning calorimetry (DSC) is a method of quantitatively measuring the heat absorbed or released by a sample through a detector during program temperature control, studying the thermal changes of the sample, and then obtaining the semi-solid temperature range of the alloy material to be formed.

[0021] In one embodiment, the semi-solid alloy billet further includes a third region, the third region is disposed on a side of the first region away from the second region, and the liquid phase volume fraction of the first region is greater than the liquid phase volume fraction of the third region;

[0022] The first region is arranged corresponding to the upper mold through the third region. In this embodiment, the first region is clamped by the second region and the third region together, which is equivalent to die-casting the first region through a deformable mold, driving the solid phase particles in the first region to move, promoting uniform mixing and forming of the liquid phase and the solid phase, and avoiding liquid phase segregation in the first region.

[0023] In a second aspect, a highly uniform semi-solid alloy is provided, which is obtained by a semi-solid alloy forming process as described in any of the above embodiments. The semi-solid alloy obtained by the above semi-solid alloy forming process has a high uniformity of microstructure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a die-casting step of a semi-solid magnesium alloy according to an embodiment;

[0025] Figure 2 The metallographic diagram of the semi-solid magnesium alloy obtained by the forming process of Example 1;

[0026] Figure 3 The metallographic diagram of the semi-solid magnesium alloy obtained by the forming process of Comparative Example 1. DETAILED DESCRIPTION

[0027] For ease of understanding of the application, the application will be described more fully below. The application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the application more thorough and comprehensive.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of the present application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0030] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0031] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0032] The percentage contents involved in this application, unless otherwise specified, refer to mass percentage for solid-liquid mixing and solid-solid mixing, and refer to volume percentage for liquid-liquid mixing.

[0033] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0034] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range of instrument control.

[0035] The "particles" mentioned in this application, or materials with a defined particle size distribution, are not necessarily spherical in shape, but may be irregular, primary particles or secondary particles. The particle size of irregular particles is the average of their maximum diameter and minimum diameter.

[0036] like Figure 1 As shown, Figure 1 The figure is a schematic diagram of the die-casting steps of a semi-solid magnesium alloy according to an embodiment.

[0037] In step 810 , the semi-solid alloy blank including the first region 110 and the second region 120 is placed inside the lower mold 220 , and the upper mold 210 moves from above toward the semi-solid alloy blank inside the lower mold 220 .

[0038] In step 820 , the upper mold 210 gradually closes with the lower mold 220 , and the second region 120 acts as a deformable “lower mold” to drive the solid phase particles in the first region 110 to move, promote uniform mixing and forming of the liquid phase and the solid phase, and avoid liquid phase segregation in the first region 110 .

[0039] In step 830 , the upper mold 210 and the lower mold 220 are closed to force the first region 110 and the second region 120 to be fully extruded and mixed with each other.

[0040] In step 840, during the forming stage, a thermal gradient is generated inside the semi-solid alloy billet due to regions with different temperatures. The liquid phase and solid phase of each part are evenly mixed under the influence of the thermal gradient, and a highly uniform semi-solid alloy 140 is obtained after cooling.

[0041] The experiment was conducted using AZ91D magnesium alloy. The AZ91D magnesium alloy used in this embodiment was analyzed by DSC differential thermal analysis, and the semi-solid temperature range was found to be 560-650°C. The solid content-temperature curve of the AZ91D magnesium alloy at 560-650°C was plotted (heat preservation for 60 minutes). The preset temperature was calculated to be 460-510°C.

[0042] The following are some specific embodiments:

[0043] Embodiment 1:

[0044] According to the solid content-temperature curve, the temperature corresponding to the liquid volume fraction of AZ91D is 25% and the temperature corresponding to the liquid volume fraction is 10% and 573.3°C.

[0045] The AZ91D magnesium alloy to be formed is processed into an initial alloy billet with a size of Φ20×h80. The weight fraction of the first region in the semi-solid alloy billet is 60%. The initial alloy billet is divided into an upper first region and a lower second region by drawing a line 32 mm from the bottom of the initial alloy billet. The second region is heated to 573.3°C by an induction furnace, and then the billet is heated and kept warm by an infrared heating device, so that the temperature of the first region is heated to 583.1°C and the temperature of the second region is maintained at 573.3°C, and the temperature is kept warm for 5 minutes.

