4-series aluminum alloy forged bar for automobile chassis suspension and production process of 4-series aluminum alloy forged bar

Abstract

The invention relates to a 4-series aluminum alloy forged bar for an automobile chassis suspension and a production process of the 4-series aluminum alloy forged bar, and belongs to the technical field of aluminum alloy processing and manufacturing. The high-strength and high-corrosion-resistance aluminum alloy forged bar is prepared through the technological processes of aluminum alloy smelting and casting, homogenizing, extruding, off-line quenching, aging and the like in sequence, specifically, by optimizing alloy components, controlling the casting process, adjusting the homogenizing system of a cast bar and controlling the parameter precision of the extruding process, the high-strength and high-corrosion-resistance aluminum alloy forged bar is obtained on the premise that the stable size of the profile is guaranteed, and the high-strength and high-corrosion-resistance aluminum alloy forged bar is obtained. The mechanical property of the high-silicon aluminum alloy bar is greatly improved, the yield strength can be larger than 360 Mpa, and the ductility is larger than 4.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy processing and manufacturing, and specifically relates to a 4-series aluminum alloy forged bar for automobile chassis suspension and a production process thereof. Background Art

[0002] 4 series aluminum alloy is a eutectic high-silicon difficult-to-deform aluminum alloy, with a silicon content of up to 11% to 13.5%, and belongs to the wrought aluminum in the A1-Si series deformed aluminum alloy. It has the characteristics of both cast aluminum alloy and deformed aluminum alloy, with good wear resistance, heat resistance, processing performance, and a small thermal expansion coefficient. Its main use is casting forgings, but it is also used to process thin plates or welding rods for welding and brazing. At the same time, due to its high high-temperature strength and good high-temperature corrosion resistance, it is also often used in the manufacture of pistons, piston bodies and other high-temperature use parts. Medium-high silicon 4 series aluminum alloy has the advantages of high strength, good resistance, and small thermal expansion, and is mainly used for parts such as automobile engine piston tails and compressor scrolls.

[0003] At present, the research on the alloy forming at home and abroad mainly focuses on the modification process, primary silicon size control, isothermal forging forming, powder sintering forming, etc., but it is rarely seen in the extrusion forming process with high manufacturing efficiency. In the technical solutions disclosed in the prior art, the aging hardening effect of 4 series aluminum alloy forging bars is poor, and there are technical problems such as low strength, insufficient mechanical properties and poor corrosion resistance. Summary of the invention

[0004] In view of this, the present invention discloses a 4 series aluminum alloy forged bar for automobile chassis suspension and a production process thereof, which are specifically as follows:

[0005] A 4-series aluminum alloy forged bar for automobile chassis suspension. The chemical composition of the 4-series aluminum alloy forged bar includes, by mass percentage, Si: 11.5%-12%, Fe: 0.10%-0.15%, Cu: 0.7%-0.74%, Mg: 1.12%-1.18%, Ni: 0.72%-0.76%, Zn: ≤0.25%, Cr: ≤0.10%, and the balance is Al.

[0006] The method of preparing a 4 series aluminum alloy forging bar using the above alloy composition comprises the following steps:

[0007] S1. Prepare the designed raw material components in proportion and put them into a smelting furnace for smelting. The smelting temperature is lower than 760°C. After the charge is completely melted, the melt is introduced into a static furnace and refined with pure nitrogen for 15 minutes. Then, the slag is removed by skimming to remove the slag and impurities on the surface of the melt. Then, the melt is refined, an aluminum strontium modifier is added, and the refining is performed for 8 to 10 minutes. Then, the aluminum alloy cast rod is obtained by casting.

[0008] S2. Homogenize the aluminum alloy casting rod, with the homogenization regime being 480°C to 500°C for 11h to 12h;

[0009] S3. Preheat the aluminum alloy casting rod, with the preheating temperature being 410°C to 430°C, and preheat the die in the extruder, with the preheating temperature being 450°C to 500°C. After preheating, feed the aluminum alloy casting rod into the extruder for extrusion, with the extrusion speed being 0.73 to 0.93 mm / s and the temperature at the extruder outlet being 390°C to 430°C to obtain an aluminum alloy forged rod;

[0010] S4. Perform off-line quenching on the aluminum alloy forged rod;

[0011] S5. Perform aging treatment on the aluminum alloy rod after off-line quenching.

[0012] As a supplement to the technical solution of the present invention, in step S1, the effective addition amount of strontium element in the aluminum strontium modifier is 0.01% to 0.05%.

[0013] As a supplement to the technical solution of the present invention, in step S2, the homogenization regime is 490°C for 12h

[0014] As a supplement to the technical solution of the present invention, in step S4, the off-line quenching regime is 510°C to 530°C for 2h to 3h, and then water-cooled.

[0015] As a supplement to the technical solution of the present invention, in step S5, the aging regime is 165°C to 175°C for 9h to 11h.

[0016] As a supplement to the technical solution of the present invention, the depth of the diversion pit of the extrusion die is 1.5 to 2 mm, the slope of the diversion pit is 15 to 30°, and the total length of the working belt of the die is 3 to 4 mm.

