阅读说明：本技术 一种铝锂合金双级连续时效处理方法 (Two-stage continuous aging treatment method for aluminum-lithium alloy ) 是由 *** 肖代红 吴名冬 于 2020-04-30 设计创作，主要内容包括：一种铝锂合金双级连续时效处理方法。本发明属于铝合金加工技术领域,涉及铝锂合金的双级连续时效热处理方法。所述铝锂合金的时效工艺的主要特点是在温度连续变化的过程中对铝合金进行时效处理,在这一过程中,该工艺包含在2个连续变温区间进行不同的升温速率,通过时效析出的特点与温度区间和升温速率的合理控制,以及减弱位错回复的影响,显著的提高了合金的拉伸性能。该双级连续时效工艺在提高铝锂合金性能的同时,缩短了时效工艺时间、降低能源消耗,提高了生产效率,能有效满足目前对高综合性能铝锂合金的需求。(A two-stage continuous aging treatment method for aluminum-lithium alloy. The invention belongs to the technical field of aluminum alloy processing, and relates to a two-stage continuous aging heat treatment method for an aluminum-lithium alloy. The aging process of the aluminum-lithium alloy is mainly characterized in that the aluminum alloy is subjected to aging treatment in the process of continuous temperature change, in the process, different heating rates are carried out in 2 continuous temperature change intervals, the characteristics of aging precipitation, the temperature intervals and the heating rates are reasonably controlled, the influence of dislocation recovery is weakened, and the tensile property of the alloy is obviously improved. The two-stage continuous aging process shortens the aging process time, reduces the energy consumption, improves the production efficiency and can effectively meet the current requirements on the aluminum lithium alloy with high comprehensive performance while improving the performance of the aluminum lithium alloy.)

1. A two-stage continuous aging treatment method for aluminum-lithium alloy is characterized by comprising the following steps: the aging process is a two-stage continuous aging treatment and comprises a first-stage low-temperature rapid heating and a second-stage high-temperature slow heating aging, and the cooling mode is furnace cooling.

2. The aluminum-lithium alloy two-stage continuous aging treatment method according to claim 1, characterized in that: the highest value of the low temperature of the first-stage low-temperature rapid aging is between 120 and 140 ℃, and the heating rate of the temperature rise from the initial temperature is 7-12 ℃/h.

3. The aluminum-lithium alloy two-stage continuous aging treatment method according to claim 1, characterized in that: the initial temperature of the second stage aging is the final temperature of the first stage aging, the highest value of the high temperature is between 150 and 170 ℃, and the heating rate of the aging interval is 4-6 ℃/h.

4. The two-stage continuous aging treatment method for the aluminum-lithium alloy according to any one of claims 1 to 3, characterized in that: the temperature span selected for the high temperature zone is 30-50 ℃.

5. The two-stage continuous aging treatment method for the aluminum-lithium alloy according to any one of claims 1 to 3, characterized in that: the error between the design temperature and the actual temperature is +/-2 ℃.

6. The two-stage continuous aging treatment method for the aluminum-lithium alloy according to any one of claims 1 to 3, characterized in that: furnace cooling rate <50 ℃/h.

7. The two-stage continuous aging treatment method for the aluminum-lithium alloy according to any one of claims 1 to 3, characterized in that: the aluminum lithium alloy comprises an aluminum lithium alloy plate.

8. The two-stage continuous aging treatment method for the aluminum-lithium alloy according to any one of claims 1 to 3, characterized in that: the aluminum lithium alloy comprises an aluminum lithium alloy extrusion.

9. The two-stage continuous aging treatment method for the aluminum-lithium alloy according to any one of claims 1 to 3, characterized in that: the aluminum lithium alloy comprises the following components:

1.1-1.15 wt.%, further preferably 1.12-1.14 wt.% Li;

cu 3.5 wt.% to 4.0 wt.%, further preferably 3.52 wt.% to 3.99 wt.%;

mg 0.45-0.65 wt.%, further preferably 0.46-0.62 wt.%;

zr 0.12-0.17 wt.%, further preferably 0.13-0.16 wt.%;

Mn 0wt.％-0.31wt.％；

Ag 0.25-0.35wt.％；

Zn<0.01wt.％，Fe<0.1％、Si<0.1wt.％、K<0.001wt.％、Na<0.001wt.％，

the balance of Al, and the sum of the weight percentages of the components is 100%.