[0046] The above-mentioned blank is transferred to the mold for die casting, and the first area is set corresponding to the upper mold, and the second area is set corresponding to the lower mold, wherein the upper mold is heated to a forming temperature of 300°C, and the temperature of the lower mold is heated to a preset temperature of 460°C, which is lower than the lower limit of the semi-solid temperature range of 100°C, and the extrusion rate is 50mm / s.

[0047] Among them, the schematic diagram of the die casting steps of the semi-solid magnesium alloy is as follows Figure 1 shown.

[0048] Example 2 differs from Example 1 in that the liquid phase fraction in the first region is 35%. According to the solid content-temperature curve, the temperature corresponding to the liquid phase volume fraction of 35% is 594°C. The temperature of the first region is heated to 594°C before die-casting.

[0049] Example 3 differs from Example 1 in that the liquid phase fraction in the second region is 15%. According to the solid content-temperature curve, the temperature corresponding to the liquid phase volume fraction of 15% is 577°C. The second region is heated to 577°C before die-casting.

[0050] Example 4 differs from Example 1 in that the liquid phase fraction in the first region is 30%. According to the solid content-temperature curve, the temperature corresponding to the liquid phase volume fraction of 30% is 588.6°C. Before die-casting, the temperature of the first region is heated to 588.6°C.

[0051] Example 5 differs from Example 1 in that the liquid phase fraction in the second region is 12%. According to the solid content-temperature curve, the temperature corresponding to the liquid phase volume fraction of 12% is 574.8°C. Before die-casting, the temperature of the second region is heated to 574.8°C.

[0052] The difference between Example 6 and Example 1 is that the forming temperature is 400°C, that is, before die-casting, the temperature of the upper mold is heated to 400°C.

[0053] Example 7 is different from Example 1 in that the extrusion rate is 150 mm / s.

[0054] Embodiment 8 differs from Embodiment 1 in that the weight fraction of the first region in the semi-solid alloy billet is 80%, that is, a line is drawn at 16 mm from the bottom of the initial alloy billet to divide the initial alloy billet into an upper first region and a lower second region.

[0055] Example 9 differs from Example 1 in that the upper die is heated to a forming temperature of 350°C, the extrusion rate is 100 mm / s, and the weight fraction of the first region in the semi-solid alloy billet is 70%, that is, a line is drawn on the initial alloy billet 24 mm from the bottom to divide the initial alloy billet into an upper first region and a lower second region.

[0056] Embodiment 10 differs from Embodiment 1 in that the temperature of the lower mold is heated to a preset temperature of 510° C., which is lower than the lower limit of the semi-solid temperature range of 50° C.

[0057] Example 11 is different from Example 1 in that the temperature of the lower mold is heated to a preset temperature of 480° C., which is lower than the lower limit of the semi-solid temperature range of 80° C.

[0058] Example 12, the same AZ91D magnesium alloy as Example 1 was used for the experiment, wherein the liquid phase volume fraction in the first region was 30%, and the liquid phase volume fraction in the second region was 12%. According to the solid content-temperature curve drawn, it is known that the temperature corresponding to the liquid phase volume fraction of 30% is 588.6°C, and the temperature corresponding to the liquid phase volume fraction of 12% is 574.8°C.

[0059] The AZ91D magnesium alloy to be formed was processed into an initial alloy billet with a size of Φ20×h80. The initial alloy billet was marked 24 mm from the bottom to divide the initial alloy billet into an upper first area and a lower second area. The second area was heated to 574.8°C by an induction furnace, and then the billet was heated and kept warm by an infrared heating device, so that the temperature of the first area was heated to 588.6°C and the temperature of the second area was maintained at 574.8°C for 5 minutes.

[0060] The above-mentioned blank is transferred to a mold for die casting, and the first area is set corresponding to the upper mold, and the second area is set corresponding to the lower mold, wherein the upper mold is heated to a forming temperature of 350°C, the temperature of the lower mold is 480°C, and the extrusion rate is 100mm / s.

[0061] Among them, the schematic diagram of the die casting steps of the semi-solid magnesium alloy is as follows Figure 1 shown.

