CN108048716A - High-strength creep resistant Al-Cu containing scandium line aluminium alloys and casting and heat treatment process - Google Patents

Abstract

The invention discloses a casting and heat treatment process of a high-strength creep-resistant scandium-containing Al-Cu series aluminum alloy. The alloy composition is: the mass percentage of Cu is 2.0-5.0%, the mass percentage of Sc is 0.1-0.5%, Si The mass percentage of Ti is 0.01-0.03%, the mass percentage of Ti is 0.01-0.03%, and the rest is Al and unavoidable impurities, which are prepared by conventional casting. The aging heat treatment process includes: homogenization treatment: heat preservation for 3 hours to 50 hours, air cooling; solid solution treatment: heat preservation for 30 minutes to 15 hours, water quenching; aging treatment: heat preservation for 1 hour to 20 hours. The present invention adds a small amount of Sc to the Al-Cu alloy, and the results show that Sc can not only significantly refine the θ′-Al ₂ Cu precipitates, but also increase the precipitation density of the θ’-Al ₂ Cu precipitates, thereby significantly increasing the Al ‑Cu alloy room temperature strength.

Description

High-strength and creep-resistant scandium-containing Al-Cu-based aluminum alloys and their casting and heat treatment processes

technical field

The invention belongs to the field of metal materials, and relates to an aluminum alloy material, in particular to a preparation and heat treatment process of a scandium-containing Al-Cu alloy. Compared with the traditional Al-Cu alloy, the strength at room temperature is greatly improved while the strength is increased. High temperature creep resistance.

Background technique

Among light alloys, aging aluminum alloys, as an important class of structural materials, have the characteristics of high specific strength, good processability and excellent corrosion resistance, and are widely used in the automotive and aerospace industries. Al-Cu alloy is the most representative binary alloy among aging aluminum alloys. Because of its low density, high specific strength, and excellent machinability, its casting alloys are widely used in aviation products, and It is mainly used as a structural part that bears a large load. However, in general, the thermal stability of Al-Cu alloys is poor, which is mainly due to the poor thermal stability of the room temperature strengthening phase θ′-Al ₂ Cu phase, and the θ′-Al ₂ Cu phase is prone to coarsening in high-temperature service environments. As a result, the high-temperature strength of the material is reduced, which in turn affects its performance. Therefore, the use temperature of traditional aluminum alloys is lower than 200°C, which is difficult to meet the requirements for materials for the development of high-speed aircraft and propellers. Aluminum alloy, and partially replace titanium alloy, has become an urgent problem to be solved for the next generation of high-temperature aluminum alloy.

Usually, the way to improve the high-temperature performance of Al-Cu alloy is to add high-temperature-resistant second-phase hardened particles, that is, metal matrix composites, to the Al-Cu alloy, which can effectively improve the high-temperature performance of Al-Cu alloy, but it is due to the first There are serious interface problems between the two phases and the matrix, resulting in poor ductility and fracture toughness. In addition, the high manufacturing and processing costs of composite materials greatly limit its industrial application.

The addition of Sc to aluminum alloy can improve the as-cast structure of the alloy and affect the precipitation behavior of the strengthening phase on the one hand, and form Al ₃ Sc particles with strong thermal stability on the other hand to improve the high temperature performance of the aluminum alloy. In addition, previous studies have shown that Sc is an effective microalloying element in aluminum alloys. The microalloying effect of Sc is mainly manifested as: fine grain strengthening, inhibition of recrystallization, precipitation strengthening and corrosion resistance. At present, the research on Sc-containing aluminum alloys mainly focuses on pure aluminum and non-heat-treatable aluminum alloys. Although the addition of Sc elements to these aluminum alloys will show aging strengthening properties, the amount of single-precipitated Al ₃ Sc particles is limited. The strengthening effect is not obvious. This patent adds a trace amount of Sc element to the Al-Cu alloy, regulates the precipitated phase through microalloying and heat treatment process, and improves the comprehensive mechanical properties at room temperature and high temperature mechanical properties at the same time, which has extremely important engineering value and application prospect.

