CN116516269A - Forming process of Mg-Gd-Zn alloy - Google Patents

Abstract

The invention discloses a forming process of Mg-Gd-Zn alloy, which mainly comprises the following steps: A. casting and machining to obtain a cuboid Mg-Gd-Zn alloy ingot blank with the cross section side length of 40-60mm and the length of 60-120 mm; B. homogenizing annealing treatment is carried out on the ingot blank, and the annealing process is as follows: after 15-40h of heat preservation at 495-525 ℃, placing the mixture at 450-480 ℃ for 3-10h of heat preservation, and then cooling the mixture to room temperature at a speed of 1-10 ℃/min; C. performing equal-diameter angular extrusion on the ingot blank subjected to the homogenizing annealing in a die with an angle of 90 degrees; before extrusion, heating the ingot blank and the mould to 300-400 ℃ respectively, and preserving heat for 1-3 hours; extruding the ingot blank along the length direction by using a hydraulic press, and co-extruding for 4-8 times, wherein the extrusion rate is 4-8mm/min; the surface temperature of the ingot blank is reduced by 20-50 ℃ in each pass of extrusion relative to the previous pass, and the surface temperature of the ingot blank is 140-200 ℃ when the extrusion is finished; D. quenching treatment is carried out immediately after extrusion is completed. By adopting the process, a large number of LPSO phase kink bands are formed in the prepared Mg-Gd-Zn alloy, so that the strength and the plasticity of the alloy are obviously improved synchronously, and the application range of the Mg-Gd-Zn component is widened.

Description

A Forming Process of Mg-Gd-Zn Alloy

technical field

The invention relates to the field of deformation processing of magnesium alloys, in particular to a plastic forming process of Mg-Gd-Zn alloys.

Background technique

As the lightest practical metal structural material at present, magnesium alloy has the advantages of low density, shock absorption and easy recycling, and is increasingly favored by aerospace, transportation and other fields. Among them, Mg-Gd-Zn alloys containing long-period ordered structure (LPSO) have excellent room temperature and high temperature strength, and have wider application potential than conventional AZ and ZK series magnesium alloys. However, compared with aluminum alloys and steel structural materials, there is still a big gap between the strength and plasticity of Mg-Gd-Zn alloys, especially in the process of improving the mechanical properties of conventional plastic forming processes. It is difficult to improve the strength and plasticity at the same time, which severely limits the application range of the alloy.

As a severe plastic deformation process, equal-diameter angular extrusion has the advantage of accumulating plastic strain without changing the initial shape of the billet. In recent years, it has been widely used in processing magnesium alloys to refine grains, accumulate dislocations, and improve strength. However, the conventional equal angular extrusion process often reduces the elongation while increasing the strength of the alloy. Therefore, there is an urgent need for a forming process that can simultaneously strengthen the plasticized Mg-Gd-Zn alloy to improve its comprehensive mechanical properties and expand its application range. The invention makes full use of the characteristics of the Mg-Gd-Zn alloy, through the close cooperation between the alloy composition, the uniform annealing system and the equal-diameter angular extrusion process, the synchronous and significant improvement of the alloy strength and plasticity is realized, and the magnesium containing LPSO phase The plastic forming and performance optimization of alloys have important guiding significance.

Contents of the invention

In order to simultaneously improve the strength and plasticity of the Mg-Gd-Zn alloy so that its comprehensive mechanical properties meet higher service requirements, the invention provides a forming process for the Mg-Gd-Zn alloy, and the specific technical scheme is as follows.

