Isothermal forging forming method for aviation titanium alloy complex die forging

Abstract

The invention discloses an isothermal forging forming method for a titanium alloy complex die forging for aviation, which is characterized in that the internal structure compactness of the forging is increased, the fiber direction and layout of the internal structure of the forging are optimized, the strength of the forging is improved, and the forging quality is improved by the technological processes of isothermal forging, isothermal pre-forging, corrosive washing, isothermal forging forming, heat treatment, secondary corrosive washing and the like at a specific temperature. The machining efficiency is improved; the machining cost is reduced; valuable material resources are saved; and the comprehensive performance of the forge piece is improved. The method is suitable for isothermal forging forming of titanium alloy complex die forgings for aviation.

Description

Technical Field

[0001] The present invention relates to a forging method, and particularly to an isothermal forging method for complex titanium alloy die forgings for aviation use. Background Art

[0002] Complex titanium alloy die forgings for aviation not only have certain requirements for their complex shapes, but also have particularly strict requirements for the internal tissue state and strength of their materials. Currently, in the processing of these parts, the commonly used process method is: according to the requirements of the material grade of the parts, bar stock is used for machining. Due to their complex shapes, it is necessary to use a variety of processing equipment such as wire cutting, electric pulse, numerical control machine tools, machining centers, and fitters for processing. The processed parts have rough appearances, low strength, are laborious and time-consuming, have many processes, low efficiency, high costs, and cause great waste of precious materials. Some use the method of pressure casting, which can overcome the problem of material waste, but the strength of the manufactured parts far fails to meet the service performance requirements. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a forming method for complex titanium alloy die forgings, which is an isothermal forging method that can not only improve the external dimensions of the forgings, but also enhance the material density and strength of the parts.

[0004] To solve the above problems, the isothermal forging method for complex titanium alloy die forgings for aviation according to the present invention uses TC4 alloy as the material, and its forging steps are as follows:

[0005] 1) When forging the billet, cut a bar of a certain specification according to the material used for making the parts, heat it to 20°C below the phase transition point, keep it warm for 2h, and then perform forging on a forging equipment. When forging, first compress and stretch radially, then compress and upset axially, and then compress and stretch radially again;

[0006] 2) The pre-forging uses die forging. Its heating temperature is 20°C below the phase transition point, the heat preservation time is 2h, the starting forging temperature is 20°C below the phase transition point, the final forging temperature is 50°C below the phase transition point, and the parting surfaces at both ends of the used die are zigzag;

[0007] 3) After pre-forging, place the pre-forged blank in an etching solution for etching and finishing to remove the surface oxide layer. Among them: the etching solution uses an aqueous solution of 5% - 15% sulfuric acid or 5% - 15% hydrochloric acid or a mixed aqueous solution of sulfuric acid and hydrochloric acid in any ratio of 5% - 15%, add 1% - 3% of potassium carbide by mass percentage, and the temperature of the etching solution is 50°C - 90°C;

[0008] 4) Adopt isothermal forging to form. Its heating temperature is 20°C below the phase transition point, the heat preservation time is 2h, the starting forging temperature is 20°C below the phase transition point, the terminal temperature is 50°C below the phase transition point, and the parting surfaces at both ends of the used die are zigzag;

[0009] 5) Anneal the formed complex titanium alloy die forging. Place the complex titanium alloy die forging in a heating furnace and heat it to 800 °C, hold for 2.5 h, take it out, and let it cool in the air; sample and inspect its metallographic structure and tensile strength according to the design requirements.

[0010] 6) Place the heat-treated complex titanium alloy die forging in an etching solution for etching and finishing to remove the surface oxide layer. Among them, the etching solution uses an aqueous solution of 5% - 15% sulfuric acid or 5% - 15% hydrochloric acid or a mixture of sulfuric acid and hydrochloric acid in any proportion of 5% - 15%, and add 1% - 3% potassium carbide by mass percentage. The temperature of the etching solution is 50 °C - 90 °C.

[0011] The heating rate during the forging blank, isothermal pre-forging, isothermal forging forming and heat treatment processes is controlled at 8 °C / min - 9 °C / min.

[0012] The mold during the isothermal pre-forging and isothermal forging forming processes is heated to 900 °C before forging.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] The isothermal forging forming method of the complex titanium alloy die forging for aviation uses isothermal forging forming, which can improve the comprehensive performance of the complex titanium alloy die forging, increase the tissue density, and the fiber direction follows the shape layout of the forging. While meeting various indicators, the strength of the forging can be increased by more than 1.1 times. At the same time, the processing efficiency is greatly improved, the processing cost can be reduced by more than 20%, and a large amount of precious material resources can be saved. The material utilization rate is increased by more than 70% compared with the traditional method. Specific Embodiments

[0015] To implement the isothermal forging forming method of the complex titanium alloy die forging for aviation described in the present invention, equipment such as a forging heating furnace, a press, and a manipulator need to be provided. Taking the TC4 alloy as an example, through processes such as forging blank, isothermal pre-forging using a mold, isothermal forging forming, and heat treatment, maintaining sufficient plasticity of the material, using a precision mold, and directly forging and forming to achieve the purpose of one-time forming of special-shaped parts. Moreover, through the rearrangement and refinement of its internal crystal lattice, the density and tensile strength of the internal tissue of the part are greatly enhanced, which is suitable for high-strength components for aviation. The specific embodiments are as follows:

