Differential temperature forging process method for magnesium alloy seat pedal limiting piece

Abstract

The application discloses a differential temperature forging process method for a magnesium alloy seat pedal limiting piece, relates to the magnesium alloy processing and forming field, and specifically comprises the following steps: magnesium ingot two-stage homogenization annealing, wagon, flaw detection and sawing to obtain a preform, mold and preform lubrication, preform preheating and mold local preheating, forging, pressure holding forming, water cooling, trimming and annealing. The magnesium alloy forging die is an open die, comprises an upper concave die and a lower concave die matched with each other, the parting surface is located on the symmetry plane of the forging, and the flash pocket is connected with the die cavity through a flash bridge, wherein the die cavity is consistent with the shape of the forging, the surface roughness is controlled to be Ra≤0.2 microns, and the upper and lower concave dies are locally provided with heating rods. The method solves the problems of local difficult forming and low forming precision of the magnesium alloy seat pedal limiting piece forging, adopts the differential temperature forging method, makes the forging blank obtain good plasticity, and improves the forming precision and production efficiency of the forging.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy processing and forming, specifically relating to a differential temperature forging process for magnesium alloy seat footrest limiting parts. Background Technology

[0002] As the lightest metal currently available, magnesium alloys possess advantages such as low density, high machinability, good impact resistance, high specific strength and specific stiffness, excellent machinability, dimensional stability, and easy recyclability, making them promising for the automotive and aerospace industries. However, magnesium alloys have relatively low room temperature formability due to the limited number of operable slip systems at room temperature. Furthermore, magnesium alloy forgings exhibit high viscosity and poor fluidity at high temperatures, and their temperature sensitivity results in a narrow forging temperature range. Therefore, during hot forging, precise control of the billet temperature is crucial to prevent excessive deformation resistance, placing high demands on the plastic processing technology of magnesium alloy forgings.

[0003] The magnesium alloy seat footrest limiting component forging is Z-shaped with a symmetrical structure, including bosses, grooves, and ribs. The longitudinal section of the forging is stepped. Areas with an aspect ratio r ≥ 1.2 are difficult to form during forging. The aspect ratio r is determined by Y / X, where Y and X are the long and short sides of the smallest outer rectangle of the forging's minimum longitudinal section, respectively. Currently, magnesium alloy forging processes primarily use isothermal forging. Excessive preheating temperature or time can lead to excessive grain growth and coarsening, resulting in decreased strength of the formed part. Magnesium alloys have high thermal conductivity; during forging, if the billet comes into contact with a lower-temperature die, it is prone to cracking due to rapid cooling, reducing forming accuracy and yield. Furthermore, magnesium alloy deformation is highly sensitive to strain rate. Excessive strain rate can easily cause cracks in the forging, while excessively slow strain rate leads to low forging efficiency and high production costs. Summary of the Invention

[0004] To address the issues raised in the background art regarding the sensitivity of magnesium alloy seat footrest forgings to temperature and strain rate, the significant changes in their plastic deformation capacity under high temperature and force, and the difficulty in forming parts with an aspect ratio r ≥ 1.2, this invention addresses the problem by improving local plastic deformation capacity through local heating, providing a differential temperature forging process for magnesium alloys, including a differential temperature forging die for magnesium alloy forgings. The invention provides the following technical solution: The magnesium alloy forging die is an open die, consisting of a mating upper die and a lower die. The parting surface is located on the symmetrical plane of the forging. The flash compartment is connected to the die cavity via a flash bridge. The die cavity conforms to the shape of the forging, and the surface roughness is controlled to Ra≤0.2μm. Heating rods are installed in difficult-to-form areas with an aspect ratio r≥1.2. The heating rods are parallel to the parting surface and 8mm~10mm away from the cavity surface. The heating rods of both the upper and lower dies have a power of P, which is determined by... , The formula is defined as follows: Q is the required heat, n is the power redundancy coefficient, t is the required time, c is the specific heat capacity of the mold, m is the mass of the mold, and ΔT is the required temperature rise.

