Heat treatment method for improving linear separation characteristic of cast magnesium alloy

Abstract

The invention provides a heat treatment method for improving linear separation characteristic of cast magnesium alloy, which mainly comprises the following steps of: putting a magnesium alloy casting with specific components into a hot isostatic pressing furnace, respectively carrying out heat treatment in low-temperature and high-pressure and high-temperature and low-pressure environments, and carrying out linear separation on the magnesium alloy by utilizing the rapid diffusion of Ag in Mg and the inhibition effect of pressure on solute diffusion. And preferential growth of part of crystal grains is promoted. The grains of the cast magnesium alloy subjected to heat treatment are distributed in a quasi double-peak structure, and the cast magnesium alloy has quasi-static obdurability and high-speed impact brittleness. By the adoption of the heat treatment method, the problem that controllable linear separation cannot be achieved under dynamic impact on the premise that a traditional magnesium alloy material meets quasi-static casting of large maneuver and large overload is effectively solved, and the light weight level of a multi-stage aircraft is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of magnesium alloys, and in particular relates to a heat treatment method for improving the linear separability of magnesium alloys. Background Art

[0002] Magnesium alloy has high specific strength and good formability, and is one of the preferred structural materials for equipment lightweighting. Casting magnesium alloy has been widely used in the aerospace field, creating huge economic, social and military benefits.

[0003] The separation of high-performance multi-stage aircraft needs to adopt the form of linear separation during flight. This means that the separation part needs to have high-speed impact brittleness while meeting the quasi-static casting requirements of large overload. Although traditional cast magnesium alloy materials have quasi-static toughness, they have a high separation dose and a large impact response. This will have a serious impact on the normal service of electronic components in the aircraft cabin, resulting in the need for thickening the aircraft design or adding bracket-type structure installation, reducing the lightweight level of the aircraft. At the same time, the installation of a large number of bracket-type buffer structures will also occupy too much space in the cabin, increasing the difficulty of integrated electrical design.

[0004] Among the existing cast light alloys, aluminum alloy grades ZL114A and ZL205A meet the requirements of quasi-static toughness, but their damping performance and lightweight level are low, and the high amount of cutting wire leads to a large separation shock response, which cannot take into account both quasi-static toughness and high-speed impact brittleness. In comparison, Mg-Gd-Y-Zr cast magnesium alloy has the advantage of being more lightweight, meets the requirements of quasi-static toughness and has higher damping performance, but Mg-Gd-Y-Zr also has the problems of high cutting wire requirements and large separation shock response. In this regard, an important way to solve the above problems is to modify the Mg-Gd-Y-Zr rare earth magnesium alloy to maintain its original toughness while improving its high-speed impact brittleness. Summary of the invention

[0005] The technical problem solved by the present invention is: to provide a heat treatment method for improving the linear separability of cast magnesium alloys. Based on alloying and special heat treatment process modification, the cast magnesium alloy has quasi-static castability and high-speed impact brittleness, thereby solving the problem of reduced lightweight level and performance loss caused by excessive linear separation impact response of multi-stage aircraft.

[0006] The technical solution provided by the present invention is as follows:

[0007] In a first aspect, a heat treatment method for improving the linear separability of a cast magnesium alloy comprises:

[0008] Step 1: placing the magnesium alloy casting in a hot isostatic pressing furnace, evacuating the furnace, raising the temperature and pressure, and maintaining the temperature and pressure at a temperature lower than the grain growth temperature;

[0009] Step 2: After the heat preservation and pressure holding in step 1 is completed, the pressure is reduced and the temperature is increased at the same time, and the heat preservation and pressure holding is completed at a temperature higher than the grain growth temperature;

[0010] Step three: After the heat preservation and pressure preservation in step two are completed, the magnesium alloy casting is cooled to normal temperature and pressure along with the furnace, and the magnesium alloy casting is taken out and aging treatment is completed in an air circulation heat treatment furnace.

