A manufacturing method of an aluminum alloy precision casting off-road vehicle frame sill welding piece

Abstract

This invention discloses a method for manufacturing a precision-cast aluminum alloy underbeam welded component for an off-road vehicle frame. The method includes: preparing an Al-Si-Mg-Mn-Zr-Ti-Sr-B series cast aluminum alloy; melting, degassing, and filtering the aluminum alloy material, followed by modification and grain refinement treatment; forming the underbeam casting blank using precision casting, and setting local feeding and / or local cooling in the welding connection area to form a refined and dense structure with a secondary dendrite spacing of no more than 35μm in the welding connection area and within 20mm to 50mm on both sides; performing solution treatment, quenching, and under-aging pre-weld heat treatment on the casting blank; performing final surface cleaning of the welding connection area before welding, and welding the underbeam casting blank to a crossbeam, reinforcement, connecting seat, mounting lug, or another underbeam segment using low heat input welding within 4 hours after cleaning; and finally performing post-weld graded artificial aging treatment. This invention improves the problems of heat-affected zone softening, weld mismatch between weld and base material properties, and fatigue cracking induced by casting defects in welded aluminum alloy vehicle frame bottom beams by coordinating material composition, casting structure, welding heat input, and post-weld structure recovery. It is applicable to off-road vehicle frame bottom beams and other aluminum alloy cast-welded composite load-bearing structural components.

Description

Technical Field

[0001] This invention belongs to the field of automotive structural component design and manufacturing technology, specifically relating to a manufacturing method for a precision-cast aluminum alloy off-road vehicle frame bottom beam welded component. Background Technology

[0002] The chassis frame's underframe is a key load-bearing component in the chassis system of an off-road vehicle. It withstands bending loads, torsional loads, impact loads, vibration loads, and alternating fatigue loads over a long period of time during vehicle operation. Traditional chassis frame underframes mostly use welded steel structures, which, while having high strength, result in a large overall weight, which is detrimental to vehicle lightweighting, fuel economy improvement, and increased range for new energy off-road vehicles.

[0003] Aluminum alloys possess advantages such as low density, high specific strength, good corrosion resistance, and excellent formability, leading to their increasing application in automotive chassis structural components. For off-road vehicle chassis beams, precision casting of aluminum alloys allows for the integrated forming of complex ribs, connecting seats, mounting holes, and localized reinforcing structures, reducing the number of parts, lowering assembly complexity, and offering significant potential for weight reduction.

[0004] However, the precision-cast aluminum alloy chassis underbeams still present numerous challenges in actual manufacturing and use. For instance, aluminum alloy castings are prone to structural defects such as porosity, shrinkage cavities, oxide inclusions, coarse eutectic silicon, and acicular iron-containing phases. Under off-road conditions, chassis underbeams are subjected to intense impacts and repeated vibrations, and these defects can easily become fatigue crack initiation points, leading to a decrease in the fatigue life of the welded underbeam components. Furthermore, conventional heat treatment methods are unsuitable for large chassis underbeam weldments. If the casting undergoes full T6 treatment before welding, the weld heat-affected zone softens, resulting in limited post-weld performance recovery. If a complete solution quenching treatment is performed after welding, large chassis underbeam weldments are prone to deformation, residual stress redistribution, and decreased dimensional accuracy, which is detrimental to vehicle assembly. Therefore, for load-bearing components like off-road vehicle chassis underbeams, which combine precision casting and welded connections, improvements to a single aspect are insufficient to simultaneously address casting defects, weld heat-affected zone softening, weld performance matching, and post-weld dimensional stability.

[0005] Therefore, it is necessary to provide a casting-welding co-manufacturing method for precision-cast aluminum alloy off-road vehicle chassis bottom beam welded parts, so that the aluminum alloy composition, pre-weld heat treatment, welding heat input and post-weld microstructure recovery can be matched with each other, thereby improving the strength, toughness, fatigue performance, dimensional stability and service reliability of the chassis bottom beam welded parts. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a manufacturing method for aluminum alloy precision casting of off-road vehicle frame bottom beam welded parts, thereby solving the problems of easy softening of the heat-affected zone, mismatch between the weld and the base material properties, fatigue cracks induced by casting defects, and easy deformation of large welded parts after complete solution treatment.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: This invention discloses a method for manufacturing a welded component of an aluminum alloy precision-cast off-road vehicle frame bottom beam, comprising the following steps: Step 1: Prepare the cast aluminum alloy material The cast aluminum alloy comprises, by mass percentage: Si 6.8%~8.4%; Mg 0.30%~0.48%; Mn 0.16%~0.38%; Zr 0.06%~0.16%; Ti 0.08%~0.18%; Sr 0.010%~0.030%; B 0.002%~0.010%; Fe≤0.16%; Cu≤0.08%; Zn≤0.10%; Ca ≤ 0.005%; Na≤0.003%; The balance consists of Al and unavoidable impurities.

[0008] Preferably, the cast aluminum alloy comprises, by weight percentage: Si 7.2%~8.0%; Mg 0.34%~0.44%; Mn 0.20%~0.32%; Zr 0.08%~0.14%; Ti 0.10%~0.16%; Sr 0.014%~0.024%; B 0.004%~0.008%; Fe ≤ 0.14%; Cu≤0.06%; Zn≤0.08%; The balance consists of Al and unavoidable impurities.

[0009] Among them, Si is used to improve the alloy's fluidity, filling capacity, and resistance to hot cracking; Mg is used to form Mg2Si precipitation strengthening phase, giving the casting base material and weld heat-affected zone subsequent aging strengthening ability; Mn is used to improve the morphology of Fe-containing phases and reduce the adverse effects of acicular and lamellar Fe-containing phases on toughness and fatigue performance; Zr is used to form thermally stable dispersed phases and improve the microstructure stability of the weld heat-affected zone; Ti and B are used for grain refinement; Sr is used for eutectic silicon modification, transforming eutectic silicon from coarse lamellar or acicular to fine fibrous or granular; low Cu and low Zn control are used to improve weldability and corrosion resistance.

[0010] Preferably, the mass ratio of Mn to Fe in the cast aluminum alloy is 1.5 to 3.0, and the mass ratio of Ti to B is 10 to 20.

[0011] Furthermore, based on the above-mentioned cast aluminum alloy, Ce and / or La rare earth elements of 0.02% to 0.10% can be added in a way that replaces part of Al to improve the morphology of oxide inclusions and the distribution of eutectic silicon.

[0012] Step two: smelting, refining, filtering, and refining treatment. Industrial pure aluminum, Al-Si master alloy, Al-Mg master alloy, Al-Mn master alloy, Al-Zr master alloy, Al-Ti-B master alloy, and Al-Sr master alloy are formulated according to the composition described in step one.

[0013] The ingredients are added to the melting furnace and melted at 730℃~760℃. After the alloying elements are fully melted and the composition is homogeneous, slag is removed. Then, argon gas is introduced at 720℃~745℃ for rotary degassing for 8min~18min, and the rotor speed is 300r / min~500r / min.