[0005] To achieve the above objectives, the following steps are specifically included: (1) Magnesium alloy ingots were selected as the forging raw material; (2) Place the magnesium alloy ingot into the resistance furnace for two-stage homogenization heat treatment. Raise the furnace temperature to 300℃~320℃ in 40min~60min and hold for 2h~4h. Then raise the furnace temperature to 380℃~420℃ in 10min~20min and hold for 8h~12h. After that, turn off the power of the resistance furnace and let it cool down to room temperature naturally. Move the magnesium alloy ingot out of the furnace for the next step of processing. (3) The ingot obtained in step (2) is machined and inspected to make its surface roughness Ra≤15μm. At the same time, the ingot is sawed to obtain a preform. The cross section of the preform is offset outward by 3mm~5mm from the maximum cross section profile of the forging to ensure that the volume of the preform is greater than the volume of the forging. (4) Apply graphite lubricant evenly to the surface of the mold cavity and the surface of the preform, and then let it air dry naturally. The composition of the graphite lubricant used is: 7% boric acid + 17% sodium nitrite + 5% graphite + the balance water. (5) The magnesium alloy preform is placed in an electric resistance furnace with argon gas for preheating. The preheating temperature is 300℃~350℃ and the holding time is 1.5h~2h. The upper and lower dies of the forging die are preheated locally by heating rods. The preheating temperature is 280℃~310℃. (6) The preheated magnesium alloy preform is loaded into the cavity of the lower die using a robotic clamp. The transfer time is controlled within 30s. After the die is positioned, it is forged on a forging hydraulic press, so that the excess part of the preform flows to the flash compartment through the flash bridge. The initial forging speed of the forging hydraulic press is 0.5mm / s~0.8mm / s. When the change amplitude of the forming pressure feedback of the hydraulic press is ≥300%, the forging speed is 0.1mm / s~0.4mm / s. ΔP is determined by P0 / Px, where P0 is the maximum pressure of the die contacting the preform within 0~2s, and Px is the pressure value during the forging process. The heating rods of the local forging die are kept in working condition during the forging process to ensure that the temperature of the difficult-to-form parts with an aspect ratio r≥1.2 is 280℃~310℃. (7) After forging is completed, the forging hydraulic press continues to be in the mold-closed state for 50s~60s to complete the forging forming; (8) Use a robotic arm to remove the forging from the workbench, take out the forging and place it in water, wait for it to cool to room temperature and then saw it to remove excess flash and shape it. (9) Anneal the forgings obtained in step (8) at a temperature of 300℃~350℃ for 0.5h~3h. After annealing, air cool the forgings after they are taken out of the furnace and then sandblasted to remove surface defects and oxides, thereby improving the surface finish and quality.

[0006] Compared with the prior art, the present invention has the following advantages and positive effects: 1. The forming method of the present invention can directly process and form the seat foot pedal limiting part by forging, while improving its mechanical properties. It avoids the cumbersome process of multiple heating, multiple mold changes and multiple pre-forming materials after forging. The operation is more convenient, the forming cycle is shortened, the production efficiency is improved, and the production cost is saved. The forging can be formed in one step using simple blanks, thereby shortening the entire forging process. 2. This invention reduces the local deformation temperature and increases the local heating height by locally increasing heating conditions within the forging die. This reduces the difference in plastic deformation capacity between the heated zone and the adjacent zone. Furthermore, within a certain temperature range, the higher the temperature, the easier the metal flows. This alters and controls the metal flow pattern, effectively reducing the forging deformation resistance, enabling the forging billet to achieve good plasticity, and improving the forming accuracy and quality of the forging. Attached Figure Description

