CN108330366A - A kind of self-reinforcing toughening magnesium alloy and preparation method thereof - Google Patents

Abstract

The invention discloses a self-reinforcing and toughening magnesium alloy and a preparation method thereof. The chemical composition of the alloy is Mg-aAl-bZn-cY-dNd wt%. solid solution, etc. During preparation, the ingot is firstly preheated to 225-325°C and kept warm for 20-30 minutes; then the preheated ingot is extruded by an extruder; finally, the extruded profile is subjected to aging heat treatment to obtain The final deformed alloy. This preparation process can refine and disperse the self-generated crystallization strengthening phase in the alloy under the action of extrusion shearing in the matrix to achieve self-reinforcement and toughening; compared with the alloy prepared by traditional extrusion, the product production is significantly simplified The process flow increases the tensile strength by about 38%, and the yield strength increases by about 24%, realizing the low-cost preparation of magnesium alloys with excellent comprehensive properties.

Description

A kind of self-reinforcing and toughening magnesium alloy and preparation method thereof

technical field

The invention belongs to the technical field of magnesium alloys, and in particular relates to a self-reinforcing and toughening magnesium alloy and a preparation method thereof.

Background technique

As the lightest metal material, magnesium alloy has been widely used in many lightweight design and manufacturing fields, ranging from communication product shells, car/bicycle hubs, door inner guards, to high-speed train parts, drones, and satellites. structure etc. With the continuous expansion of the application of magnesium alloy materials, the requirements of different products for the comprehensive mechanical properties of magnesium alloys are also increasing. The realization of low-cost preparation of magnesium alloy materials with excellent comprehensive mechanical properties will help to further broaden the application of magnesium alloy materials.

Magnesium alloy ingots are generally obtained by non-equilibrium solidification. At present, commercial magnesium alloys generally homogenize the ingots before extrusion. For example, when performing conventional extrusion on Mg-8Al-0.5Zn (AZ80) magnesium alloy, the AZ80 magnesium alloy ingot should be homogenized at 400-420℃/8-24h to eliminate casting defects such as segregation and shrinkage cavity. At the same time, the dissociated eutectic structure (Fig. 1(a)) produced in the solidification process disappeared completely, and most of the β-Mg ₁₇ Al ₁₂ crystalline phase dissolved back into the α-Mg matrix, finally obtaining the “α-Mg solid solution + A small amount of β-Mg ₁₇ A _l2 precipitated phase" structure (Fig. 1(b)). Subsequent conventional extrusion and aging heat treatment can obtain medium-strength magnesium alloy profiles. However, the tensile strength of the AZ80 wrought magnesium alloy obtained through this processing route generally does not exceed 380MPa, and the elongation is generally 12-16%, and the elongation decreases after aging heat treatment.

Contents of the invention

In view of the above prior art, the present invention provides a self-reinforcing and toughening magnesium alloy and its preparation method to solve the problems of low strength of magnesium alloy after conventional extrusion and obvious decrease of elongation after aging strengthening.

In order to achieve the above object, the technical solution adopted in the present invention is to provide a self-reinforcing and toughening magnesium alloy and a preparation method thereof. The chemical composition of the alloy is: Mg-aAl-bZn-cY-dNd wt%, wherein: 6≤a≤8, 0.5≤b≤1, 0≤c≤0.2, 0≤d≤0.2; the alloy includes the following volume fractions organize:

Self-generated crystal strengthening phase 8-15vol%;

Nano dynamic precipitated phase 1~2vol%;

The balance is α-Mg solid solution;

Among them, the authigenic crystallization strengthening phase is the eutectic reinforcement β-Mg _{17 Al2} and/or the Laves phase reinforcement, and the Laves phase reinforcement is Al ₂ Y or Al ₂ Nd; the nano dynamic precipitation phase is β-Mg ₁₇ Al ₂ . The grain size of the alloy is 5-10 μm, the equivalent diameter of the self-generated crystal strengthening phase is 1-3 μm, and the diameter of the dynamic precipitated phase is 200-800 nm.