10. The aluminum-lithium alloy two-stage continuous aging treatment method according to claim 9, characterized in that:

when the aluminum lithium alloy comprises the following components: 1.12 wt.% of Li, 3.99 wt.% of Cu, 0.62 wt.% of Mg, 0.1699 wt.% of ZrC, 0.31 wt.% of Mn, 0.33 wt.% of Ag, 0.01 wt.% of Zn, 0.1 wt.% of Fe, 0.1 wt.% of Si, 0.001 wt.% of K, 0.001 wt.% of Na, and the balance Al, wherein the sum of the weight percentages of the components is 100%; after two-stage continuous aging treatment, the tensile strength of the obtained product is more than or equal to 620MPa, the yield strength is more than or equal to 525MPa, and the elongation is more than or equal to 8.5 percent;

when the aluminum lithium alloy comprises the following components: 1.14 wt.% of Li, 3.53 wt.% of Cu, 0.46 wt.% of Mg, 0.1 wt.% of Zr0, 3 wt.% of Zr0, 0.26 wt.% of Ag, 0.01 wt.% of Zn, 0.31 wt.% of Mn, 0.1 wt.% of Fe, 0.1 wt.% of Si, 0.001 wt.% of K, 0.001 wt.% of Na, and the balance Al, wherein the sum of the weight percentages of the components is 100%; after two-stage continuous aging treatment, the tensile strength of the obtained product is greater than or equal to 570MPa, the yield strength is greater than or equal to 520MPa, and the elongation is greater than or equal to 9.5%.

Technical Field

The invention belongs to the technical field of aluminum alloy processing, and relates to a two-stage continuous aging heat treatment method for an aluminum-lithium alloy.

Technical Field

Li is the lightest metal element, and the alloy density can be reduced by 3 percent and the elastic modulus can be increased by 6 percent when 1 percent of Li is added into the aluminum alloy. Compared with the traditional aluminum alloy, the Al-Li alloy has the advantages of low density, high specific strength, high specific stiffness, high fracture toughness, good corrosion resistance and the like, and meanwhile, the aluminum-lithium alloy has more advantages than the composite material in the aspects of reducing the weight of an airplane and reducing the production cost, so that the aluminum-lithium alloy has wide application prospect in the field of aerospace. For example, air passenger, boeing and Chinese business fly in the newly produced commercial passenger plane by adopting the aluminum-lithium alloy component, the aim of reducing weight is better achieved.

The aging precipitation strengthening is the key for obtaining good performance of the aluminum alloy, so the method is very important for regulating and controlling the aging process. The conventional aging treatment process of the aluminum-lithium alloy is deformation isothermal treatment, namely, after certain pre-deformation is applied after solid solution, the aluminum-lithium alloy is kept at a certain constant temperature for a period of time to obtain a certain amount, size and distribution of precipitated phases so as to realize the strengthening of the alloy (Metallurgical transformations A,1991,22(2):299-306.), however, the single temperature often has the defects of single evolution and poor controllability of the precipitated phases, so that the performance is difficult to control. The multistage aging process increases the regulation and control of precipitated phases by an aging mode of low temperature firstly and high temperature secondly (120 ℃/12h +150 ℃/48h), although the comprehensive performance is increased, the defects of complicated aging process and long aging time exist (Materials Characterization,2018,141: 163-. Recently, in Al-Zn-Mg-Cu alloy, Liu et Al (Materials & Design,2014,60: 116-. Chinese patent (patent No. CN 102400068A) discloses a non-isothermal aging process of 7xxx series aluminum alloy, and finds that the slower the temperature change rate is, the better the effect is, especially the secondary precipitation of the alloy is the key for improving the performance when the cooling rate is small, but in the process of cooling, on one hand, the supersaturated solute atoms are increased to increase the precipitation driving force; on the other hand, the reduction of the diffusion rate of atoms leads to the reduction of the precipitation speed, so that the precipitation mechanism of the process is complex and difficult to regulate. Meanwhile, the high initial temperature in the cooling process is mainly grown to inhibit nucleation, and subsequent secondary precipitation can reduce the uniformity of the precipitated phase of the alloy and is unfavorable for the performance of the alloy. Relevant further research on the influence of the cooling rate (140-220 ℃ to 100 ℃, 5-80 ℃/h) on the precipitated phase and the performance in the aging process shows that the high initial temperature (200 ℃) and the slow cooling rate (20 ℃/h) can enable the precipitated phase to grow and new precipitated phase to form so as to reduce the uniformity of the precipitated phase, particularly the difference of the average values of the precipitated phases in the long axis direction reaches 33nm, and the performance is remarkably reduced (Materials & Design,2014,57: 79-86.). Peng et al (Materials Science & Engineering A,2017,688: 146-. The researches show the feasibility and the potential of the continuous variable temperature aging treatment on the performance improvement of the Al alloy to a certain extent, but have certain limitations.