[0014] After degassing, the aluminum alloy melt is filtered through a 30ppi to 50ppi ceramic filter plate to reduce oxide inclusions and non-metallic inclusions.

[0015] After filtration, Al-Sr master alloy is added to the aluminum alloy melt for modification treatment, and Al-Ti-B master alloy and Al-Zr master alloy are added for composite grain refinement treatment. After modification and refinement, the mixture is allowed to stand for 10 to 25 minutes to allow the modifiers and refiners to fully exert their effects.

[0016] Preferably, the hydrogen content of the molten aluminum is controlled below 0.15 mL / 100gAl before casting.

[0017] Step 3: Precision casting of the chassis bottom beam casting blank The aluminum alloy melt, after being smelted, refined, filtered, and modified for finer treatment, is used to form the chassis bottom beam casting blank using precision casting. The precision casting method includes low-pressure casting, vacuum-assisted gravity casting, vacuum-assisted low-pressure casting, or reverse-pressure precision casting.

[0018] Preferably, low-pressure casting or vacuum-assisted low-pressure casting is used. The pouring temperature is 690℃~725℃, the mold temperature is 180℃~260℃, the liquid lifting pressure is 0.015MPa~0.035MPa, the filling pressure is 0.035MPa~0.075MPa, and the holding pressure is 0.08MPa~0.18MPa.

[0019] The cast blank of the chassis bottom beam includes the bottom beam body, welding connection area, reinforcing rib area, mounting base area, and transition fillet area. The welding connection area is used for welding to the crossbeam, reinforcing member, connecting base, mounting lug, or another bottom beam section.

[0020] Local chills, conformal cooling channels, or localized pressure-feeding structures are installed near the welded joint area to create a refined and dense microstructure in the welded joint area and its adjacent region. The adjacent region is preferably within a 20mm to 50mm radius on either side of the welded joint area.

[0021] Preferably, the secondary dendrite spacing within a 20mm to 50mm range on both sides of the welded joint area is no greater than 35μm, more preferably 20μm to 32μm. Through-hole shrinkage cavities, cold shuts, and cracks are not permitted in the welded joint area.

[0022] By controlling the local structure as described above, the base material region where the heat-affected zone of subsequent welding is located can have a high degree of structural uniformity and a low level of defects, thereby reducing the risk of fatigue crack initiation from the source.

[0023] Step 4: Casting cleaning, pre-machining of the welding area, and final surface treatment before welding. After casting, the cast blanks of the chassis bottom beam are cleaned by removing the gating system and risers, deburring, sandblasting, shot blasting, or mechanical cleaning.

[0024] The welded joint area is machined to remove surface casting oxide scale and potential surface defects. The amount of surface layer removed from the welded joint area is 0.20 mm to 0.80 mm, preferably 0.30 mm to 0.50 mm.

[0025] Depending on the welded structure, the weld joint area should undergo beveling pre-machining or allowance for pre-welding finishing. For bottom beams with a wall thickness of 4mm to 8mm, an I-shaped bevel or a single-sided V-shaped bevel can be used; for connecting seats or reinforcing areas with a thickness of 8mm to 16mm, a V-shaped bevel or a double V-shaped bevel can be used. The bevel angle is 45° to 70°, the blunt edge height is 0.5mm to 1.5mm, and the assembly clearance is 0.5mm to 2.0mm.

[0026] The aforementioned machining is a pre-processing step before pre-weld heat treatment, used to remove casting oxide scale, surface segregation layer, and potential surface defects; after pre-weld heat treatment and before low-heat input welding, the weld joint area is then cleaned for final surface treatment.

[0027] Step 5, Pre-welding under-aging heat treatment The cast blank of the chassis bottom beam is subjected to pre-weld heat treatment. The pre-weld heat treatment includes solution treatment, quenching treatment, and under-aging treatment.

[0028] The solution treatment temperature is 520℃~535℃, and the holding time is 2h~6h; then quenching is carried out in water or polymer quenching medium at 50℃~80℃, and the quenching transfer time does not exceed 20s; after quenching, under-aging treatment is carried out at 120℃~145℃, and the holding time is 1h~4h.

[0029] Preferably, the solution treatment temperature is 525℃~532℃, and the holding time is 3h~5h; the under-aging temperature is 130℃~140℃, and the holding time is 1.5h~3h.

[0030] By performing pre-weld under-aging treatment, the castings have a certain strength and dimensional stability before welding, while retaining the potential for further aging strengthening after welding, thus avoiding the problem of difficult-to-recover softening of the heat-affected zone after welding in the full T6 state.

[0031] Step 6, Low Heat Input Welding The pre-welded under-aging cast blank of the chassis bottom beam is welded to the crossbeam, reinforcement, connecting seat, mounting lug or another bottom beam section.

[0032] The welding method is pulsed MIG welding, cold metal transfer welding, pulsed TIG welding, or TIG-MIG hybrid welding. Pulsed MIG welding or cold metal transfer welding is preferred.

[0033] The welding heat input is controlled between 0.25 kJ / mm and 0.65 kJ / mm, preferably between 0.30 kJ / mm and 0.50 kJ / mm. The welding heat input is calculated according to Q = ηUI / v, where η is the thermal efficiency, U is the welding voltage, I is the welding current, and v is the welding speed. The interpass temperature should not exceed 120℃, preferably not exceeding 100℃. The shielding gas is high-purity Ar or an Ar-He mixture, with a gas flow rate of 15 L / min to 25 L / min.

[0034] During the welding process, a symmetrical segmented welding, back-welding, or skip-welding sequence is adopted to reduce welding deformation and residual stress concentration. For left-right symmetrical bottom beam structures, a welding sequence of alternating left and right sides, inner and outer segments, and short weld passes with multiple cycles is preferred.

[0035] Preferably, the welding wire used for welding is an Al-Si-Mg-Zr matched welding wire, and the welding wire comprises, by mass percentage: Si 4.5%~6.5%; Mg 0.15%~0.45%; Zr 0.03%~0.15%; Ti 0.03%~0.12%; Sr 0.005%~0.020%; Fe ≤ 0.15%; Cu≤0.05%; The balance consists of Al and unavoidable impurities.

[0036] More preferably, the welding wire comprises 5.0% to 6.0% Si, 0.20% to 0.35% Mg, 0.05% to 0.12% Zr, 0.04% to 0.10% Ti, 0.008% to 0.015% Sr, with the balance being Al and unavoidable impurities.

[0037] In this welding wire, Si is used to improve the hot crack resistance of the weld metal, Mg is used to impart aging response capability to the weld metal, and Zr and Ti are used to improve the solidification structure and thermal stability of the weld, thereby improving the performance matching degree between the weld zone and the casting base material zone.

[0038] Step 7: Post-weld graded artificial aging treatment After welding, the welded components of the chassis bottom beam are subjected to post-weld graded artificial aging treatment instead of overall post-weld high-temperature solution quenching treatment.

