Friction stir welding method for selective laser melting forming aluminum alloy

Abstract

The invention discloses a friction stir welding method for aluminum alloy formed by selective laser melting, which comprises the following steps: carrying out annealing treatment on aluminum alloy such as AlSi10Mg formed by selective laser melting so as to eliminate residual stress; a special tool clamp is designed, and movement of the to-be-welded base metal is limited through the clamp; before welding, the aluminum alloy surface is polished by abrasive paper to remove an oxidation film, and the plate is wiped by acetone, alcohol and the like to remove surface greasy dirt; welding joints in different forms such as butt joint or lap joint are formed through pre-welding assembly; and reasonable friction stir welding process parameters are selected, welding is completed, and the selective laser melting forming aluminum alloy welding joint with excellent quality is obtained. The method can meet the high-quality connection requirement of the selective laser melting forming aluminum alloy.

Description

Technical Field

[0001] The invention relates to a friction stir welding method for laser selective melting of aluminum alloy, and belongs to the field of additive manufacturing technology and welding. Background Art

[0002] Selective Laser Melting (SLM) is an additive manufacturing technology that uses laser as an energy source to scan the metal powder bed layer by layer according to the 3D CAD model, so that the metal powder melts and solidifies to form the required 3D parts. This technology plays an important role in modern industry, especially in the manufacture of parts with complex shapes. The advantages of SLM technology include no need for molds, reduced production time and cost, improved material utilization, and the ability to manufacture parts with complex structures, such as cavities and 3D spatial structures. Currently, SLM technology has become the preferred and necessary forming method for complex parts.

[0003] Aluminum alloys are widely used in aerospace, weapons, automobiles and other fields due to their technical characteristics such as light weight, high specific strength, good processing performance, excellent weldability, good corrosion resistance, heat treatment strengthening, and good fatigue resistance. SLM forming of aluminum alloy complex components has become a trend in the field of advanced manufacturing, but SLM forming technology is limited by the size of the powder bed. The size of the formed structure is generally below 1m, while the size of the overall aluminum alloy components in the fields of aerospace, automobiles, etc. is often more than 1m. This requires the combination of aluminum alloy parts formed by SLM to achieve the preparation of the overall component through connection. Welding, as a technology that can achieve the atomic bonding of materials, is more efficient and lighter than mechanical connection methods such as riveting. It is currently the preferred structural connection method in the industry. For SLM forming aluminum alloys, traditional melting welding methods such as argon arc welding, laser welding, electron beam welding, etc. are used, which are prone to produce more pores inside, affecting the connection strength and making it difficult to meet the use requirements. This urgently requires a new type of high-quality connection method to achieve the connection of SLM-formed aluminum alloys. Summary of the invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a friction stir welding method for aluminum alloy formed by laser selective melting, thereby avoiding technical problems such as pores that are easily generated by traditional welding methods in the prior art and meeting the high-quality connection requirements of aluminum alloys manufactured by additive manufacturing.

[0005] The technical solution of the present invention is: a friction stir welding method for aluminum alloy formed by laser selective melting, comprising:

[0006] The AlSi10Mg aluminum alloy sheet was prepared by laser selective melting forming process;

[0007] The AlSi10Mg aluminum alloy sheet is annealed by heat treatment to eliminate the residual stress of the substrate;

[0008] The AlSi10Mg aluminum alloy sheet was cut from the substrate by wire cutting to serve as the welding base material;

[0009] Use sandpaper to grind the welding position of the welding base metal to make the welding contact surface smooth and flat; and use organic solvent to remove impurities on the welding base metal;

[0010] Assemble the welding base metal and the welding workpiece by using a fixture, so that the welding base metal and the welding workpiece are butted and clamped;

[0011] Select the appropriate stirring needle type and set the welding process parameters; after determining the welding starting point, press the stirring needle down. When the stirring needle reaches the preset downward pressure, part of the aluminum alloy is plasticized and the deformation resistance is reduced. The stirring needle reaches the specified position and starts welding.

[0012] When the welding process is completed, the stirring needle is withdrawn, and the flash defects on the weld surface are polished, thus completing the aluminum alloy welding formed by laser selective melting.

[0013] Preferably, the stirring needle is fixed at the stirring head position by using a corresponding clamp, the stirring head position is reset to zero before welding, and the welding start position and end position are calibrated through experiments to ensure welding accuracy.

[0014] Preferably, when the stirring needle is a threaded three-plane cone, the welding process parameters are set to:

[0015] Stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle penetration depth: 0.8-8mm, stirring head inclination angle: 0-5°.

[0016] Preferably, when the stirring needle is a concave integral stirring needle, the welding process parameters are set to:

[0017] Stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle penetration depth: 0.8-8mm, stirring head inclination angle: 0-5°.

