Mg-Bi wrought magnesium alloy suitable for rapid extrusion and extrusion forming process thereof

Abstract

The invention discloses an Mg-Bi wrought magnesium alloy suitable for rapid extrusion and an extrusion forming process thereof, relates to the field of magnesium alloys, and mainly provides a magnesium alloy profile alloy system and an extrusion forming process thereof, the alloy component system of the magnesium alloy profile alloy system is Mg-Bi-Al-Mn-Sn, and the magnesium alloy profile alloy system comprises the following components in percentage by mass: 4-6% of Bi, 2-4% of Al, 0.2-0.6% of Mn, 0.2-0.6% of Sn, and the balance of Mg and inevitable impurities. The balance is Mg and inevitable impurity elements; in addition, the extrusion profile mainly comprises the steps of homogenization treatment, extrusion forming and isothermal aging treatment. According to the alloy system, by adding Sn, a large number of fine and compact Mg2Sn phases can be formed, the large number of Mg2Sn phases are distributed at the grain boundary in a short rod shape, the effect of refining recrystallized grains can be achieved through precipitation of the second phase, and the strong plasticity matching of the alloy can be effectively changed.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and particularly relates to the design of an alloy composition system and an extrusion forming process for a new type of non-rare-earth magnesium alloy profile suitable for rapid extrusion. Background Art

[0002] Currently, with the increasingly strict international environmental regulations, light-duty vehicles with lower carbon dioxide emissions and higher fuel economy have become the main focus of the automotive industry. Therefore, magnesium alloys have attracted great attention in the industry. The density of magnesium alloys is approximately 1.7 g / cm³, about two-thirds of the density of aluminum alloys and one-fourth of the density of steel. Extruded magnesium alloys have superior mechanical properties compared to cast magnesium alloys and are particularly suitable for body and chassis components such as bumper beams, radiator supports, engine mounts, and subframes. However, compared with extruded aluminum alloys, the low strength and high price of extruded magnesium alloys are major obstacles to their widespread application.

[0003] In highly alloyed commercial Mg-Al- and Mg-Zn-based alloys (such as AZ91 and ZK60), Mg17Al12 or MgZn2 forms phases with melting temperatures below 440 °C during hot extrusion, resulting in local melting under high-speed extrusion conditions and increasing the sensitivity to thermal cracking. Therefore, the extrudability of high-strength commercial magnesium alloys is low, and the maximum extrusion speed for producing crack-free alloys is 0.6 mm / s or lower. To overcome the shortcomings of these industrial alloys, Mg-Bi-based alloys with high mechanical properties and excellent extrudability have been developed in recent years. The maximum solubility of Bi in Mg is as high as 8.9 wt%. Mg-Bi alloys can ensure excellent extrudability by forming thermally stable second phases. For example, a large amount of Mg-Bi phases will precipitate during the extrusion process in Mg-Bi-based alloys. By forming a large number of fine precipitates, the nucleation sites of the alloy can be increased, and by forming a fine recrystallized grain structure, the strength can be improved while ensuring high ductility.

[0004] Sn can form Mg2Sn with a high melting point (778 °C) with Mg. Adding Sn during extrusion is expected to improve the heat resistance of Mg-Bi alloys. In addition, by adding a small amount of Sn, the Mg-Bi phases existing during extrusion are refined, and the strength is increased through the Orowan strengthening mechanism.

[0005] Based on this alloy, higher tensile strength was obtained by adding a small amount of Mn. However, so far, the ultimate tensile strength of the extruded Mg-Bi-based alloy is still less than 250 MPa. Therefore, 1%-3% of Al can be added as an additive alloying element to improve the mechanical properties of the alloy and significantly improve its tensile ductility. Therefore, the purpose of this invention patent is to improve the mechanical properties of Mg-Bi alloy by adding alloying elements on the basis of the previous Mg-Bi-based alloy, in order to obtain a non-rare-earth low-cost magnesium alloy composition system with good mechanical properties. Summary of the Invention

[0006] Based on the deficiencies existing in the prior art, the purpose of the present invention is to provide a design of the alloy composition system and an extrusion forming process for a new non-rare-earth magnesium alloy profile suitable for rapid extrusion, and to significantly refine the grains by promoting the nucleation process during the recrystallization of the alloy. On the one hand, the reduction of grain size can effectively enhance the strengthening effect brought by the Hall-Petch effect; on the other hand, the increase in grain boundary density can significantly enhance the strengthening effect of grain boundaries hindering the movement of dislocations.