[0039] The post-weld graded artificial aging treatment includes a first-stage aging and a second-stage aging. The first-stage aging temperature is 150℃~165℃, and the holding time is 2h~6h; the second-stage aging temperature is 170℃~185℃, and the holding time is 2h~5h.

[0040] Preferably, the first stage of aging is maintained at 155℃~162℃ for 3h~5h; the second stage of aging is maintained at 175℃~180℃ for 2h~4h.

[0041] The first stage of aging is used to promote the precipitation of fine strengthening phases in the weld heat-affected zone and the cast base material zone; the second stage of aging is used to improve the microstructure stability of the weld zone and heat-affected zone, and reduce performance fluctuations during subsequent service.

[0042] For large-sized, long-length welded components of the chassis bottom beam, or components with strong welding constraints, a low-temperature homogenization treatment can be added before graded artificial aging. The low-temperature homogenization treatment temperature is 100℃~120℃, and the holding time is 1h~3h.

[0043] Step 8, optional weld toe strengthening treatment For welded components of the chassis bottom beam of off-road vehicles that are subjected to high impact, high vibration or high fatigue load, the weld toe area can be locally rolled, ultrasonically impacted or shot peened after the post-weld graded artificial aging is completed.

[0044] The treatment area is 3mm to 12mm on each side of the weld toe. By localizing plastic strengthening and introducing surface compressive stress, the risk of fatigue crack initiation at the weld toe is reduced.

[0045] This step is a preferred step and is not a necessary condition for realizing the present invention.

[0046] Compared with the prior art, the present invention has at least the following beneficial effects: By customizing Al-Si-Mg-Mn-Zr series cast aluminum alloys and setting local cooling and feeding structures in the welded joint area to obtain a refined and dense as-cast microstructure, combined with pre-weld solution quenching, under-aging pretreatment, low heat input matching welding wire welding, and post-weld graded artificial aging processes, the system systematically solves the problems of fatigue cracks induced by casting defects, softening of the weld heat-affected zone, performance mismatch between weld and base material, and easy deformation of large components after post-weld solution treatment in existing aluminum alloy vehicle frame bottom beam welded parts. This results in a continuous transition of microstructure and hardness distribution between the weld area, heat-affected zone, and cast base material, effectively improving the load-bearing strength, fatigue reliability, and dimensional stability of the components. Moreover, the process can be implemented industrially based on existing general equipment and can be widely used in off-road vehicle frame bottom beams and various aluminum alloy cast-welded composite load-bearing structural components that are subjected to impact and alternating loads.

[0047] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time. Attached Figure Description

[0048] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the casting-welding collaborative manufacturing method for the aluminum alloy precision cast off-road vehicle frame bottom beam welded parts of the present invention.

[0049] Figure 2 This is a schematic diagram of the overall casting blank of the chassis bottom beam of the present invention.

[0050] Figure 3 This is a schematic diagram of the local shrinkage compensation and local cooling control in the welded joint area of ​​the present invention.

[0051] Figure 4 This is a schematic diagram of the welding and assembly of the cast blank of the chassis bottom beam and the crossbeam or reinforcement of the present invention.

[0052] Figure 5 This is a schematic diagram of the heat treatment curves for pre-weld under-aging and post-weld graded artificial aging according to the present invention.

[0053] Figure 6 This is a schematic diagram showing the transition of microstructure and hardness in the weld zone, heat-affected zone, and cast base material zone after welding according to the present invention.

[0054] Figure 7 This is a schematic diagram of the localized strengthening treatment area of ​​the weld toe in this invention.

[0055] Explanation of reference numerals in the attached figures: 1. Cast blank of chassis bottom beam; 2. Bottom beam body; 3. Welded connection area; 4. Reinforcing rib area; 5. Mounting seat area; 6. Transition fillet area; 7. Crossbeam or reinforcing member; 8. Bevel; 9. Weld area; 10. Heat-affected zone; 11. Casting base material area; 12. Local chills; 13. Conformal cooling channel; 14. Local pressure feeding structure; 15. Welding wire; 16. First stage aging treatment section; 17. Second stage aging treatment section; 18. Weld toe; 19. Weld toe strengthening area; 20. Assembly gap; 21. Fixture positioning part; 22. Bottom beam inner cavity; 23. Weight reduction cavity; 24. Connection hole position; 25. Local thick area. Detailed Implementation

[0056] The technical solution of the present invention will be described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions, modifications or improvements made to the present invention by those skilled in the art without departing from the concept of the present invention should all fall within the scope of protection of the present invention.

[0057] This invention provides a casting-welding collaborative manufacturing method for aluminum alloy precision cast off-road vehicle frame bottom beam welded components. This method primarily addresses problems encountered after welding in aluminum alloy precision cast frame bottom beams, such as softening of the heat-affected zone, performance mismatch between the weld zone and the base material, fatigue cracks induced by casting defects in the weld joint zone, and easy deformation of large welded components after overall solution quenching following welding.

[0058] like Figure 1 As shown, the manufacturing method of the present invention includes the following steps: alloy batching, melting, degassing and filtration, modification and grain refinement, precision casting, local feeding and / or local cooling of the weld joint area, cleaning and machining, pre-weld solution treatment-quenching-under-aging treatment, low heat input welding, post-weld graded artificial aging treatment, and optional weld toe strengthening treatment.

[0059] The frame bottom beam casting blank 1 of the present invention is as follows Figure 2As shown, the cast blank, as the object of the process of this invention, includes a bottom beam body 2, a welding connection area 3, a reinforcing rib area 4, a mounting base area 5, a transition fillet area 6, a bottom beam inner cavity 22, a weight reduction cavity 23, connecting holes 24, and a locally thick area 25. The above structure is only used to illustrate the application area of ​​the process of this invention in the cast blank of the chassis bottom beam, wherein the welding connection area 3, the locally thick area 25, and the area near the weld are the key control areas of this invention.

[0060] I. Configuration of Cast Aluminum Alloy Materials In this invention, the frame bottom beam casting blank 1 is made of Al-Si-Mg-Mn-Zr-Ti-Sr-B series cast aluminum alloy.

[0061] The cast aluminum alloy comprises, by mass percentage: Si 6.8%~8.4%; Mg 0.30%~0.48%; Mn 0.16%~0.38%; Zr 0.06%~0.16%; Ti 0.08%~0.18%; Sr 0.010%~0.030%; B 0.002%~0.010%; Fe≤0.16%; Cu≤0.08%; Zn≤0.10%; Ca ≤ 0.005%; Na≤0.003%; The balance consists of Al and unavoidable impurities.

[0062] Preferably, the cast aluminum alloy comprises, by weight percentage: Si 7.2%~8.0%; Mg 0.34%~0.44%; Mn 0.20%~0.32%; Zr 0.08%~0.14%; Ti 0.10%~0.16%; Sr 0.014%~0.024%; B 0.004%~0.008%; Fe ≤ 0.14%; Cu≤0.06%; Zn≤0.08%; The balance consists of Al and unavoidable impurities.