[0018] Preferably, when the stirring needle is a spiral grooved integral stirring needle, the welding process parameters are set to:

[0019] Stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle penetration depth: 0.8-8mm, stirring head inclination angle: 0-5°.

[0020] Preferably, when the stirring needle is a cylindrical stirring needle, the welding speed is 150 to 240 mm / min, and the rotation speed is 400 to 800 r / min.

[0021] Preferably, after the welding process is completed, the performance of the welded joint is regulated by heat treatment, the heat treatment temperature is 200-350°C, and the insulation time is 1-4h.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention proposes to use a stir friction welding method to achieve the connection of SLM-formed aluminum alloys. Different stirring needle structures and process parameters can be selected according to the thickness of the aluminum alloy materials to be connected and the different joint forms, so as to achieve high-quality welding of SLM-formed aluminum alloys. Compared with the traditional fusion welding method, the present invention can avoid the melting of aluminum alloy materials and reduce the probability of defects. On the other hand, this technology belongs to green manufacturing and can significantly reduce the waste of raw materials.

[0024] (2) When argon arc welding, laser welding and other methods are used to achieve the connection of SLM-formed aluminum alloy, the heat-affected zone is likely to become larger, and the grains in the heat-affected zone will grow, which is likely to become a weak point in the mechanical properties of the entire joint. The method of the present invention can reduce the heat generated during the welding process through the design of the stirring needle and the process. During the welding process, the metal is in a plastic flow state and does not melt. During the welding process, the parts are not easily deformed and the residual stress is small.

[0025] (3) The method of the present invention can realize real-time adjustment of key process parameters such as stirring needle type, rotation speed, welding speed, and pressure amount, thereby realizing precise control of input energy, and further realizing effective control of the energy of the bonding zone, so that the bonding zone can locally reach a high temperature state instantaneously, and the bonding zone simultaneously undergoes mechanical mixing of high strain rate and strong deformation, thereby obtaining a continuous and dense joint structure.

[0026] (4) The connection method of the present invention is stir friction connection forming, and no molten pool is formed during the process, which can avoid the contamination of the prepared material by impurity elements such as O and N in the gas during the preparation process, thereby improving the material performance;

[0027] (5) The method of the present invention is combined with additive manufacturing. The equipment involved in the method process has a high degree of automation and is easy to operate. The entire system has a high level of automation and can be fully computer controlled. The operating steps are simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart of the method of the present invention;

[0029] Figure 2A schematic diagram of a welding joint provided by an embodiment of the present invention;

[0030] Figure 3 This is a macroscopic morphology of the joint after welding provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0032] The present invention provides a welding method suitable for AlSi10Mg aluminum alloy components manufactured by laser selective melting additive manufacturing. The method can suppress defects such as pores and unfused components generated during the welding process of AlSi10Mg aluminum alloy manufactured by laser selective melting additive manufacturing, improve the internal quality of the joint, and enhance the performance of the joint.

[0033] The present invention solves the problem that the conventional fusion welding method easily leads to the accumulation of gas elements in the laser selective melting additive manufacturing AlSi10Mg aluminum alloy, which easily forms a large number of hole defects, and realizes the high-quality preparation of the laser selective melting additive manufacturing AlSi10Mg aluminum alloy.

[0034] S1 uses laser selective melting forming process to prepare AlSi10Mg aluminum alloy sheet. The process parameters are as follows: laser power: 370W, scanning speed: 1500mm / s, scanning spacing: 130μm;

[0035] S2 uses heat treatment to anneal the AlSi10Mg after SLM forming in order to eliminate the residual stress of the substrate. The process parameters are as follows: heat treatment temperature: 250-350℃; holding time: 1.5-3h;

[0036] S3 uses wire cutting to cut the AlSi10Mg aluminum alloy sheet from the substrate.

[0037] S4 uses sandpaper to grind the position to be welded to make the welding contact surface smooth and flat;

[0038] S5 uses organic solvents such as acetone or anhydrous alcohol to remove impurities such as oil, dust, etc. on the board;

[0039] S6 uses fixtures to assemble welding workpieces. The assembly method is butt-jointing, and top screws are used to tighten the two sides of the workpieces.

[0040] The S7 stirring needle adopts a cylindrical stirring head, the welding speed is 150-240mm / min, and the rotation speed is: 400-800r / min.

[0041] In step S1, the additive manufacturing process can be selected from:

[0042] Laser molten deposition forming method, electron beam selective melting forming method, arc fuse forming method.

[0043] In step S2, the plate is directly cut off from the substrate:

[0044] In step S3, the plate is cut by sawing:

[0045] In step S6, the top of the workpiece is pressed by a pressing plate.