[0017] As a supplement to the technical solution of the present invention, the working belt includes a flow-promoting part and a flow-stabilizing part. The flow-promoting part is a diversion angle provided at the feeding port position of the working belt, and the angle of the diversion angle is 11 to 13°. The flow-stabilizing part does not have a diversion angle, and the flow-promoting part accounts for two-thirds of the total length of the working belt.

[0018] As a supplement to the technical solution of the present invention, the die material is high-molybdenum steel, and the molybdenum element content is 5% to 6%

[0019] As a supplement to the technical solution of the present invention, in step S3, after processing the aluminum alloy forged rod into 500 mm, it is fed into a 1250T horizontal extruder for extrusion. Brief Description of the Drawings

[0020] Figure 1 It is a schematic cross-sectional structure diagram of the extrusion die of the present invention.

[0021] Figure 2 is Figure 1 The enlarged schematic diagram of the structure at position A in

[0022] Figure 3 This is the high-magnification tissue schematic diagram of Example 1 of the present invention.

[0023] Figure 4 This is the intergranular corrosion detection schematic diagram of Example 1 of the present invention.

[0024] Figure 5 This is the high-magnification tissue schematic diagram of Example 2 of the present invention.

[0025] Figure 6 This is the intergranular corrosion detection schematic diagram of Example 2 of the present invention.

[0026] Figure 7 This is the high-magnification tissue schematic diagram of Example 3 of the present invention.

[0027] Figure 8 This is the intergranular corrosion detection schematic diagram of Example 3 of the present invention.

[0028] Figure 9 This is the physical diagram of the bar prepared in Comparative Example 1.

[0029] Figure 10 This is the physical diagram of the bar prepared in Comparative Example 2.

[0030] Figure 11 This is the physical diagram of the bar prepared in Comparative Example 3.

[0031] Figure 12 This is the physical diagram of the bar prepared in Comparative Example 4.

[0032] In the figure: 1. Diversion pit, 2. Working belt, 3. Relief, 4. Runner, 5. Flow-promoting part, 6. Flow-stabilizing part.

[0033] Beneficial effects: By optimizing the alloy composition of the 4-series aluminum alloy and strictly controlling the content of each element, the present invention realizes the technical effects of high corrosion resistance and high strength of the forged bars of the 4-series aluminum alloy prepared. In another aspect of the present invention, through the optimization of the process parameters in the extrusion stage and the improvement of the die structure, the technical problem of poor surface quality and no fracture of the produced aluminum alloy forged bars is avoided. Specific embodiments

[0034] The present invention discloses a 4-series aluminum alloy forged bar for automobile chassis suspension and its production process, and the specific content is as follows:

[0035] This application first discloses the composition of a 4-series aluminum alloy forging bar used in an automotive chassis suspension. The forging bar is used for subsequent forging. By mass percentage, the chemical composition of the 4-series aluminum alloy forging bar includes: Si: 11.5% - 12%, Fe: 0.10% - 0.15%, Cu: 0.7% - 0.74%, Mg: 1.12% - 1.18%, Ni: 0.72% - 0.76%, Zn: ≤0.25%, Cr: ≤0.01%, impurities ≤0.05%, and the balance is Al.

[0036] Control the Si content to 11.5 - 12% to make it close to the eutectic composition. When the melt solidifies, a large amount of Al-Si eutectic liquid phase is formed, reducing the viscosity and improving the fluidity. Excessive Si (>12%) will precipitate coarse primary Si phase, becoming the crack source, resulting in increased brittleness and reduced elongation. Insufficient Si (<11.5%) will cause a decrease in fluidity, an increase in the coefficient of thermal expansion, and insufficient wear resistance.

[0037] The main strengthening item of the alloy is Mg2Si. Ensure that the Si:Mg molar ratio is close to 2:1 to provide precipitation strengthening effect and improve the alloy strength.

[0038] The control of Cu in this alloy can improve the stability of the product's high-temperature performance, improve wear resistance, and synergistically act with elements such as Si and Mg in the alloy to optimize the distribution of precipitation phases and further improve the comprehensive mechanical properties. When the Cu content exceeds 0.74%, coarse Al2Cu phase will be formed, resulting in a decrease in the corrosion resistance of the alloy. When the Cu content is less than 0.7%, it will cause insufficient matrix strengthening and a decrease in high-temperature performance. Therefore, Cu is precisely controlled at 0.7% - 0.74%.

[0039] Adding a certain amount of Ni to the alloy will combine with Al to form the orthorhombic Al3Ni phase. Its crystal structure is composed of alternating Al and Ni atomic layers and has extremely high thermal stability. When the Ni content exceeds 0.76%, coarse Al3Ni phase will be formed, becoming the crack source. When the Ni content is less than 0.72%, it will cause insufficient high-temperature strength and high-temperature deformation. Therefore, Ni is precisely controlled at 0.72% - 0.76%.

[0040] Adding Fe to the alloy mainly regulates the morphology and distribution of intermetallic compounds to balance the high-temperature strength, toughness, and corrosion resistance of the alloy. When the Fe content is less than 0.1%, it will cause insufficient high-temperature strength and reduced corrosion resistance. When the Fe content exceeds 0.15%, a large amount of β-AlFeSi needle-like phase will be generated, resulting in a decrease in toughness. Therefore, Fe is controlled at 0.1% - 0.15%.

