CN114164381B - Method for optimizing mechanical properties of TC21 titanium alloy linear friction welding joint - Google Patents

Abstract

The invention discloses a method for optimizing the mechanical properties of a TC21 titanium alloy linear friction welded joint, which is specifically implemented according to the following steps: Step 1, perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; The sample in step 1 is placed in a heat treatment furnace for annealing heat treatment; in step 3, the sample subjected to heat treatment in step 2 is subjected to secondary annealing heat treatment. The invention effectively improves the joint structure, homogenizes the microhardness value of the joint and the base material, and improves the impact toughness value of the joint.

Description

Optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint

technical field

The invention belongs to the technical field of optimization methods for titanium alloy welding parts, in particular to a method for optimizing the mechanical properties of TC21 titanium alloy linear friction welding joints.

Background technique

Ti-6Al-3Mo-2Nb-2Sn-2Zr-1Cr, namely TC21 titanium alloy, is an α+β multi-structure titanium alloy developed by Northwest Nonferrous Metals Research Institute. The alloy has the comprehensive properties of high strength, high toughness and high damage tolerance, which meets the requirements of aircraft structural parts for the static strength and fatigue performance of damaged materials. , hanging engine joints and other parts, as well as the production of important or key load-bearing components that require high strength and durability. As a solid-phase welding technology, linear friction welding has the advantages of non-melting joints, high connection quality, less weld defects, and short welding time compared with traditional fusion welding methods. It can also overcome other friction welding methods. limitations, has broad application prospects.

For the TC21 titanium alloy connected by linear friction welding, the hardness value of the weld zone of the joint is significantly higher than that of the base metal, and the impact toughness value of the joint is significantly reduced, which seriously restricts the safe and reliable application of welded parts.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for optimizing the mechanical properties of a TC21 titanium alloy linear friction welded joint, so as to solve the problem of uneven joint hardness values existing in the prior art.

The technical solution adopted in the present invention is to carry out the overall double annealing heat treatment on the TC21 titanium alloy linear friction welded joint, and specifically implement it according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in step 2.

The feature of the present invention also lies in:

The annealing temperature in step 2 is 880-940°C, and the secondary annealing temperature in step 3 is 450-550°C.

Step 2 is implemented according to the following steps:

Step 2.1, heating the heat treatment furnace from room temperature to 880-940°C, then placing the sample in step 1 in the heat-treatment furnace, heating the heat-treatment furnace to 880-940°C again, and then maintaining the temperature;

In step 2.2, the heat preservation sample is cooled to room temperature in a heat treatment furnace to complete the annealing heat treatment.

In step 2.1, the heating rate of the heat treatment furnace is 1-15°C/min, and the holding time is 2-4h.

Step 3 is implemented according to the following steps:

Heat the heat treatment furnace to 450-550℃, then place the annealed and heat-treated samples in the heat-treatment furnace, and then heat up to 450-550℃ again at a speed of 1-15℃/min and keep the temperature. The middle furnace is cooled to room temperature, and the secondary annealing heat treatment is completed.

The holding time is 3.5-5.5h.

The beneficial effects of the invention are as follows: the invention provides a method for optimizing the mechanical properties of a TC21 titanium alloy linear friction welded joint, which can effectively improve the joint structure, homogenize the microhardness values of the joint and the base metal, and improve the impact toughness of the joint.

Description of drawings

Fig. 1 is the microstructure diagram of unheated joint after welding of the method for optimizing the mechanical properties of TC21 titanium alloy linear friction welded joint of the present invention;

Fig. 2 is the microstructure diagram of the joint after double annealing heat treatment in the method for optimizing the mechanical properties of the TC21 titanium alloy linear friction welded joint of the present invention;

Fig. 3 is the microhardness value of joint and base metal before and after double annealing heat treatment in the method for optimizing the mechanical properties of TC21 titanium alloy linear friction welded joints of the present invention;

Fig. 4 is the impact fracture position diagram of unheated joint after welding in the method for optimizing the mechanical properties of TC21 titanium alloy linear friction welded joint of the present invention;