The preparation method of self-reinforcing and toughening magnesium alloy in the present invention comprises the following steps:

(1) Quickly preheat the ingot to 225-325°C and keep it warm for 20-30 minutes;

(2) Use an extruder to extrude the preheated ingot; the extrusion ratio is 30 to 35, and the extrusion rod advances at a speed of 0.5 to 1mm/s during the extrusion process. The load corresponding to 50% to 70% of the yield strength of the material at temperature is used as the traction force;

(3) Perform aging heat treatment on the extruded profile to obtain the final extruded alloy.

Wherein, the ingot in the step (1) is AZ61, AZ80 or AZ91 modified with a small amount of rare earth, wherein the rare earth content is 0-0.2wt%.

Step (1) The ingot is preheated by using an electromagnetic induction heating system, and the preheating power is 30-60kW.

In step (2), the temperature of the extruding barrel in the extruder is 200-300°C.

The beneficial effects of the present invention are:

1. Make full use of the self-generated crystallization strengthening phase in the non-equilibrium solidification structure of the ingot, and through the design of the extrusion process, a large number of self-generated crystallization strengthening phases are genetically retained, effectively increasing the dynamic recrystallization nucleation and inhibiting the growth of recrystallization grains, and the extrusion structure is obvious Uniform refinement. At the same time, there are 200-800nm nanometer dynamic precipitation phases in the grain boundary, which realizes multiple types of time series (crystallization phase during solidification and dynamic precipitation phase during extrusion), multi-scale (micron crystallization phase and nanoscale precipitation phase) composite self-generated strengthening, combined with subsequent heat treatment process , can increase the tensile strength of the magnesium alloy by 30-50%, and the yield strength by 20-30%, significantly improving the comprehensive mechanical properties of existing extruded profiles, and realizing in-situ strengthening and toughening.

2. Using the electromagnetic induction heating system to preheat the ingot, the ingot can be quickly heated through to prevent the self-generated crystal strengthening phase from melting back into the matrix, so as to ensure the self-generated strengthening phase with the designed volume content. In addition, the electromagnetic induction heating system simplifies the pretreatment process of magnesium alloy extrusion processing, shortens the processing cycle, and can operate continuously, which is beneficial to the preparation of low-cost and high-performance magnesium alloys.

3. Strong compatibility with the existing extrusion process, the forming size and production efficiency are significantly higher than the previous special extrusion (reciprocating extrusion, pre-aging before extrusion, low temperature and slow extrusion, equal channel extrusion, etc.), which is conducive to upgrading , At the same time, it is easy to prepare multi-specification products.

4. The self-reinforcement and toughening method designed and used in the present invention is not only applicable to magnesium alloys with crystallization strengthening phases, but also applicable to other extruded alloys such as aluminum alloys, titanium alloys, and steels that have similar characteristics of self-generated crystallization strengthening phases.

Description of drawings

Figure 1 is a comparison diagram of conventional extrusion and self-generated strengthening and toughening extrusion structure under the same extrusion conditions of ZA80 magnesium alloy;

Among them, (a) is the optical picture of the as-cast microstructure of AZ80 before extrusion;

(b) is the scanning electron microscope picture of AZ80 conventional extrusion state tissue;

(c) is a scanning electron microscope picture of AZ80 in situ self-generated strengthening and toughening extrusion state tissue;

(d) and (e) are the shell structure characteristics of the inherited β crystal phase and the high-magnification scanning electron microscope topography of the dynamically precipitated β phase in the extruded structure of the present invention, respectively.

Detailed ways

The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. In the preparation process, the ingot used is a heat-treatable magnesium alloy such as AZ61, AZ80 or AZ91 modified with a small amount of rare earth, and the rare earth content is 0-0.2 wt%. For the convenience of explaining the problem, the embodiments of the present invention all take the AZ80 series alloy as an example.