[0041] This application also discloses a production process for a 4-series aluminum alloy forging bar used in an automotive chassis suspension using the above alloy composition, which specifically includes the following steps:

[0042] S1. Prepare the designed raw material components in proportion and put them into a melting furnace for melting, with the melting temperature below 760°C.

[0043] The casting rod is specifically produced by the semi - continuous casting method. During the casting process, foam ceramic filtration is used to improve the purity of the molten metal. Control the melting temperature not to exceed 760°C to reduce metal burning loss and the change in the size of primary silicon, thereby affecting the formation of the second phase. By restricting alloy components and avoiding aluminum mixing, control the content of the second phase Mg2Si within the range of 1.5% - 1.8% and the content of CuAl2 within the range of 0.7% - 0.8%. This can retain a large amount of primary silicon, a small amount of the second - phase strengthening phases Mg2Si and CuAl2 particles in the aluminum matrix, which is used to improve the strength and corrosion resistance of the product.

[0044] After all the furnace charge is melted, transfer the melt into a holding furnace, refine it with pure nitrogen for 15 minutes, then skim the scum and impurities on the surface of the melt, and then refine the melt. Adding an aluminum - strontium modifier mainly aims to refine eutectic silicon, improve strength, plasticity and toughness, and improve casting fluidity, reducing defects. The strontium content is precisely controlled within the range of 0.01 - 0.05%, which needs to be achieved through master alloy addition, melt protection and real - time detection. This range can not only ensure sufficient refinement of the silicon phase but also avoid excessive refinement of the silicon phase or the formation of brittle Sr compounds due to excessive amount. Refine for 8 - 10 minutes, and then carry out casting treatment to obtain an aluminum alloy casting rod;

[0045] S2. Perform homogenization treatment on the aluminum alloy casting rod, and the homogenization regime is 480°C - 500°C x 11h - 12h;

[0046] Preferably, the homogenization regime is specifically 490°C x 12h.

[0047] S3. Preheat the aluminum alloy casting rod, with the preheating temperature being 410°C - 430°C, preheat the die in the extruder, with the preheating temperature being 450°C - 500°C. After preheating, send the aluminum alloy casting rod into the extruder for extrusion, with the extrusion speed being 0.73 - 0.93 mm / s, to obtain an aluminum alloy forged bar; This regime can more effectively eliminate dendritic segregation and non - equilibrium phases, reduce the cracking tendency during later extrusion, lay a better tissue foundation for later heat treatment, and ensure the precipitation strengthening effect.

[0048] Controlling the heating temperature of the ingot to 410℃~430℃ can not only improve the extrudability of the aluminum rod, but also improve the surface quality of the rod product after extrusion. When the heating temperature of the ingot is lower than 410℃, the metal fluidity is poor, resulting in increased extrusion force, thereby reducing the extrudability. When the heating temperature of the ingot is higher than 430℃, the surface tension of the aluminum metal increases when it is extruded by the mold at high temperature and high pressure. The second phase in the aluminum matrix, such as eutectic silicon and primary silicon, tends to aggregate and grow, and the bonding force with the aluminum matrix becomes poor, resulting in continuous microcracks on the surface of the product. In order to better improve the surface quality of the product, the outlet temperature should also be controlled within the range of 390~430℃, the temperature should be controlled from the initial end of the extruded product, and the extrusion speed should be within the range of 0.73~0.93mm / s. If the extrusion speed is too low or too fast, the product outlet temperature will immediately get out of control and affect the extrudability and surface quality of the product.

[0049] Since 4 series aluminum alloys are hard alloys, they have poor extrusion performance, are difficult to form during the extrusion process, and have a large deformation resistance. The material hardness is close to that of ordinary gray cast iron. In order to improve the extrudability of 4 series aluminum alloys, reduce deformation resistance, optimize extrusion process parameters, and obtain extruded bar products with good surface, the traditional extrusion process is used. During the extrusion process, defects such as mold blocking, aluminum return of the extrusion barrel, and cracking of the profile surface will occur. The present application improves the surface quality of the bars while avoiding the technical problem of fracture by reducing the preheating temperature of the cast bars and the extrusion die and reducing the extrusion speed. However, the traditional technical solution uses the higher preheating temperature of the cast bars and the extrusion die and the higher extrusion speed, which easily leads to the technical problem that the extruded bars have poor surface quality and are prone to fracture.

[0050] S4. Offline quenching is performed on aluminum alloy forging bars, and the specific offline quenching system is 510℃~530℃×2h~3h; due to the limitation of extrusion process, the 4 series bar products cannot reach the required solid solution temperature and cooling rate of the material, and cannot be continuously extruded and quenched online to obtain higher mechanical properties. Offline quenching should be adopted, and the high-temperature solid solution system is (510℃~530℃×2h~3h). The Si, Cu, and Mg atoms in the alloy diffuse faster at high temperature, causing them to dissolve into the aluminum matrix to form a supersaturated solid solution with severe lattice distortion. In addition, a high cooling rate and water cooling are used to obtain more vacancy concentrations around the solid solution, which is a necessary condition for subsequent aging strengthening.

[0051] Preferably, the off-line quenching system is 515°C×3h.