A forming process of Mg-Gd-Zn alloy mainly comprises the following steps:

A. Casting and machining a Mg-Gd-Zn alloy cuboid ingot with a side length of 40-60mm and a length of 60-120mm; the mass percentage of the alloy is Gd: 4.0-7.0%, Zn: 0.5-1.5 %, the rest are Mg and non-removable impurity elements;

B. Carry out homogenization annealing treatment to ingot;

C. Extrude the homogenized annealed ingot in a mold with an angle of 90°; before extrusion, heat the ingot and the mold to 300-400°C for 1-3 hours; take it out after the heat preservation The ingot is loaded into the mold, and the ingot is immediately extruded along the length direction with a hydraulic press, co-extruded for 4-8 passes; the mold and the sample are not heated in the middle, and the surface temperature of the ingot is controlled by natural cooling during each pass. 20-50°C lower than the previous pass;

D. Quenching immediately after extrusion, the water temperature is 20-40°C.

Preferably, in the step B, the homogenization annealing process is as follows: heat at 495-525°C for 15-40h, heat at 450-480°C for 3-10h, and then cool down to room temperature at a rate of 1-10°C/min.

Preferably, in the step C, the extrusion rate is 4-8 mm/min.

Preferably, in the step C, the surface temperature of the billet at the end of extrusion is 140-200°C.

Wherein, in the step C, during each pass of equal radial angle extrusion, the length direction of the ingot is reversed sequentially from the beginning to the end, and the sample does not rotate along the length direction.

Wherein, the room temperature yield strength of the member after quenching in the step D along the extrusion direction is ≥ 200 MPa, the tensile strength is ≥ 250 MPa, and the elongation after fracture is ≥ 10%.

In the above scheme, the purpose of homogenizing the rectangular parallelepiped ingot mainly includes the following aspects: holding at 495-525°C for 15-40h is to promote the dissolution of the eutectic structure in the as-cast alloy, so that the Gd and Zn atoms are transferred to the Mg Sufficient diffusion in the matrix provides sufficient solid-solution atoms for the subsequent precipitation of a large amount of LPSO phase in the α-Mg grains; in addition, it can make the microstructure of the ingot more uniform, eliminate casting residual stress, and improve its machinability. Insulation at 450-480°C for 3-10h can promote the uniform formation of stacking faults inside the α-Mg grains, so that Gd and Zn elements can fully gather near the stacking faults, providing a favorable place for the subsequent massive nucleation and growth of needle-like LPSO phases . Then it drops to room temperature at a rate of 1-10°C/min. On the one hand, the solid solubility of Gd and Zn elements decreases with the decrease of temperature, so that they can be precipitated at the stacking fault position in the form of LPSO phase; on the other hand, it prevents the temperature from falling too much Rapidly and significantly reduce the diffusion rate of solid-solution atoms, resulting in the severe inhibition of the precipitation of the LPSO phase. Through the homogenization treatment of this process, a dense needle-like LPSO phase is regulated inside the α-Mg grains of the Mg-Gd-Zn alloy, which lays the foundation for the subsequent extensive LPSO phase kink deformation.

With the initial temperature of 300-400°C, the equal-diameter angular extrusion with a cooling range of 20-50°C per pass can not only prevent the alloy from cracking due to too low temperature during the deformation process, but also inhibit the non-base surface slip of the alloy. shift. When the alloy undergoes 1-3 extrusions with head-to-tail rotation and no rotation along the length direction, the dense needle-like LPSO phase tends to be arranged in parallel in a specific direction, and this orientation also leads to the inhibition of LPSO phase basal slip. Subsequent extrusion of 4-8 passes prompts these acicular LPSO phases to undergo extensive kink deformation and form a large number of kink bands under the condition that the basal plane and non-basal plane slip are simultaneously suppressed, and these kink bands can hinder The dislocation movement hinders the expansion of microcracks, which can significantly improve the strength and elongation of the alloy at the same time. However, continuing to increase the number of extrusion passes will cause the LPSO phase to be broken and refined, and the kink band will also decrease or disappear. The strength of the alloy can be slightly increased, but the elongation is significantly reduced. Quenching treatment can maintain the structure after extrusion and prevent recrystallization during air cooling to destroy the kink band. Through the above forming process, a large number of LPSO phase kink bands are obtained, and the strength and plasticity of the Mg-Gd-Zn alloy are significantly improved simultaneously.