[0062] Example 13 differs from Example 12 in that the weight fraction of the first region in the semi-solid alloy billet is 65%, that is, a line is drawn at 28 mm from the bottom of the initial alloy billet to divide the initial alloy billet into an upper first region and a lower second region.

[0063] Example 14 differs from Example 12 in that the weight fraction of the first region in the semi-solid alloy billet is 68%, that is, a line is drawn at 25.6 mm from the bottom of the initial alloy billet to divide the initial alloy billet into an upper first region and a lower second region.

[0064] Example 15: The same AZ91D magnesium alloy as Example 1 was used for the experiment, and the AZ91D magnesium alloy to be formed was processed into an initial alloy billet with a size of Φ20×h80, wherein the initial alloy billet was divided into three regions in a ratio of 1:3:1, including a first region, a second region arranged on one side of the first region, and a third region arranged on the side of the first region away from the second region. The liquid phase volume fraction of the first region is 25%, and the liquid phase volume fractions of the second region and the third region are 10% respectively. According to the solid content-temperature curve drawn, it is known that the temperature corresponding to the liquid phase volume fraction of 25% is 583.1℃, and the temperature corresponding to the liquid phase volume fraction of 10% is 573.3℃.

[0065] The second and third areas were heated to 573.3°C by an induction furnace, and then the blank was heated and kept warm by an infrared heating device, so that the temperature of the first area was heated to 583.1°C, while the temperature of the second and third areas was maintained at 573.3°C for 5 minutes.

[0066] The above-mentioned blank is transferred to the mold for die casting, and the third area is set corresponding to the upper mold, and the second area is set corresponding to the lower mold, wherein the upper mold is heated to a forming temperature of 300°C, the temperature of the lower mold is a preset temperature of 460°C, and the extrusion rate is 50mm / s.

[0067] Comparative Example 1:

[0068] The experiment was conducted using the same AZ91D magnesium alloy as in Example 1.

[0069] The AZ91D magnesium alloy was processed into a billet with a size of Φ20*h80, heated to 573.3°C by an induction furnace, and then heated and kept warm by an infrared heating device so that the billet temperature was maintained at 583.1°C for 5 minutes.

[0070] The mold closing method of the die-casting step is the same as that of Example 1, except that the overall temperature of the blank when entering the mold is 583.1°C, the upper mold is heated to 300°C, and the lower mold is heated to 460°C.

[0071] Comparative Example 2:

[0072] The AZ91D magnesium alloy was processed into a billet with a size of Φ20*h80 and heated to 573.3℃ in an induction furnace for 5 minutes.

[0073] The mold closing method of the die-casting step is the same as that of Example 1, except that the overall temperature of the blank when entering the mold is 573.3°C, the upper mold is heated to 300°C, and the lower mold is heated to 460°C.

[0074] Test: The Vickers hardness of the semi-solid magnesium alloy cup-shaped part was tested from top to bottom at a distance of 10 mm. A total of 5 points were tested and the average value was taken. The Vickers hardness of the semi-solid magnesium alloy cup-shaped part obtained in the above embodiment and the comparative example is compared as shown in Tables 1 and 2 below.

[0075] Table 1: Experimental parameters and test results of Examples 1-14 and Comparative Examples 1 and 2

[0076] Table 2: Experimental parameters and test results of Example 15

[0077] By comparing Example 1 and Comparative Example 1 in Table 1, it can be found that the average Vickers hardness of each position of the semi-solid magnesium alloy product obtained in Example 1 is higher, and the maximum and minimum hardness difference (hereinafter referred to as hardness difference) is smaller. It can be seen that compared with Comparative Example 1, the finished product of Example 1 has higher hardness and uniformity. Figure 1 In steps 810 and 820, during the mold closing process, the larger solid phase particles in the second region 120 are mixed with the smaller solid phase particles in the first region 110, and the second region 120 drives the solid phase particles in the first region 110 to move, promoting the uniform mixing and forming of the liquid phase and the solid phase, thereby forming a semi-solid magnesium alloy with higher uniformity, while the blank of comparative example 1 is uniformly arranged, and the liquid phase flows rapidly during the die casting process while the solid phase remains in place, causing liquid phase segregation, reducing the uniformity of the finished product, so that the Vickers hardness of the finished product of comparative example 1 is smaller and the hardness difference is larger. The hardness and hardness difference of comparative example 2 are both deteriorated compared with those of embodiment 1, and its solid phase amount is too high and its fluidity is poor, so it is difficult to fill the mold uniformly and fully during the die casting process, thus causing the reduction of alloy performance.