[0016] Cut the TC4 alloy into bars according to certain specifications. Heat it to 20°C below the phase transformation point, and the heating rate should be controlled at 8°C / min. Keep it warm for 2 hours to make the temperature inside and outside the bar uniform. Then, forge it on a forging equipment. When forging, first compress and elongate it radially, compress and upset it axially, and then compress and elongate it radially; destroy the original crystal structure to form a coarse lattice structure and form a new fine lattice, and rearrange them to increase its density and strength to make a forging blank;

[0017] Heat the forging blank to 20°C below the phase transformation point, and the heating rate is controlled at 8°C / min. Keep it warm for 2 hours. Use a pre-forging die for pre-forging. The pre-forging die should be preheated to 900°C before forging to prevent the surface temperature of the forging blank from dropping too fast during forging, resulting in a decrease in surface plasticity and affecting forging. The starting forging temperature during forging is 20°C below the phase transformation point, and the final forging temperature should not be lower than 50°C below the phase transformation point to meet the requirements of forging for material plasticity, and cut off the flash. For easy die removal, the longer parting surface on the pre-forging die is made into a broken line shape;

[0018] Clean and trim the pre-forged blank in an etching solution to remove the oxide layer to prevent its surface from being brittle and hard, which affects isothermal forging forming. The etching solution uses an aqueous solution of 5% - 15% sulfuric acid or 5% - 15% hydrochloric acid or a mixture of sulfuric acid and hydrochloric acid in any proportion of 5% - 15%. Add 1% - 3% of potassium carbide by mass percentage. When etching, heat the etching solution to 50°C - 90°C to accelerate the etching speed and improve the etching efficiency;

[0019] Heat the pre-forged blank after etching and trimming to 20°C below the phase transformation point, and the heating rate is controlled at 8°C / min. The holding time is 2 hours. Perform isothermal forging forming on a forging equipment using a forming die. The die is preheated to 900°C before forging. During forging, the starting forging temperature should be controlled at 20°C below the phase transformation point, and the final forging temperature should not be lower than 50°C below the phase transformation point. Cut off the flash after isothermal forging forming;

[0020] Anneal the responsible die forgings formed by isothermal forging to improve the internal structure of the parts and increase the strength of the forgings. The method is to put the titanium alloy complex die forgings into a heating furnace and heat them to 800°C, and the heating rate is controlled at 8°C / min. Keep it warm for 2.5 hours, then take it out and cool it in the air. Sample and test its metallographic structure and tensile strength according to the design requirements;

[0021] Place the heat-treated isothermal forging formed complex titanium alloy die forging into the etching solution for etching to remove the oxide layer. The etching solution is an aqueous solution of 5% - 15% sulfuric acid or 5% - 15% hydrochloric acid or a mixture of sulfuric acid and hydrochloric acid in any proportion of 5% - 15%, and 1% - 3% of potassium carbide is added by mass percentage. The temperature of the hydrochloric acid is 50°C - 90°C. Trim the etched parts, and perform grinding and shot peening cleaning to eliminate burrs and rough surfaces.

Claims

1. An isothermal forging forming method for a complex die forging of titanium alloy for aviation, characterized in that It includes the following steps: 1) When forging the blank, cut a bar of a certain specification according to the material used for making the part, heat it to 20°C below the phase transformation point, keep it warm for 2 hours, and then forge it on a forging equipment. When forging, first compress and stretch it radially, then compress and upset it axially, and then compress and stretch it radially again; 2) The pre-forging adopts die forging, its heating temperature is 20°C below the phase transformation point, the holding time is 2 hours, the starting forging temperature is 20°C below the phase transformation point, the final forging temperature is 50°C below the phase transformation point, and the parting surfaces at both ends of the used die are zigzag; 3) After pre-forging, place the pre-forged blank in the etching solution for etching and finishing to remove the surface oxide layer. Among them: the etching solution adopts an aqueous solution of 5% - 15% sulfuric acid or 5% - 15% hydrochloric acid or a mixture of sulfuric acid and hydrochloric acid in any ratio of 5% - 15%, add 1% - 3% potassium carbide by mass percentage, and the temperature of the etching solution is 50°C - 90°C; 4) Adopt isothermal forging to form, its heating temperature is 20°C below the phase transformation point, the holding time is 2 hours, the starting forging temperature is 20°C below the phase transformation point, the terminal temperature is 50°C below the phase transformation point, and the parting surfaces at both ends of the used die are zigzag; 5) Anneal the formed complex die forging. Put the complex die forging into a heating furnace and heat it to 800°C, keep it warm for 2.5 hours, take it out, and place it in the air to cool; sample and test its metallographic structure and tensile strength according to the design requirements; 6) Place the heat-treated complex die forging in the etching solution for etching and finishing to remove the surface oxide layer. Among them, the etching solution adopts an aqueous solution of 5% - 15% sulfuric acid or 5% - 15% hydrochloric acid or a mixture of sulfuric acid and hydrochloric acid in any ratio of 5% - 15%, add 1% - 3% potassium carbide by mass percentage, and the temperature of the etching solution is 50°C - 90°C.

2. The isothermal forging forming method of the titanium alloy complex die forging for aviation according to claim 1, characterized in that: The heating rate during the forging blank, isothermal pre-forging, isothermal forging forming and heat treatment processes is controlled at 8°C / min - 9°C / min.

3. The isothermal forging forming method of the titanium alloy complex die forging for aviation according to claim 1, characterized in that: The die during the isothermal pre-forging and isothermal forging forming processes is heated to 900°C before forging.