[0011] In the low temperature and high pressure stage, the easily soluble eutectic phase begins to dissolve, and the solute elements are concentrated near the grain boundaries under high pressure; after entering the high temperature and low pressure stage, more solute elements are concentrated at some grain boundaries, and some grain boundaries contain more undissolved insoluble phases, which can inhibit the growth of grains at high temperatures, and the remaining grains grow rapidly under high temperatures. The grains of magnesium alloy castings have undergone a preferential growth process and are distributed in a "bimodal structure".

[0012] Furthermore, the rare earth magnesium alloy is a sand-cast Mg-Gd-Y-Ag-Zr magnesium alloy casting, and its composition, by mass percentage, is: Gd 5.5%-15.0%, Y 0-3%, Ag 0.5%-3%, Zr 0.3%-1.0%, and the rest is Mg.

[0013] Furthermore, in the step of placing the magnesium alloy casting into a hot isostatic pressing furnace, increasing the temperature and pressure, and maintaining the temperature and pressure below the grain growth temperature, before increasing the temperature and pressure, the hot isostatic pressing furnace is evacuated and nitrogen or an inert gas such as argon is introduced as a protective gas and pressure medium.

[0014] Furthermore, in the step of placing the magnesium alloy casting into a hot isostatic pressing furnace, increasing the temperature and pressure, and maintaining the temperature and pressure at a temperature below the grain growth temperature, the pressure is increased to 160-180 MPa and the temperature is increased to 430-450°C at a heating rate of 0.02-0.06°C / s, and then the temperature and pressure are maintained for 3-5 hours.

[0015] Furthermore, after the step 1 of heat preservation and pressure holding is completed, the pressure is reduced and the temperature is increased at the same time. In the step of completing heat preservation and pressure holding at a temperature higher than the grain growth temperature, after the pressure is reduced to 120-140 MPa and the temperature is increased to 480-510°C at a heating rate of 0.02-0.06°C / s, the heat preservation and pressure holding is performed for 3-5 hours.

[0016] Furthermore, in step three, the magnesium alloy casting after hot isostatic pressing is subjected to aging treatment, the aging temperature is 175-215° C., and the aging time is 20-30 hours.

[0017] In the second aspect, a magnesium alloy casting is obtained by using the heat treatment method for improving the linear separability of the cast magnesium alloy as described in the first aspect, the grain size presents a bimodal tissue distribution, and the grain size of the magnesium alloy casting is concentrated at 40-80μm and 180-230μm.

[0018] The present invention makes full use of the rapid diffusion of Ag element in Mg in Mg-Gd-Y-Ag-Zr magnesium alloy castings and the influence of pressure and temperature of a hot isostatic pressing furnace on the segregation of rare earth element solutes in rare earth magnesium alloys. The grains in the magnesium alloy castings have undergone a preferential growth process and are distributed in a "bimodal structure", so that the magnesium alloy castings have both quasi-static toughness and high-speed impact brittleness.

[0019] The invention provides a heat treatment method for improving the linear separability of a cast magnesium alloy. Compared with magnesium alloy materials subjected to conventional heat treatment, the invention has the following advantages:

[0020] (1) The present invention provides a heat treatment method for improving the linear separability of cast magnesium alloys. The heat treatment process utilizes the diffusion of Ag elements in Mg and the solute segregation effect under the action of pressure and temperature to effectively inhibit the growth of some grains and preferentially grow the grains, ultimately making the grain size of the casting have a "double-peak structure" distribution characteristic. After the casting is subjected to high-speed impact, the cracks generated at the penetration front end can easily expand along the direction of the large-size grains of the casting. Therefore, under the same cutting wire dosage, the overall penetration depth of the casting with a "double-peak structure" is deeper, and low-dose separation can be achieved.