Fig. 5 is the topography of the impact fracture of the unheated joint after welding in the method for optimizing the mechanical properties of the TC21 titanium alloy linear friction welded joint of the present invention;

6 is a diagram of the impact fracture position of the joint after double annealing heat treatment in the method for optimizing the mechanical properties of the TC21 titanium alloy linear friction welded joint of the present invention;

Fig. 7 is the topography of the impact fracture of the joint after double annealing heat treatment in the method for optimizing the mechanical properties of the TC21 titanium alloy linear friction welded joint of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The method for optimizing the mechanical properties of the TC21 titanium alloy linear friction welded joint of the present invention is specifically implemented according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment, and the annealing temperature is 880-940°C;

Step 2 is implemented according to the following steps:

Step 2.1. Heat the heat treatment furnace from room temperature to 880 to 940 °C at a rate of 1 to 15 °C/min, then place the sample in step 1 in the heat treatment furnace, and the heat treatment furnace is heated to 880 to 940 °C again, and then heat preservation. 2-4h;

Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in step 2, and the secondary annealing temperature is 450-550°C;

Step 3 is implemented according to the following steps:

The heat treatment furnace was heated to 450-550°C, and then the annealed and heat-treated samples were placed in the heat-treatment furnace, and then heated to 450-550°C again at a rate of 1-15°C/min and kept for 3.5-5.5 hours. The sample is cooled to room temperature together with the heat treatment furnace to complete the secondary annealing heat treatment.

Comparing the change law of microhardness and impact toughness of TC21 titanium alloy joints before and after heat treatment, it is found that the hardness value of the weld zone of the unheated joint after welding is about 460±10HV, the weld zone is narrow, and the hardness value gradually decreases after entering the thermally affected zone. , until the hardness value of the base metal is reached, which is stable in the range of 360±10HV; the impact toughness value is very low, and its average value is only 16.7±0.3J/cm ² . The TC21 titanium alloy linear friction welded joint obtained after the above steps of heat treatment has close hardness values of the joint and the base metal, approximately a horizontal straight line, and the fluctuation range of the hardness value is around 350±10HV; its impact toughness value is greatly increased to 49.4±0.3J /cm ² , which is about 3 times the impact toughness value of unheated joints. It can be seen that the microstructure of the joint after the heat treatment of the present invention is effectively improved, the hardness values of the joint and the base metal are approximately the same, and the impact toughness value of the joint is greatly increased.

Example 1

The optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint is implemented according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment, and the annealing temperature is 880°C;

Step 2 is implemented according to the following steps:

Step 2.1. The heat treatment furnace is heated from room temperature to 880°C at a rate of 1°C/min, then the sample in step 1 is placed in the heat treatment furnace, the heat treatment furnace is heated to 880°C again, and then kept for 2h;

Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in step 2, and the secondary annealing temperature is 450-550°C;

Step 3 is implemented according to the following steps:

Heat the heat treatment furnace to 450°C, then place the annealed and heat-treated samples in the heat treatment furnace, and then heat up to 450-550°C again at a rate of 1°C/min and keep it for 3.5h, the samples after the heat preservation are cooled together with the heat treatment furnace To room temperature, the secondary annealing heat treatment is completed.

Example 2

The optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint is implemented according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment, and the annealing temperature is 940°C;

Step 2 is implemented according to the following steps:

Step 2.1. The heat treatment furnace is heated from room temperature to 940 °C at a rate of 15 °C/min, then the sample in step 1 is placed in the heat treatment furnace, the heat treatment furnace is heated to 940 °C again, and then kept for 4 hours;

Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in step 2, and the secondary annealing temperature is 550°C;

Step 3 is implemented according to the following steps:

The heat treatment furnace was heated to 550°C, and then the annealed and heat-treated samples were placed in the heat treatment furnace, and then heated to 550°C again at a rate of 15°C/min and kept for 5.5 hours. The samples after the heat preservation were cooled to room temperature together with the heat treatment furnace. , complete the secondary annealing heat treatment.