[0078] It can be seen from Examples 1 to 3 that within the range of 25-35% of the liquid phase volume fraction in the first region and 10-15% of the liquid phase volume fraction in the second region, the semi-solid magnesium alloy finished product can obtain good hardness and uniformity. In addition, the hardness of the finished product of Example 2 is relatively high. This is because after the liquid phase volume fraction in the first region is relatively increased, it is matched with the second region, and the mixing effect between it and the solid phase particles is better, so that the forming effect of the first region is better. The first region itself accounts for a large proportion of the blank, so that the overall forming effect of the finished product is better.

[0079] It can be seen from Examples 1, 2 and 4 that the first region liquid phase volume fraction of Example 4 is set to 30%, which can make the finished product have better hardness and hardness difference compared with 25% and 35% liquid phase volume fractions. It can be seen from Examples 1, 3 and 5 that the second region liquid phase volume fraction of Example 5 is set to 12%, which can make the finished product have better hardness and hardness difference compared with 10% and 15% liquid phase volume fractions.

[0080] By comparing Example 1, Example 6, Example 7 and Example 8, it can be seen that the forming temperature is 300°C to 400°C, the extrusion rate is 50 to 150 mm / s, and the first region specific gravity is 60% to 80%, all of which can achieve a finished product with good hardness and a small hardness difference. Combined with Example 9, it can be seen that when the forming temperature, extrusion rate and first region specific gravity are at a better intermediate value, the hardness is higher than that of Example 1, Example 6, Example 7 and Example 8, and the hardness difference is smaller than that of Example 1, Example 6, Example 7 and Example 8, which is conducive to obtaining a finished product with higher uniformity.

[0081] From the comparison between Example 1 and Example 10, it can be seen that the preset temperature of 50°C~100°C, which is lower than the lower limit of the semi-solidification temperature range, can achieve a finished product with better hardness and lower hardness difference. In combination with Example 11, it can be seen that when the preset temperature is at a better value, the hardness of the finished product can be further increased and the hardness difference can be reduced, thereby obtaining a more uniform semi-solid alloy.

[0082] By comparing Example 1 and Example 12, it can be seen that when the liquid volume fraction of the first region is set to 30%, the liquid volume fraction of the second region is set to 12%, the forming temperature is 350°C, the lower mold temperature is 480°C, the extrusion rate is 100mm / s and the specific gravity of the first region is 70%, each component is in a better ratio, which helps to obtain better hardness and lower hardness difference. At this time, the finished product has better uniformity and better quality.

[0083] By comparing Examples 12 to 14, it can be seen that when the specific gravity of the first region is in the range of 65% to 70%, the finished products have better hardness and smaller hardness difference. In particular, in Example 14, the specific gravity of the first region and the second region are preferably matched so that the two reach a better balance. The second region hinders the liquid phase flow in the first region, and drives the solid phase particles in the first region to move, promoting uniform mixing and forming of the liquid and solid phases. The first region itself also has a larger specific gravity. After it is better formed, the semi-solid magnesium alloy finished product as a whole also has better hardness and uniformity. Furthermore, in combination with Example 1, Example 8 and Example 9, it can be found that when the ratio of the liquid phase volume fraction in the first region and the second region is not good, the change in the specific gravity of the first region does not have a significant effect on improving the hardness and hardness difference. However, when the liquid phase volume fractions in the first region and the second region are better, the influence of the specific gravity of the first region on the finished product results increases significantly. This is because the first region and the second region can cooperate with each other through a better liquid phase volume fraction and a better specific gravity, and the favorable factors are superimposed, and ultimately the finished product has a higher hardness and a lower hardness difference, so that the semi-solid magnesium alloy finished product has excellent uniformity.

[0084] Comparing Example 15 with Example 1, it can be seen that the difference between Example 15 and Example 1 is the number and distribution of regions, and the other experimental parameters are the same. After the blank is divided into three regions, the finished product can still have good hardness and low hardness difference, and Example 15 has better hardness and lower hardness difference than Example 1. It can be seen that the finished product of Example 15 has higher uniformity. This is because the second region and the third region sandwich the first region from both sides to form a "deformable mold" that wraps both sides of the first region. In this way, the second region and the third region drive the solid phase particles in the first region from both sides to move, promote the uniform mixing and forming of the liquid phase and the solid phase, and better avoid the liquid phase segregation in the first region.