[0046] In step S7, the stirring needle may be any of the following:

[0047] Conical stirring needle, double-shouldered stirring needle, threaded stirring needle, static-shouldered stirring needle, backfill stirring needle, etc.

[0048] like Figure 1 As shown, the principle of the forming method of the present invention is as follows:

[0049] 1. Before welding, clean the parts to be welded of the workpiece to be welded, remove the oxide layer and oil stains on both sides of the surface of the aluminum alloy to be welded by grinding and polishing, and fix the aluminum alloy substrate to be welded after grinding and cleaning on the welding fixture;

[0050] 2. Fix the stirring needle at the stirring head position with the corresponding fixture, reset the stirring head position to zero before welding, and calibrate the welding start and end positions through tests to ensure welding accuracy;

[0051] 3. Select the appropriate stirring needle shape. The stirring needle shape can be a conical stirring needle with threads; set the welding process parameters: stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle pressure depth: 0.8-8mm, stirring head inclination angle: 0-5°;

[0052] 4. Use the robot integrated system to control the welding process parameters set in step 3. First, determine the welding starting point and press the stirring needle downward to overcome the material's resistance to deformation. When the stirring needle reaches the preset downward pressure, part of the aluminum alloy is plasticized and the resistance to deformation is reduced. The stirring needle reaches the specified position and welding begins. During the welding process, the stability of the product is ensured by the tooling fixture. When the welding process is completed, the stirring needle is withdrawn and defects such as flash on the weld surface are polished to complete the aluminum alloy welding formed by laser selective melting.

[0053] The oxide layer and oil stains described in step 1 are removed by chemical cleaning methods such as alkali cleaning and acid cleaning;

[0054] The stirring needle described in step 3 has a cylindrical shape;

[0055] The stirring needle described in step 3 is an integral structure, including a stirring needle and a shaft shoulder, and the shaft shoulder has a concave shape;

[0056] The stirring needle described in step 3 is an integral structure, including a stirring needle and a shoulder, and the shoulder morphology is a spiral groove morphology;

[0057] The stirring needle described in step 3 is an integral structure, including a stirring needle and a shaft shoulder, and the shaft shoulder has a concentric annular shape;

[0058] When the stirring needle in step 3 is a concentric annular integral stirring needle, the stirring needle length is 0.8-8 mm; the welding speed is 0.5-5 mm / s; the rotation speed is 1000-2500 rpm; the stirring needle is pressed into the depth of 0.8-8 mm, and the stirring head inclination angle is 0-5°;

[0059] When the stirring needle in step 3 is a monolithic stirring needle with an inward concave shape, the stirring needle length is 0.8-8 mm; the welding speed is 0.5-5 mm / s; the rotation speed is 1000-2500 rpm; the stirring needle insertion depth is 0.8-8 mm, and the stirring head inclination angle is 0-5°;

[0060] When the stirring needle in step 3 is a one-piece stirring needle with a spiral groove morphology, the stirring needle length is 0.8-8mm; the welding speed is 0.5-5mm / s; the rotation speed is 1000-2500rpm; the stirring needle is pressed into the depth of 0.8-8mm, and the stirring head inclination angle is 0-5°;

[0061] After the welding process described in step 4 is completed, the performance of the welded joint is regulated by heat treatment, the heat treatment temperature is 200-350°C, the holding time is 1-4h, and the furnace is cooled;

[0062] The content of the present invention is not limited to the content of the above-mentioned embodiments. The combination of one or several specific embodiments can also achieve the purpose of the invention.

[0063] The beneficial effects of the present invention are verified by the following examples:

[0064] Friction stir welding was used to weld 6 mm thick AlSi10Mg aluminum alloy prepared by selective laser melting.

[0065] Example:

[0066] The friction stir welding method of this embodiment is operated as follows:

[0067] Step 1: Before welding, according to the plate thickness and technical requirements, the welding test plate is processed into a lock bottom form, the lock bottom thickness is 3mm, and the butt thickness is 3mm. Before welding, the surface to be welded is polished or chemically cleaned. The polished or cleaned aluminum alloy test plate is fixed on the fixture, and the fixture is fixed with a pressure block.

[0068] Step 2: Use a threaded conical stirring needle to weld 3mm thick laser selective melting AlSi10Mg aluminum alloy, the stirring needle length is selected to be 2.83mm; welding speed: 3mm / s; rotation speed: 1500rpm; stirring needle pressure depth: 2.8mm, stirring head inclination angle: 2.5°;

[0069] Step 3: After welding is completed, pull out the stirring needle from the workpiece to be welded, and backfill the welding keyhole by manual laser fuse to ensure the integrity of the weld joint, and use grinding to remove defects such as flash around the weld.