Contents of the invention

The invention aims to solve the problem of improving the mechanical properties of cast Al-Cu alloy at room temperature, especially the high temperature mechanical properties. Compared with the composite material, while improving the high temperature performance of the Al-Cu alloy, the ductility of the material is increased. Therefore, an Al-Cu alloy material with excellent high-temperature performance, its preparation technology and heat treatment method are proposed.

In order to solve the above problems, the technical solution of the present invention is:

The invention provides a casting Al-Cu alloy material containing Sc with excellent high temperature performance, which comprises the following components, the mass percentage of Cu is 2.0-5.0%, the mass percentage of Sc is 0.1-0.5%, and the mass percentage of Si is 0.01-0.03%, the mass percentage of Ti is 0.01-0.03%, the rest is Al and unavoidable impurities;

The preparation method of the alloy is to place pure Al in a smelting furnace and heat it up to 660-780°C to melt, then add the specified ratio of Al-Cu master alloy and Al-Sc master alloy, and continue to stir until they are completely melted, and then Control the temperature to 735-750°C, add an appropriate amount of refining agent for refining, let it stand for 10-30 minutes, and then cast it in a metal mold.

In order to achieve the above technical purpose, the present invention provides a casting Al-Cu alloy material containing Sc and the corresponding aging heat treatment process. The heat treatment process adopts: (1) Homogenization treatment: 420-480 ° C, heat preservation for 3 hours - 50 hours, air cooling; (2) solution treatment: 510°C-610°C, heat preservation for 30 minutes-15 hours, water quenching; (5) aging treatment: 200°C-350°C, heat preservation for 1 hour-20 hours.

The inventors have found that the addition of Sc elements to cast Al-Cu alloys can promote the precipitation of θ′-Al ₂ Cu precipitates, resulting in increased density and reduced size. In addition, due to the precipitation of Sc atoms in θ′-Al ₂ Cu The segregation of the phase and the matrix interface inhibits the growth and coarsening of the θ′-Al ₂ Cu precipitated phase, especially in a high temperature environment (250°C-300°C), and the material passes through the creep test for more than 300h under the θ′-Al ₂ There is almost no coarsening of Cu precipitates, which greatly improves the high-temperature performance of Al-Cu alloys and expands the application of Al-Cu alloys at high temperatures.

Compared with the traditional Al-Cu alloy, the present invention has the advantage that: the rapid coarsening of the room temperature strengthening phase θ′-Al ₂ Cu of the traditional Al-Cu alloy under high temperature environment greatly limits its high temperature application. Composite materials with high-temperature stable particles are not only difficult to manufacture and high in cost, but also have poor ductility and fracture toughness due to the instability of the interface between the added particles and the matrix, making it difficult to meet the requirements of industrial applications. The alloy composition and heat treatment process of the present invention can regulate the aging precipitation of θ′-Al ₂ Cu precipitates in the matrix, and suppress the θ′-Al ₂ Cu precipitates in the θ′-Al ₂ Cu/matrix interface through Sc segregation The rapid coarsening in high temperature environment improves the high temperature performance while ensuring the room temperature strength of the alloy material. Compared with composite materials, it can greatly improve the ductility of materials and expand the application space of Al-Cu alloys.

Description of drawings

Fig. 1 is the engineering stress-engineering strain curve of the alloy sample after the traditional Al-2.3Cu alloy T6 treatment and the Al-2.3Cu-0.22Sc alloy aging treatment containing Sc;

Figure 2 is the TEM micrograph of the traditional Al-2.3Cu alloy T6 treatment and the aging treatment of the Al-2.3Cu-0.22Sc alloy containing Sc;

Figure 3 is the time-strain curve of the tensile creep test of the alloy sample after the traditional Al-2.3Cu alloy T6 treatment and the aging treatment of the Al-2.3Cu-0.22Sc alloy containing Sc at 250 ° C and 50 Mpa;

Detailed ways

Implementation example 1

A high-strength creep-resistant Sc-containing cast Al-Cu alloy and its aging heat treatment process include the following steps: (1) the preparation method of the alloy is to place pure Al in a melting furnace and heat it up to 730 ° C to melt, Then add Al-50wt.%Cu master alloy and Al-2wt.%Sc master alloy in specified ratio, and keep stirring until they are completely melted. Then control the temperature to 730°C, add 2% refining agent for refining, let it stand for 30 minutes, and cast it in a metal mold to obtain Al-2.5wt.%Cu-0.1wt.%Sc (hereinafter referred to as Al-2.5Cu- 0.1Sc) aluminum alloy. (2) Homogenize the alloy ingot at 450°C for 4 hours; (3) Perform solution treatment at 590°C for 3 hours on the sample that has been homogenized in step (2), and then quench in cold water (4) Carry out aging treatment for 8 hours at 250 ℃ to the sample that step (3) solid solution treatment is completed.