[0063] Among them, Si is used to improve the alloy's fluidity, filling capacity, and resistance to hot cracking; Mg is used to form Mg2Si precipitation strengthening phase, enabling the casting base material zone 11 and the weld heat-affected zone 10 to have subsequent aging strengthening capabilities; Mn is used to improve the morphology of Fe-containing phases and reduce the adverse effects of acicular and lamellar Fe-containing phases on toughness and fatigue performance; Zr is used to improve the microstructure stability of the weld heat-affected zone 10 under welding thermal cycling; Ti and B are used for grain refinement; Sr is used for eutectic silicon modification, transforming eutectic silicon from coarse lamellar or acicular to fine fibrous or granular.

[0064] In a preferred embodiment, the mass ratio of Mn to Fe is controlled at 1.5–3.0, and the mass ratio of Ti to B is controlled at 10–20. By controlling the Mn to Fe ratio, the adverse effects of acicular and flaky Fe-containing structures on relative fatigue performance can be reduced; by controlling the Ti to B ratio, the grain refinement effect can be improved, making the microstructure near the welded joint zone 3 more uniform.

[0065] In some embodiments, the cast aluminum alloy may also incorporate 0.02% to 0.10% of rare earth elements Ce and / or La in order to replace part of the Al, in order to improve the morphology of oxide inclusions, the distribution of eutectic silicon, and the uniformity of the microstructure in the locally thick regions 25.

[0066] II. Smelting, degassing, filtration and refining treatment According to the above alloy composition, industrial pure aluminum, Al-Si master alloy, Al-Mg master alloy, Al-Mn master alloy, Al-Zr master alloy, Al-Ti-B master alloy and Al-Sr master alloy are batched.

[0067] During smelting, industrial pure aluminum and Al-Si master alloy are first added to the smelting furnace and melted at 730℃~760℃. After they are completely melted, Al-Mn master alloy and Al-Zr master alloy are added. After the melt composition is homogeneous, the melt temperature is adjusted to 720℃~745℃, and then Al-Mg master alloy is added to reduce the loss of Mg element. Slag removal is then performed.

[0068] After slag removal, the molten aluminum alloy is degassed by argon rotation. The degassed temperature is 720℃~745℃, the degassed time is 8min~18min, and the rotor speed is 300r / min~500r / min. Preferably, the hydrogen content of the molten aluminum is controlled below 0.15mL / 100gAl before casting.

[0069] After degassing, the molten aluminum alloy is filtered through a 30ppi to 50ppi ceramic filter plate to reduce oxide film, non-metallic inclusions, and large-sized inclusion particles. For the frame bottom beam casting blank 1, which has high quality requirements in the welded joint area 3, a two-stage filtration method can be adopted, namely, coarse filtration through a 30ppi ceramic filter plate first, and fine filtration through a 50ppi ceramic filter plate.

[0070] After filtration, Al-Sr master alloy is added to the aluminum alloy melt for modification treatment, and Al-Ti-B master alloy and Al-Zr master alloy are added for composite grain refinement treatment. After modification and refinement, the mixture is allowed to stand for 10 min to 25 min to allow the modifiers and refiners to fully dissolve, diffuse, and exert their effects.

[0071] Through the above-mentioned smelting, degassing, filtration, modification and refining processes, the gas content and inclusion content of the melt can be reduced, the internal quality of the casting can be improved, and a foundation can be provided for the subsequent microstructure control of the welded joint zone 3.

[0072] III. Local Microstructure Control in Precision Casting Forming and Welded Joint Zones The processed aluminum alloy melt is used to form the chassis bottom beam casting blank 1 by low-pressure casting, vacuum-assisted gravity casting, vacuum-assisted low-pressure casting or reverse pressure precision casting.

[0073] Preferably, low-pressure casting or vacuum-assisted low-pressure casting is used. The pouring temperature is 690℃~725℃, the mold temperature is 180℃~260℃, the liquid lifting pressure is 0.015MPa~0.035MPa, the filling pressure is 0.035MPa~0.075MPa, and the holding pressure is 0.08MPa~0.18MPa.

[0074] like Figure 3 As shown, at least one of the following is provided near the welded joint area 3: a local chill 12, a conformal cooling channel 13, or a local pressure-compensating structure 14.

[0075] Local chills 12 are installed in the local area of ​​the mold corresponding to the welded joint area 3 to increase the cooling rate in this area and refine the secondary dendrites and eutectic structure. Conformal cooling channels 13 are arranged along the extension direction of the welded joint area 3 to stably control the solidification rate of the welded joint area 3 and its adjacent areas. Local pressure-compensating structures 14 are installed near the welded joint area 3 or the local thick area 25 to compensate for shrinkage in the welded joint area 3 and the local thick area 25, reducing micro-shrinkage porosity and central porosity.

[0076] Preferably, a refined and dense microstructure is formed in the welded joint area 3 and within a range of 20 mm to 50 mm on both sides, with a secondary dendrite spacing of no more than 35 μm, more preferably 20 μm to 32 μm. The welded joint area 3 is not allowed to contain through-hole shrinkage cavities, cold shuts, hot cracks, or inclusions visible to the naked eye.

[0077] Through the aforementioned localized structural control, the casting base material region where the subsequent welding heat-affected zone 10 is located has finer grains, lower porosity, and lower shrinkage tendency, thereby reducing the risk of fatigue cracks initiating near the weld toe 18 or heat-affected zone 10 after welding from the source.

[0078] IV. Casting cleaning, welding area machining and surface treatment After the bottom beam casting blank 1 is formed, it is subjected to gate removal, riser removal, flash removal, burr removal, sandblasting, shot blasting, or mechanical cleaning. For the inner cavity 22 and weight reduction cavity 23 of the bottom beam, residual sand, oxides and loose inclusions can be removed by compressed air purging, endoscopic inspection or local cleaning.

[0079] Subsequently, the welded joint area 3 is machined to remove surface oxide scale, segregation layer, casting surface defects, and local uneven areas. The amount of surface material removed from the welded joint area 3 is 0.20 mm to 0.80 mm, preferably 0.30 mm to 0.50 mm.

[0080] The weld joint area 3 is machined with a bevel 8 according to the welding method. The bevel 8 can be an I-shaped bevel, a single-sided V-shaped bevel, a V-shaped bevel, a double V-shaped bevel, or a U-shaped bevel. For areas with a thickness of 4mm to 8mm, an I-shaped bevel or a single-sided V-shaped bevel is preferred; for areas with a thickness of 8mm to 16mm, a V-shaped bevel or a double V-shaped bevel is preferred. The bevel angle is preferably 45° to 70°, the blunt edge height is preferably 0.5mm to 1.5mm, and the assembly gap 20 is preferably 0.5mm to 2.0mm.

