CN107058776B

CN107058776B - Method for modifying and microalloying hypoeutectic cast aluminum-silicon alloy

Info

Publication number: CN107058776B
Application number: CN201710216865.5A
Authority: CN
Inventors: 杨金德; 潘冶; 李陈林; 陆韬; 陈铭; 曹培新
Original assignee: Jiangsu Macro Special Components Ltd By Share Ltd; Southeast University
Current assignee: Jiangsu Macro Special Components Ltd By Share Ltd; Southeast University
Priority date: 2017-04-05
Filing date: 2017-04-05
Publication date: 2019-12-10
Anticipated expiration: 2037-04-05
Also published as: CN107058776A; WO2018184400A1

Abstract

The invention discloses a method for modifying and microalloying a hypoeutectic cast aluminum-silicon alloy. Melting hypoeutectic cast aluminum-silicon alloy, adding a refining agent to degas and remove slag, then adding a rare earth element La, standing at a certain temperature for heat preservation, adding an Mg element, standing at a certain temperature for heat preservation, and finally pouring at a certain temperature for forming. The rare earth La has good modification effect, the modification latency is short, the modification effective time is long, the added Mg also has certain modification effect, and the modification effect of the La and the Mg are mutually promoted, so that the aluminum-silicon alloy is modified well; meanwhile, La and Mg as microalloying elements can strengthen the aluminum-silicon alloy, which is beneficial to the improvement of alloy performance. In addition, the method has the functions of dehydrogenation and degassing, oxide inclusion reduction and melt purification on the aluminum alloy melt, thereby improving the alloy structure and the mechanical property of the alloy.

Description

Method for modifying and microalloying hypoeutectic cast aluminum-silicon alloy

Technical Field

the invention belongs to the technical field of aluminum alloy, and particularly relates to a modification and microalloying treatment method for hypoeutectic cast aluminum-silicon alloy.

Technical Field

the hypoeutectic cast aluminum-silicon alloy has small density, high specific strength and easy forming, is suitable for producing various structural members with complicated shapes and high performance, and is widely applied to various industries of aviation, aerospace, automobiles and machinery. However, in the as-cast alloy, the eutectic silicon exhibits coarse needle-like or plate-like shapes without being modified, and this form of silicon cracks the alloy matrix, greatly reducing the strength and plasticity of the aluminum-silicon alloy. Currently, in industrial production, a modification treatment is generally adopted to eliminate the adverse effect of coarse needle-like or plate-like silicon phases. The modification treatment is to improve the shape, size and distribution of eutectic silicon by adding some microelements, so that the eutectic silicon phase is modified into fine fibrous shape from thick plate shape, and the mechanical property of the alloy is greatly improved.

The modification method of hypoeutectic cast aluminum-silicon alloy mainly comprises Na modification, Sr modification and Sb modification. Na is easy to decay and lose efficacy although the deterioration effect is good, and smoke is easy to generate in the adding process to pollute the environment; although Sr deterioration has the advantages of obvious deterioration effect, long-acting property and the like, the Sr deterioration has the defects of long deterioration latency period, serious inspiration tendency, serious burning loss, easy generation of pores, shrinkage porosity and the like in tissues; sb has the advantages of no fading, small gas suction tendency and the like, but the Sb has a common deterioration effect, has toxicity, can generate toxic gas in the smelting and casting processes, and is only approved to be used under special conditions.

Aluminum-silicon alloys used in engineering application are all multi-element alloys, namely, a certain amount of elements La and Mg are required to be introduced in advance for microalloying, and then modification treatment is carried out, so that the smelting process is complicated.

Disclosure of Invention

the technical problem is as follows: the invention provides a method for carrying out microalloying while modifying hypoeutectic casting aluminum-silicon alloy by using rare earth element La and element Mg. The method has the advantages of good deterioration effect, short incubation period, no deterioration, no inhalation tendency, etc.; meanwhile, La and Mg which are added as micro-alloying elements can strengthen the alloy; in addition, the method also has the functions of dehydrogenation degassing, oxide inclusion reduction and melt purification.