With the rapid development of the aerospace industry, the demand on the aluminum lithium alloy is increasingly wide, a novel aging process is developed to fully exert the potential of the alloy, and the method has very important significance on the regulation and control of the performance of the aluminum lithium alloy and the future application. Li Qian Feng et al proposed a T8 aging method for cooling Al-Li, namely, uniformly cooling to 145 ℃ at 0.6 ℃/h at 160 ℃, then carrying out isothermal aging at 145 ℃, although the strength of the alloy can be increased while maintaining plasticity compared with T8 isothermal aging treatment, the strength increase is not obvious (<50MPa) and the aging time is longer (>40h) (rare metal materials and engineering, 2017,46(1): 183-188). Aiming at the defects of the existing aluminum lithium aging process and based on the research, the invention provides a two-stage continuous aging process which is simple in process, can obviously improve the alloy performance and obviously shortens the aging time by combining the relationship between aging parameters (pre-deformation, multiple temperature ranges and multiple heating rates) and the aging precipitation state.

Disclosure of Invention

The invention aims to obtain an aluminum-lithium alloy with good toughness by a bipolar continuous aging treatment method. The prepared alloy has higher strength and good plasticity, and simultaneously shortens the aging time, reduces the heat treatment period and improves the production efficiency on the premise of improving the performance.

The invention carries out proper pre-deformation before artificial aging, can increase the dislocation density in the matrix and the entanglement degree thereof, and has T₁Phase (Al)₂CuLi) provides more sites for nucleation within the crystal, resulting in fine and dense phase precipitation. The high density of dislocations caused by the predeformation can cause some of the vacancies to escape into the dislocations or to be regularly arranged and disappear, which reduces the number of vacancies, thereby suppressing theta' (Al)₂Cu) phase nucleation. Therefore, one is often applied before the aluminum lithium agingThe pre-deformation in a certain degree achieves the effects of reducing quenching residual stress and introducing dislocation, the subsequent aging treatment usually adopts single temperature or heating rate, however, the only variable is difficult to control the relation between nucleation and growth of a precipitated phase; the multistage aging combines the characteristics of aging precipitation, namely, low-temperature aging is firstly carried out to be beneficial to the formation of solute atom clusters, the nucleation core is increased to improve the precipitation density of the alloy in the final aging state, and then high-temperature aging promotes the further growth of the strengthening phase to obtain precipitation phases with certain sizes and dispersion distribution, so that the performance of the alloy is improved. Although the strengthening effect of the precipitated phase is obviously increased by multi-stage aging, the work hardening generated by pre-deformation can be partially recovered by long-time aging at higher temperature, so that the contribution to the strength is reduced, and the defects of complicated process and long aging time exist.

