CN114523187A - Friction stir point connection process based on concave pin-free shoulder reinforced light alloy/thermoplastic composite material connection strength - Google Patents

Abstract

The invention relates to the technical field of friction solid phase connection of metal and thermoplastic non-metal composite materials, in particular to a friction stir point connection process based on concave pin-free shaft shoulder reinforced light alloy/thermoplastic composite material connection strength. The invention provides a method for adopting a pin-free concave shaft shoulder tool head on the basis of a conventional friction stir point connecting process, which promotes the outer side metal below a shaft shoulder to be pressed and deformed, forms outer side high pressure on a lap joint interface, improves the interface heat distribution state and strengthens the mechanical anchoring and physical bonding connection between a metal surface and a melting layer. The method has the advantages of high applicability, simplicity in operation, no obvious increase in production cost and the like, ensures the surface quality of the joint, overcomes the defects of low bonding strength, obvious joint thinning and the like in the conventional technology, and obviously improves the performance of the joint.

Description

A friction stir point joining process based on concave needleless shoulder to strengthen the connection strength of light alloy/thermoplastic composites

technical field

The invention relates to the technical field of friction solid phase connection of lightweight metal and metal composite materials, in particular to a friction stirring point connection method of metal and carbon fiber reinforced thermoplastic polymer matrix composite materials using a needle-free concave shaft shoulder stirring head.

Background technique

The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not necessarily be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.

The urgent need for structural lightweighting has prompted the further application of lap-bonded composite structures of lightweight metal and thermoplastic composites. The use of carbon fiber reinforced thermoplastic polymer matrix composites (hereinafter referred to as CFRP) with high specific strength and high specific stiffness to replace the traditional single metal structure can significantly reduce the structural self-weight while meeting the mechanical performance requirements of the structure. The huge difference in physical and chemical properties between metal and CFRP makes it extremely challenging to optimize the joining process conditions to achieve high-strength bonding between the two. At present, the friction solid-phase joining process has developed into one of the advanced joining technologies of metal and thermoplastic composite materials by virtue of the technical advantages of low heat input, few process parameters and high process flexibility, and has attracted much attention from domestic and foreign researchers. Among them, the friction stir point connection is especially suitable for the lap joint connection of metal and CFRP plate structural parts. During the friction stir joining process, the high-speed rotating stirring head presses down and contacts the upper metal plate, and the frictional heat generates the temperature of the metal plate to rise rapidly; at the same time, the heat is conducted to the overlapping surface of the upper metal plate and the lower CFRP plate, heating And melt the thermoplastic matrix in the CFRP; with the downward pressure of the stirring tool head, the upper metal plate is concavely deformed; affected by the pressure and plastic deformation of the upper metal plate, the melting zone of the lower surface of the metal plate and the upper surface of CFRP is completed. The process of physical bonding and chemical joining to form a lap joint. At present, most of the stirring heads used in the friction stir point connection are conventional tool heads for friction stir welding, that is, a shaft shoulder and a stirring needle, or a stirring head with a flat shoulder without a stirring needle. Among them, using the former conventional stirring head, the pressure is too large, the penetration of the stirring needle or the large concave deformation may damage the CFRP side fiber structure; while the latter has no needle flat shoulder stirring head, although the stirring needle is avoided. However, the strength of the lap surface of the obtained metal and CFRP joints is limited. Increasing the heat input and increasing the fusion area can improve the overall load resistance to a certain extent. However, overheating leads to a large amount of molten resin matrix outflow and residual bubble defects that make the joint The bearing capacity per unit area of the region decreased significantly.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention proposes a new needle-free inner concave shoulder shoulder connection process of metal and CFRP friction stir points, and designs a needle-free inner concave shoulder shoulder tool bit suitable for metal and CFRP friction stir point connection, And formulate the corresponding connection process to solve the technical problems existing in the existing process using conventional and needleless tool heads.

For realizing the above-mentioned technical purpose, the present invention adopts following technical scheme:

A first aspect of the present invention provides a friction stir point connection process based on concave needleless shoulders to strengthen the connection strength of light alloy/thermoplastic composite materials, including:

A cylindrical tool head is prepared from steel or ordinary alloy steel material for the mold. The inner side of the shoulder end face of the tool head is designed with a groove surface with a certain degree of concavity, and the connection between the groove surface and the original end face adopts a 45° chamfer transition form; The tool head is fixed in the welding equipment stirring tool head holder;

The workpiece is pretreated and clamped and fixed, and the workpiece is a metal plate to be welded and a CFRP plate to be connected;

The workpiece is welded by the needle-free shoulder stirring point connection process, that is, it is obtained.

The study found that: in the friction stir point bonding metal and CFRP process, the connection mechanism of the bonding area mainly involves the macro/micro mechanical interlocking effect, physical adhesion effect and chemical bonding effect formed by the molten viscous flowing resin matrix on the metal surface. The formation of the three main connection mechanisms is closely related to the thermal distribution state of the overlapping interface region, so one of the keys to improve the bonding performance lies in how to optimize the process conditions to create favorable temperature and pressure distribution conditions. In order to achieve the above purpose, the present invention proposes a new type of needle-free concave shoulder shoulder metal and CFRP friction stir point connection process, by changing the heat distribution and pressure distribution of the friction contact surface between the tool head and the metal plate, and then improve the metal The lap surface with CFRP plastic is combined with the thermal state to further improve the joint performance.

