CN108486509B

CN108486509B - Two-stage solution treatment process for Al-Er-Li alloy

Info

Publication number: CN108486509B
Application number: CN201810261404.4A
Authority: CN
Inventors: 高坤元; 刘琦兵; 丁宇升; 聂祚仁; 黄晖; 文胜平; 吴晓蓝
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2018-03-28
Filing date: 2018-03-28
Publication date: 2019-12-20
Anticipated expiration: 2038-03-28
Also published as: CN108486509A

Abstract

An Al-Er-Li alloy two-stage solution treatment process belongs to the technical field of nonferrous metals. The alloy comprises the following components in percentage by mass, Er0.1-0.19%, Li2.0-2.1%, unavoidable impurity content less than 0.1%, and the balance Al, and comprises the following steps: after the Al-Er-Li alloy is cast, first-stage solution treatment is carried out at 580 ℃/24h, and then solution treatment is carried out at 640 ℃/24 h. The process achieves the purpose of solid solution of Er with higher content on the premise of not overburning the alloy through two-stage solid solution treatment, and provides enough driving force for Er precipitation in the subsequent aging process.

Description

Two-stage solution treatment process for Al-Er-Li alloy

Technical Field

The invention belongs to the technical field of nonferrous metals, and particularly relates to an Al-Er-Li alloy two-stage solution treatment process.

Background

The aluminum lithium alloy has attracted extensive attention in the aspects of aerospace due to the characteristics of low density, high elastic modulus and high specific strength. The density of the aluminum alloy can be reduced by 3% and the modulus can be improved by 6% when 1% of Li is added into the aluminum. According to the calculation, if the advanced aluminum-lithium alloy is adopted to replace the traditional aluminum alloy to manufacture the boeing aircraft, the structural mass can be reduced by 14.6 percent, the fuel can be saved by 5.4 percent, the cost of the aircraft can be reduced by 2.1 percent, and the annual flying cost of each aircraft can be reduced by 2.2 percent; the emission cost of the space vehicle can be saved by 2 ten thousand dollars for each lightening of 1kg, so the aluminum-lithium alloy has important significance in the field of aerospace.

The strengthening effect of the aluminum-lithium alloy is mainly derived from the alloy with L1₂Structural Al₃Metastable phase of Li. The strength of the Al-Li alloy can be further improved by adding a micro-alloying element Er, but Er has lower solid solubility in Al, the solid solubility is only 0.046 at% at 640 ℃, the solid solubility treatment temperature of the conventional Al-Li alloy is lower than 600 ℃, and the solid solubility of Er in Al is extremely low at the temperature, so that Er cannot be separated out in the subsequent aging process. In order to increase the Er solid solution content in Al-Li alloys, the Er-containing aluminum-lithium alloys must be treated at a higher temperature to obtain a larger amount of Er solid solutionThe solid solubility of Er component needs to ensure that the alloy does not over-burn.

Disclosure of Invention

The invention aims to provide a solid solution treatment process for an Al-Er-Li alloy, which is used for obtaining an Er component with higher solid solubility on the premise of not overburning the alloy through solid solution treatment.

The invention provides an Al-Er-Li alloy two-stage solution treatment process, which comprises the following components in percentage by mass, Er0.1-0.19%, Li2.0-2.1%, unavoidable impurity content less than 0.1%, and the balance of Al, and comprises the following steps: after the Al-Er-Li alloy is cast, first-stage solution treatment is carried out at 580 ℃/24h, and then solution treatment is carried out at 640 ℃/24 h.

In order to carry out solid solution treatment on the Al-Er-Li alloy, firstly, the phenomenon of overburning of the alloy is ensured not to occur in the solid solution treatment process; secondly, as much as possible of the solid-soluted Er element is required. According to the solid solubility of Er in Al at different temperatures, the solid solution temperature corresponding to Er with the content of 0.19 percent is about 630 ℃, and considering that the solid solubility of Er can be reduced by adding Li, the solid solution treatment temperature is increased to 640 ℃ so as to achieve the purpose of fully dissolving Er element, but after the Al-Er-Li alloy is directly subjected to the solid solution treatment at 640 ℃, the serious overburning phenomenon of the alloy can occur. Therefore, a two-stage solution treatment mode is adopted, firstly, the Al-Li and Al-Er eutectic structures on the grain boundary are re-dissolved through the primary solution treatment of 580 ℃/24h, and then, the secondary solution treatment of 640 ℃/24h is carried out, so that the Al-Er is re-dissolved in one phase, and the aim of obtaining the Er content with higher solid solution component on the premise of ensuring that the alloy is not over-sintered is fulfilled.

The technical scheme of the invention has the advantages that:

by adopting the Al-Er-Li alloy two-stage solution treatment process, the Er content of a higher solid solution component can be obtained on the premise of no overburning of the alloy, and a foundation is laid for Er precipitation in the subsequent aging process.

Drawings

FIG. 1 shows a metallographic structure of Al-Er-Li alloy after two-stage solution treatment at 580 ℃/24h +640 ℃/24 h;

FIG. 2 is SEM and EDS photographs of Al-Er-Li alloy after two-stage solution treatment at 580 ℃/24h +640 ℃/24 h;

FIG. 3 is a metallographic structure of the Al-Er-Li alloy after solution treatment at 640 ℃/24 h;

FIG. 4 is a metallographic structure of the Al-Er-Li alloy after solution treatment at 590 ℃/24 h;

FIG. 5 is a metallographic structure of the Al-Er-Li alloy after solution treatment at 580 ℃/24 h;

FIG. 6 is an SEM photograph and an EDS map of the Al-Er-Li alloy after 580 ℃/24h solution treatment;

wherein Fe in FIGS. 2 and 6 is an impurity.