The present invention is based on the above consideration that if the temperature is raised rapidly in the low temperature region, the nucleation rate is reduced, but the temperature is raised slowly in the high temperature stage to promote T₁The phases grow larger, reducing their number density. When kept at high temperature for a long time, the growth and coarsening of the precipitates are accelerated to form a small amount of coarse T₁And (4) phase(s). The strength of the aluminum-lithium alloy is mainly determined by T₁The influence of the number density, thickness and diameter of the phases is more pronounced, in particular as the diameter increases, and their properties are improved by optimizing them in coordination with one another by means of appropriate aging. Before aging, proper cold rolling pre-deformation treatment is carried out, the two-stage continuous aging process selects rapid temperature rise at low temperature, and slow temperature rise at high temperature so as to reduce the adverse effect of excessive refining of precipitated phases on the strength. Meanwhile, under the condition of ensuring that the precipitated phase strengthening effect is optimal, the aging time at high temperature is obviously shortened, so that the contribution of work hardening to strength is maximized. Thus, the primary strengthening mechanism of two-stage non-isothermal aging combines better the contributions of precipitation strengthening and work hardening to alloy performance.

The aging process of the aluminum lithium alloy is characterized by comprising the following steps: the aging process is an aging process of sectional continuous heating, and comprises first-stage low-temperature rapid heating and second-stage high-temperature slow heating aging, wherein the cooling mode is furnace cooling.

According to some embodiments of the invention, the maximum low temperature of the first stage low temperature rapid aging is between 120 ℃ and 140 ℃ and the heating rate of the first stage is 7-12 ℃/h, preferably 8-10 ℃/h. Researches find that the temperature in the aging process is low, and mainly takes nucleation of a precipitated phase, so that the microstructure of the material can be well controlled in the temperature range and the temperature rise rate, and the condition that the final aged state tissue is not ideal due to long-time aging is avoided.

According to some embodiments of the invention, the initial temperature of the second stage aging is the final temperature of the first stage aging, the maximum high temperature is between 150 ℃ and 170 ℃, and the heating rate of the second stage aging is 4-6 ℃/h. It was found that slow heating will facilitate further growth of the strengthening phase at the first stage of ageing to obtain a precipitate phase of a certain size and dispersed distribution.

As one embodiment of the present invention, the conditions of the first-stage low-temperature rapid heating are as follows: putting the sample into a resistance furnace heated to 22 ℃, and then heating to 130 ℃ after 12 hours, wherein the heating rate is 9 ℃/h; the conditions of the second-stage high-temperature aging are as follows: then the temperature is raised from 130 ℃ to 160 ℃ over 6h, the temperature raising rate is 5 ℃/h, and the cooling mode is furnace cooling. Researches find that under the condition, the aging treatment effect is optimal, and the strength of the aluminum-lithium alloy is obviously improved.

The invention relates to a two-stage continuous aging treatment method for an aluminum-lithium alloy, wherein the span of the temperature selected in a high-temperature interval is 30-50 ℃. In the invention, the high temperature range is a range from the initial temperature of the second stage aging to the highest temperature of the second stage aging.

The invention relates to a two-stage continuous aging treatment method for an aluminum-lithium alloy, wherein the error between the design temperature and the actual temperature is +/-2 ℃.

The invention relates to a two-stage continuous aging treatment method for aluminum-lithium alloy, wherein the furnace cooling rate is less than 50 ℃/h.

The invention relates to a two-stage continuous aging treatment method for an aluminum lithium alloy.

The invention relates to a two-stage continuous aging treatment method for an aluminum lithium alloy.

In a preferred embodiment of the present invention, the aluminum-lithium alloy has a composition of:

1.1-1.15 wt.%, further preferably 1.12-1.14 wt.% Li;

cu 3.5 wt.% to 4.0 wt.%, further preferably 3.52 wt.% to 3.99 wt.%;

mg0.45wt.% to 0.65 wt.%, more preferably 0.46 wt.% to 0.62 wt.%;

zr0.12wt.% to 0.17 wt.%, further preferably 0.13 wt.% to 0.16 wt.%;

Mn0wt.％-0.31wt.％；

Ag0.25-0.35wt.％；

Zn<0.01wt.％，Fe<0.1％、Si<0.1wt.％、K<0.001wt.％、Na<0.001wt.％，

the balance of Al, and the sum of the weight percentages of the components is 100%.