[0070] Figure 2 The joint is welded by stir friction welding, the plate thickness is 6mm, and the joint form is a 3mm+3mm butt joint with a locked bottom. Figure 3 This is the macroscopic morphology of the test plate after welding. It can be found that after stir friction welding, the weld surface morphology is good and no macroscopic welding defects are found. The joint is subjected to a tensile test. The results are shown in Table 1. The joint strength is 262-275MPa, and the elongation is 3.0-4.0%. The strength of the laser selective melting AlSi10Mg alloy after annealing is about 320MPa. It can be seen that the strength of the stir friction welding joint is about 80% of the strength of the parent material.

[0071] Table 1 Strength of friction stir welded joints of AlSi10Mg alloy formed by laser selective melting

[0072]

[0073] In summary, friction stir welding is a welding method suitable for high-quality welding of aluminum alloys formed by laser selective melting.

[0074] Since there are a lot of other elements such as H and O in atomic state inside the SLM-formed aluminum alloy, the gas elements are easy to gather and grow to form pores when using traditional welding methods. Friction stir welding is a solid-phase connection technology. The high-speed rotating stirring head is inserted into the workpiece to be welded. The rotating stirring needle rubs against the welded material and plasticizes it. The joint metal is in a plastic state and is combined under the combined action of heat and machine, thereby achieving material connection. This technology can provide a new technical approach for SLM-formed aluminum alloy connection. The grades used include but are not limited to AlSi10Mg.

[0075] The present invention has been described in detail above in conjunction with specific embodiments and exemplary examples, but these descriptions cannot be understood as limitations of the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims. "Exemplary" means "used as an example, embodiment or illustrative", and any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings need not be drawn to scale unless otherwise indicated.

[0076] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

Claims

1. A friction stir welding method for aluminum alloy formed by laser selective melting, characterized in that include: The AlSi10Mg aluminum alloy sheet was prepared by laser selective melting forming process; The AlSi10Mg aluminum alloy sheet is annealed by heat treatment to eliminate the residual stress of the substrate; The AlSi10Mg aluminum alloy sheet was cut from the substrate by wire cutting to serve as the welding base material; Use sandpaper to grind the welding position of the welding base metal to make the welding contact surface smooth and flat; and use organic solvent to remove impurities on the welding base metal; Assemble the welding base metal and the welding workpiece by using a fixture, so that the welding base metal and the welding workpiece are butted and clamped; Select the appropriate stirring needle type and set the welding process parameters; after determining the welding starting point, press the stirring needle down. When the stirring needle reaches the preset downward pressure, part of the aluminum alloy is plasticized and the deformation resistance is reduced. The stirring needle reaches the specified position and starts welding. When the welding process is completed, the stirring needle is withdrawn, and the flash defects on the weld surface are polished, thus completing the aluminum alloy welding formed by laser selective melting.

2. The friction stir welding method for aluminum alloy formed by laser selective melting according to claim 1, characterized in that: Use the corresponding clamp to fix the stirring needle at the stirring head position, reset the stirring head position to zero before welding, and calibrate the welding start and end positions through experiments to ensure welding accuracy.

3. The friction stir welding method for aluminum alloy formed by laser selective melting according to claim 1, characterized in that: When the stirring needle is a three-plane cone with threads, the welding process parameters are set as follows: Stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle penetration depth: 0.8-8mm, stirring head inclination angle: 0-5°.

4. The friction stir welding method for aluminum alloy formed by laser selective melting according to claim 1, characterized in that: When the stirring needle is a concave integral stirring needle, the welding process parameters are set as follows: Stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle penetration depth: 0.8-8mm, stirring head inclination angle: 0-5°.

5. The friction stir welding method for aluminum alloy formed by laser selective melting according to claim 1, characterized in that: When the stirring needle is a spiral groove integral stirring needle, the welding process parameters are set as follows: Stirring needle length: 0.8-8mm; welding speed: 0.5-5mm / s; rotation speed: 1000-2500rpm; stirring needle penetration depth: 0.8-8mm, stirring head inclination angle: 0-5°.

6. The friction stir welding method for aluminum alloy formed by laser selective melting according to claim 1, characterized in that: When the stirring needle is a cylindrical stirring needle, the welding speed is 150-240 mm / min, and the rotation speed is 400-800 r / min.

7. The friction stir welding method for aluminum alloy formed by laser selective melting according to claim 1, characterized in that: After the welding process is completed, the performance of the welding joint is adjusted by heat treatment. The heat treatment temperature is 200-350℃ and the insulation time is 1-4h.

Images