Implementation example 2

A high-strength creep-resistant Sc-containing cast Al-Cu alloy and its aging heat treatment process include the following steps: (1) the preparation method of the alloy is to place pure Al in a melting furnace and heat it up to 730 ° C to melt, Then add Al-50wt.%Cu master alloy and Al-2wt.%Sc master alloy in specified ratio, keep stirring until completely melted, then control the temperature to 730°C, add 2% refining agent for refining, and let stand for 30min, Cast in a metal mold to prepare Al-2.3wt.%Cu-0.22wt.%Sc (hereinafter referred to as Al-2.3Cu-0.22Sc) aluminum alloy. (2) Homogenize the alloy ingot at 450°C for 4 hours; (3) Perform solution treatment at 590°C for 3 hours on the sample that has been homogenized in step (2), and then quench in cold water (4) Carry out aging treatment for 8 hours at 250 ℃ to the sample that step (3) solid solution treatment is completed.

Implementation example 3

The high-strength, creep-resistant, Sc-containing cast Al-Cu alloy and its aging heat treatment process include the following steps: (1) The alloy is prepared by heating pure Al in a melting furnace to 730°C until melting, and then adding The specified ratio of Al-50wt.% Cu master alloy and Al-2wt.% Sc master alloy is continuously stirred until it is completely melted, and then the temperature is controlled to 730°C, and 2% refining agent is added for refining. After standing for 30 minutes, the metal Casting in a mold to prepare an Al-2.5wt.%Cu-0.6wt.%Sc (hereinafter referred to as Al-2.5Cu-0.6Sc) aluminum alloy. (2) Homogenize the alloy ingot at 450°C for 4 hours; (3) Perform solution treatment at 590°C for 3 hours on the sample that has been homogenized in step (2), and then quench in cold water (4) Carry out aging treatment for 8 hours at 250 ℃ to the sample that step (3) solid solution treatment is completed.

Comparative example 1

Casting Al-Cu alloy and T6 aging heat treatment process, including the following steps: (1) The preparation method of the alloy is to heat pure Al in a smelting furnace to 730 ° C until melting, and then add a specified ratio of Al- 50wt.% Cu intermediate alloy, keep stirring until it is completely melted, then control the temperature to 730°C, add 2% refining agent for refining, let it stand for 30 minutes, and cast it in a metal mold to obtain Al-2.3wt.% Cu (below Referred to as Al-2.3Cu) aluminum alloy. (2) Homogenize the alloy ingot at 450°C for 4 hours; (3) Perform solution treatment at 590°C for 3 hours on the sample that has been homogenized in step (2), and then quench in cold water (4) Perform pre-aging treatment for 8 hours at 250° C. on the sample after solution treatment in step (3).