Description of drawings

Fig. 1 is the macrophotograph of equal-diameter angular extrusion finished product in embodiment 1;

Fig. 2 is the scanning electron microscope microstructure of uniform annealed state alloy in embodiment 1;

Fig. 3 is the scanning electron microscope microstructure of the equal diameter angular extrusion finished product in embodiment 1;

Fig. 4 is the scanning electron microscope microstructure of the equal diameter angular extrusion finished product in embodiment 2;

Fig. 5 is the scanning electron microscope microstructure of the equal-diameter angular extrusion finished product in Comparative Example 1;

Fig. 6 is the scanning electron microscope microstructure of the equal-diameter angular extrusion finished product in Comparative Example 2;

Fig. 7 is the scanning electron microscope microstructure of the equal-diameter angular extrusion finished product in Comparative Example 3;

Fig. 8 is the tensile stress-strain curve at room temperature of samples in Examples and Comparative Examples.

Detailed ways

In the present invention, a large number of comparative experiments have been done by adjusting the forming process parameters. Some examples are given below to further illustrate the present invention. These examples are used to illustrate the present invention, but not to limit the present invention. Improvements to the process of the present invention under the premise of the concept of the present invention all belong to the protection scope of the present invention.

Example 1

A cuboid ingot with a size of 60×60×120 mm is cast and machined, and the mass percentage content of the ingot is Mg-7.0Gd-0.5Zn. The homogenization annealing process is to hold at 525°C for 15 hours, then place at 480°C for 3 hours, and then cool down to room temperature at a rate of 10°C/min. The homogenized ingot is subjected to equal-diameter angular extrusion in a die with an angle of 90°. Before extrusion, heat the billet and mold to 400°C for 1 hour. After the heat preservation is over, take out the ingot and put it into the mold, and immediately use a hydraulic press to extrude the ingot along the length direction, and extrude 4 times in total. The rate is 8mm/min. The mold and the sample are not heated in the middle, and the surface temperature of the ingot is lowered by 50°C during each pass of extrusion by natural cooling, and the surface temperature of the billet is 200°C at the end of extrusion, and it is quenched in water at 25°C immediately After processing, the finished product is finally obtained as shown in Figure 1. The scanning photo of the homogenized annealed alloy is shown in Figure 2, the tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the stress-strain curve is shown in Figure 8. The scanned photo of the extruded product is shown in Figure 3, the tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the strain-strain curve is shown in Figure 8.

Example 2

A cuboid ingot with a size of 40×40×60 mm is cast and machined, and the mass percentage content of the ingot is Mg-4.0Gd-1.5Zn. The homogenization annealing process is to hold at 495°C for 40 hours, then place at 450°C for 10 hours, and then cool down to room temperature at a rate of 1°C/min. The homogenized ingot is subjected to equal-diameter angular extrusion in a die with an angle of 90°. Before extrusion, heat the billet and mold to 300°C for 3 hours. After the heat preservation is over, take out the ingot and put it into the mold, and immediately use a hydraulic press to extrude the ingot along the length direction, and extrude 8 times in total. The rate is 4 mm/min. The mold and sample are not heated in the middle, and the surface temperature of the ingot is lowered by 20°C during each pass of extrusion by natural cooling, and the surface temperature of the billet is 140°C at the end of extrusion, and it is quenched in water at 30°C immediately deal with. The scanned photo of the extruded product is shown in Figure 4, the tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the stress-strain curve is shown in Figure 8.

Example 3

A cuboid ingot with a size of 50×50×100 mm is cast and machined, and the mass percentage content of the ingot is Mg-5.7Gd-1.1Zn. The homogenization annealing process is to hold at 515°C for 25h, then place at 465°C for 7h, and then cool down to room temperature at a rate of 5°C/min. The homogenized ingot is subjected to equal-diameter angular extrusion in a die with an angle of 90°. Before extrusion, heat the billet and mold to 350°C for 2 hours. After the heat preservation is over, take out the ingot and put it into the mold, and immediately use a hydraulic press to extrude the ingot along the length direction, and extrude 6 times in total. The rate is 6 mm/min. The mold and sample are not heated in the middle, and the surface temperature of the ingot is lowered by 30°C during each pass of extrusion by natural cooling, and the surface temperature of the billet is 170°C at the end of extrusion, and it is quenched in water at 30°C immediately deal with. The tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the stress-strain curve is shown in Figure 8.