[0052] S5. Aging treatment is performed on the aluminum alloy bars after offline quenching, and the specific aging treatment system is 165℃~175℃×9h~11h. After offline solution treatment of the profile, the second phase dissolved in the matrix has high distortion energy, while the surrounding vacancy energy is low. The second phase, such as eutectic silicon, CuAl2, AlFeMgCu, Mg2Si and other multi-element eutectic replacements, will spontaneously precipitate at the vacancies to form GP zones, achieving the effect of second phase precipitation strengthening. When the aging temperature is lower than 165℃ and the insulation aging time is less than 9h, the concentration of the second phase precipitation is low, the number of GP zones is small, and the strengthening effect is not obvious. When the temperature and insulation time are higher than the control range, the GP zone will aggregate and coarsen, detach from the parent item, and be incoherent with the aluminum matrix, forming a stable second item cluster, and the strengthening effect will be significantly reduced.

[0053] In the above step S3, the extrusion die in the extruder is as follows Figure 1 As shown, the die is provided with a guide pit, a working belt, an empty knife and a flow channel in sequence along the extrusion direction.

[0054] The present invention optimizes the depth of the channel pit of the extrusion die to improve the fluidity of the ingot in the die, improve the extrudable performance of the product, and optimize the die structure. The traditional flat die structure die has no diversion pit. The present invention adopts a die structure with a diversion pit design. The diversion pit has a depth of 1.5 to 2 mm. The diversion pit is funnel-shaped with a slope of 15 to 30 degrees. This design optimizes the material flow so that the metal enters the die hole evenly, reduces turbulence and stress concentration, and avoids cracks. The flow velocity distribution can be controlled more accurately, and the coarse grain layer and streamline defects can be reduced, thereby ensuring the stability of the mechanical properties of the product. Reducing the extrusion force allows the material to gradually transition to the die hole, reducing the peak pressure and reducing die loss.

[0055] Preferably, the working belt includes a flow-promoting part and a flow-stabilizing part. The flow-promoting part is a flow-guiding angle set at the inlet of the working belt, and the flow-guiding angle is 11-13°. The flow-stabilizing part does not have a flow-guiding angle and has the same structure as the traditional working belt. The flow-promoting part occupies two-thirds of the total length of the working belt. By setting the flow-promoting part, the metal fluidity can be improved, and the surface quality of the bar can be further improved.

[0056] To improve the surface quality of the product, the width of the working belt is reduced from 5mm to 3-4mm. This change reduces the friction between the surface and the working belt during the product forming process and greatly improves the surface quality. To increase the pressure that the mold can withstand on high-hardness aluminum ingots, high-molybdenum steel specially used for extrusion molds is used, with a molybdenum content of 5%-6%.

[0057] Embodiment 1. A production process of 4 series aluminum alloy forging bars for automobile chassis suspension, specifically comprising the following steps:

[0058] S1. Prepare the following raw materials in proportion and put them into the melting furnace for melting.

[0059] Si: 11.53%, Fe: 0.10%, Cu: 0.7%, Mg: 1.12%, Ni: 0.72%, Zn: 0.01%, Cr: 0.010%, impurities ≤ 0.05%, the balance is Al.

[0060] The casting rod is specifically produced by the semi - continuous casting method. During the casting process, foam ceramic filtration is used to improve the purity of the molten metal. The melting temperature is controlled not to exceed 760°C.

[0061] After all the furnace charges are melted, the melt is introduced into the holding furnace, refined with pure nitrogen for 15 minutes, then skimmed to remove the scum and impurities on the surface of the melt, and then the melt is refined. An aluminum - strontium modifier is added, and the effective addition amount of strontium element is controlled at 0.03%. After refining for 8 minutes, casting treatment is carried out to obtain an aluminum alloy casting rod;

[0062] S2. Homogenize the aluminum alloy casting rod, and the homogenization system is 480°C x 11h;

[0063] S3. Preheat the aluminum alloy casting rod. The diameter of the aluminum alloy casting rod is 151mm and the length of the ingot is 500mm. The preheating temperature of the ingot is 430°C, and the die in the extruder is preheated to 460°C. After preheating, the aluminum alloy casting rod is fed into the extruder for extrusion. The temperature of the extrusion cylinder is 422°C, and the extrusion speed is 0.81mm / s to obtain an aluminum alloy forged bar; the depth of the diversion pit of the extrusion die is 1.6mm, the slope is 17°, the width of the working belt is 3mm, the slope angle of the flow - promoting part of the working belt is 12°, and the molybdenum content of the die steel is 5.2%.

[0064] S4. Perform off - line quenching on the aluminum alloy forged bar, and the off - line quenching system is specifically 515°C × 2.5h.

[0065] S5. Perform aging treatment on the aluminum alloy bar after off - line quenching, and the aging treatment system is specifically 175°C × 10h.

[0066] Perform high - magnification microstructure inspection on the forged bar prepared in this embodiment. Testing equipment: AXIO universal research - grade inverted material microscope. Testing standard: GB / T6892 - 2015 Aluminum and aluminum alloy extruded profiles for general industrial use. Testing method: GB / T3246.1 - 2012 Test methods for the microstructure of wrought aluminum and aluminum alloy products - Part 1: Microstructure inspection methods.

[0067] As Figure 3 shown in (a) and 3(b), the microstructure is uniform and no over - burning defects are found.