[0081] The aforementioned beveling process is a pre-processing step before pre-weld heat treatment, and a small amount of finishing allowance can be reserved based on the deformation amount after subsequent heat treatment. After pre-weld heat treatment and before low-heat input welding, the weld joint area 3 undergoes final surface cleaning to remove the oxide film, adsorbed moisture, and assembly contaminants regenerated after heat treatment. Final surface cleaning can be performed using mechanical brushing, degreasing, alkaline washing, acid washing, or plasma cleaning; mechanical brushing is preferably done using a stainless steel wire brush or a special surface treatment tool for aluminum alloys to avoid iron contamination. After final surface cleaning, welding should preferably be completed within 4 hours.

[0082] V. Pre-welding under-aging heat treatment The pre-welding heat treatment is performed on the cleaned and machined frame bottom beam casting blank 1. The pre-welding heat treatment includes solution treatment, quenching treatment and under-aging treatment.

[0083] The solution treatment temperature is 520℃~535℃, and the holding time is 2h~6h. The solution treatment is used to fully dissolve elements such as Mg and Si, and to cause some eutectic silicon to spheroidize and fracture, thereby improving the plasticity and toughness of the casting base material region 11.

[0084] After solution treatment, quenching is performed. The quenching medium is water or polymer quenching medium at 50℃~80℃, and the quenching transfer time does not exceed 20s. For the large-sized frame bottom beam casting blank 1, warm water quenching or polymer quenching medium with stirring is preferred to balance the solution strengthening effect and deformation control.

[0085] After quenching, a partial aging treatment is performed. The partial aging treatment temperature is 120℃~145℃, and the holding time is 1h~4h. Preferably, the partial aging temperature is 130℃~140℃, and the holding time is 1.5h~3h.

[0086] like Figure 5 As shown, the pre-weld under-aging treatment gives the cast blank 1 of the chassis bottom beam a certain strength and dimensional stability before welding, while retaining the potential for further artificial aging strengthening after welding. Compared with welding in the fully T6 state, the cast base material zone 11 in the under-aging state still has a better aging response capability after experiencing welding thermal cycles, which is beneficial for restoring the microstructure and hardness of the heat-affected zone 10 through subsequent post-weld graded artificial aging treatment.

[0087] VI. Low heat input welding like Figure 4 As shown, the pre-welded under-aging cast blank 1 of the chassis bottom beam is assembled with the crossbeam or reinforcement 7. Before or after assembly, the welded joint area 3 undergoes final surface cleaning, and low-heat input welding is performed within 4 hours after the final surface cleaning is completed. During assembly, positioning is achieved using the fixture positioning part 21, and the assembly gap 20 is controlled to be 0.5mm to 2.0mm.

[0088] Welding methods can include pulsed MIG welding, cold metal transfer welding, pulsed TIG welding, or TIG-MIG hybrid welding. Pulsed MIG welding or cold metal transfer welding is preferred to reduce welding heat input and welding deformation.

[0089] The welding heat input is controlled between 0.25 kJ / mm and 0.65 kJ / mm, preferably between 0.30 kJ / mm and 0.50 kJ / mm. The welding heat input is calculated according to Q = ηUI / v, where η is the thermal efficiency, U is the welding voltage, I is the welding current, and v is the welding speed. The interpass temperature should not exceed 120℃, preferably not exceeding 100℃. The shielding gas is high-purity Ar or an Ar-He mixture, with a gas flow rate of 15 L / min to 25 L / min.

[0090] During the welding process, symmetrical segmented welding, back welding, or skip welding sequences are adopted. For left-right symmetrical structures, alternating welding between left and right is preferred; for long weld seams, short weld beads and multiple cycles of welding are preferred; for the mounting area 5 with high constraint, it is preferred to weld the less constrained area first, and then weld the more constrained area, in order to reduce residual stress concentration.

[0091] During welding, welding wire 15 is fed into the molten pool along the bevel 8, forming weld zone 9. Heat-affected zones 10 are formed on both sides of weld zone 9, and the outer side of heat-affected zone 10 is the cast base metal zone 11. Due to the use of low heat input welding, the width of heat-affected zone 10 is controlled, and the effects of welding thermal cycle on the coarsening and over-aging of precipitated strengthening phases in cast base metal zone 11 are reduced.

[0092] Preferably, the welding wire 15 used for welding is an Al-Si-Mg-Zr system matched welding wire. The welding wire 15 comprises, by weight percentage: Si 4.5%~6.5%; Mg 0.15%~0.45%; Zr 0.03%~0.15%; Ti 0.03%~0.12%; Sr 0.005%~0.020%; Fe ≤ 0.15%; Cu≤0.05%; The balance consists of Al and unavoidable impurities.

[0093] More preferably, the welding wire 15 comprises, by weight percentage: Si 5.0%~6.0%; Mg 0.20%~0.35%; Zr 0.05%~0.12%; Ti 0.04%~0.10%; Sr 0.008%~0.015%; The balance consists of Al and unavoidable impurities.

[0094] The Si in welding wire 15 is used to improve the hot crack resistance of weld zone 9; Mg is used to impart a certain age hardening ability to weld zone 9; Zr and Ti are used to improve the solidification structure and thermal stability of weld zone 9; and Sr is used to improve the silicon phase morphology in weld zone 9. By matching the composition system of welding wire 15 with that of the cast base material zone 11, the performance matching between weld zone 9, heat-affected zone 10 and cast base material zone 11 can be improved.

[0095] VII. Post-weld graded artificial aging treatment After welding, the welded components of the chassis bottom beam undergo graded artificial aging treatment instead of overall post-weld high-temperature solution hardening. This avoids large deformations, residual stress redistribution, or assembly dimensional deviations in large chassis bottom beam welded components caused by overall high-temperature solution hardening and rapid quenching.

[0096] like Figure 5As shown, the post-weld graded artificial aging treatment includes a first-stage aging treatment section 16 and a second-stage aging treatment section 17.

[0097] The temperature of the first-stage aging treatment section 16 is 150℃~165℃, and the holding time is 2h~6h. The first-stage aging is mainly used to promote the formation of fine precipitates in the heat-affected zone 10 and the casting base material zone 11, so as to initially restore the softened zone caused by the welding thermal cycle.

[0098] The temperature of the second-stage aging treatment section 17 is 170℃~185℃, and the holding time is 2h~5h. The second-stage aging is mainly used to further improve the microstructure stability of the weld zone 9 and the heat-affected zone 10, so as to form a relatively continuous hardness transition between the weld zone 9, the heat-affected zone 10 and the casting base material zone 11.

[0099] Preferably, the first stage of aging is maintained at 155℃~162℃ for 3h~5h, and the second stage of aging is maintained at 175℃~180℃ for 2h~4h.

[0100] For chassis bottom beam welded components that are large in size, have long weld lengths, or require strong welding restraints, a low-temperature homogenization treatment can be added before the first-stage aging treatment section 16. The low-temperature homogenization treatment temperature is 100℃~120℃, and the holding time is 1h~3h.