[0007] Figure 1 A schematic diagram of the differential temperature forging process of magnesium alloy seat footrest limit component; Figure 2 Schematic diagram of a precast blank for a magnesium alloy seat footrest limiting component; Figure 3 This is a schematic diagram of a differential temperature forging die for a magnesium alloy seat footrest limiting component, where: 1. Upper die cavity; 2. Lower die cavity; 3. Parting surface; 4. Flash compartment; 5. Flash bridge; 6. Heating hole; 7. Heating rod; Figure 4 Schematic diagram of a magnesium alloy seat footrest limiting component forging; Figure 5 This is a graph showing the change in forging pressure over forging time during the forging process of a magnesium alloy seat footrest limiter. Detailed Implementation

[0008] This invention discloses a differential temperature forging process for magnesium alloy seat footrest limiting parts. The embodiments described below are only some embodiments of this process and should not be construed as limiting the scope of this process.

[0009] Using a ZA21EX square ingot with dimensions of 200mm*90mm*30mm as an example, its chemical composition and microstructure are shown in Table 1. The mold material is H-13 with a density of ρ=7.8g / cm³. 3 The specific heat capacity is c = 320 J / (kg*℃).

[0010] Specifically, the steps include the following: (1) Place the square ingot into the resistance furnace, raise the furnace temperature to 320°C in 50 minutes, keep it at that temperature for 2 hours, then raise the furnace temperature to 420°C in 10 minutes, keep it at that temperature for 12 hours, then turn off the power to the resistance furnace and let it cool down to room temperature naturally. Move the magnesium alloy ingot out of the furnace for the next step of processing. (2) The ingot obtained in step (1) is machined and inspected to make its surface roughness Ra≤15μm. At the same time, the ingot is sawed to obtain a preform. The cross section of the preform is offset outward by 5mm from the maximum cross section profile of the forging, and the height is 20mm, to ensure that the volume of the preform is greater than the volume of the forging. (3) Apply graphite lubricant evenly to the surface of the mold cavity and the surface of the preform, and then let it air dry naturally. The composition of the graphite lubricant used is: 7% boric acid + 17% sodium nitrite + 5% graphite + the balance water. (4) The magnesium alloy preform is placed in an argon-filled resistance furnace for preheating at 350°C for 2 hours. The upper and lower dies of the forging mold are preheated locally at 310°C using heating rods. , It can be seen that the heating rods configured for the upper and lower dies each have a power P of 0.5 kW, where the power redundancy factor n is taken as 2. (5) Use a robotic clamp to load the preheated magnesium alloy preform into the cavity of the lower die. The transfer time is controlled within 30s. After the die is positioned, forging is carried out on the forging hydraulic press, so that the preform flows to the surrounding flash compartment. The initial forging speed of the forging hydraulic press is 0.6mm / s, and the maximum feedback forming pressure of the forging hydraulic press within 0~2s is 250kN. When the feedback forming pressure of the hydraulic press is 750KN, at this time, the change amplitude of the feedback forming pressure of the hydraulic press △P≥300%, and the forging speed is uniformly adjusted to 0.2mm / s; (6) After forging is completed, the forging hydraulic press continues to maintain the mold closed state for 60 seconds to complete the forging forming; (7) Use a robotic arm to remove the forging from the workbench, take out the forging and place it in water, wait for it to cool to room temperature and then saw it to remove excess flash and shape it. (8) Anneal the forging obtained in step (7) at a temperature of 300°C for 2 hours. After annealing, air cool the forging and then sandblast it to remove surface defects and oxides, thereby improving the surface finish and quality.