[0021] (2) The present invention provides a heat treatment method for improving the linear separability of cast magnesium alloys, which ensures the use environment of high-level precision instruments and the conditions for integrated electrical design by reducing the low-dose impact response; and the low impact response can greatly reduce the installation of various types of brackets and thickening designs, thereby improving the lightweight level.

[0022] (3) The present invention provides a heat treatment method for improving the linear separability of cast magnesium alloys. The composition of the magnesium alloy casting is Mg-Gd-Y-Ag-Zr. In addition to promoting the formation of a bimodal structure, the Ag element is also beneficial to the precipitation of basal plane precipitation phases during aging, thereby improving the mechanical properties of the alloy.

[0023] (4) The present invention provides a heat treatment method for improving the linear separability of cast magnesium alloys. The heat treatment of the casting completes the solid solution treatment in a hot isostatic pressing furnace. The pores inside the casting can also be closed at this stage, thereby improving the qualified rate of the casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a metallographic photograph of the as-cast structure of the Mg-10Gd-3Y-1Ag-0.5Zr alloy before hot isostatic pressing;

[0025] Figure 2 This is a metallographic photograph of the as-cast structure of the Mg-10Gd-3Y-1Ag-0.5Zr alloy after hot isostatic pressing;

[0026] Figure 3 This is a metallographic photograph of the as-cast structure of the Mg-10Gd-3Y-0.5Zr alloy before hot isostatic pressing;

[0027] Figure 4 This is a metallographic photograph of the as-cast structure of the Mg-10Gd-3Y-0.5Zr alloy after hot isostatic pressing;

[0028] Figure 5 It is to cut the specific shape and size of the simulated structural parts. DETAILED DESCRIPTION

[0029] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0030] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0031] In order to simulate the linear separation of multi-stage aircraft, experiments on melting, pouring, heat treatment and energy-focusing cutting of cutting simulation structural castings were carried out.

[0032] Mg-Gd-Y-Ag-Zr magnesium alloy castings, calculated by mass percentage, have the following components: Gd 5.5% to 15.0%, Y 0 to 3%, Ag 0.5 to 3%, Zr 0.3% to 1.0%, and the rest is Mg, and are prepared by sand mold counter-gravity casting process. The selected smelting equipment is a crucible resistance furnace (GR-150-9), and the raw materials are pure magnesium, Mg-20Y, Mg-20Gd master alloy, pure Ag, and Mg-30Zr master alloy is selected as a grain refiner. The alloy is prepared by the following smelting and casting process: preheating the raw materials at 300°C, placing the preheated raw materials in a crucible furnace in order for smelting; spreading JDMF covering agent on the melt for flame retardancy, and using JDMJ refining agent for refining, slag removal and impurity removal; after the melt is allowed to stand for 25-40 minutes, the waste slag at the bottom of the crucible is removed, and counter-gravity pouring is used into a sand mold at 710°C.

[0033] The Mg-Gd-Y-Ag-Zr magnesium alloy casting is subjected to hot isostatic pressing treatment in a hot isostatic pressing equipment.

[0034] Specific hot isostatic pressing treatment includes:

[0035] Step 1: Place the Mg-Gd-Y-Ag-Zr magnesium alloy casting into a hot isostatic pressing furnace, evacuate the vacuum, introduce protective gas, and start heating at the same time. After the pressure rises to 160-180MPa and the temperature rises to 430-450℃ at a rate of 0.02-0.06℃ / s, keep the temperature and pressure for 3-5h. During the heat and pressure holding process, the easily soluble Mg5(Gd,Ag) grain boundary divorced eutectic phase begins to dissolve slowly, and the rare earth elements are concentrated near the grain boundaries under the action of high pressure.

[0036] In particular, in the temperature range of 430-450°C, the eutectic phase of Mg5(Gd,Ag) grain boundaries can be slowly decomposed, and the grains will not grow; the pressure of 160-180MPa can inhibit the diffusion of rare earth elements near the grain boundaries into the crystals.

