Heating and cooling circulation heat treatment method near primary precipitation phase initial melting temperature of cast alloy

文档序号:1872111 发布日期:2021-11-23 浏览:17次 中文

阅读说明:本技术 铸造合金一次析出相初熔温度附近的升温、降温循环热处理方法 (Heating and cooling circulation heat treatment method near primary precipitation phase initial melting temperature of cast alloy ) 是由 王渠东 雷川 魏杰 于 2021-08-18 设计创作,主要内容包括:本发明提供了一种铸造合金一次析出相初熔温度附近的升温、降温循环热处理方法,将铸造合金在其一次析出相初熔温度附近进行循环升温、降温处理。利用一次析出相与合金基体的界面能量较高,且一次析出相越尖锐的部位界面能量越高,越易发生初熔的特点,将合金加热至超过一次析出相初熔温度,使一次析出相发生初熔,然后降温使初熔后的一次析出相凝固钝化,并采用循环升降温处理使一次析出相反复经历初熔-凝固钝化过程;使铸造合金中一次析出相从粗大的块状、片状、尖锐的长针状等形貌变得钝化、圆润细小,解决了普通热处理加热温度低于固相线温度,难以改善因一次析出相粗大、尖锐而导致的合金塑性低等缺点,同时优化组织和提高合金性能。(The invention provides a heating and cooling cyclic heat treatment method for a cast alloy near the primary precipitated phase primary melting temperature, which is used for carrying out cyclic heating and cooling treatment on the cast alloy near the primary precipitated phase primary melting temperature. By utilizing the characteristics that the interface energy of a primary precipitated phase and an alloy matrix is higher, and the interface energy of a part with a sharper primary precipitated phase is higher and primary melting is more likely to occur, the alloy is heated to a temperature higher than the primary melting temperature of the primary precipitated phase, so that the primary precipitated phase is subjected to primary melting, then the temperature is reduced to solidify and passivate the primary precipitated phase after primary melting, and the primary precipitated phase is subjected to primary melting-solidification and passivation processes again by adopting cyclic heating and cooling treatment; the primary precipitated phase in the cast alloy is passivated, rounded and fine from the shapes of thick blocks, sheets, sharp long needles and the like, the defects that the heating temperature of common heat treatment is lower than the solidus temperature, the plasticity of the alloy is low and the like caused by thick and sharp primary precipitated phases are difficult to improve are overcome, and meanwhile, the structure is optimized and the alloy performance is improved.)

1. The heating and cooling circulation heat treatment method of the cast alloy near the primary precipitation phase initial melting temperature is characterized in that: setting the heating temperature of the alloy to be higher than the primary melting temperature of the primary precipitated phase to enable the primary precipitated phase to be subjected to primary melting by utilizing the characteristics that the interface energy of the primary precipitated phase and the alloy matrix is higher, and the interface energy of the part with the sharper primary precipitated phase is higher and the primary melting is easier to occur, and then adopting cooling treatment to solidify and passivate the primary precipitated phase after the primary melting; and the alloy is cooled to the temperature required by the subsequent process by adopting the circulating heating and cooling treatment, and utilizing the principle that the sharp part in the primary precipitated phase is firstly subjected to primary melting during heating and is solidified and passivated during cooling to ensure that the primary precipitated phase is reversely subjected to the primary melting-solidification passivation process.

2. The method for cyclic heat treatment of a cast alloy according to claim 1, wherein the method comprises the steps of: the method specifically comprises the following steps:

(1) heating the alloy to be heat-treated to a temperature a ℃ above the primary melting temperature of the primary precipitated phase, and preserving the heat at the temperature for a period of time t1 to ensure that the primary precipitated phase is subjected to primary melting;

(2) cooling the alloy subjected to primary melting in the step (1) to b ℃ below the primary melting temperature of a primary precipitated phase of the alloy, and preserving the heat at the temperature for a period of time t2 to enable the primary precipitated phase after primary melting to be solidified and passivated;

(3) taking the step (1) and the step (2) as a cycle, repeatedly carrying out heating and cooling cyclic heat treatment for multiple times, and enabling one-time precipitation to reversely and repeatedly undergo an initial melting-solidification passivation process;

(4) and cooling the cast alloy to the temperature required by the subsequent process.

3. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (1), the alloy comprises a cast aluminum alloy and a cast magnesium alloy;

preferably, in the step (1), the primary precipitated phase is a phase directly precipitated from a liquid phase during solidification of the cast alloy.

4. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (1), the primary precipitated phase incipient melting temperature is a temperature at which the primary precipitated phase starts to melt.

5. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (1), the temperature a is within the range of 0-10 ℃, and the heat preservation time t1 is within the range of 0-1-60 min;

preferably, in the step (1), the temperature a is more than 0 and less than or equal to 5 ℃, and the heat preservation time t1 is more than 0 and less than or equal to t1 and less than or equal to 30 min.

6. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (2), the temperature b is within the range of 0-10 ℃, and the heat preservation time t2 is within the range of 0-2-60 min;

preferably, in the step (2), the temperature b is more than 0 and less than or equal to 5 ℃, and the heat preservation time t2 is more than 0 and less than or equal to t2 and less than or equal to 30 min.

7. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (1) and the step (2), the temperature raising and reducing device is selected from a program temperature control furnace or an induction heating furnace.

8. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (1), the step (2) and the step (3), the heating and cooling rates are 0.01-500 ℃/s;

preferably, in the step (1), the step (2) and the step (3), the temperature rising and reducing rate is 0.1-100 ℃/s.

9. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (3), the circulation frequency is 1-20 times;

preferably, in step (3), the number of cycles is 1 to 10.

10. The method for cyclic heat treatment of a cast alloy according to claim 2, wherein the method comprises the steps of: in the step (4), the temperature required by the subsequent process refers to room temperature, aging temperature or stress relief annealing temperature.

Technical Field

The invention belongs to the technical field of metal material heat treatment, and particularly relates to a heating and cooling cyclic heat treatment method near the primary melting temperature of a primary precipitated phase of a cast alloy.

Background

The cast aluminum alloy and the magnesium alloy have the advantages of small density, high specific strength and the like, and are widely applied to the industries of automobiles, aerospace and the like. In the cast alloy, a plurality of primary precipitated phases are formed inevitably, and the primary precipitated phases often have the shapes of long strips, long and thin needles, dendrites and the like, and are sharp in shape and large in size. The primary precipitated phases can seriously crack the matrix structure, have great adverse effects on the comprehensive mechanical properties of the alloy, and attract high attention of technologists.

At present, in order to improve the mechanical properties of cast alloys, technologists and industries often adopt ways of improving solidification conditions, refining modification treatment, adding physical fields and the like to improve the form, size and distribution of primary precipitated phases in the cast alloys, so that the primary precipitated phases are uniformly distributed in the alloys in favorable shapes and smaller sizes, and the comprehensive mechanical properties of the alloys are improved. The size of the primary precipitated phase can be reduced by improving the solidification conditions and accelerating the cooling rate when the cast alloy is solidified, but the method is not suitable for large castings. The addition of the refiner or modifier can improve the form and size of a primary precipitated phase in the cast alloy, for example, sodium, strontium, antimony and the like can change eutectic silicon in the aluminum-silicon eutectic alloy from a lamellar state to a fibrous state, but the development of the specific refiner or modifier is required aiming at the specific primary precipitated phase, and the refining and modification effects are not ideal because of the refining and modification capability and the decline of the refiner or modifier. The distribution of the primary precipitated phase in the alloy can be improved by using a physical field such as an electromagnetic field, but the method is complicated in equipment and has a poor effect of improving the primary precipitated phase. Therefore, at present, no method for improving the primary precipitated phase microstructure in the cast alloy generally and efficiently exists.

In addition to the above methods, heat treatment is also widely used to improve the morphology of the primary precipitate phase in cast alloys. Chinese patent CN106367700A discloses a spheroidizing heat treatment method for eutectic silicon-aluminum alloy, which is to keep the eutectic silicon-aluminum alloy at eutectic temperature for a period of time, thereby achieving the purpose of spheroidizing the eutectic silicon. Because the heating temperature is lower, the improvement of the appearance of the primary precipitated phase is only carried out by element diffusion, and therefore, the heat treatment effect is poor and the time is long.