Embodiment one

Taking the heat treatable strengthened magnesium alloy AZ80 as an example, the characteristics and implementation process of the method of the present invention are described.

(1) Put the AZ80 ingots with a diameter of 90mm into the electromagnetic induction heating furnace in turn, the electromagnetic induction heating power is 30-60kW, and the frequency is about 1000Hz. At the same time, the temperature is constantly monitored by the contact type K-type thermocouple, and the parameters of the electromagnetic induction heating furnace are adjusted to ensure that the temperature of the ingot reaches about 250°C, and the heating time is 30 minutes to ensure the β crystal phase in the divorced eutectic structure under the premise of AZ80 ingot heat penetration. Can be retained in large quantities, effectively shortening the pre-extrusion processing time. Put the extrusion die with a diameter of 16mm into a resistance heating furnace and heat it for standby. The heating temperature is 400°C, and the heating time is 4-6 hours.

(2) After the temperature of the extrusion die and the extrusion cylinder reaches the preset conditions, the AZ80 ingot that has reached the preset temperature is fed to the extrusion cylinder through the pneumatic push rod in the electromagnetic induction heating furnace, and the extrusion ratio is controlled to be about 32 . During the extrusion process, the advancing speed of the extrusion rod is kept at about 0.5mm/s. At the same time, the 16mm extruded bar is pulled by a tractor at the exit of the extrusion material. The traction force is equal to the load corresponding to the yield strength of the material at the exit temperature. 50%.

(3) Air-cool the extruded 16mm extruded bar to room temperature, set the temperature of the blast heating furnace to 170°C, and cut off a fixed-length (about 1.0m) AZ80 extruded bar sample and put it into the drum In the air heating furnace, keep warm for 20 hours, then take it out and air cool.

Embodiment two

Taking the heat-treatable and strengthened magnesium alloy AZ80+0.2Y (rare earth Y content is 0.2wt%) as an example, the characteristics and implementation process of the method of the present invention are described.

(1) Put AZ80+0.2Y ingots with a diameter of 90mm into the electromagnetic induction heating furnace in turn, the electromagnetic induction heating power is 30-60kW, and the frequency is about 1000Hz. At the same time, the temperature is constantly monitored by the contact K-type thermocouple, and the parameters of the induction heating furnace are adjusted so that the temperature of the ingot is at 300°C, and the heating time is 20 minutes. A large amount of phase is retained, which effectively shortens the pre-extrusion treatment time. Put the extrusion die with a diameter of 16mm into a resistance heating furnace in advance to heat for standby, the heating temperature is 400°C, and the heating time is 4-6 hours; at the same time, set the temperature of the extrusion barrel of the extruder to 300-320°C, and heat up for standby.

(2) After the temperature of the extrusion die and extrusion cylinder reaches the preset conditions, the AZ80+0.2Y ingot that has reached the preset temperature is fed to the extrusion cylinder through the pneumatic push rod in the electromagnetic induction heating furnace to control the extrusion ratio About 32. During the extrusion process, the advancing speed of the extrusion rod of the extruder is kept at about 1mm/s. At the same time, the 16mm extruded bar is pulled by a tractor at the exit of the extruded material. The traction force is equal to the yield strength of the material at the exit temperature. 50% of the load.

(3) Air-cool the extruded 16mm extruded bar to room temperature, set the temperature of the blast heating furnace to 220°C, and cut off the fixed-length (about 1.0m) AZ80+0.2Y extruded bar sample Put it in the blast heating furnace, keep it warm for 15 hours, then take it out and let it cool in air.

Embodiment three

Taking the heat-treatable strengthened magnesium alloy AZ80+0.1Y+0.1Nd (rare earth Y content is 0.1 wt%, rare earth Nd content is 0.1 wt%) as an example, the characteristics and implementation process of the method of the present invention are described.