Comparative example 1

A cuboid ingot with a size of 60×60×120 mm is cast and machined, and the mass percentage content of the ingot is Mg-7.0Gd-0.5Zn. The homogenization annealing process is to hold at 525°C for 15 hours and then air cool to room temperature. The homogenized ingot is subjected to equal-diameter angular extrusion in a die with an angle of 90°. Before extrusion, heat the billet and mold to 400°C for 1 hour. After the heat preservation is over, take out the ingot and put it into the mold, and immediately use a hydraulic press to extrude the ingot along the length direction, and extrude 4 times in total. The rate is 8mm/min. The mold and the sample are not heated in the middle, and the surface temperature of the ingot is lowered by 50°C during each pass of extrusion by natural cooling, and the surface temperature of the billet is 200°C at the end of extrusion, and it is quenched in water at 25°C immediately deal with. The scanned photo of the extruded product is shown in Figure 5, the tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the stress-strain curve is shown in Figure 8.

Comparative example 2

A cuboid ingot with a size of 60×60×120 mm is cast and machined, and the mass percentage content of the ingot is Mg-7.0Gd-0.5Zn. The homogenization annealing process is to hold at 525°C for 15 hours, then place at 480°C for 3 hours, and then cool down to room temperature at a rate of 10°C/min. The homogenized ingot is subjected to equal-diameter angular extrusion in a die with an angle of 90°. Before extrusion, heat the billet and mold to 450°C for 1 hour. After the heat preservation is over, take out the ingot and put it into the mold, and immediately use a hydraulic press to extrude the ingot along the length direction, and extrude 4 times in total. The rate is 8mm/min. The mold and sample are not heated in the middle, and the surface temperature of the ingot is lowered by 50°C during each pass of extrusion by natural cooling, and the surface temperature of the billet is 250°C at the end of extrusion, and quenched in water at 25°C immediately deal with. The scanned photo of the extruded product is shown in Figure 6, the tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the stress-strain curve is shown in Figure 8.

Comparative example 3

A cuboid ingot with a size of 40×40×60 mm is cast and machined, and the mass percentage content of the ingot is Mg-4.0Gd-1.5Zn. The homogenization annealing process is to hold at 495°C for 40 hours, then place at 450°C for 10 hours, and then cool down to room temperature at a rate of 1°C/min. The homogenized ingot is subjected to equal-diameter angular extrusion in a die with an angle of 90°. Before extrusion, heat the billet and mold to 300°C for 3 hours. After the heat preservation is over, take out the ingot and put it into the mold, and immediately use a hydraulic press to extrude the ingot along the length direction, and extrude 10 times in total. The rate is 4 mm/min. The mold and sample are not heated in the middle, and the surface temperature of the ingot is lowered by 20°C during each pass of extrusion by natural cooling, and the surface temperature of the billet is 100°C at the end of extrusion, and it is quenched in water at 30°C immediately deal with. The scanned photo of the extruded product is shown in Figure 7, the tensile mechanical properties at room temperature along the length direction are listed in Table 1, and the stress-strain curve is shown in Figure 8.

Mechanical properties of magnesium alloy members in the embodiment and comparative examples in table 1

It can be seen from Fig. 2 that dense acicular LPSO phases appear in the Mg-Gd-Zn alloy after homogenization annealing in the process of the present invention. It can be seen from Figures 3 and 4 that a large number of twisted bands are formed in the equal diameter angular extrusion products in Examples 1 and 2. At the same time, it can be seen from Table 1 and Figure 8 that the enhanced plasticizing effect of the Mg-Gd-Zn alloy ESA components of Examples 1 and 2 is significantly better than that of Comparative Examples 1-3.