[0068] The mechanical properties of the forged bars prepared in this embodiment were tested. Testing equipment: AG-X100KN electronic universal testing machine. Testing standard: GB / T16865-2013 Samples and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloy Products.

[0069] The yield strength was 383 Mpa, the tensile strength was 415 Mpa, and the elongation after fracture was 5.0%.

[0070] The intergranular corrosion of the forged bars prepared in this embodiment was tested. Testing equipment: AXIO universal research-grade inverted material microscope. Testing standard: ISO11846 Method B.

[0071] As Figure 4 shown, the intergranular corrosion depth of the forged bars prepared in this application was 233.22 microns.

[0072] Example 2. A production process of 4-series aluminum alloy forged bars for automobile chassis suspension specifically includes the following steps:

[0073] S1. Prepare and put the following raw material components into the melting furnace according to the proportion for melting.

[0074] Si: 11.53%, Fe: 0.14%, Cu: 0.73%, Mg: 1.14%, Ni: 0.73%, Zn: 0.01%, Cr: 0.01%, impurities ≤ 0.05%, the balance is Al.

[0075] The cast bars were specifically produced by the semi-continuous casting method. During the casting process, foam ceramic filtration was used to improve the purity of the molten metal. The melting temperature was controlled not to exceed 760 °C.

[0076] After all the furnace charges were melted, the melt was introduced into the holding furnace, refined with pure nitrogen for 15 minutes, then skimmed to remove the scum and impurities on the surface of the melt, and then the melt was refined. An aluminum-strontium modifier was added, and the effective addition amount of strontium element was controlled to be 0.04%. After refining for 9 minutes, casting treatment was carried out to obtain aluminum alloy cast bars;

[0077] S2. The aluminum alloy cast bars were subjected to homogenization treatment, and the homogenization system was 490 °C x 12 h;

[0078] S3. Preheat the aluminum alloy casting rod with a diameter of 151 mm and a length of 500 mm. The preheating temperature of the casting ingot is 425 °C, and preheat the die in the extruder with a preheating temperature of 450 °C. After preheating, feed the aluminum alloy casting rod into the extruder for extrusion. The temperature of the extrusion cylinder is 422 °C, and the extrusion speed is 0.9 mm / s to obtain an aluminum alloy forged bar; the depth of the diversion pit of the extrusion die is 1.6 mm, the slope is 17°, the width of the working belt is 3 mm, the slope angle of the flow-promoting part of the working belt is 12.2°, and the molybdenum content of the die steel is 5.2%.

[0079] S4. Perform off-line quenching on the aluminum alloy forged bar, and the off-line quenching regime is specifically 510 °C × 2 h.

[0080] S5. Perform aging treatment on the aluminum alloy bar after off-line quenching, and the aging treatment regime is specifically 170 °C × 9 h.

[0081] Perform mechanical property testing on the forged bar prepared in this example. Testing equipment: AG-X100KN electronic universal testing machine. Testing standard: GB / T16865-2013 Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys.

[0082] The yield strength is 366 Mpa, the tensile strength is 394 Mpa, and the elongation after fracture is 5.0%.

[0083] As Figure 5 (a), 5(b) show the schematic diagram of the high-magnification structure detection of this example. The structure is uniform and no overburn defects are found.

[0084] Perform intergranular corrosion detection on the forged bar prepared in this example. Testing equipment: AXIO universal research-grade inverted material microscope. Testing standard: ISO11846 Method B.

[0085] As Figure 6 shown is the schematic diagram of the intergranular corrosion detection of this example. The intergranular corrosion depth of the forged bar prepared in this application is 281.36 microns.

[0086] Example 3. A production process for a 4-series aluminum alloy forged bar for an automotive chassis suspension, specifically including the following steps:

[0087] S1. Prepare and put the following raw material components in proportion into the melting furnace for melting.

[0088] Si: 11.82%, Fe: 0.12%, Cu: 0.72%, Mg: 1.18%, Ni: 0.72%, Zn: 0.01%, Cr: 0.01%, impurities ≤ 0.05%, and the balance is Al.

[0089] The casting rod is specifically produced by the semi - continuous casting method, and foam ceramic filtration is used during the casting process to improve the purity of the molten metal. The melting temperature is controlled not to exceed 760 °C.

[0090] After all the furnace charge is melted, the melt is introduced into the holding furnace, refined with pure nitrogen for 15 minutes, then slag is skimmed off to remove the dross and impurities on the surface of the melt, and then the melt is refined again. An aluminum - strontium modifier is added, and the effective addition amount of strontium element is controlled at 0.04%. After refining for 10 minutes, casting treatment is carried out to obtain an aluminum alloy casting rod.

[0091] S2. The aluminum alloy casting rod is subjected to homogenization treatment, and the homogenization system is 490 °C x 12 h.

[0092] S3. The aluminum alloy casting rod is pre - heated. The diameter of the casting rod is 151 mm and the length of the ingot is 500 mm. The pre - heating temperature of the ingot is 420 °C, and the die in the extruder is pre - heated, with the pre - heating temperature being 450 °C. After pre - heating, the aluminum alloy casting rod is fed into the extruder for extrusion. The temperature of the extrusion cylinder is 422 °C, and the extrusion speed is 0.75 mm / s to obtain an aluminum alloy forged bar; the depth of the diversion pit of the extrusion die is 1.6 mm, the slope is 17°, the width of the working belt is 3 mm, the slope angle of the flow - promoting part of the working belt is 11.8°, and the molybdenum content of the die steel is 5.2%.