Disclosure of Invention

Aiming at the problem that a method for universally and efficiently improving the coarse and sharp appearance of a primary precipitated phase in a cast alloy is lacked in the prior art, the invention aims to provide a simple, efficient and universally applicable method for circularly heat treating the primary precipitated phase of the cast alloy, namely, the alloy to be subjected to heat treatment is subjected to circular heat treatment of temperature rise and temperature reduction near the primary melting temperature of the primary precipitated phase, so that the structure appearance and the comprehensive mechanical property of the cast alloy are improved to the maximum extent by the most economic means.

In order to achieve the above purpose, the solution of the invention is as follows:

the cyclic heat treatment method for raising and lowering temperature near the initial melting temperature of the primary precipitated phase of cast alloy is characterized by that the alloy to be heat-treated is circularly heat-treated by raising and lowering temperature for several times near its initial melting temperature. Specifically, the method utilizes the characteristics that the interface energy of a primary precipitated phase is higher than that of an alloy matrix, and the interface energy of a part with a sharper primary precipitated phase is higher, so that primary melting is more likely to occur, sets the heating temperature of the alloy to be higher than the primary melting temperature of the primary precipitated phase, causes the primary precipitated phase to undergo primary melting, then causes the primary precipitated phase after primary melting to be solidified and passivated by adopting temperature reduction treatment, and adopts cyclic heating and temperature reduction treatment, wherein the primary melting is firstly caused at the sharp part in the primary precipitated phase during heating, and the primary precipitation is reversely subjected to the primary melting-solidification passivation process by utilizing the principle of solidification and passivation during temperature reduction, and then cools the alloy to the temperature required by the subsequent working procedures. The method ensures that the coarse and sharp primary precipitation phase in the cast alloy is changed into the passivated and fine particles, solves the defects of low alloy plasticity and the like caused by the difficulty in improving the appearance of the primary precipitation phase due to low heating temperature in common heat treatment, and simultaneously optimizes the structure to improve the alloy performance.

Preferably, the heating and cooling cyclic heat treatment method for the primary precipitated phase of the cast alloy near the primary melting temperature specifically comprises the following steps:

(1) heating the alloy to be heat-treated to a temperature a ℃ slightly above the primary melting temperature of the primary precipitated phase, and preserving the temperature for a period of time t1 to ensure that the primary precipitated phase is subjected to primary melting;

(2) cooling the alloy subjected to primary melting in the step (1) to b ℃ below the primary melting temperature of a primary precipitated phase of the alloy, and preserving the heat at the temperature for a period of time t2 to enable the primary precipitated phase after primary melting to be solidified and passivated;

(3) taking the step (1) and the step (2) as a cycle, repeatedly carrying out heating and cooling cyclic heat treatment for multiple times, and enabling one-time precipitation to reversely and repeatedly undergo an initial melting-solidification passivation process;

(4) and cooling the cast alloy to the temperature required by the subsequent process.

Preferably, in the step (1), the alloy is an aluminum alloy and a magnesium alloy cast in various manners.

Preferably, in the step (1), the primary precipitated phase is a phase directly precipitated from a liquid phase during solidification of the cast alloy.

Preferably, in the step (1), the primary precipitate incipient melting temperature is a temperature at which the primary precipitate just starts to melt.

Preferably, in the step (1), the temperature a is in the range of 0 & lt a & lt 10 ℃, more preferably 0 & lt a & lt 5 ℃; the temperature holding time t1 is more preferably 0-t 1-60 min, still more preferably 0-t 1-30 min. The primary melting of a precipitated phase can be ensured in the processes of temperature rising and heat preservation.

Preferably, in the step (2), the temperature b is within the range of 0 < b < 10 ℃ and more preferably 0 < b < 5 ℃; the temperature holding time t2 is more preferably 0-t 2-60 min, still more preferably 0-t 2-30 min. The cooling and heat preservation process can ensure the solidification and passivation of the primary precipitated phase after the initial melting.

Preferably, in the step (1) and the step (2), the temperature raising and reducing device can be a programmed temperature control furnace, an induction heating furnace or other devices capable of realizing temperature raising and lowering.

Preferably, in the step (1), the step (2) and the step (3), the rates of temperature rise and temperature fall are 0.01-500 ℃/s, and more preferably 0.1-100 ℃/s.