[0085] Furthermore, the semi-solid magnesium alloy products of Example 1 and Comparative Example 1 were placed under a metallographic microscope to observe the microstructure, wherein: Figure 2 and Figure 3 The scanning electron microscope metallographic images of AZ91D of Example 1 and Comparative Example 1 are shown respectively, wherein the gray pixel portion in the figure represents the matrix α-Mg phase of the semi-solid magnesium alloy, and the white pixel portion represents the β-Mg 17 Al 12 Precipitation phase. By comparison, Figure 2 Semi-solid magnesium alloy β-Mg 17 Al 12 The precipitated phase is finer and more uniform, accounts for a smaller proportion, and no segregation occurs, showing that the semi-solid magnesium alloy has good uniformity. Figure 3 β-Mg 17 Al12 The precipitated phase is thicker and distributed in a continuous network, accounting for a larger proportion. It can be seen that the semi-solid magnesium alloy in Comparative Example 1 has segregation phenomenon, and the uniformity of the semi-solid magnesium alloy is poor. When used subsequently, the semi-solid magnesium alloy is easy to be distributed along the β-Mg 17 Al 12 The network structure of the precipitated phase is broken, which reduces the mechanical properties of the semi-solid magnesium alloy.

[0086] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A high uniformity semi-solid alloy forming process, characterized in that: The steps include: Obtaining a semi-solid temperature range of the alloy material to be formed; Preheating the temperature of the lower mold of the mold to a preset temperature, the preset temperature is 50-100° C. lower than the lower limit of the semi-solid temperature range, and preheating the upper mold of the mold to a forming temperature, wherein the forming temperature is lower than the preset temperature; Using the alloy material to be formed as a raw material to prepare a semi-solid alloy billet, wherein the semi-solid alloy billet comprises a first region and a second region, and the liquid phase volume fraction of the first region is greater than the liquid phase volume fraction of the second region; Placing the semi-solid alloy billet in the mold for die casting, wherein the first region is arranged corresponding to the upper mold, and the second region is arranged corresponding to the lower mold; Wherein, the semi-solid alloy billet further includes a third region, the third region is arranged on a side of the first region away from the second region, and the liquid phase volume fraction of the first region is greater than the liquid phase volume fraction of the third region; The first region is disposed corresponding to the upper mold through the third region.

2. The high uniformity semi-solid alloy forming process according to claim 1, characterized in that: The alloy material to be formed is a magnesium alloy material.

3. The high uniformity semi-solid alloy forming process according to claim 2, characterized in that: The liquid volume fraction of the first region is 25-35%, and the liquid volume fraction of the second region is 10-15%.

4. The high uniformity semi-solid alloy forming process according to claim 1, characterized in that: In the step of placing the semi-solid alloy billet in the mold for die casting, the die casting extrusion rate is 50-150 mm / s.

5. The high uniformity semi-solid alloy forming process according to claim 1, characterized in that: The weight fraction of the first region in the semi-solid alloy billet is 60-80%.

6. The high uniformity semi-solid alloy forming process according to claim 5, characterized in that: The weight fraction of the first region in the semi-solid alloy billet is 65-70%.

7. The high uniformity semi-solid alloy forming process according to claim 1, characterized in that: The preparation method of the semi-solid alloy blank comprises: Using the alloy material to be formed as a raw material, an initial alloy blank is prepared, wherein the initial alloy blank comprises the first region and the second region; The first region is heated to a liquid phase volume fraction of 25-35%, and the second region is heated to a liquid phase volume fraction of 10-15%, to obtain the semi-solid alloy billet.

8. The high uniformity semi-solid alloy forming process according to claim 1, characterized in that: In the step of obtaining the semi-solid temperature range of the alloy material to be formed, the semi-solid temperature range of the alloy material to be formed is obtained by DSC differential thermal analysis.

9. A highly uniform semi-solid alloy, characterized in that: The alloy is prepared by the semi-solid alloy forming process as described in any one of claims 1 to 8.

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