Detailed Description

The invention is further illustrated by the following examples in conjunction with the accompanying drawings, but the invention is not limited to the following examples:

example 1:

the mass percentages of the components of the alloy are respectively Er 0.19%, Li 2.1%, unavoidable impurity content less than 0.1% and the balance Al, and the alloy is smelted to obtain an ingot.

The ingot is firstly subjected to primary solution treatment at 580 ℃/24h, then is continuously heated to 640 ℃, is subjected to secondary solution treatment for 24h, is subjected to Keller reagent corrosion for 3min, and is observed by utilizing metallographic microscopic structure, as shown in figure 1.

As can be seen from FIG. 1, after the alloy is subjected to the two-stage solution treatment of 580 ℃/24h +640 ℃/24h, no overburning structures such as re-soluble balls appear on the grain boundary, which indicates that the alloy is not overburnt after the two-stage solution treatment process. As shown in FIG. 2, when SEM observation and energy spectrum analysis were performed on the alloy after the two-stage solution treatment, it was found from FIG. 2 that only a small amount of Al remained in the alloy matrix after the two-stage solution treatment once₃An Er phase.

Comparative example 1:

the alloy material, processing and corrosion process used were the same as in example 1.

After obtaining the ingot, the ingot is directly subjected to solid solution treatment at 640 ℃/24h, the alloy is subjected to Keller reagent corrosion for 3min, and the structure of the alloy is observed by a metallographic microscope, as shown in figure 3.

As can be seen from FIG. 3, after the alloy is directly subjected to the solution treatment at 640 ℃/24h, the alloy obviously has an overburnt structure, which shows that the alloy obviously has overburnt structure after the direct treatment of the process.

Comparative example 2:

After obtaining the ingot, the ingot is directly subjected to 590 ℃/24h solution treatment, the alloy is subjected to Keller reagent corrosion for 3min, and the structure of the alloy is observed by a metallographic microscope, as shown in figure 4.

As can be seen from FIG. 4, the alloy has reduced over-sintered characteristics after the alloy is subjected to solution treatment at 590 ℃/24h, but remelted balls still exist on the grain boundaries, which indicates that the alloy is still in an over-sintered state at the temperature.

Comparative example 3:

After obtaining the ingot, the ingot is directly subjected to 580 ℃/24h solution treatment, the alloy is subjected to Keller reagent corrosion for 3min, and the structure of the alloy is observed by a metallographic microscope, as shown in figure 5.

As is clear from FIG. 5, the alloy was subjected to solution treatment at 580 ℃/24 hours, and then no overburning structure such as grain boundary coarsening or remelted balls was observed, indicating that the alloy was not overburnt at this temperature. The results of SEM observation and energy spectrum analysis of the alloy after the solution treatment are shown in fig. 6.

As can be seen from FIG. 6, after 580 deg.C/24 h solution treatment, a large amount of Al still exists in the matrix₃The primary Er phase has low solid solubility in Al, about 0.21% at 640 ℃ and only 0.1% at 580 ℃, so that a large amount of Al remains in the matrix after solution treatment at this temperature₃Primary phase of Er.

Comparative example 4:

as shown in Table 1, the solid solubility data of Er in Al at different temperatures shows that when the Er content is 0.19%, the corresponding solid solution temperature is 630-640 deg.C, so that the solid solution temperature is 580 deg.C/24 hHowever, since Er in this composition cannot be sufficiently dissolved in a solid solution, it is necessary to subject the Al-Er-Li alloy to a secondary solution treatment at a higher temperature. The maximum solution treatment temperature of the conventional Al-Er binary alloy is 640 ℃, overburning is easy to occur when the temperature is over the temperature, and meanwhile, the solid solubility of Er is possibly reduced by adding Li, so that the secondary solution treatment temperature is selected to be 640 ℃ when the Al-Er alloy is subjected to the secondary solution treatment, the Al-Er-Li alloy is subjected to the 580 ℃/24h +640 ℃/24h double-stage solution treatment, an overburning structure does not occur in metallographic observation, and only a small amount of Al is remained in SEM observation₃The primary phase of Er shows that the aim of solid solution of more Er elements is fulfilled by the two-stage aging process on the premise of no overburning. Table 1 shows the solid solubility of Er in Al at different temperatures.

TABLE 1

Temperature (. degree.C.)	Solid solubility (wt.%)
		580	0.10
590	0.11
		600	0.12
610	0.15
		620	0.17
630	0.19
		640	0.21

In summary, the two-stage solution treatment process of the Al-Er-Li alloy provided by the invention comprises the following steps: the 580 ℃/24h +640 ℃/24 double-stage solution treatment process achieves the purpose of dissolving more Er element in solid on the premise of no overburning through the double-stage aging process.

Claims

1. The Al-Er-Li alloy two-stage solution treatment process is characterized in that the mass percentages of the components are Er0.1-0.19%, Li2.0-2.1%, the content of unavoidable impurities is less than 0.1%, and the balance is Al; after the Al-Er-Li alloy is cast, first-stage solution treatment is carried out at 580 ℃/24h, and then solution treatment is carried out at 640 ℃/24 h.