[0101] like Figure 6 As shown, after post-weld graded artificial aging treatment, the microhardness was measured along the direction perpendicular to the weld. A continuous transition in microstructure and hardness distribution was formed between the weld zone 9, the heat-affected zone 10, and the casting base material zone 11, avoiding the formation of abrupt softening zones, thereby improving the reliability of the chassis bottom beam welded parts under off-road impact and cyclic load.

[0102] 8. Local strengthening treatment of weld toe In some preferred embodiments, for the welded components of the underbeam of the off-road vehicle frame that are subjected to high impact, high vibration or high fatigue load, the weld toe 18 can be locally strengthened after the post-weld graded artificial aging treatment is completed.

[0103] like Figure 7 As shown, the weld toe strengthening zone 19 is located within a range of 3mm to 12mm on both sides of the weld toe 18. Local strengthening treatment of the weld toe can be achieved by rolling, ultrasonic impact, or micro-shot peening. By introducing local plastic deformation and surface compressive stress, the tensile stress concentration at the weld toe 18 can be reduced, thus delaying the initiation of fatigue cracks.

[0104] Local strengthening treatment of the weld toe is a preferred step, but not a necessary condition for realizing the technical solution of this invention. This step can be omitted in chassis underbeam welded components where load-bearing requirements are low or the weld location is not in a major fatigue-sensitive area. Example 1

[0105] This embodiment provides a casting-welding collaborative manufacturing method applicable to welded components of the chassis bottom beam of conventional off-road vehicles.

[0106] First, a cast aluminum alloy is prepared. The cast aluminum alloy comprises, by weight percentage: Si 7.6%; Mg 0.38%; Mn 0.25%; Zr 0.10%; Ti 0.13%; Sr 0.018%; B 0.006%; Fe 0.12%; Cu 0.04%; Zn 0.05%; The balance consists of Al and unavoidable impurities.

[0107] Industrial pure aluminum, Al-Si master alloy, Al-Mn master alloy, and Al-Zr master alloy were added to a melting furnace and melted at 745°C. After the melt was completely melted and homogenized, the temperature was adjusted to 735°C, and Al-Mg master alloy was added. Slag removal was then performed.

[0108] Argon rotary degassing was performed at 730℃ for 12 minutes at a rotor speed of 400 r / min. After degassing, the melt was filtered through a 40 ppi ceramic filter plate. After filtration, Al-Sr master alloy, Al-Ti-B master alloy, and Al-Zr master alloy were added for modification and refinement treatment. After standing for 15 minutes, it was ready for casting.

[0109] The chassis bottom beam casting blank 1 is formed using low-pressure casting. The pouring temperature is 710℃, the mold temperature is 220℃, the liquid injection pressure is 0.025MPa, the filling pressure is 0.055MPa, and the holding pressure is 0.12MPa. Local chills 12 are set at corresponding positions in the welded joint area 3, and local pressure-feeding structures 14 are set near the locally thickened area 25 to form a refined and dense microstructure in the welded joint area 3 and its adjacent areas on both sides.

[0110] After casting, the risers and burrs are removed, and the casting is sandblasted cleaned. Then, the weld joint area 3 is pre-machined by removing a 0.4mm thick layer of surface material and machining a V-groove or leaving a pre-welding finishing allowance. The groove angle is 60°, the blunt edge height is 1.0mm, and the assembly gap 20 is 1.2mm.

[0111] The cast blank 1 of the chassis bottom beam was then subjected to pre-weld heat treatment. The pre-weld heat treatment included: solution treatment at 530℃ for 4 hours, followed by quenching in water at 60℃ with the quenching transfer time controlled within 20 seconds; and then under-aging treatment at 135℃ for 2 hours after quenching. After the pre-weld heat treatment was completed, the weld joint area 3 was subjected to final mechanical brushing and degreasing cleaning with anhydrous ethanol, and welding was carried out within 4 hours after the cleaning was completed.

[0112] During welding, the cast blank 1 of the chassis bottom beam is assembled and fixed to the crossbeam or reinforcement 7. Pulsed MIG welding is used, with high-purity Ar as the shielding gas at a flow rate of 20 L / min, a welding heat input of 0.40 kJ / mm, and the interpass temperature controlled below 100℃. The welding process employs an alternating left-right, segmented back-welding sequence.

[0113] The welding wire 15 used for welding is an Al-Si-Mg-Zr system matched welding wire. The welding wire 15 comprises, by mass percentage: Si 5.5%; Mg 0.28%; Zr 0.08%; Ti 0.06%; Sr 0.010%; Fe 0.10%; Cu 0.03%; The balance consists of Al and unavoidable impurities.

[0114] After welding, the welded components of the chassis bottom beam undergo post-weld graded artificial aging treatment. Specifically, the temperature is maintained at 160℃ for 4 hours, then raised to 178℃ and maintained for 3 hours, and finally air-cooled to room temperature.

[0115] This embodiment achieves a relatively continuous hardness transition between the weld zone 9, the heat-affected zone 10, and the cast base material zone 11 by using a special aluminum alloy composition, controlling the local densification of the welded joint zone 3, under-aging before welding, low heat input welding, and graded artificial aging treatment after welding. Example 2

[0116] This embodiment provides a casting-welding collaborative manufacturing method suitable for welded components of thin-walled, long-welded vehicle frame bottom beams.

[0117] This embodiment is basically the same as Embodiment 1, except that: The cast aluminum alloy comprises, by mass percentage: Si 7.3%; Mg 0.35%; Mn 0.22%; Zr 0.09%; Ti 0.12%; Sr 0.016%; B 0.005%; Fe 0.10%; Cu 0.03%; Zn 0.04%; The balance consists of Al and unavoidable impurities.

[0118] The precision casting method employs vacuum-assisted low-pressure casting. The pouring temperature is 705℃, the mold temperature is 210℃, the liquid injection pressure is 0.020MPa, the filling pressure is 0.050MPa, and the holding pressure is 0.10MPa.

[0119] The welded joint area 3 uses a conformal cooling channel 13 to control the local cooling rate, so that the welded joint area 3 and its adjacent areas obtain a more uniform and refined structure.

[0120] The pre-welding heat treatment was as follows: solution treatment at 528℃ for 3.5 hours, followed by quenching in water at 65℃, and then under-aging treatment at 132℃ for 2 hours.

[0121] The welding method employed is cold metal transfer welding. The shielding gas is high-purity Ar, with a flow rate of 18 L / min. The welding heat input is controlled at 0.32 kJ / mm, and the interpass temperature is maintained below 90°C. Short weld bead skip welding is used during the welding process to reduce heat accumulation and welding deformation in thin-walled, long-weld components.

[0122] After welding, the sample was first subjected to a low-temperature homogenization treatment at 110℃ for 2 hours, followed by a graded artificial aging treatment. The graded artificial aging process was as follows: 158℃ for 4 hours, followed by 175℃ for 3 hours, and then air-cooled to room temperature.