Combining Figure 3 and Figure 5, by comparing Example 1 and Comparative Example 1, it is found that if the homogenization annealing process described in the present invention is not adopted, even if the subsequent equal-diameter angular extrusion process is the same, a large number of kink bands cannot be obtained, resulting in an increase in the strength of the alloy. And the effect of improving plasticity is poor. Combining Figure 3 and Figure 6, by comparing Example 1 and Comparative Example 2, it is found that the holding temperature of the ingot and the mold is too high, which promotes the dynamic recrystallization of the alloy and the dissolution of the LPSO phase, resulting in a sharp decrease in the number of kink bands. As a result, the strength of the alloy is significantly reduced, while the elongation is slightly increased relative to the homogenized state. Combining Figure 4 and Figure 7, by comparing Example 2 and Comparative Example 3, it is found that the increase in the number of extrusion passes and the decrease in the final temperature lead to an increase in the degree of fragmentation and dissolution of the LPSO phase in the sample, grain refinement, and kink bands. If the number is reduced, although the effect of improving the strength is better, the elongation drops sharply, which cannot play the role of synchronous reinforcement and plasticization, and the comprehensive mechanical properties of the alloy are not as good as those of the examples.

The embodiments of the present invention have been described above with reference to the accompanying drawings, and the embodiments and features in the embodiments of the present invention can be combined with each other if there is no conflict. The present invention is not limited to the above specific implementation, the above specific implementation is only illustrative, rather than limiting, those skilled in the art under the enlightenment of the present invention, without departing from the purpose and rights of the present invention In the case of requiring the scope of protection, many forms can also be made, and these all belong to the scope of protection of the present invention.

Claims (7)

1. a forming process of Mg-Gd-Zn alloy, is characterized in that, mainly comprises the following steps: A. Casting and machining a Mg-Gd-Zn alloy cuboid ingot with a side length of 40-60mm and a length of 60-120mm; the mass percentage of the alloy is Gd: 4.0-7.0%, Zn: 0.5-1.5 %, the rest are Mg and non-removable impurity elements; B. Carry out homogenization annealing treatment to ingot; C. Extrude the homogenized annealed ingot in a mold with an angle of 90°; before extrusion, heat the ingot and the mold to 300-400°C for 1-3 hours; take it out after the heat preservation The ingot is loaded into the mold, and the ingot is immediately extruded along the length direction with a hydraulic press, co-extruded for 4-8 passes; the surface temperature of the billet is reduced by 20-20% compared with the previous pass through natural cooling control. 50°C; D. Quenching treatment immediately after extrusion. 2. The forming process of a Mg-Gd-Zn alloy according to claim 1, characterized in that: in the step B, the homogenization annealing process is: after holding at 495-525°C for 15-40h, place it at 450 Incubate at -480°C for 3-10h, then cool down to room temperature at a rate of 1-10°C/min. 3. The forming process of a Mg-Gd-Zn alloy according to claim 1, characterized in that: in the step C, the extrusion rate is 4-8 mm/min. 4. The forming process of a Mg-Gd-Zn alloy according to claim 1, characterized in that: in the step C, the surface temperature of the billet at the end of extrusion is 140-200°C. 5. The forming process of a Mg-Gd-Zn alloy according to claim 1, characterized in that: in the step C, the length direction of the ingot is reversed sequentially from the beginning to the end during each pass of equal diameter angular extrusion, and the sample Does not rotate along length. 6. The forming process of a Mg-Gd-Zn alloy according to claim 1, characterized in that: in the step D, the water temperature for the quenching treatment is 20-40°C. 7. The forming process of a Mg-Gd-Zn alloy according to claim 1, characterized in that: in the step D, the room temperature yield strength of the member after quenching along the extrusion direction is ≥200MPa, the tensile strength is ≥250MPa, Elongation after breaking ≥ 10%.