(1) Put AZ80+0.1Y+0.1Nd ingots with a diameter of 90mm into the electromagnetic induction heating furnace in turn, the electromagnetic induction heating power is 30-60kW, and the frequency is about 1000Hz. At the same time, the temperature is constantly monitored by the contact type K-type thermocouple, and the parameters of the induction heating furnace are adjusted to ensure that the ingot temperature is 300°C, and the heating time is 30 minutes, so as to ensure the divorced eutectic under the premise of AZ80+0.1Y+0.1Nd ingot heat penetration. The β crystal phase in the tissue can be retained in a large amount, effectively shortening the processing time before extrusion. Put the extrusion die with a diameter of 16mm into a resistance heating furnace in advance to heat for standby, the heating temperature is 400°C, and the heating time is 4-6 hours; at the same time, set the temperature of the extrusion barrel of the extruder to 300-320°C, and heat up for standby.

(2) After the temperature of the extrusion die and the extrusion cylinder reaches the preset conditions, the AZ80+0.1Y+0.1Nd ingot that has reached the preset temperature is automatically fed to the extrusion cylinder through the pneumatic push rod of the electromagnetic induction heating furnace, Control the squeeze ratio to about 32. During the extrusion process, the advancing speed of the extrusion rod of the extruder is kept at 1mm/s, and at the same time, the 16mm extruded bar is pulled by a tractor at the exit of the extruded material, and the traction force is equal to the material yield strength at the exit temperature. 70% of the load.

(3) Air-cool the extruded 16mm extruded bar to room temperature, set the temperature of the blast heating furnace to 220°C, and cut off the fixed length (about 1.0m) AZ80+0.1Y+0.1Nd extrusion The bar sample was placed in a blast heating furnace and kept warm for 30 hours. Then remove and air cool.

comparative example

(1) Put AZ80 ingots with a diameter of 90 mm into the resistance heating furnace for homogenization treatment in sequence, adjust the parameters of the heating furnace so that the temperature of the ingot is at 420 ° C, and the heating time is 10 to 20 hours to eliminate segregation, shrinkage cavity, etc. Casting defects; at the same time, the divorced eutectic structure (Fig. 1(a)) _produced during _the casting solidification process (Fig. -Mg solid solution + a small amount of β-Mg ₁₇ A _l2 precipitated phase". Put the extrusion die of the 16mm diameter rod into a resistance heating furnace in advance to heat for standby, the heating temperature is 400°C, and the heating time is 4-6 hours; at the same time, set the temperature of the extrusion barrel of the extruder to 300-320°C, and heat up for standby.

(2) Perform conventional extrusion treatment on the AZ80 ingot after homogenization treatment; the advancing speed of the extrusion rod of the extruder is kept at 1mm/s, and at the same time, the 16mm extruded rod is pulled by a tractor at the exit of the extruded material , the magnitude of the traction force is 50% of the yield strength of the material at the outlet temperature. The microstructure of the alloy after extrusion is shown in Fig. 1(b).

(3) Air-cool the extruded 16mm extruded bar to room temperature, set the temperature of the blast heating furnace to 170°C, and cut off a fixed-length (about 1.0m) AZ80 extruded bar sample and put it into the drum In the wind heating furnace, keep warm for 20 hours. Then take out the air-cooled, regular extruded AZ80 product.

Result analysis

Table 1 provided the components and contents of the products in each group of examples.

Table 1 product components and content (wt%)

Mg Al Zn Y Nd other Embodiment one 91.5 7.8 0.6 / / 0.1 Embodiment two 91.4 7.8 0.5 0.2 / 0.1 Embodiment three 91.3 7.8 0.6 0.1 0.1 0.1 comparative example 91.4 8.0 0.5 / / 0.1

In order to facilitate the description of the composition of the alloy, the self-reinforcing and toughening magnesium alloy is expressed in the following form among the present invention:

Mg-aAl-bZn-cY-dNd wt%

According to the data in Table 1, 6≤a≤8, 0.5≤b≤1, 0≤c≤0.2, 0≤d≤0.2.