[0093] S4. The aluminum alloy forged bar is subjected to offline quenching, and the offline quenching system is specifically 525 °C × 2 h.

[0094] S5. The aluminum alloy bar after offline quenching is subjected to aging treatment, and the aging treatment system is specifically 1175 °C × 10 h.

[0095] The mechanical properties of the forged bar prepared in this example are detected. Testing equipment: AG - X100KN electronic universal testing machine. Testing standard: GB / T16865 - 2013 Test Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys.

[0096] The yield strength is 415 Mpa, the tensile strength is 428 Mpa, and the elongation after fracture is 4.5%.

[0097] As Figure 7 (a), 7(b) show the high - magnification structure detection schematic diagram of this example. The structure is uniform and no over - burning defects are found.

[0098] As Figure 8 This is the schematic diagram of intergranular corrosion detection of this example, and the intergranular corrosion depth is 273.22 microns.

[0099] Comparative Example 1. A production process of a 4 - series aluminum alloy forged bar for automobile chassis suspension specifically includes the following steps:

[0100] S1. Prepare and put the following raw material components in proportion into a melting furnace for melting.

[0101] Si: 12.6%, Fe: 0.2%, Cu: 0.36%, Mg: 1%, Ni: 0.58%, Zn: 0.01%, Cr: 0.01%, impurities ≤ 0.05%, the balance is Al.

[0102] The cast rod is specifically produced by the semi - continuous casting method. During the casting process, foam ceramic filtration is used to improve the purity of the molten metal. Control the melting temperature not to exceed 760 °C.

[0103] After all the furnace charge is melted, pour the melt into a holding furnace, refine it with pure nitrogen for 15 minutes, then skim the scum and impurities on the surface of the melt, then refine the melt again, add an aluminum - strontium modifier, control the effective addition amount of strontium element to 0.04%, refine for 9 minutes, and then carry out casting treatment to obtain an aluminum alloy cast rod;

[0104] S2. Carry out homogenization treatment on the aluminum alloy cast rod, and the homogenization system is 490 °C x 12 h;

[0105] Preheat the aluminum alloy cast rod. The diameter of the aluminum alloy cast rod is 151 mm and the length of the ingot is 500 mm. The preheating temperature of the ingot is 425 °C, preheat the die in the extruder, the preheating temperature is 450 °C. After preheating, send the aluminum alloy cast rod into the extruder for extrusion. The temperature of the extrusion cylinder is 422 °C, the extrusion speed is 0.9 mm / s, and an aluminum alloy forged bar is obtained; the depth of the diversion pit of the extrusion die is 1.6 mm, the slope is 17°, the width of the working belt is 3 mm, the slope angle of the flow - promoting part of the working belt is 12.2°, and the molybdenum content of the die steel is 5.2%.

[0106] S4. Carry out off - line quenching on the aluminum alloy forged bar, and the off - line quenching system is specifically 510 °C × 2 h.

[0107] S5. Carry out aging treatment on the aluminum alloy bar after off - line quenching, and the aging treatment system is specifically 170 °C × 9 h.

[0108] Carry out mechanical property testing on the forged bar prepared in this comparative example. Testing equipment: AG - X100KN electronic universal testing machine. Testing standard: GB / T16865 - 2013 Test Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys.

[0109] The yield strength is 344 Mpa, the tensile strength is 388 Mpa, and the elongation after fracture is 5.0%.

[0110] Carry out intergranular corrosion testing on the forged bar prepared in this example. Testing equipment: AXIO universal research - grade inverted material microscope. Testing standard: ISO11846 Method B.

[0111] As Figure 4 shown, the intergranular corrosion depth of the forged bar prepared in this application is 233.22 microns.

[0112] The forged bar prepared in this comparative example was subjected to intergranular corrosion detection. Testing equipment: AXIO universal research-grade inverted material microscope. Testing standard: ISO11846 Method B.

[0113] As Figure 9 shown in the figure is the schematic diagram of the intergranular corrosion detection of the comparative example. The intergranular corrosion depth of the forged bar prepared in this application is 309.15 microns.

[0114] Comparative Example 2. A production process of a 4-series aluminum alloy forged bar for automotive chassis suspension, specifically including the following steps:

[0115] S1. Prepare and put into the melting furnace for melting according to the following raw material components in proportion.

[0116] Si: 11.53%, Fe: 0.14%, Cu: 0.73%, Mg: 1.14%, Ni: 0.73%, Zn: 0.01%, Cr: 0.01%, impurities ≤ 0.05%, the balance is Al.

[0117] The cast bar is specifically produced by the semi-continuous casting method. During the casting process, foam ceramic filtration is used to improve the purity of the molten metal. Control the melting temperature not to exceed 760°C.