In one embodiment of the present invention, the aluminum lithium alloy sheet material comprises: 1.12 wt.% for Li, 3.99 wt.% for Cu, 0.62 wt.% for Mg, 0.16 wt.% for Zr, 0.31 wt.% for Mn, 0.33 wt.% for Ag, 0.01 wt.% for Zn, 0.1% for Fe, 0.1 wt.% for Si, 0.001 wt.% for K, 0.001 wt.% for Na, and the balance Al, the sum of the weight percentages of the components being 100%. The plate prepared according to the components is processed into a tensile sample with the length of 80mm by warp cutting, the sample is subjected to gradual temperature rise and solid solution treatment, the sample is subjected to solid solution treatment in a salt bath, and after the solid solution treatment, the sample is quickly taken out and cooled to room temperature by water. The quenched samples were cold rolled to 5% pre-deformation. By adopting the component design, after two-stage continuous aging treatment, the tensile strength of the obtained product is more than or equal to 620MPa, the yield strength is more than or equal to 525MPa, and the elongation is more than or equal to 8.5%.

In another embodiment of the present invention, the aluminum-lithium alloy extruded material comprises the following components: 1.14 wt.% for Li, 3.53 wt.% for Cu, 0.46 wt.% for Mg, 0.13 wt.% for Zr, 0.26 wt.% for Ag, 0.01 wt.% for Zn, 0.31 wt.% for Mn, 0.1 wt.% for Fe, 0.1 wt.% for Si, 0.001 wt.% for K, 0.001 wt.% for Na, and the balance Al, the sum of the weight percentages of the components being 100%. The extruded material prepared by the components is processed into a tensile sample with the length of 80mm by warp cutting along the extrusion direction, the sample is subjected to gradual temperature rise and solid solution treatment, the sample is subjected to solid solution in a salt bath, and after the solid solution treatment, the sample is quickly taken out and cooled to room temperature by water. The quenched samples were cold rolled to 5% pre-deformation. By adopting the component design, after two-stage continuous aging treatment, the tensile strength of the obtained product is greater than or equal to 570MPa, the yield strength is greater than or equal to 520MPa, and the elongation is greater than or equal to 9.5%.

According to the embodiment of the invention, as the process for effectively improving the strength of the alloy, the alloy with different components and the hot forming process has the same effect, and the change of the content of trace alloy elements and the influence of the casting process on the alloy are weaker.

The aluminum lithium alloy adopts the two-stage continuous aging treatment method to obtain the aging strengthening type aluminum lithium alloy with excellent mechanical property, and the prepared alloy has excellent room-temperature tensile strength, yield strength and good elongation.

In addition, on the premise of ensuring the performance, the non-isothermal aging process effectively shortens the aging time, not only solves the problem of the production efficiency of a factory, but also reduces the energy consumption and improves the benefit of an enterprise.

The invention has the characteristics that:

before the aging process is implemented, the aluminum alloy plate needs to be subjected to solid solution quenching treatment, solid solution is carried out in salt bath, and after the solid solution treatment, the aluminum alloy plate is quickly taken out and cooled to room temperature by water. The quenched samples were cold rolled to 5% pre-deformation. The aging treatment method is mainly characterized in that the aging treatment is carried out on the aluminum alloy in the continuous change of the temperature, 2 heating rates and different continuous temperature changing intervals are included in the process, namely the non-isothermal process of two-stage continuous heating, the microstructure is controlled by adjusting the heating rates of different temperature intervals, the performance is reasonably adjusted, and the performance requirement of the component is finally met. The advantages of sectional regulation and control of precipitated phase nucleation and growth in different temperature intervals are combined, and the influence on strength caused by recovery of dislocation generated during aging at higher temperature is reduced. The aging process can not only control the microstructure of the alloy to obtain good performance, but also reduce the aging period, thereby achieving the purposes of saving energy, reducing emission and increasing benefit.

Drawings

FIG. 1 is a schematic diagram of an aging process: a is a single-stage continuous aging process control chart; b is a control chart of the two-stage continuous aging process; c is a four-level aging process control chart; d is a T8 isothermal aging process control chart.

Fig. 2 is a microstructure of an aluminum lithium alloy: a is a microstructure of the product obtained in comparative example 1 after a single stage of continuous ageing; b is the microstructure of the product obtained in example 1 after two-stage sequential ageing.