Example 3

The optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint is implemented according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment, and the annealing temperature is 890°C;

Step 2 is implemented according to the following steps:

Step 2.1, the heat treatment furnace is heated from room temperature to 890 °C at a rate of 10 °C/min, then the sample in step 1 is placed in the heat treatment furnace, the heat treatment furnace is heated to 890 °C again, and then kept for 3 hours;

Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in Step 2, and the secondary annealing temperature is 470°C;

Step 3 is implemented according to the following steps:

The heat treatment furnace was heated to 470°C, then the annealed and heat-treated samples were placed in the heat treatment furnace, and then heated to 470°C again at a rate of 10°C/min and kept for 4.5 hours. The samples after the heat preservation were cooled to room temperature together with the heat treatment furnace. , complete the secondary annealing heat treatment.

Example 4

The optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint is implemented according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment, and the annealing temperature is 920°C;

Step 2 is implemented according to the following steps:

Step 2.1. The heat treatment furnace is heated from room temperature to 920°C at a rate of 13°C/min, then the sample in step 1 is placed in the heat treatment furnace, the heat treatment furnace is heated to 920°C again, and then kept for 3.5h;

Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in Step 2, and the secondary annealing temperature is 470°C;

Step 3 is implemented according to the following steps:

The heat treatment furnace was heated to 530 °C, and then the annealed and heat-treated samples were placed in the heat treatment furnace, and then heated to 530 °C again at a rate of 5 °C/min and kept for 5 hours. The samples after heat preservation were cooled to room temperature together with the heat treatment furnace. Complete the secondary annealing heat treatment.

Example 5

The optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint is implemented according to the following steps:

Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint;

Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment, and the annealing temperature is 900°C;

Step 2 is implemented according to the following steps:

Step 2.1. Heat the heat treatment furnace from room temperature to 900 °C at a rate of 13 °C/min, then place the sample in step 1 in the heat treatment furnace, and heat the heat treatment furnace to 900 °C again, and then keep it for 2.5h;

Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed;

Step 3. Perform secondary annealing heat treatment on the heat-treated sample in step 2, and the secondary annealing temperature is 500°C;

Step 3 is implemented according to the following steps:

The heat treatment furnace was heated to 500 °C, and then the annealed and heat-treated samples were placed in the heat treatment furnace, and then heated to 500 °C again at a rate of 13 °C/min and kept for 4 hours. Complete the secondary annealing heat treatment.

Figure 1 is the microstructure diagram of the post-weld unheated joint of TC21 titanium alloy linear friction welded joint. It can be seen from Figure 1(a) that the TC21 base metal is a needle-shaped mesh basket structure, and on the β-phase matrix, A large number of elongated primary α _p phases and a large number of small lamellar secondary α _s phases are interlaced with each other, and there is no obvious grain boundary; Figure 1(b) shows the structure of the joint weld zone, the coarse grains are clearly visible, and the grain boundaries are formed by long grains. The strip-shaped primary α _p phases are separated, and a large number of secondary α _s phases are dispersed in the grains.

Figure 2 is the microstructure diagram of the double annealed joint for the optimization method of the mechanical properties of the TC21 titanium alloy linear friction welded joint. It can be seen from Figure 2(a) that after double annealing, the long strip-shaped primary α _p phase of the base metal structure is transformed into short rod-shaped primary α At the same time, due to the longer annealing time, the dynamic recovery and recrystallization of the _{structure are relatively sufficient, and the proportion of the primary α p phase} increases significantly. Figure 2(b) shows the microstructure of the joint weld area after double annealing. The grains are broken, the primary α _p phase at the grain boundary is transformed into a short rod shape, and the intragranular secondary α _s phase undergoes dynamic recovery and recrystallization, transforming into an equiaxed shape And lamellar, that is, the grains are refined as a whole.