[0118] After all the furnace charges are melted, pour the melt into the holding furnace, refine it with pure nitrogen for 15 minutes, then skim the scum and impurities on the surface of the melt, then refine the melt, add an aluminum strontium modifier, control the effective addition amount of strontium element to 0.04%, refine for 9 minutes, and then carry out casting treatment to obtain an aluminum alloy cast bar;

[0119] S2. Perform homogenization treatment on the aluminum alloy cast bar. The homogenization system is 490°C x 12h;

[0120] S3. Preheat the aluminum alloy cast bar. The diameter of the aluminum alloy cast bar is 151 mm and the length of the ingot is 500 mm. The preheating temperature of the ingot is 425°C, preheat the die in the extruder, the preheating temperature is 450°C, after preheating, send the aluminum alloy cast bar into the extruder for extrusion, the temperature of the extrusion cylinder is 422°C, the extrusion speed is 0.9 mm / s, and obtain an aluminum alloy forged bar; the extrusion die adopts a traditional bar die, without a diversion pit, the working belt width is 2 mm, and the molybdenum content of the die steel is 5.2%.

[0121] S4. Perform offline quenching on the aluminum alloy forged bar. The offline quenching system is specifically 510°C × 2h.

[0122] S5. The aluminum alloy bars after offline quenching are subjected to aging treatment, and the aging treatment regime is specifically 170 °C × 9 h.

[0123] The mechanical properties of the forged bars prepared in this comparative example are tested. Testing equipment: AG-X100KN electronic universal testing machine. Testing standard: GB / T16865-2013 Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys.

[0124] The yield strength is 366 Mpa, the tensile strength is 410 Mpa, and the elongation after fracture is 5.0%.

[0125] As Figure 10 shown, the physical diagram of the bars prepared in this comparative example is presented, and it can be seen that cracks appear on the surface of the bars.

[0126] Comparative Example 3. A production process of 4-series aluminum alloy forged bars for automotive chassis suspension specifically includes the following steps:

[0127] S1. Prepare and put the following raw material components into the melting furnace according to the proportion for melting.

[0128] Si: 11.53%, Fe: 0.14%, Cu: 0.73%, Mg: 1.14%, Ni: 0.73%, Zn: 0.01%, Cr: 0.01%, impurities ≤ 0.05%, and the balance is Al.

[0129] The cast bars are specifically produced by the semi-continuous casting method, and foam ceramic filtration is used during the casting process to improve the purity of the molten metal. Control the melting temperature not to exceed 760 °C.

[0130] After all the furnace charges are melted, the melt is introduced into the holding furnace, refined with pure nitrogen for 15 minutes, then skimmed to remove the dross and impurities on the surface of the melt, and then the melt is refined. An aluminum-strontium modifier is added, and the effective addition amount of strontium element is controlled to be 0.04%. Refine for 9 minutes, and then carry out casting treatment to obtain aluminum alloy cast bars;

[0131] S2. The aluminum alloy cast bars are subjected to homogenization treatment, and the homogenization regime is 490 °C x 12 h;

[0132] S3. The aluminum alloy cast bars are preheated. The diameter of the aluminum alloy cast bars is 151 mm, and the length of the ingot is 500 mm. The preheating temperature of the ingot bottom is 476 °C, the die in the extruder is preheated, and the preheating temperature is 485 °C. After preheating, the aluminum alloy cast bars are fed into the extruder for extrusion. The temperature of the extrusion cylinder is 422 °C, the extrusion speed is 1.8 mm / s, the depth of the diversion pit of the extrusion die is 1.6 mm, the slope is 17°, the width of the working belt is 3 mm, the slope angle of the flow-promoting part of the working belt is 12.2°, and the molybdenum content of the die steel is 5.2%.

[0133] S4. Perform off-line quenching on the forged aluminum alloy bar, and the off-line quenching regime is specifically 510 °C × 2 h.

[0134] S5. Perform aging treatment on the off-line quenched aluminum alloy bar, and the aging treatment regime is specifically 170 °C × 9 h.

[0135] Perform mechanical property testing on the forged bar prepared in this comparative example. Testing equipment: AG-X100KN electronic universal testing machine. Testing standard: GB / T16865-2013 Specimens and methods for tensile testing of wrought aluminum, magnesium and their alloys.

[0136] The yield strength is 354 Mpa, the tensile strength is 403 Mpa, and the elongation after fracture is 5.0%.

[0137] Observe the surface quality of the forged bar prepared in this comparative example. As Figure 11 shown, it is the physical drawing of the bar prepared in this comparative example, and it can be seen that the surface of the bar is rough and has cracks.

[0138] Comparative Example 4. A production process of a 4-series aluminum alloy forged bar for automobile chassis suspension, specifically including the following steps:

[0139] S1. Prepare and put into the melting furnace for melting according to the following raw material components in proportion.

[0140] Si: 11.82%, Fe: 0.12%, Cu: 0.72%, Mg: 1.18%, Ni: 0.72%, Zn: 0.01%, Cr: 0.01%, impurities ≤ 0.05%, and the balance is Al.

[0141] The casting rod is specifically produced by the semi-continuous casting method, and foam ceramic filtration is used during the casting process to improve the purity of the molten metal. Control the melting temperature not to exceed 760 °C.