The composition of the alloy in Example 1 is: Mg-7.8Al-0.6Zn;

The composition of the alloy in Example 2 is: Mg-7.8Al-0.5Zn-0.2Y;

The composition of the alloy in Example 3 is: Mg-7.8Al-0.6Zn-0.1Y-0.1Nd.

Table 2 provided the metallographic structure and volume fraction of the products in each group of examples.

Table 2 Product metallographic structure and its volume fraction (vol%)

Table 3 shows the tensile strength (MPa), yield strength (MPa) and elongation (%) of the products in each group of examples.

The mechanical property parameter of table 3 product

Tensile strength (MPa) Yield strength (MPa) Elongation (%) Embodiment one 421 302 16 Embodiment two 433 309 14 Embodiment three 448 319 13 comparative example 340 220 14

As can be seen from Table 3, compared with the magnesium alloy prepared by the conventional extrusion method, the tensile strength of the magnesium alloy prepared by the method of the present invention is increased by more than 30%, and the yield strength is improved by more than 20%. The elongation remains basically unchanged. This is because the ingot is heated by electromagnetic induction for 20-30 minutes before extrusion, and the ingot is quickly preheated to the extrusion temperature of 225-325°C. This temperature is not only conducive to the realization of conventional extrusion, but also more important It is much lower than the melting point temperature of the β-Mg ₁₇ A _l2 crystal phase in the divorced eutectic structure (about 437 ° C), so during the extrusion process, a large amount of β-Mg ₁₇ A _l2 crystal phase will be retained, and in the extrusion During the extrusion process, it is crushed and dispersed in the deformed magnesium alloy material due to extrusion and shearing, and finally the extruded structure is "α-Mg solid solution + a large amount of β-Mg ₁₇ A _l2 crystal phase (or Laves phase) + a small amount of Nano-sized β-Mg ₁₇ A _l2 precipitated phase" (Fig. 1(c)), which achieves the strengthening effect of dispersed particles similar to composite materials, and realizes self-generated reinforcement and toughening, but there is no reinforcement particles outside the alloy system. Composite joining, this is the difference from composite materials. At the same time, through the extrusion process of the present invention, casting defects such as segregation and shrinkage cavities in the original ingot can be eliminated in the process of extrusion shear flow, and the structure after extrusion is uniform (Fig. 1(c)). Furthermore, the alloy material designed in the present invention also includes AZ80 magnesium alloy with 0.1 to 0.2wt% rare earth elements (yttrium (Y), niobium (Nd), etc.) The high melting point Laves phase (such as Al ₂ Y, Al ₂ Nd) provides more in-situ crystallization strengthening phases for the subsequent strengthening and toughening of magnesium alloys modified with trace amounts of rare earths. Finally, through the electromagnetic induction preheating process before extrusion and subsequent aging heat treatment similar to the above-mentioned AZ80, the magnesium alloy profile with self-reinforcing and toughening effect can also be obtained.