The technical scheme is as follows: the method for modifying and microalloying hypoeutectic cast aluminum-silicon alloy synergistically comprises the following steps:

step 1: in a crucible resistance furnace, melting the dried hypoeutectic casting aluminum-silicon alloy in a graphite clay crucible at 760 ℃, and preserving heat for 20-30 minutes to obtain a uniform aluminum melt;

Step 2, cooling the aluminum alloy melt obtained in the step 1 to 720 ℃, adding 0.6-1.0 mass percent of C ₂ Cl ₆ for refining, preserving heat for 20-30 minutes, and then skimming;

And step 3: adding rare earth La into the aluminum alloy melt obtained in the step 2 at the temperature of 720-740 ℃, controlling the mass percentage of the La element in the alloy melt to be 0.2-0.5%, and preserving the heat for 20-30 minutes after adding the La element;

And 4, step 4: raising the temperature of the aluminum alloy melt obtained in the step 3 to 750-770 ℃, adding Mg, controlling the mass percentage of the Mg in the alloy melt to be 0.5-0.8%, and preserving the heat for 10-20 minutes after adding the Mg;

And 5: and (4) reducing the temperature of the aluminum alloy melt obtained in the step (4) to 700-740 ℃, and then casting and forming.

As a preferable scheme: the weight percentage of silicon in hypoeutectic casting aluminum-silicon alloy is 4-12%.

As a preferable scheme: the hypoeutectic cast aluminum-silicon alloy is hypoeutectic aluminum-silicon binary alloy and hypoeutectic aluminum-silicon series multi-element alloy.

as a preferable scheme: the La element is added in the form of pure La and various Al-La master alloys.

As a preferable scheme: the Mg element is added in the form of pure Mg and various Al-Mg master alloys.

Has the advantages that: according to the method, rare earth element La and element Mg are used for modification and are subjected to microalloying treatment, the La and the Mg have modification effects, the modification effects of the La and the Mg can be mutually promoted, the hypoeutectic casting aluminum-silicon alloy can be modified well, and the La and the Mg serving as microalloying elements can be used for strengthening the alloy.

compared with the prior art, the invention has the following advantages:

(1) The method provided by the invention can still keep good deterioration effect when the heat preservation time is 1-2h, and overcomes the characteristic that Na deterioration is easy to decline; when the method is used, the porosity and the shrinkage rate in the alloy cast structure are very low, and the defects of serious Sr deterioration and air suction tendency, easy generation of pores and shrinkage porosity are overcome; the raw materials used in the method are safe and environment-friendly, have good modification effect, and overcome the defects that Sb modification has toxicity and the modification effect is common.

(2) The addition of La and Mg also realizes the microalloying of the aluminum-silicon alloy, namely, the microalloying is carried out while the aluminum-silicon alloy is modified, the smelting process of independently carrying out the microalloying in industrial application is reduced, and the production efficiency is improved.

(3) the rare earth La and the hydrogen form stable rare earth hydride, a large amount of hydrogen in the aluminum liquid is absorbed in a solid form, the hydrogen content is reduced, and meanwhile Mg has a certain removing effect on the hydrogen in the aluminum liquid, so that pinholes can be eliminated. The atomic rare earth La dissolved in the aluminum liquid and oxide inclusions generate oxidation-reduction reaction, and the rare earth oxide generated by the reaction has higher specific gravity than the aluminum liquid and can quickly sink to the bottom of the melt to be separated from the melt, thereby purifying the melt. La and Mg are surface active elements, and are concentrated on the surface of the aluminum liquid after being added with the aluminum liquid, so that the oxide on the surface of the aluminum liquid is more compact, and further oxidation of the aluminum liquid is weakened.

drawings

FIG. 1 is a schematic view of a metallographic structure of an as-cast structure of an Al-7Si alloy which is not denatured or microalloyed at 500 times;

FIG. 2 is a metallographic structure diagram showing an as-cast structure of an Al-7Si alloy which is sufficiently degenerated and microalloyed at 500 times.

Detailed Description

The invention is further described with reference to the following examples and the accompanying drawings.