Claims

1. A differential temperature forging process for a magnesium alloy seat footrest limiting component, characterized in that, The magnesium alloy seat footrest limiting forging is Z-shaped with a symmetrical structure, including bosses, grooves, and ribs. The longitudinal section of the forging is stepped. The process includes the following steps: Step 1: Use magnesium alloy ingots as forging blanks. Step 2: Homogenize the magnesium alloy ingot, then cool it to room temperature in the furnace. Step 3: The ingot obtained in Step 2 is machined, inspected for flaws, and sawn to obtain a precast billet. Step 4: Evenly coat the mold cavity surface and the magnesium alloy preform surface with graphite lubricant, and then air dry naturally. The graphite lubricant used has the following composition: 7% boric acid + 17% sodium nitrite + 5% graphite + balance water. Step 5: The preform obtained in Step 4 is sent to an electric resistance furnace for preheating. Simultaneously, the forging die is locally preheated using heating rods. Step Six: Place the preheated preform into the forging mold cavity using a robotic arm, controlling the transfer time within 30 seconds. After mold positioning, forge the preform on a hydraulic forging press according to the set forging process, allowing excess material to flow through the flash bridge to the flash storage area. Step 7: After forging is completed, the forging hydraulic press remains in the mold-closed state for 50-60 seconds to complete the forging process. Step 8: Remove the forging and cool it in water to room temperature. Then, mill and shape the edges while it is still cold. Step 9: Heat treat the forgings obtained in Step 8, and simultaneously sandblast to remove surface defects and oxides, thereby improving surface finish and quality; In step three, the preform cross-section is offset outward by 3mm to 5mm from the maximum cross-sectional profile of the magnesium alloy forging, ensuring that the volume of the preform is larger than the volume of the forging. The forging die in step five is an open die, including an upper die and a lower die that cooperate with each other. The parting surface is located on the symmetrical plane of the forging. The flash compartment is connected to the die cavity through a flash bridge. The die cavity is consistent with the shape of the forging, and the surface roughness is controlled to Ra≤0.2μm. Heating rods are installed in difficult-to-form areas where the aspect ratio r≥1.

2. The aspect ratio r is determined by Y / X, where Y and X are the long side and short side of the smallest outer rectangle of the smallest longitudinal section of the forging, respectively. The heating rods are parallel to the parting surface and 8mm~10mm away from the surface of the cavity. The heating rods configured for the upper die and the lower die each have a power of P, which is determined by... , The formula is defined as follows: Q is the required heat, n is the power redundancy coefficient, t is the required time, c is the specific heat capacity of the mold, m is the mass of the mold, and ΔT is the required temperature rise.

2. The differential temperature forging process for a magnesium alloy seat footrest limiting component as described in claim 1, characterized in that: In step two, the magnesium alloy ingot is first held at 300℃~320℃ for 2h~4h, and then the temperature is raised to 380℃~420℃ and held for 8h~12h for a two-stage homogenization heat treatment to eliminate casting segregation and make the microstructure uniform.

3. The differential temperature forging process for a magnesium alloy seat footrest limiting component as described in claim 1, characterized in that: In step five, the preheating temperature of the forging is 300℃~350℃, the holding time is 1.5h~2h, and argon gas is introduced into the resistance furnace as a protective gas. The local preheating temperature of the forging die is 280℃~310℃.

4. The differential temperature forging process for a magnesium alloy seat footrest limiting component as described in claim 1, characterized in that: In step six, the heating rods in the local area of ​​the forging die remain in working condition during the forging process to ensure that the temperature of the difficult-to-form parts with an aspect ratio r ≥ 1.2 is 280℃~310℃.

5. The differential temperature forging process for a magnesium alloy seat footrest limiting component as described in claim 1, characterized in that: In step six, the initial forging speed is 0.5 mm / s to 0.8 mm / s. When the change amplitude of the forming pressure feedback from the hydraulic press is ≥300%, the forging speed is 0.1 mm / s to 0.4 mm / s. ΔP is determined by P0 / Px, where P0 is the maximum pressure within 0 to 2 seconds of the die contacting the preform, and Px is the pressure value during the forging process.

6. The differential temperature forging process for a magnesium alloy seat footrest limiting component as described in claim 1, characterized in that: In step nine, the heat treatment process is annealing at a temperature of 300℃~350℃ for 0.5h~3h. After holding, the furnace is removed and air-cooled to eliminate residual stress generated during forging deformation and ensure forming accuracy.

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