[0037] Step 2: Reduce the pressure and increase the temperature at the same time. After the pressure is reduced to 120-140 MPa and the temperature is increased to 480-510 °C at a rate of 0.02-0.06 °C / s, keep the temperature for 3-5 hours. During the heat and pressure holding process, due to the large amount of rare earth elements concentrated near some grains or the presence of insoluble Mg at some grain boundaries, 85 (Gd,Ag) 15 phase, which grows preferentially under the influence of temperature and solute segregation.

[0038] Step 3: Perform conventional aging treatment on the casting after hot isostatic pressing, the aging temperature is 175-215°C, the aging time is 20-30h, and a magnesium alloy casting with a grain size showing a "bimodal structure" distribution is obtained. The small grain size of the "bimodal structure" is 40-80μm, and the large grain size is 180-230μm.

[0039] The "bimodal structure" magnesium alloy casting obtained by the present invention is highly sensitive to high-speed impact due to the presence of some large grains. Therefore, when the thickness of the structural parts is the same, less cutting wire is required to achieve linear separation, and the separation impact response is lower. In addition, since the heat treatment process is completed in a hot isostatic pressing furnace, if defects such as looseness and pores occasionally appear in the casting, they can be closed during the heat treatment process to improve the yield rate.

[0040] The energy-focused cutting performance test was carried out on the cutting simulation structural castings to find out the minimum cutting charge amount of the structural parts obtained by different heat treatment methods under the same thickness.

[0041] Example

[0042] Example 1

[0043] This example provides a heat treatment method for improving the linear separability of a cast magnesium alloy, comprising:

[0044] Step 1: Cut the simulated structural casting (see Figure 5 ) is placed in a hot isostatic pressing furnace, and then the temperature and pressure are increased and the temperature and pressure are maintained; specifically: the casting is heated from room temperature to 430°C in the hot isostatic pressing furnace, with a heating rate of 0.06°C / s, and is maintained at 430°C and a pressure of 180MPa for 4 hours; the cutting simulation structure casting is a cast magnesium alloy Mg-10Gd-3Y-1Ag-0.5Zr.

[0045] Step 2: Reduce the pressure, increase the temperature, and continue to maintain the temperature and pressure; specifically: increase the temperature to 490°C, the heating rate is 0.06°C / s, reduce the pressure to 140MPa, and maintain the temperature and pressure for 4 hours;

[0046] Step 3: After the heat preservation and pressure holding in step 2 is completed, the temperature naturally drops with the hot isostatic pressing equipment, and the pressure reducing valve is opened to reduce the pressure. The end point of temperature and pressure reduction is normal temperature and pressure. The casting after hot isostatic pressing is subjected to conventional aging treatment, with an aging temperature of 200°C and an aging time of 25h. The grain distribution test of the cut simulation structure casting after heat treatment is carried out. The casting grains are distributed in a "double peak structure" between 40-80μm and 180-230μm. The metallographic photos of the casting before and after hot isostatic pressing are shown in Figure 1 and Figure 2 .

[0047] Carry out concentrated energy cutting performance test and test the minimum cutting charge amount.

[0048] Example 2

[0049] This example provides a heat treatment method for improving the linear separability of a cast magnesium alloy, comprising:

[0050] Step 1: Cut the simulated structural casting (see Figure 5 ) is placed in a hot isostatic pressing furnace, and then the temperature and pressure are increased and the temperature and pressure are maintained; specifically: the casting is heated from room temperature to 430°C in the hot isostatic pressing furnace, with a heating rate of 0.06°C / s, and is maintained at 430°C and a pressure of 160MPa for 4 hours; the cutting simulation structure casting is a cast magnesium alloy Mg-10Gd-3Y-1Ag-0.5Zr.