Preferably, in step (3), the number of cycles is 1 to 20, more preferably 1 to 10. The primary precipitated phase can repeatedly generate the primary melting-solidification passivation process through multiple cycles, so that the primary precipitated phase is changed from a thick and sharp blocky or needle-shaped appearance into a passivated, fine and uniform appearance by utilizing the principle that the sharp part in the primary precipitated phase is firstly subjected to primary melting during heating and the solidification passivation during cooling.

Preferably, in the step (4), the temperature required for the subsequent process refers to the temperature of the workpiece in the subsequent processes such as processing, heat treatment, storage or transportation, such as room temperature, aging temperature, stress relief annealing temperature, and the like.

Due to the adoption of the scheme, the invention has the beneficial effects that:

firstly, the invention utilizes the principle that the sharper part of the primary precipitated phase has higher interface energy and is more easy to generate primary melting, adopts the circulating temperature rise and drop treatment to ensure that the primary precipitated phase reversely and repeatedly undergoes the primary melting-solidification passivation process, thereby changing the primary precipitated phase in the cast alloy from the shapes of thick blocks, sharp long needles and the like into the shapes of passivation, roundness and fineness, solving the problems that the heating temperature of the common heat treatment is lower than the solidus temperature, the defects of lower alloy plasticity and the like caused by the thick and sharp shapes of the primary precipitated phase are difficult to improve, and simultaneously optimizing the structure and improving the alloy performance.

Secondly, the heat treatment technology for regulating and controlling the appearance of the primary precipitated phase in the cast alloy by adopting the method has strong operability, high efficiency and wide application range.

Drawings

Fig. 1 is a schematic diagram of a metallographic structure of an aluminum alloy sample before and after a temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase incipient melting temperature in example 1 of the present invention (fig. 1(a) is a schematic diagram of a metallographic structure of an aluminum alloy sample in this example before a temperature-increasing and temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase incipient melting temperature, and fig. 1(b) is a schematic diagram of a metallographic structure of an aluminum alloy sample in this example after a temperature-increasing and temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase incipient melting temperature).

Fig. 2 is a schematic diagram of a metallographic structure of an aluminum alloy sample before and after a temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase initial melting temperature in example 2 of the present invention (fig. 2(a) is a schematic diagram of a metallographic structure of an aluminum alloy sample in this example before a cycle heat treatment at a temperature around the primary precipitated phase initial melting temperature, and fig. 2(b) is a schematic diagram of a metallographic structure of an aluminum alloy sample in this example after a temperature-increasing and temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase initial melting temperature).

Fig. 3 is a schematic metallographic structure of an aluminum alloy sample before and after a temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase incipient melting temperature in example 3 of the present invention (fig. 3(a) is a schematic metallographic structure of an aluminum alloy sample in this example before a temperature-increasing and temperature-decreasing cycle heat treatment at a temperature around the primary precipitated phase incipient melting temperature, and fig. 3(b) is a schematic metallographic structure of an aluminum alloy sample in this example after a cycle heat treatment at a temperature around the primary precipitated phase incipient melting temperature).

FIG. 4 is a schematic scanning electron microscope before and after a cyclic heat treatment of temperature increase and temperature decrease near the primary precipitated phase incipient melting temperature of a magnesium alloy sample in example 4 of the present invention (FIG. 4(a) is a schematic scanning electron microscope before a heat treatment of temperature increase and temperature decrease near the primary precipitated phase incipient melting temperature of a magnesium alloy sample in this example, and FIG. 4(b) is a schematic scanning electron microscope after a heat treatment near the primary precipitated phase incipient melting temperature of a magnesium alloy sample in this example).

Detailed Description

The invention provides a heating and cooling circulation heat treatment method near the primary melting temperature of a primary precipitated phase of a cast alloy.

The present invention will be further described with reference to the following examples.