Comparing Figure 1(b) and Figure 1(c), it can be found that under the premise of the same settings of extrusion barrel temperature, extrusion ratio, extrusion die temperature, extrusion speed, and extrusion billet temperature, the homogenized AZ80 The grain size of the extruded magnesium alloy profile is 20-30 μm, and only a small amount of second phase is dynamically precipitated at the grain boundary. The tensile strength is 340-360MPa, the yield strength is 220-250MPa, and the elongation is 12-16%. For the AZ80 magnesium alloy extruded profile designed by in-situ self-generated toughening in the present invention, the grain size is obviously refined, and the grain size 5-10 μm, the volume content of self-generated crystal strengthening phase is 10-15%, and it is distributed in the grain boundary and in the grain at the same time, effectively inhibiting the growth of recrystallized grains during the extrusion process. At the same time, there are 200-800nm dynamic precipitates at the grain boundary (Figure 1(e)), which realizes time-sequence multi-type (crystal phase during solidification and dynamic precipitate phase during extrusion), multi-scale (micro crystal phase and nano-precipitate phase) composite autogenous reinforcement. The tensile strength is 420-450MPa, the yield strength is 300-320MPa, and the elongation is 12-16%. The comprehensive mechanical properties are significantly improved, and self-reinforcement and toughening are realized. Also for AZ80+0.2Y, AZ80+0.1Y+0.1Nd and other trace rare earth modified magnesium alloys, due to the presence of eutectic reinforcement β-Mg _{17 Al2} or Laves phase reinforcement Al ₂ Y, Al ₂ Nd, its There are more types of crystal strengthening phases, similar to AZ80 magnesium alloy, which can also achieve self-reinforcing and toughening effects.

Based on the above principles, the self-reinforcement and toughening method designed and used in the present invention is not only applicable to magnesium alloys with self-generated crystallization strengthening phases, but also applicable to other extruded profiles such as aluminum alloys, titanium alloys, and steels with similar characteristics of self-generated crystallization strengthening phases .

Although the specific implementation of the present invention has been described in detail, it should not be construed as limiting the protection scope of this patent. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative efforts still belong to the protection scope of this patent.

Claims (7)

1. a kind of self-reinforcing toughening magnesium alloy, characterized in that chemical composition is Mg-aAl-bZn-cY-dNd wt%, wherein：6≤ A≤8,0.5≤b≤1,0≤c≤0.2,0≤d≤0.2；The alloy includes the tissue of following volumes score：

8~15vol% of spontaneous crystallization hardening constituent；

1~2vol% of nanometer Dynamic Precipitation phase；

Surplus is α-Mg solid solution；

Wherein, spontaneous crystallization hardening constituent is eutectic reinforcement β-Mg₁₇A_l2And/or Laves phase reinforcements, the Laves phases enhance Body is Al₂Y and/or Al₂Nd；Nanometer Dynamic Precipitation is mutually β-Mg₁₇A_l2。

2. self-reinforcing toughening magnesium alloy according to claim 1, it is characterized in that：Alloy grain size is 5~10 μm, spontaneous The equivalent diameter for crystallizing hardening constituent is 1~3 μm, a diameter of 200~800nm of nanometer Dynamic Precipitation phase.

3. the method for preparing self-reinforcing toughening magnesium alloy as described in claim 1, characterized in that include the following steps：

(1) by ingot casting rapidly pre-warming to 225~325 DEG C, 20~30min is kept the temperature；

(2) extrusion process is carried out to the ingot casting after preheating using extruder；Extrusion ratio is 30~35, and pressure ram pushes away in extrusion process It is 0.5~1mm/s into speed, while to 50%~70% corresponding load of material yield strength at a temperature of extrudate application outlet Lotus is as tractive force；

(3) aging strengthening model is carried out to the proximate matter after extruding, obtains final extruded alloy.

4. preparation method according to claim 3, it is characterized in that：In step (1) ingot casting be trace rare-earth be modified AZ61, AZ80 or AZ91, Rare-Earth Content are 0~0.2wt%.

5. preparation method according to claim 3, it is characterized in that：Step (1) is using electromagnetic induction heating system to ingot casting It is preheated, warm-up power is 30~60kW.

6. preparation method according to claim 3, it is characterized in that：In step (2) temperature of extruder extrusion cylinder be 200~ 300℃。

7. preparation method according to claim 3, characterized in that aging heat treatment method is in step (3)：It will squeeze Proximate matter afterwards is air-cooled to room temperature, then under the conditions of 170~220 DEG C keep the temperature 10~30h, further take out it is air-cooled, obtain finally squeeze close Gold.