[0051] Step 2: Reduce the pressure, increase the temperature, and continue to maintain the temperature and pressure; specifically: increase the temperature to 490°C, the heating rate is 0.06°C / s, reduce the pressure to 120MPa, and maintain the temperature and pressure for 4 hours;

[0052] Step 3: After the heat preservation and pressure holding in step 2 is completed, the temperature naturally decreases with the hot isostatic pressing equipment, and the pressure reducing valve is opened to reduce the pressure. The end point of the temperature reduction and pressure reduction is normal temperature and pressure. The castings after hot isostatic pressing are subjected to conventional aging treatment, with an aging temperature of 200°C and an aging time of 25h. The grain distribution test of the cut simulation structure casting after heat treatment is carried out, and the casting grains are distributed in a "double peak organization" between 40-80μm and 180-230μm.

[0053] Carry out concentrated energy cutting performance test and test the minimum cutting charge amount.

[0054] Example 3

[0055] This example provides a heat treatment method for improving the linear separability of a cast magnesium alloy, comprising:

[0056] Step 1: Cut the simulated structural casting (see Figure 5 ) is placed in a hot isostatic pressing furnace, and then the temperature and pressure are increased and the temperature and pressure are maintained; specifically: the casting is heated from room temperature to 430°C in the hot isostatic pressing furnace, with a heating rate of 0.06°C / s, and is maintained at 430°C and a pressure of 180MPa for 3 hours; the cutting simulation structure casting is a cast magnesium alloy Mg-10Gd-3Y-1Ag-0.5Zr.

[0057] Step 2: Reduce the pressure, increase the temperature, and continue to maintain the temperature and pressure; specifically: increase the temperature to 490°C, the heating rate is 0.06°C / s, reduce the pressure to 140MPa, and maintain the temperature and pressure for 3h;

[0058] Step 3: After the heat preservation and pressure holding in step 2 is completed, the temperature naturally decreases with the hot isostatic pressing equipment, and the pressure reducing valve is opened to reduce the pressure. The end point of the temperature reduction and pressure reduction is normal temperature and pressure. The castings after hot isostatic pressing are subjected to conventional aging treatment, with an aging temperature of 200°C and an aging time of 25h. The grain distribution test of the cut simulation structure casting after heat treatment is carried out, and the casting grains are distributed in a "double peak organization" between 40-80μm and 180-230μm.

[0059] Carry out concentrated energy cutting performance test and test the minimum cutting charge amount.

[0060] Example 4

[0061] This example provides a heat treatment method for improving the linear separability of a cast magnesium alloy, comprising:

[0062] Step 1: Cut the simulated structural casting (see Figure 5 ) is placed in a hot isostatic pressing furnace, and then the temperature and pressure are increased and the temperature and pressure are maintained; specifically: the casting is heated from room temperature to 450°C in the hot isostatic pressing furnace, with a heating rate of 0.06°C / s, and is maintained at 450°C and a pressure of 180MPa for 4 hours; the cutting simulation structure casting is a cast magnesium alloy Mg-10Gd-3Y-1Ag-0.5Zr.

[0063] Step 2: Reduce the pressure, increase the temperature, and continue to maintain the temperature and pressure; specifically: increase the temperature to 510°C, the heating rate is 0.06°C / s, reduce the pressure to 140MPa, and maintain the temperature and pressure for 4 hours;

[0064] Step 3: After the heat preservation and pressure holding in step 2 is completed, the temperature naturally decreases with the hot isostatic pressing equipment, and the pressure reducing valve is opened to reduce the pressure. The end point of the temperature reduction and pressure reduction is normal temperature and pressure. The castings after hot isostatic pressing are subjected to conventional aging treatment, with an aging temperature of 200°C and an aging time of 25h. The grain distribution test of the cut simulation structure casting after heat treatment is carried out, and the grain size of the casting is distributed in a "double peak organization" between 40-80μm and 180-230μm.

[0065] Carry out concentrated energy cutting performance test and test the minimum cutting charge amount.