Detailed Description

Comparative example 1

In the present comparative example, the aluminum lithium alloy sheet material had a composition designed to: 1.12 wt.% for Li, 3.99 wt.% for Cu, 0.62 wt.% for Mg, 0.16 wt.% for Zr, 0.31 wt.% for Mn, 0.33 wt.% for Ag, 0.01 wt.% for Zn, 0.1% for Fe, 0.1 wt.% for Si, 0.001 wt.% for K, 0.001 wt.% for Na, and the balance Al, the sum of the weight percentages of the components being 100%. The plate prepared according to the components is processed into a tensile sample with the length of 80mm by warp cutting, the sample is subjected to gradual temperature rise and solid solution treatment, the sample is subjected to solid solution treatment in a salt bath, and after the solid solution treatment, the sample is quickly taken out and cooled to room temperature by water. The quenched samples were cold rolled to 5% pre-deformation. The aging process adopts a traditional isothermal aging mode (T8 aging), combines with an age hardening curve, selects the aging treatment under peak aging, namely heats the plate to 145 ℃ and preserves the temperature for 36 h. The final mechanical properties of the resulting material are shown in table 1.

FIG. 2a is a transmission electron micrograph of the comparative example.

Comparative example 2

In this comparative example, an aluminum lithium alloy sheet was produced using the same composition and production process as in comparative example 1, and the solution quenching and pre-deformation processes were also the same as in comparative example 1.

The aging process comprises the following steps: the sample was placed in a resistance furnace heated to 22 ℃ and subsequently heated to 160 ℃ over 18h, during which the heating rate was 7.7 ℃/h and the cooling was furnace cooling, the final mechanical properties of the resulting material being shown in table 1.

Comparative example 3

In this comparative example, an aluminum lithium alloy sheet was produced using the same composition and production process as in comparative example 1, and the solution quenching and pre-deformation processes were also the same as in comparative example 1.

The aging process comprises the following steps: putting the sample into a resistance furnace heated to 22 ℃, and then heating to 130 ℃ after 12 hours, wherein the heating rate is 9 ℃/h; then heating from 130 ℃ to 145 ℃ over 3h, keeping the temperature constant at 145 ℃ for 6h, finally heating from 145 ℃ to 160 ℃ over 3h, wherein the heating rate is 5 ℃/h, the cooling mode is furnace cooling, and the final mechanical properties of the obtained material are shown in Table 1.

Comparative example 4

In the present comparative example, the aluminum lithium alloy extruded material had a composition designed to: 1.14 wt.% for Li, 3.53 wt.% for Cu, 0.46 wt.% for Mg, 0.13 wt.% for Zr, 0.26 wt.% for Ag, 0.01 wt.% for Zn, 0.31 wt.% for Mn, 0.1 wt.% for Fe, 0.1 wt.% for Si, 0.001 wt.% for K, 0.001 wt.% for Na, and the balance Al, the sum of the weight percentages of the components being 100%. The extruded material prepared by the components is processed into a tensile sample with the length of 80mm by warp cutting along the extrusion direction, the sample is subjected to gradual temperature rise and solid solution treatment, the sample is subjected to solid solution in a salt bath, and after the solid solution treatment, the sample is quickly taken out and cooled to room temperature by water. The quenched samples were cold rolled to 5% pre-deformation. The aging process adopts a traditional isothermal aging mode, combines an age hardening curve, selects the peak aging to perform aging treatment, namely, heats the plate to 130 ℃ and preserves the temperature for 24 hours. The final mechanical properties of the resulting material are shown in table 1.

Comparative example 5

In this comparative example, an aluminum lithium alloy extruded material prepared using the same composition and production process as in comparative example 4 was used, and the solution quenching and pre-deformation processes were also the same as in comparative example 4.

The aging process comprises the following steps: the sample was placed in a resistance furnace heated to 22 ℃ and subsequently heated to 160 ℃ over 18h, during which the heating rate was 7.7 ℃/h and the cooling was furnace cooling, the final mechanical properties of the resulting material being shown in table 1.