[0007] To achieve the above technical objectives, the technical solutions adopted by the present invention are as follows.

[0008] A Mg-Bi-based wrought magnesium alloy suitable for high-speed extrusion, characterized in that its components are in mass percentages: Bi: 4% - 6%, Al: 2 - 4%, Mn: 0.2 - 0.6%, and the balance is Mg and inevitable impurity elements.

[0009] Preferably, the wrought magnesium alloy further contains Sn element, wherein the percentage of Sn is: 0 - 1.5%.

[0010] Further optimized, Bi: 4% - 5%, Al: 2 - 3%, Mn: 0.2 - 0.3%, and the balance is Mg and inevitable impurity elements.

[0011] More perfectly, its components are in mass percentages: Bi: 5%, Al: 3%, Mn: 0.3%, and the balance is Mg and inevitable impurity elements.

[0012] An extrusion forming process for a new non-rare-earth Mg-Bi-based wrought magnesium alloy profile suitable for rapid extrusion, the steps of which are as follows. (a) Perform homogenization treatment on the target non-rare-earth magnesium alloy ingot; the homogenization temperature is 480 °C and the homogenization time is 12 h; (b) Perform primary extrusion forming on the alloy ingot after homogenization treatment and the as-cast magnesium alloy ingot to obtain an extruded forming rod with a diameter of 15; the extrusion temperature is 380 °C and the extrusion rate is 1 - 2 mm / s; (c) Isothermally age the extruded bar; the isothermal aging temperature is 180 °C, and the isothermal aging time varies from 40 to 70 h.

[0013] The beneficial effects brought by the alloy system and the forming technical solution of the present invention are as follows: As a new high-strength and low-cost magnesium alloy system, many fine Mg3Bi2 precipitates can be dynamically formed during the extrusion process. Due to the high thermal stability particles of Mg3Bi2 (melting point 823 °C) with high density inside, they will not melt and crack under high-speed extrusion, thus ensuring the high-speed extrusion production of the alloy. At the same time, the dynamically precipitated fine and high-thermal-stability Mg3Bi2 can also significantly refine the average grain size of the Mg-Bi alloy system and effectively improve the mechanical properties of the alloy; the addition of Al can achieve the "solution strengthening and plasticizing" effect and greatly improve the deformability of the alloy. At the same time, adding Sn can form a large number of fine and dense Mg2Sn phases. A large number of Mg2Sn phases are distributed in the form of short rods at the grain boundaries, and the precipitation of this second phase can play the role of refining the recrystallized grains. Description of the Drawings Figure 1 It is the tensile stress-strain curve of the extruded alloy profile in Example 4.

[0015] Figure 2 It is the scanning image of the solution-state ingot extruded alloy profile in Example 4. Specific Embodiments

[0016] Example 1 Take a Mg-5Bi-3Al-0.3Mn (wt.%) ingot, perform homogenization treatment at 480 °C for 12 h, and immediately quench it in warm water at 60 - 100 °C after the homogenization treatment. Keep the homogenized ingot and the original as-cast ingot at 380 °C for 15 - 25 min and then put them into the extrusion cylinder for extrusion. The extrusion equipment is an 1800T extrusion press, where the temperature of the extrusion cylinder is 400 °C, the die temperature is 420 °C, and the extrusion is carried out at a rate of 1.0 mm / s. After extrusion, quench it in cold water to obtain the extruded profile. Then isothermally age the extruded profile at 180 °C for 70 h.

[0017] Carry out room-temperature mechanical property tests on the alloy prepared in Example 1 of the present invention according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction is parallel to the extrusion direction, and the test results are listed in Table 1.