Example 1: the aluminum-zinc-magnesium-copper-chromium alloy is circularly heat treated for 5 times at the temperature of about 481 ℃ by gravity casting of a metal mold

The material used in the embodiment is aluminum-zinc-magnesium-copper-chromium cast aluminum alloy, and the chemical composition of the aluminum-zinc-magnesium-copper-chromium cast aluminum alloy comprises the following components in percentage by mass: 5% of magnesium, 3% of zinc, 1% of copper, 2% of chromium, 78.6% of aluminum, 0.2% of iron and 0.2% of silicon; the primary precipitation phase primary melting temperature of the aluminum-zinc-magnesium-copper-chromium casting aluminum alloy is 481 ℃: melting Al-5 wt.% Mg-3 wt.% Zn-1 wt.% Cu-2 wt.% Cr-0.2 wt.% Fe-0.2 wt.% Si alloy in an iron crucible by using a crucible resistance furnace, pouring the alloy liquid into a metal mold to obtain an ingot with the size of 150mm × 100mm × 20mm, then cutting a sample with the size of 10mm × 10mm × 10mm at the center of the ingot, and carrying out the following treatment on the sample:

the sample was warmed from room temperature to 491 ℃ at a ramp rate of 10 ℃/min in a programmable air circulation furnace, followed by 5min incubation at 491 ℃. Then, the temperature of the sample is reduced to 471 ℃ at the temperature reduction rate of 10 ℃/min, and the temperature is kept for 5 min. After repeating the cycle of raising and lowering the temperature for 5 times, the sample was taken out and air-cooled to room temperature. As shown in FIG. 1(a), the alloy of the present example contained a large amount of massive, sharp and coarse primary precipitated phases in the original structure, and the matrix was severely fractured. The microstructure of the aluminum-zinc-magnesium-copper-chromium cast aluminum alloy subjected to the cyclic heat treatment is shown in fig. 1(b), and therefore, after the temperature rise and reduction cycle is carried out for 5 times, the original thick and sharp blocks in the alloy are separated out once to be subjected to phase change to be passivated and fine, and the distribution is more uniform. The properties of the alloy after heat treatment are shown in table 1.

Example 2: the metal type low-pressure cast aluminum-silicon alloy is subjected to heating and cooling circulation heat treatment for 20 times at the temperature of about 577 DEG C

The material used in this embodiment is an aluminum-silicon cast aluminum alloy, which comprises the following components in parts by mass: 20% of silicon and the balance of aluminum (80%); the primary precipitation phase initial melting temperature of the cast Al-20 wt.% Si alloy is 577 ℃: melting Al-20 wt.% Si alloy in a graphite crucible by using a crucible resistance furnace, then obtaining a disc-shaped part with the size of phi 350mm multiplied by 120mm by using a metal mold low-pressure casting method, then cutting a sample with the size of 10mm multiplied by 10mm from the center of the casting, and carrying out the following treatment on the sample:

the sample was warmed from room temperature to 587 ℃ at a ramp rate of 5 ℃/min, followed by incubation at 587 ℃ for 30 min. Then the temperature of the sample is reduced to 567 ℃ at the temperature reduction rate of 5 ℃/min, and the temperature is preserved for 30 min. After repeating the cycle of heating and cooling for 5 times, the sample was taken out and cooled to room temperature. As shown in fig. 2(a), the original structure of the alloy of the present example contains a large amount of massive sharp and coarse primary precipitated phases, and the microstructure of the cast magnesium-aluminum-rare earth alloy after the heat treatment is shown in fig. 2(b), it can be seen that after 5 times of temperature rise and temperature reduction cycles, the coarse sharp and coarse primary precipitated phases are transformed into uniformly distributed fine passive particles, and the alloy properties after the heat treatment are shown in table 1.

Example 3: heating and cooling the centrifugally cast Al-Mg-Er alloy at 450 deg.C for 10 times