[0123] This embodiment is applicable to chassis bottom beam welded parts with thin walls, long welds, and high requirements for controlling dimensional deformation after welding. Example 3

[0124] This embodiment provides a casting-welding collaborative manufacturing method for welded components of vehicle frame bottom beams suitable for high-impact and high-fatigue conditions.

[0125] This embodiment is basically the same as Embodiment 1, except that: The cast aluminum alloy comprises, by mass percentage: Si 7.8%; Mg 0.42%; Mn 0.30%; Zr 0.12%; Ti 0.15%; Sr 0.020%; B 0.007%; 0.06% mixed rare earth elements of Ce and La; Fe 0.11%; Cu 0.04%; Zn 0.05%; The balance consists of Al and unavoidable impurities.

[0126] The mass ratio of Ce to La is 1:1.

[0127] During precision casting, a local chill 12 is set in the welded connection area 3, and a local pressure feeding structure 14 is set near the mounting base area 5 to reduce shrinkage defects in the local thick area 25.

[0128] The pre-welding heat treatment was as follows: solution treatment at 532℃ for 4.5 hours, followed by quenching in water at 60℃, and then under-aging treatment at 138℃ for 2.5 hours.

[0129] The welding method used was pulsed MIG welding, with a welding heat input of 0.45 kJ / mm and an interpass temperature not exceeding 100℃. The post-weld graded artificial aging regime was as follows: 162℃ for 4 hours, followed by 180℃ for 3 hours.

[0130] After the post-weld graded artificial aging is completed, the weld toe strengthening zone 19 within an 8mm range on both sides of the weld toe 18 is subjected to ultrasonic impact strengthening treatment. The ultrasonic impact treatment is carried out continuously along the extension direction of the weld, so as to form a smooth transition surface at the weld toe 18 and introduce surface compressive stress.

[0131] This embodiment is applicable to welded components of the chassis bottom beam of off-road vehicles used under conditions of high impact, high vibration, and high fatigue load. Example 4

[0132] This embodiment provides a casting-welding collaborative manufacturing method for chassis bottom beam welded components applicable to locally thick and large connection areas.

[0133] This embodiment is basically the same as Embodiment 1, except that: The frame bottom beam casting blank 1 includes a locally thick area 25, which is located near the welded connection area 3. To reduce the shrinkage porosity in this area, a local pressure feeding structure 14 is provided near the locally thick area 25, and a local chill 12 is provided on its outer side, so that the solidification sequence proceeds from the area away from the feeding source towards the feeding source.

[0134] The welding method adopts TIG-MIG composite welding, the shielding gas is Ar-He mixed gas, the welding heat input is 0.48kJ / mm, and the interpass temperature does not exceed 110℃.

[0135] Welding wire 15 is an Al-Si-Mg-Zr series matched welding wire, in which Si is 5.8%, Mg is 0.32%, Zr is 0.10%, Ti is 0.08%, Sr is 0.012%, and the balance is Al and unavoidable impurities.

[0136] After welding, the material is first subjected to a low-temperature homogenization treatment at 115℃ for 2 hours, followed by a graded artificial aging treatment at 155℃ for 5 hours and 180℃ for 2.5 hours.

[0137] This embodiment is applicable to chassis bottom beam welded parts with large local connection area thickness, high weld joint restraint, and high requirements for weld penetration.

[0138] Comparative Example To verify the synergistic effect of the various technical features of this invention, the following comparative examples can be set up.

[0139] Comparative Example 1 The chassis bottom beam casting blank was prepared using conventional A356 cast aluminum alloy. After conventional T6 heat treatment, the casting was welded using ordinary MIG welding with conventional Al-Si welding wire. No graded artificial aging treatment was performed after welding.

[0140] This comparative example is used to verify the effects of the special cast aluminum alloy composition, pre-weld under-aging treatment, and post-weld graded artificial aging treatment in this invention.

[0141] Comparative Example 2 The same cast aluminum alloy composition as in Example 1 is used, but during the precision casting process, local chills 12, conformal cooling channels 13, or local pressure feeding structures 14 are not provided in the welded joint area 3. The remaining pre-weld heat treatment, welding, and post-weld graded artificial aging treatment are the same as in Example 1.

[0142] This comparative example is used to verify the impact of local microstructure control in the welded joint zone 3 on casting defects, heat-affected zone performance, and fatigue reliability.

[0143] Comparative Example 3 The same cast aluminum alloy composition and precision casting process as in Example 1 were used, but the castings were fully heat-treated with T6 before welding, and no graded artificial aging treatment was performed after welding.

[0144] This comparative example is used to verify the advantages of pre-weld under-aging condition compared to full T6 condition welding.

[0145] Comparative Example 4 The same cast aluminum alloy composition, precision casting process and pre-weld under-aging treatment as in Example 1 were used, but conventional Al-Si welding wire was used during welding, and only a single-stage artificial aging treatment was performed after welding.

[0146] This comparative example is used to verify the effect of Al-Si-Mg-Zr system matched welding wire and post-weld graded artificial aging treatment on the performance matching of weld zone 9, heat-affected zone 10 and cast base material zone 11.

[0147] The chassis bottom beam welded components obtained in the embodiments and comparative examples can be tested and evaluated in the following manner.

[0148] First, internal quality inspection of the casting. X-ray flaw detection or industrial CT is used to inspect the welded joint area 3 and the area within 20mm to 50mm on both sides for porosity, shrinkage porosity, inclusions and cracks, and to evaluate the control effect of local cooling and local feeding on casting defects.

[0149] Second, microstructure analysis. Samples from weld zone 9, heat-affected zone 10, and cast base material zone 11 were taken and observed using metallographic microscope, scanning electron microscope, and energy dispersive spectroscopy to examine grain morphology, secondary dendrite spacing, eutectic silicon morphology, Fe-containing phase morphology, and precipitate distribution.

[0150] Third, hardness distribution testing. Measuring points were arranged perpendicular to the weld direction, sequentially passing through the cast base metal zone 11, heat-affected zone 10, weld zone 9, the other side of the heat-affected zone 10, and the other side of the cast base metal zone 11, to test the microhardness changes. The ratio of the lowest hardness in the heat-affected zone 10 to the average hardness in the cast base metal zone 11 was used to evaluate the softening degree of the heat-affected zone and the post-weld graded artificial aging recovery effect.

[0151] Fourth, mechanical property testing of welded joints. Tensile specimens containing welds were prepared, and their tensile strength, yield strength, and elongation were tested. The results were compared with those of specimens from the cast base material zone 11 to evaluate the strength coefficient of the welded joint.

[0152] Fifth, bending and torsional performance testing. Based on the actual stress state of the welded components of the chassis bottom beam when installed on the vehicle, three-point bending, four-point bending, or torsional loading tests are conducted to evaluate the overall load-bearing capacity and deformation coordination of the welded components of the bottom beam.

[0153] Sixth, fatigue performance testing. Bending fatigue, torsional fatigue, or welded joint fatigue tests are conducted on bottom beam samples or scaled-down specimens containing welds to observe whether fatigue cracks preferentially initiate near the weld toe 18, heat-affected zone 10, or casting defects.