[0018] Example 2 Take an Mg-4Bi-2Al-0.2Mn (wt.%) ingot and adopt a homogenization treatment plan of 480ºC - 12h. Immediately after the homogenization treatment, quench it in warm water at 60 - 100ºC. After holding the homogenized ingot and the original as-cast ingot at 380ºC for 15 - 25 min, put them into the extrusion cylinder for extrusion. The extrusion equipment is an 1800T extrusion press, where the temperature of the extrusion cylinder is 400ºC, the die temperature is 420ºC, and the extrusion is carried out at a rate of 2.0 mm / s. After extrusion, quench it in cold water to obtain an extruded profile. Then, perform isothermal aging treatment on the extruded profile at 180ºC for a holding time of 70h.

[0019] According to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the room temperature mechanical properties of the alloy prepared in Example 2 of the present invention were tested. The tensile direction was parallel to the extrusion direction, and the test results are listed in Table 1.

[0020] Example 3 Take an Mg-6Bi-4Al-0.6Mn (wt.%) ingot and adopt a homogenization treatment plan of 480ºC - 12h. Immediately after the homogenization treatment, quench it in warm water at 60 - 100ºC. After holding the homogenized ingot and the original as-cast ingot at 380ºC for 15 - 25 min, put them into the extrusion cylinder for extrusion. The extrusion equipment is an 1800T vertical extrusion press, where the temperature of the extrusion cylinder is 400ºC, the die temperature is 420ºC, and the extrusion is carried out at a rate of 1.0 mm / s. After extrusion, quench it in cold water to obtain an extruded profile. Then, perform isothermal aging treatment on the extruded profile at 180ºC for a holding time of 70h.

[0021] According to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the room temperature mechanical properties of the alloy prepared in Example 3 of the present invention were tested. The tensile direction was parallel to the extrusion direction, and the test results are listed in Table 1.

[0022] Example 4 Take an Mg-5Bi-3Al-0.3Mn (wt.%) ingot and adopt a homogenization treatment plan of 480ºC - 12h. Immediately after the homogenization treatment, quench it in warm water at 60 - 100ºC. After holding the homogenized ingot and the original ingot at 350ºC for 15 - 25 min, put them into the extrusion cylinder for extrusion. The extrusion equipment is an 1800T extrusion press, where the temperature of the extrusion cylinder is 400ºC, the die temperature is 420ºC, and the extrusion is carried out at a rate of 1 mm / s. After extrusion, quench it in cold water to obtain an extruded profile. Then, perform isothermal aging treatment on the extruded profile at 180ºC for a holding time of 40h.

[0023] The room temperature mechanical properties of the alloy prepared in Example 4 of the present invention were tested according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction was parallel to the extrusion direction, and the test results are listed in Table 1.

[0024] Example 5 Take a Mg-5Bi-3Al-0.3Mn (wt.%) ingot and adopt a homogenization treatment plan of 480 °C - 12 h. Immediately after the homogenization treatment, quench it in warm water at 60 - 100 °C. After holding the homogenized ingot and the original ingot at 350 °C for 15 - 25 min, put them into the extrusion cylinder for extrusion. The extrusion equipment is an 1800T extrusion press, where the extrusion cylinder temperature is 400 °C, the die temperature is 420 °C, and the extrusion is carried out at a rate of 2 mm / s. After extrusion, quench it in cold water to obtain an extruded profile. Then, perform isothermal aging treatment on the extruded profile at 180 °C for 70 h.

[0025] The room temperature mechanical properties of the alloy prepared in Example 5 of the present invention were tested according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction was parallel to the extrusion direction, and the test results are listed in Table 1.

[0026] Example 6 Take a Mg-5Bi-3Al-0.3Mn-0.5Sn (wt.%) ingot and adopt a homogenization treatment plan of 480 °C - 12 h. Immediately after the homogenization treatment, quench it in warm water at 60 - 100 °C. After holding the homogenized ingot and the original ingot at 380 °C for 15 - 25 min, put them into the extrusion cylinder for extrusion. The extrusion equipment is an 1800T extrusion press, where the extrusion cylinder temperature is 400 °C, the die temperature is 420 °C, and the extrusion is carried out at a rate of 1 mm / s. After extrusion, quench it in cold water to obtain an extruded profile. Then, perform isothermal aging treatment on the extruded profile at 180 °C for 70 h.