The material used in this embodiment is an aluminum-magnesium-erbium cast aluminum alloy, which contains the following components in parts by mass: 5% of magnesium, 0.5% of erbium and the balance of aluminum (94.5%); the primary precipitation phase initial melting temperature of the cast Al-5 wt.% Mg-0.5 wt.% Er alloy is 450 ℃: melting Al-5 wt.% Mg-0.5 wt.% Er alloy in a graphite crucible by using a crucible resistance furnace, then forming a casting by using a metal mold horizontal chamber centrifugal casting method to obtain a casting with the size of phi 300mm multiplied by 400mm, then cutting a sample with the size of 10mm multiplied by 10mm on the casting, and processing the sample as follows:

the sample was warmed from room temperature to 455 ℃ at a ramp rate of 5 ℃/min, followed by 30min incubation at 455 ℃. Then the temperature of the sample is reduced to 445 ℃ at the cooling rate of 5 ℃/min, and the temperature is preserved for 30 min. After repeating the heating and cooling cycle for 8 times, the sample was taken out and water-cooled to room temperature. As shown in FIG. 3(a), the alloy of this example contained a large amount of dendritic, sharp and coarse primary precipitated phases in the original structure, and the matrix was severely cleaved. The microstructure of the cast magnesium-aluminum-rare earth alloy after the heat treatment is shown in fig. 3(b), and it can be seen that after the temperature rise and reduction cycle is carried out for 8 times, the coarse dendritic primary precipitated phase is broken and passivated into uniformly distributed fine round particles, and the alloy performance after the heat treatment is shown in table 1.

Example 4: heating and cooling circulation heat treatment of sand mould gravity casting magnesium-aluminum rare earth alloy for 20 times at the temperature of about 550 DEG C

The material used in the embodiment is magnesium-aluminum-rare earth casting magnesium alloy, and the magnesium-aluminum-rare earth casting alloy comprises the following components in parts by mass: 4% of aluminum, 2.6% of lanthanum, 2.7% of cerium and 90.7% of magnesium; the primary precipitated phase primary melting temperature of the cast magnesium-aluminum rare earth alloy is 550 ℃: smelting Mg-4 wt.% Al-2.6 wt.% La-2.7 wt.% Ce alloy in a graphite crucible by using a crucible resistance furnace, pouring the alloy liquid into a resin sand mold to obtain an ingot with the size of 150mm multiplied by 100mm multiplied by 20mm, then cutting a sample with the size of 10mm multiplied by 10mm at the center of the ingot, and carrying out the following treatment on the sample:

the sample was warmed from room temperature to 560 ℃ at a ramp rate of 10 ℃/min, followed by incubation at 565 ℃ for 60 min. Then the temperature of the sample is reduced to 540 ℃ at the temperature reduction rate of 5 ℃/min, and the temperature is preserved for 60 min. After repeating the cycle of raising and lowering the temperature for 20 times, the sample was taken out and cooled to room temperature by water. As shown in FIG. 4(a), the alloy of this example contained a large amount of primary precipitates having sharp long needle shapes in the original structure, and the matrix was severely cleaved. The microstructure of the cast magnesium-aluminum-rare earth alloy after the heat treatment is shown in fig. 4(b), and after 20 times of temperature rise and temperature reduction circulation, the sharp long needle-shaped primary precipitated phase is changed into uniformly distributed fine round particles, and the alloy performance after the heat treatment is shown in table 1.

TABLE 1 mechanical property data of the cast alloy samples of each example before and after the temperature-raising and temperature-lowering cyclic heat treatment around the primary precipitation phase initial melting temperature

As is clear from Table 1, the tensile strength of the alloy obtained by heat treatment at around the primary precipitation phase incipient melting temperature of the metal-type gravity casting aluminum-zinc-magnesium-copper-chromium alloy of example 1 was improved by 37%, and the elongation thereof was improved by 533%. The tensile strength of the alloy after the heat treatment near the primary precipitation phase initial melting temperature of the metal mold low-pressure casting aluminum-silicon alloy of the embodiment 2 is increased by 50 percent, and the elongation is improved by 183 percent. The centrifugal casting aluminum-magnesium-erbium alloy of the embodiment 3 has the tensile strength increased by 68.8% and the elongation increased by 118.5% after the heat treatment near the primary precipitation phase primary melting temperature. After the heat treatment is carried out near the primary precipitated phase primary melting temperature of the sand mold gravity casting magnesium-aluminum rare earth alloy in the embodiment 4, the tensile strength of the alloy is increased by 34.7 percent, and the elongation is improved by 223 percent.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. It will be readily apparent to those skilled in the art that various modifications to these embodiments and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments. Those skilled in the art should appreciate that many modifications and variations are possible in light of the above teaching without departing from the scope of the invention.

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