Referring to the accompanying drawings, the alloy Al-2.3Cu-0.22Sc alloy obtained in Example 2 and the alloy Al-2.3Cu alloy obtained in Comparative Example 1 are subjected to tensile testing according to GB/T228.1-2010, and the engineering stress-strain curve is shown in the figure 1, the test results show that the strength of Al-2.3Cu-0.3Sc is much higher than that of Al-2.3Cu, and the comparison results are shown in Table 1. It can be seen from Table 1 that the strength of Al-2.3Cu-0.22Sc is not only higher than Al-2.3Cu but also higher than other cast Al-Cu alloys (such as ZL203, ZL207). In order to study the effect of Sc on the strength improvement of Al-Cu alloy, TEM observations were carried out on Al-2.3Cu-0.22Sc alloy and Al-2.3Cu alloy respectively. Figure 2 shows Al-2.3Cu alloy respectively (Figure 2(a)) Compared with the TEM structure photo of Al-2.3Cu-0.22Sc alloy (Fig. 2(b)), comparing Fig. 2(a) and (b), it is obvious that the addition of Sc significantly increases the density of θ′-Al ₂ Cu precipitates in the matrix , reducing the size of θ′-Al ₂ Cu. There are two main reasons for this: on the one hand, the addition of Sc will promote the nucleation of θ′-Al ₂ Cu during the aging stage; on the other hand, Sc atoms tend to segregate at the interface between the θ′-Al ₂ Cu precipitate and the matrix. The growth and coarsening of θ′-Al ₂ Cu precipitates are suppressed during the aging process. Therefore, the size of θ′-Al ₂ Cu in Al-2.3Cu-0.22Sc alloy is smaller and the density is higher. Therefore, adding a small amount of Sc element to Al-Cu alloy can effectively improve the strength of Al-Cu alloy. In order to compare the high temperature creep resistance of the two alloys, the Al-2.3Cu-0.22Sc alloy and the Al-2.3Cu alloy were subjected to a high temperature tensile creep test according to GB/T2039. The test temperature was 250°C, and the test tensile force was 50Mpa. The test results are shown in Figure 3, Figure 3(a) is the time-strain curve of Al-2.3Cu alloy under the test condition of 250℃/50MPa, Figure 3(b) is the time-strain curve of Al-2.3Cu-0.22Sc alloy at 250℃ /50MPa time-strain curve under test conditions. The corresponding minimum creep rates (steady-state creep rates) of the two alloys are shown in Table 2. It can be seen that the minimum creep rate of the Al-2.3Cu-0.22Sc alloy is lower than that of the Al-2.3Cu alloy by 2 quantities The experimental results show that the high temperature creep resistance of Al-2.3Cu-0.22Sc alloy is obviously better than that of Al-2.3Cu alloy.

Table 1. Part of the cast Al-Cu alloy national standard (GB/T1173-1995) mechanical properties and the present invention

Performance comparison of Sc cast Al-Cu aluminum alloys

Table 2. Comparison of the creep properties of the cast Al-Cu aluminum alloy containing Sc in the T6 state and the regression reaging state

Alloy Code alloy state Minimum creep rate Comparative example 1 T6 9.47E-7 Implementation example 1 aging state 1.089E-8 Implementation example 2 aging state 1.089E-9 Implementation example 3 aging state 8.089E-9

Claims (4)

1. a kind of systems of Al-Cu containing the scandium cast aluminium alloy gold of high-strength creep resistant, it is characterised in that：The mass percent of Cu for 2.0- The mass percent that the mass percent that the mass percent of 5.0%, Sc are 0.1-0.5%, Si is 0.01-0.03%, Ti For 0.01-0.03%, remaining is Al and inevitable impurity.

2. casting and the heat treatment process of a kind of systems of Al-Cu containing the scandium cast aluminium alloy gold of high-strength creep resistant, it is characterised in that：It will be pure Al, which is placed in smelting furnace, is heated to 660-780 DEG C to melting, and then adds in Al-Cu intermediate alloys, the Al-Sc of regulation proportioning Intermediate alloy continues stirring until whole fusings, and temperature control adds in mass percentage 2%-5% refining agents to 735-750 DEG C afterwards It is refined, after standing 10-30min, casts in metal die, then carry out heat treatment process.

3. the casting and heat treatment of a kind of systems of Al-Cu containing the scandium cast aluminium alloy gold of high-strength creep resistant according to claim 2 Technique, it is characterised in that：The heat treatment process refers to：Homogenization Treatments-solution treatment-ageing treatment；Homogenization Treatments Temperature is：420-480 DEG C, soaking time is：3 it is small when -50 it is small when；Solid solution temperature is：510 DEG C -610 DEG C, during heat preservation Between be：30 minutes -15 it is small when, subsequent water quenching；Aging temperature is：200 DEG C -350 DEG C, soaking time is：1 it is small when -20 Hour.

4. the casting and heat treatment of a kind of systems of Al-Cu containing the scandium cast aluminium alloy gold of high-strength creep resistant according to claim 2 Technique, it is characterised in that：The refining agent refers to：General Al alloys refining agent.