[0066] Example 5

[0067] This example provides a heat treatment method for improving the linear separability of a cast magnesium alloy, comprising:

[0068] Step 1: Cut the simulated structural casting (see Figure 5 ) is placed in a hot isostatic pressing furnace, and then the temperature and pressure are increased and the temperature and pressure are maintained; specifically: the casting is heated from room temperature to 430°C in the hot isostatic pressing furnace, with a heating rate of 0.06°C / s, and is maintained at 430°C and a pressure of 180MPa for 4 hours; the cutting simulation structure casting is a cast magnesium alloy Mg-10Gd-1Ag-0.5Zr.

[0069] Step 2: Reduce the pressure, increase the temperature, and continue to maintain the temperature and pressure; specifically: increase the temperature to 490°C, the heating rate is 0.06°C / s, reduce the pressure to 140MPa, and maintain the temperature and pressure for 4 hours;

[0070] Step 3: After the heat preservation and pressure holding in step 2 is completed, the temperature naturally decreases with the hot isostatic pressing equipment, and the pressure reducing valve is opened to reduce the pressure. The end point of the temperature reduction and pressure reduction is normal temperature and pressure. The castings after hot isostatic pressing are subjected to conventional aging treatment, with an aging temperature of 200°C and an aging time of 25h. The grain distribution test of the cut simulation structure casting after heat treatment is carried out, and the casting grains are distributed in a "double peak organization" between 50-80μm and 190-230μm.

[0071] Carry out concentrated energy cutting performance test and test the minimum cutting charge amount.

[0072] Example 6

[0073] This example provides a heat treatment method for improving the linear separability of a cast magnesium alloy, comprising:

[0074] Step 1: Cut the simulated structural casting (see Figure 5) is placed in a hot isostatic pressing furnace, and then the temperature and pressure are increased and the temperature and pressure are maintained; specifically: the casting is heated from room temperature to 430°C in the hot isostatic pressing furnace, with a heating rate of 0.06°C / s, and is maintained at 430°C and a pressure of 180MPa for 4 hours; the cutting simulation structure casting is a Mg-Gd-Y-Ag-Zr cast magnesium alloy Mg-10Gd-2Ag-0.5Zr.

[0075] Step 2: Reduce the pressure, increase the temperature, and continue to maintain the temperature and pressure; specifically: increase the temperature to 490°C, the heating rate is 0.06°C / s, reduce the pressure to 140MPa, and maintain the temperature and pressure for 4 hours;

[0076] Step 3: After the heat preservation and pressure holding in step 2 is completed, the temperature naturally decreases with the hot isostatic pressing equipment, and the pressure reducing valve is opened to reduce the pressure. The end point of the temperature reduction and pressure reduction is normal temperature and pressure. The castings after hot isostatic pressing are subjected to conventional aging treatment, with an aging temperature of 200°C and an aging time of 25h. The grain distribution test of the cut simulation structure casting after heat treatment is carried out, and the casting grains are distributed in a "double peak organization" between 50-80μm and 190-230μm.

[0077] Carry out concentrated energy cutting performance test and test the minimum cutting charge amount.

[0078] Comparative Example

[0079] Comparative Example 1

[0080] The same sand casting process was used to prepare Mg-10Gd-3Y-1Ag-0.5Zr cutting simulation structure castings with the same composition. The castings were subjected to conventional solution aging treatment, with solution treatment parameters of 495℃×14h and aging parameters of 200℃×25h. The energy-gathering cutting performance test was carried out to test the minimum cutting charge amount.

[0081] Comparative Example 2

[0082] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, except that the heat preservation and pressure holding time at 430° C. and 180 MPa is 8 h.

[0083] Comparative Example 3

[0084] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, except that the heat preservation and pressure holding time at 430° C. and 180 MPa is 2 h.

[0085] Comparative Example 4

[0086] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, except that the heat preservation and pressure holding time at 490° C. and 140 MPa is 8 h.