The first embodiment is as follows: the modification and microalloying method of the hypoeutectic cast aluminum-silicon alloy in the embodiment is as follows:

Step 1: melting the dried Al-7Si alloy in a graphite clay crucible at 760 ℃ in a crucible resistance furnace, and preserving heat for 20-30 minutes to obtain a uniform aluminum melt;

Step 2, cooling the aluminum alloy melt obtained in the step 1 to 720 ℃, adding 0.8 mass percent of C ₂ Cl ₆ for refining, preserving heat for 20-30 minutes, and then skimming;

And step 3: adding rare earth La into the aluminum alloy melt obtained in the step 2 at 730 ℃, controlling the mass percentage of La element in the alloy melt to be 0.25-0.35%, and keeping the temperature for 25 minutes after adding the La element;

and 4, step 4: raising the temperature of the aluminum alloy melt obtained in the step 3 to 760 ℃, adding Mg, controlling the mass percentage of the Mg in the alloy melt to be 0.65-0.75%, and keeping the temperature for 15 minutes after adding the Mg;

and 5: and (4) reducing the temperature of the aluminum alloy melt obtained in the step (4) to 720 ℃, and further casting and forming.

FIG. 1 is a metallographic photograph of an as-cast structure of an Al-7Si alloy which is not denatured or microalloyed at 500 times, wherein the bright part in the photograph is primary aluminum and eutectic aluminum, the dark part is eutectic silicon, and the eutectic silicon is in a thick sheet shape or a needle shape.

FIG. 2 is a metallographic photograph of an as-cast structure of an Al-7Si alloy which is fully degenerated and microalloyed at 500 times, wherein the bright part in the photograph is primary aluminum and eutectic aluminum, the dark part is eutectic silicon, and the eutectic silicon is in a fine granular shape.

Example two: the difference between the embodiment and the first embodiment is that in the step 3, the rare earth La is added at 720 ℃, the mass percentage of the La element in the alloy melt is controlled at 0.2%, and after the La element is added, the temperature is kept for 20 minutes. The rest is the same as the first embodiment.

Example three: the difference between the embodiment and the first embodiment is that in the step 3, the rare earth La is added at 740 ℃, the mass percentage of the La element in the alloy melt is controlled at 0.5%, and after the La element is added, the temperature is kept for 30 minutes. The rest is the same as the first embodiment.

Example four: the difference between the embodiment and the first embodiment is that the temperature of the aluminum alloy melt in the step 4 is raised to 750 ℃, the Mg element is added, the mass percentage content of the Mg element in the alloy melt is controlled to be 0.5%, and the temperature is kept for 10 minutes after the Mg element is added. The rest is the same as the first embodiment.

example five: the difference between the embodiment and the first embodiment is that the temperature of the aluminum alloy melt in the step 4 is raised to 770 ℃, the Mg element is added, the mass percentage of the Mg element in the alloy melt is controlled to 0.8%, and the temperature is kept for 20 minutes after the Mg element is added. The rest is the same as the first embodiment.

The above examples are only preferred embodiments of the present invention, it should be noted that: it will be apparent to those skilled in the art that various modifications and equivalents can be made without departing from the spirit of the invention, and it is intended that all such modifications and equivalents fall within the scope of the invention as defined in the claims.

Claims

1. A method for modifying and microalloying a hypoeutectic cast aluminum-silicon alloy is characterized by comprising the following steps: the method comprises the following steps:

Step 1: in a crucible resistance furnace, melting the dried hypoeutectic casting aluminum-silicon alloy in a graphite clay crucible at 760 ℃, and preserving heat for 20-30 minutes to obtain a uniform aluminum alloy melt;

and step 3: adding rare earth La into the aluminum alloy melt obtained in the step 2 at 740 ℃, controlling the mass percentage of La element in the alloy melt to be 0.2-0.5%, and preserving heat for 20-30 minutes after adding the La element;

And 5: reducing the temperature of the aluminum alloy melt obtained in the step 4 to 740 ℃, and then casting and forming;

Wherein, the mass percentage of silicon in the hypoeutectic casting aluminum-silicon alloy is 4 percent; the hypoeutectic cast aluminum-silicon alloy is hypoeutectic aluminum-silicon binary alloy and hypoeutectic aluminum-silicon series multi-element alloy; la element is added in the form of pure La and various Al-La intermediate alloys; the Mg element is added in the form of pure Mg and various Al-Mg master alloys.