[0154] Seventh, corrosion resistance testing. Neutral salt spray test, cyclic corrosion test, or mud-water corrosion test are conducted on the welded components of the chassis floor beams after welding to evaluate their corrosion resistance in the chassis service environment.

[0155] The above tests verify that the present invention can improve the problems of heat-affected zone softening, weld mismatch between weld and base material properties, fatigue cracking induced by casting defects, and insufficient dimensional stability of aluminum alloy precision cast off-road vehicle frame bottom beam welded parts through the synergistic effect of aluminum alloy composition, precision casting structure control, pre-weld under-aging, low heat input welding, matching welding wire, and post-weld graded artificial aging.

[0156] Preferably, the secondary dendrite spacing within the welded joint zone 3 and its two sides within a range of 20mm to 50mm, the ratio of the minimum hardness of the heat-affected zone 10 to the average hardness of the cast base material zone 11, the weld joint strength coefficient, and the fatigue crack initiation location can be used as comprehensive evaluation indicators. These indicators can more clearly characterize the synergistic effects between local feeding / cooling, pre-weld under-aging, low heat input welding, and post-weld graded artificial aging.

[0157] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for manufacturing a welded component of an aluminum alloy precision-cast off-road vehicle frame bottom beam, characterized in that, Includes the following steps: S1. Prepare a cast aluminum alloy material, wherein the cast aluminum alloy comprises, by mass percentage: Si 6.8%~8.4%, Mg 0.30%~0.48%, Mn 0.16%~0.38%, Zr 0.06%~0.16%, Ti 0.08%~0.18%, Sr 0.010%~0.030%, B 0.002%~0.010%, Fe≤0.16%, Cu≤0.08%, Zn≤0.10%, with the balance being Al and unavoidable impurities; S2. The cast aluminum alloy material is melted, degassed and filtered to obtain a purified aluminum alloy melt. S3. The aluminum alloy melt is subjected to modification and grain refinement treatment; S4. The aluminum alloy melt, after modification and grain refinement treatment, is formed into a chassis bottom beam casting blank using precision casting. S5. Local feeding and / or local cooling are provided in the welding connection area of ​​the cast blank of the frame bottom beam to form a refined and dense structure with a secondary dendrite spacing of no more than 35μm in the welding connection area and within a range of 20mm to 50mm on both sides. S6. Clean the casting blank of the chassis bottom beam and pre-process the welding connection area; S7. Perform pre-welding heat treatment on the cast blank of the chassis bottom beam, the pre-welding heat treatment including solution treatment, quenching treatment and under-aging treatment; S8. Perform final surface cleaning on the welding connection area of ​​the pre-welding heat-treated frame bottom beam casting blank, and perform low heat input welding with the crossbeam, reinforcement, connecting seat, mounting lug or another bottom beam section within 4 hours after cleaning. The welding heat input is 0.25kJ / mm~0.65kJ / mm. S9. Perform post-weld graded artificial aging treatment on the welded components of the chassis bottom beam to create a continuous transition in microstructure and hardness distribution between the weld zone, heat-affected zone, and cast base material zone.

2. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, The cast aluminum alloy comprises, by mass percentage: Si 7.2%–8.0%, Mg 0.34%–0.44%, Mn 0.20%–0.32%, Zr 0.08%–0.14%, Ti 0.10%–0.16%, Sr 0.014%–0.024%, B 0.004%–0.008%, Fe≤0.14%, Cu≤0.06%, Zn≤0.08%, with the balance being Al and unavoidable impurities.

3. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1 or 2, characterized in that, The mass ratio of Mn to Fe in the cast aluminum alloy is 1.5 to 3.0, and the mass ratio of Ti to B is 10 to 20; based on the cast aluminum alloy of claim 1 or 2, it also contains 0.02% to 0.10% of Ce and / or La rare earth elements in order to replace part of Al.

4. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, In steps S2 and S3, the melting temperature is 730℃~760℃, the degassing temperature is 720℃~745℃, the degassing method is argon rotary degassing, the degassing time is 8min~18min, and the rotor speed is 300r / min~500r / min; the filtration method is filtration with a 30ppi~50ppi ceramic filter plate, and after filtration, Al-Sr master alloy, Al-Ti-B master alloy and Al-Zr master alloy are added for modification and composite grain refinement treatment.

5. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, In steps S4 and S5, the precision casting method is low-pressure casting, vacuum-assisted gravity casting, vacuum-assisted low-pressure casting, or reverse-pressure precision casting; at least one of the following is provided in the welded connection area: local chill, conformal cooling channel, and local pressure feeding structure, so that the secondary dendrite spacing in the welded connection area and within a range of 20mm to 50mm on both sides is not greater than 35μm.

6. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, In step S6, the welding connection area of ​​the cast blank of the chassis bottom beam is pre-processed to remove the surface material with a thickness of 0.20mm to 0.80mm; in step S8, the welding connection area is mechanically brushed, degreased, alkaline washed, acid washed or plasma cleaned before low heat input welding, and welding is carried out within 4 hours after cleaning.

7. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, In step S7, the solution treatment temperature is 520℃~535℃, and the holding time is 2h~6h; the quenching medium is water or polymer quenching medium at 50℃~80℃, and the quenching transfer time does not exceed 20s; the under-aging treatment temperature is 120℃~145℃, and the holding time is 1h~4h.

8. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, In step S8, the low heat input welding adopts pulsed MIG welding, cold metal transfer welding, pulsed TIG welding, or TIG-MIG composite welding, with an interpass temperature not exceeding 120°C, and the shielding gas is high-purity Ar or Ar-He mixture; the welding process adopts symmetrical segmented welding, back welding, or skip welding sequence; the welding heat input is calculated according to Q=ηUI / v, where η is thermal efficiency, U is welding voltage, I is welding current, and v is welding speed.

9. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 8, characterized in that, The welding wire used in step S8 is an Al-Si-Mg-Zr matched welding wire, which, by mass percentage, comprises: Si 4.5%–6.5%, Mg 0.15%–0.45%, Zr 0.03%–0.15%, Ti 0.03%–0.12%, Sr 0.005%–0.020%, Fe ≤0.15%, Cu ≤0.05%, with the balance being Al and unavoidable impurities.

10. The manufacturing method of the aluminum alloy precision cast off-road vehicle frame bottom beam welded component according to claim 1, characterized in that, In step S9, the post-weld graded artificial aging treatment includes a first-stage aging and a second-stage aging. The first-stage aging temperature is 150℃~165℃, and the holding time is 2h~6h. The second-stage aging temperature is 170℃~185℃, and the holding time is 2h~5h. Furthermore, before the post-weld graded artificial aging treatment, a low-temperature homogenization treatment of 100℃~120℃ for 1h~3h is also included, or after the post-weld graded artificial aging treatment, rolling, ultrasonic impact, or micro-shot peening is performed on a 3mm~12mm area on both sides of the weld toe.

Images