[0087] Comparative Example 5

[0088] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, except that the heat preservation and pressure holding time at 490° C. and 140 MPa is 2 h.

[0089] Comparative Example 6

[0090] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, with the only difference being that the insulation temperature of the low-temperature and high-pressure insulation stage in step 1 is 400°C.

[0091] Comparative Example 7

[0092] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, with the only difference being that the insulation temperature of the low-temperature and high-pressure insulation stage in step 1 is 470°C.

[0093] Comparative Example 8

[0094] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, with the only difference being that the insulation temperature of the high-temperature and low-pressure insulation stage in step 2 is 440°C.

[0095] Comparative Example 9

[0096] The casting and heat treatment processes of this comparative example are basically the same as those of Example 1, with the only difference being that the insulation temperature of the high-temperature and low-pressure insulation stage in step 2 is 530°C.

[0097] Comparative Example 10

[0098] The casting and heat treatment process of this comparative example is basically the same as that of Example 1, except that the Mg-Gd cast magnesium alloy is Mg-10Gd-3Y-0.5Zr, and the metallographic photos of the casting before and after heat treatment are shown in Figure 3 and Figure 4 .

[0099] Effect verification:

[0100] The performance of the alloy castings prepared in the examples and comparative examples was tested, and the test results are shown in Table 1.

[0101] It can be seen from Table 1 that after the Mg-Gd-Y-Ag-Zr magnesium alloy cutting simulation structure casting is treated by the heat treatment process of the present invention, the strength and toughness are equivalent to those of conventional heat treatment, but the minimum cutting charge amount is significantly reduced.

[0102]

[0103] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0104] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A heat treatment method for improving the linear separability of a cast magnesium alloy, characterized in that: The following steps are involved: Step 1: placing the magnesium alloy casting into a hot isostatic pressing furnace, evacuating the furnace, raising the temperature and pressure, and maintaining the temperature and pressure at a temperature lower than the grain growth temperature; Step 2: After the heat preservation and pressure holding in step 1 is completed, the pressure is reduced and the temperature is increased at the same time, and the heat preservation and pressure holding is completed at a temperature higher than the grain growth temperature; Step three: After the heat preservation and pressure preservation in step two are completed, the magnesium alloy casting is cooled to normal temperature and pressure along with the furnace, and the magnesium alloy casting is taken out and aging treatment is completed in an air circulation heat treatment furnace.

2. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: The magnesium alloy is a sand-cast Mg-Gd-Y-Ag-Zr magnesium alloy casting, and its components are as follows by mass percentage: Gd 5.5%-15.0%, Y 0-3%, Ag 0.5%-3%, Zr 0.3%-1.0%, and the rest is Mg.

3. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: In step 1, the gas introduced for increasing the pressure after evacuation is nitrogen or argon.

4. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: In step 1, after the pressure is increased to 160-180 MPa and the temperature is increased to 430-450° C., the temperature and pressure are maintained for 3-5 hours.

5. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: In step 1, the heating rate is 0.02-0.06°C / s.

6. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: In step 2, after the pressure is reduced to 120-140 MPa and the temperature is increased to 480-510° C., the temperature and pressure are maintained for 3-5 hours.

7. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: In step 2, the heating rate is 0.02-0.06°C / s.

8. The heat treatment method for improving the linear separability of cast magnesium alloy according to claim 1, characterized in that: In step three, the parameters of the aging treatment include: an aging temperature of 175 to 215° C. and an aging time of 20 to 30 hours.

9. A magnesium alloy casting, characterized in that: The heat treatment method for improving the linear separability of the cast magnesium alloy according to any one of claims 1 to 8 is used to obtain a bimodal distribution of grain size.

10. The magnesium alloy casting according to claim 9, characterized in that: The grain sizes of the magnesium alloy casting are concentratedly distributed at 40-80 μm and 180-230 μm.

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