[0027] The room temperature mechanical properties of the alloy prepared in Example 6 of the present invention were tested according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction was parallel to the extrusion direction, and the test results are listed in Table 1.

[0028] Example 7 Take an Mg-5Bi-3Al-0.3Mn-1.5Sn (wt.%) ingot and adopt a homogenization treatment plan of 480ºC for 12 h. Immediately after the homogenization treatment, quench it in warm water at 60 - 100ºC. Put the homogenized ingot and the original ingot into the extrusion cylinder for extrusion after holding at 380ºC for 15 - 25 min. The extrusion equipment is an 1800T extrusion press, where the temperature of the extrusion cylinder is 400ºC, the die temperature is 420ºC, and the extrusion is carried out at a rate of 2 mm / s. After extrusion, quench it in cold water to obtain an extruded profile. Then, perform isothermal aging treatment on the extruded profile at 180ºC for a holding time of 70 h.

[0029] According to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the room-temperature mechanical properties of the alloy prepared in Example 7 of the present invention were tested. The tensile direction was parallel to the extrusion direction, and the test results are listed in Table 1.

[0030] Table 1. Room-temperature mechanical properties of the alloys prepared in Examples 1 to 7 in the extrusion direction Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A Mg-Bi-based wrought magnesium alloy suitable for high-speed extrusion, characterized in that, The components are in mass percentages as follows: Bi: 4% - 6%, Al: 2 - 4%, Mn: 0.2 - 0.6%, and the balance is Mg and inevitable impurity elements.

2. The Mg-Bi-based wrought magnesium alloy applicable to high-speed extrusion according to claim 1, characterized in that, The wrought magnesium alloy further contains Sn element, wherein the percentage of Sn is 0 - 1.5%.

3. A Mg-Bi based wrought magnesium alloy suitable for high-speed extrusion according to claim 1, characterized in that, The components are in mass percentages as follows: Bi: 4% - 5%, Al: 2 - 3%, Mn: 0.2 - 0.3%, and the balance is Mg and inevitable impurity elements.

4. The Mg-Bi based wrought magnesium alloy applicable to high-speed extrusion according to claim 3, characterized in that, The components are in mass percentages as follows: Bi: 5%, Al: 3%, Mn: 0.3%, and the balance is Mg and inevitable impurity elements.

5. A Mg-Bi-based wrought magnesium alloy suitable for high-speed extrusion according to claim 1, characterized in that, The components are in mass percentages as follows: Bi: 6%, Al: 4%, Mn: 0.6%, and the balance is Mg and inevitable impurity elements.

6. The Mg-Bi based wrought magnesium alloy applicable to high-speed extrusion according to claim 1, wherein The components are in mass percentages as follows: Bi: 5%, Al: 3%, Mn: 0.3%, and the balance is Mg and inevitable impurity elements.

7. An Mg-Bi-based wrought magnesium alloy applicable to high-speed extrusion according to claim 6, characterized in that, The components are in mass percentages as follows: Bi: 5%, Al: 3%, Mn: 0.3%, Sn: 0.5 - 1.5%, and the balance is Mg and inevitable impurity elements.

8. The extrusion forming process of a high thermal stability particle-reinforced Mg-Bi series wrought magnesium alloy mentioned in any one of claims 1 - 7, the steps of which are as follows. (a) Homogenize the target non-rare-earth magnesium alloy ingot. (b) Extrude the alloy after homogenization once to obtain an extruded profile with a complex cross-sectional shape. (c) Perform isothermal aging treatment on the extruded profile.

9. The shaping process according to claim 8, characterized in that, In step a, the homogenization temperature is 480 °C and the homogenization time is 12 h; in step b, the extrusion temperature is 380 °C and the extrusion rate is 1 - 2 mm / s.

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