Figure 3 shows the microhardness values of the joint and base metal before and after double annealing heat treatment of the mechanical properties optimization method of TC21 titanium alloy linear friction welded joints. It can be seen from Figure 3 that the hardness value of the weld zone before heat treatment is about 460±10HV. The hardness value from the seam zone to the heat-affected zone gradually decreased, and finally stabilized at 360±10HV, reaching the hardness value of the base metal of TC21 titanium alloy. After double annealing, the hardness values of the joint and the base metal are close, approximately in a horizontal line, and the hardness value fluctuates around 350±10HV.

Figure 4 is a diagram of the impact fracture position of the unheated joint after welding of the mechanical properties optimization method of TC21 titanium alloy linear friction welded joint. It can be seen from Figure 4 that the impact fracture position of the original welded joint is in the center of the weld and near the thermally affected zone, and its expansion The path is slightly deflected.

Figure 5 is the impact fracture topography of the post-weld unheated joint of the TC21 titanium alloy linear friction welded joint. It can be seen from the figure that there are obvious cleavage facets and tearing edges in the crack initiation zone (Figure 5a). Clear river patterns can be seen in both the crack propagation zone (Fig. 5b) and the shear lip zone (Fig. 5c), which are typical cleavage fracture characteristics.

Figure 6 is a diagram of the impact fracture position of the joint after double annealing heat treatment for the optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint. It can be seen from the figure that after double annealing heat treatment, the fracture propagation path of the joint structure is divided into three parts: I, II and III. At this stage, it exhibits two approximately 90° bends.

Figure 7 is the topography of the impact fracture of the joint after double annealing heat treatment for the optimization method of mechanical properties of TC21 titanium alloy linear friction welded joint. It can be seen from the figure that after double annealing heat treatment, the crack initiation zone (Fig. 7b) and the shear lip area (Fig. 7c) are both composed of a large number of dimples, and there is no river pattern in the crack propagation area, which is a typical ductile fracture.

Comparing the change law of microhardness value and impact toughness value of TC21 titanium alloy linear friction welded joint before and after heat treatment, it is found that the impact toughness value of unheated joint is only 16.7±0.3J/cm ² ; after the above steps of heat treatment, the impact toughness value increases to 49.4 ±0.3J/cm ² , an increase of about 200%; the hardness values of the joint and the base metal after heat treatment are approximately equal, indicating that the joint and the base metal are uniform and stable. It can be seen that through the double annealing heat treatment of the present invention, the structure of the joint and the base metal can be effectively controlled, the hardness values of the joint and the base metal can be homogenized, and the impact toughness value of the joint can be significantly improved.

Claims (3)

1. TC21 titanium alloy linear friction welded joint mechanical property optimization method, is characterized in that, is specifically implemented according to the following steps: Step 1. Perform linear friction welding on the TC21 titanium alloy to obtain a TC21 titanium alloy sample with the original welded joint; Step 2, placing the sample in step 1 in a heat treatment furnace for annealing heat treatment; The step 2 is specifically implemented according to the following steps: Step 2.1, the heat treatment furnace is heated from room temperature to 880~940 °C, then the sample in step 1 is placed in the heat treatment furnace, and the heat treatment furnace is heated to 880~940 °C again, and then heat preservation; Step 2.2, the sample after heat preservation is cooled to room temperature in the heat treatment furnace, and the annealing heat treatment is completed; Step 3. Perform secondary annealing heat treatment on the heat-treated sample in step 2; The step 3 is specifically implemented according to the following steps: Heat the heat treatment furnace to 450~550 °C, then place the annealed and heat-treated samples in the heat treatment furnace, and then heat up to 450~550 °C again at a rate of 1~15 °C/min and keep warm. The samples after heat preservation are placed in the heat treatment furnace The middle furnace is cooled to room temperature, and the secondary annealing heat treatment is completed. 2. TC21 titanium alloy linear friction welded joint mechanical property optimization method according to claim 1, is characterized in that, in described step 2.1, the heating rate of heat treatment furnace is 1～15 ℃/min, and the holding time is 2～4h. 3. The method for optimizing the mechanical properties of TC21 titanium alloy linear friction welded joints according to claim 1, wherein the holding time of step 3 is 3.5～5.5h.

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