[0142] After all the furnace charges are melted, pour the melt into the holding furnace, refine it with pure nitrogen for 15 minutes, then skim the scum and impurities on the surface of the melt, then refine the melt, add an aluminum-strontium modifier, control the effective addition amount of strontium element to 0.04%, refine for 10 minutes, and then perform casting treatment to obtain an aluminum alloy casting rod;

[0143] S2. Perform homogenization treatment on the aluminum alloy casting rod, and the homogenization regime is 490 °C x 12 h;

[0144] S3. Preheat the aluminum alloy casting rod. The diameter of the aluminum alloy casting rod is 151 mm, and the length of the ingot is 500 mm. The preheating temperature of the ingot is 420 °C. Preheat the die in the extruder, and the preheating temperature is 450 °C. After preheating, send the aluminum alloy casting rod into the extruder for extrusion. The temperature of the extrusion cylinder is 422 °C, and the extrusion speed is 0.75 mm / s to obtain an aluminum alloy forged bar; the depth of the diversion pit of the extrusion die is 1.6 mm, the slope is 17°, the width of the working belt is 3 mm, the slope angle of the flow-promoting part of the working belt is 11.8°, and the molybdenum content of the die steel is 5.2%.

[0145] S4. Perform online quenching on the aluminum alloy forged bar. The outlet temperature of the online quenching is 474 °C, and the quenching method is water cooling with a cooling rate of 3.3 °C / s.

[0146] S5. Perform aging treatment on the aluminum alloy bar after offline quenching. The aging treatment regime is specifically 175 °C × 8 h.

[0147] Perform mechanical property testing on the forged bar prepared in this comparative example. Testing equipment: AG-X100KN electronic universal testing machine. Testing standard: GB / T16865-2013 Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys.

[0148] The yield strength of the bar prepared in this comparative example is 377 Mpa, meeting the usage requirements. The tensile strength is 382 Mpa, lower than 390 Mpa, not meeting the usage requirements, and the elongation after fracture is relatively low, specifically 2.6%.

[0149] The summary results of the mechanical property testing and intergranular corrosion testing of the forged bars produced in Examples 1-3 and Comparative Examples 1-4 are as follows in the table.

[0150] Table 1. Testing Results of Mechanical Properties, Intergranular Corrosion, and Surface Quality

[0151]

[0152]

[0153] As mentioned above, only the specific preferred embodiments of the present invention are described. However, the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A 4 series aluminum alloy forged bar for automobile chassis suspension, characterized in that: Chemical composition of 4 series aluminum alloy forging bars by mass percentage Including: Si: 11.5% ~ 12%, Fe: 0.10% ~ 0.15%, Cu: 0.7% ~ 0.74%, Mg: 1.12% ~ 1.18%, Ni: 0.72% ~ 0.76%, Zn: ≤ 0.25%, Cr: ≤ 0.10%, and the balance is Al.

2. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 1, characterized in that: The following steps are involved: S1. Prepare the designed raw material components in proportion and put them into a smelting furnace for smelting. The smelting temperature is lower than 760°C. After the charge is completely melted, the melt is introduced into a static furnace and refined with pure nitrogen for 15 minutes. Then, the slag is removed by skimming to remove the slag and impurities on the surface of the melt. Then, the melt is refined, an aluminum strontium modifier is added, and the refining is performed for 8 to 10 minutes. Then, the aluminum alloy cast rod is obtained by casting. S2. The aluminum alloy casting rod is homogenized at 480℃~500℃x11h~12h; S3. The aluminum alloy cast rod is preheated at a preheating temperature of 410°C to 430°C, the die in the extruder is preheated at a preheating temperature of 450°C to 500°C, and after preheating, the aluminum alloy cast rod is fed into the extruder for extrusion at an extrusion speed of 0.73 to 0.93 mm / s, and the extruder outlet temperature is 390°C to 430°C to obtain an aluminum alloy forging rod; S4. Offline quenching of the aluminum alloy forging bar; S5. Perform aging treatment on the aluminum alloy bar after offline quenching.

3. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 2, characterized in that: In the step S1, the effective amount of strontium element added in the aluminum strontium modifier is 0.01% to 0.05%.

4. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 2, characterized in that: In the step S2, the homogenization temperature is 490° C. x 12 h.

5. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 2, characterized in that: In step S4, the off-line quenching system is 510° C. to 530° C.×2 h to 3 h, followed by water cooling.

6. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 5, characterized in that: In step S5, the aging system is 165°C to 175°C×9h to 11h.

7. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 2, characterized in that: The depth of the diversion pit of the extrusion die is 1.5 to 2 mm, the slope of the diversion pit is 15 to 30 degrees, and the total length of the die working belt is 3 to 4 mm.

8. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 7, characterized in that: The working belt includes a flow-promoting portion and a flow-stabilizing portion. The flow-promoting portion is a flow guide angle set at the inlet of the working belt, and the flow guide angle is 11 to 13°. The flow-stabilizing portion does not have a flow guide angle. The flow-promoting portion occupies two-thirds of the total length of the working belt.

9. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 7, characterized in that: The mold is made of high-molybdenum steel with a molybdenum content of 5% to 6%.

10. The production process of 4 series aluminum alloy forging bars for automobile chassis suspension according to claim 1, characterized in that: In the step S3, the aluminum alloy forged bar is processed into 500 mm and then put into a 1250T horizontal extruder for extrusion.

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