The second aspect of the present invention provides the light alloy/thermoplastic composite material prepared by the above method.

A third aspect of the present invention provides a needle-free shoulder tool head based on a friction stir point connection process based on a concave needle-free shoulder to strengthen the connection strength of a light alloy/thermoplastic composite material, and the tool head is cylindrical , The inner side of the shoulder end face is designed with a certain concave groove surface, and the connection between the groove surface and the original end face adopts a 45° chamfer transition form.

The beneficial effects of the present invention are:

(1) The process of the present invention is simple, and it only needs to use a concave shaft shoulder tool head in the original process, and it can be completed by matching suitable connection process parameters, and the connection parameters are few and easy to control. The design scheme of the concave shaft shoulder, on the one hand, avoids the large concave deformation of the metal under the same pressing amount, and reduces the thinning of the lap interface; on the other hand, it can change the friction contact mode to reduce the heat input at the same speed and expand the speed. adjustable range. During the formation of the connection mechanism, the concave shoulder forcibly changed the stress characteristics of plastic deformation on the metal side and the distribution characteristics of frictional heat generation, thereby promoting the formation of an annular high pressure distribution in the outer area of the metal and CFRP lap interface directly under the tool head. At the same time, the concave deformation of the metal is reduced, which is conducive to promoting the fusion layer to be more concentrated in the bonding area directly under the stirring head to form a connection with the lower surface of the metal; in addition, the outer annular high pressure restrains the flow of the molten layer from the outside to the inside, which is conducive to strengthening the interface. The mechanical occlusion and physical bonding that have been formed on the surface further enhance the bonding strength.

(2) The operation method of the present invention is simple, low in cost, universal, and easy for large-scale production.

Description of drawings

The accompanying drawings forming a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Fig. 1 is the schematic diagram of the friction stir point connection tool head designed by the present invention;

Fig. 2 is the metal and thermoplastic composite material friction stir point connection principle diagram designed by the present invention;

Figure 3 is a schematic diagram of the strengthening effect of mechanical anchoring and physical bonding in the bonding area of the lap interface during the pressing process of the concave shaft shoulder during the welding process;

Figure 4 shows the results of the lap interface of the aluminum alloy/CFRP friction stir point connection strengthened by the concave shoulder in a specific example.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

A friction stir point joining process based on concave needleless shoulders to strengthen the connection strength of light alloy/thermoplastic composite materials, comprising:

Step 1: Design of the new needleless shoulder tool head

The cylindrical tool head is made of mold steel or ordinary alloy steel. Its main body shape is similar to that of the conventional friction stir welding tool head. The size of the fixed end is based on the specification of the welding machine bushing; the difference is that the inner side of the shoulder end face is designed The groove surface with a certain concave degree, the connection between the groove surface and the original end face adopts a 45° chamfer transition form, and it is fixed in the holder of the stirring tool head of the welding equipment;

Step 2: Prepare and fix the workpiece before welding

First, use alcohol to wipe clean the surface of the metal to be welded and the surface of the CFRP plate to be connected, and stack the two together to form an overlapping surface area. The upper side is the metal plate and the lower side is the CFRP plate; On the platform, the upper surface of the metal is fixed with a clamp to prevent rigid slippage during the connection process;

Step 3: Welding parameter selection and welding start and completion;

Set the process parameters of the friction stir point connection, such as the rotation speed of the stirring tool head, the amount of pressing down, the pressing speed and the dwell time, etc.; then, the friction stir point connection process is started, and the tool head is pressed down to contact the metal plate to reach a certain amount of pressing down. Then withdraw immediately or keep for a certain period of time before withdrawing. After cooling for a period of time, unload the speed, remove the tooling, and complete the welding process.

in,

The diameter range of the needle-free shoulder stirring tool head described in step 1 is 10-30mm, and the adjustable depth of the groove in the end face of the shaft shoulder is 1/10-1/5 of the thickness of the metal plate, about 0.1-1mm (with 1 -5mm metal plate for reference), the diameter adjustable range is 1/2-2/3 of the shoulder diameter, about 5-20mm;

The roughness of the surface of the stirring tool head in step 1 is subject to the original metal luster, and it can be clamped and fixed on the tool head holder of a conventional friction stir welding machine or spot welding machine, and no special design is required;

The light metal materials described in step 2 include titanium alloys, aluminum alloys, magnesium alloys, etc., and the plate thickness is 1-5 mm; carbon fiber reinforced thermoplastic composite materials include short-range or continuous carbon fiber reinforced polyetheretherketone (PEEK), polyphenylene sulfide Ether (PPS) or nylon six (PA6), etc., the thickness of the composite material is 2-5mm;

The metal surface described in step 2 can be pretreated, including but not limited to surface micro-texture preparation, silane coupling agent coating and mechanical grinding to increase roughness, etc. The micro-texture can be femtosecond, picosecond or nanosecond. Prepared by laser processing technology, the texture is recommended to be composed of an elliptical groove array structure, with a spacing of 80-200μm and a depth of 200-450μm; silane coupling agent coating is recommended to be completed at 100-120℃ for 40-60min;

The connection process parameters described in step 3 are as follows, the rotational speed of the tool head is 250-2000 rpm, the pressing speed is 0.05-0.2 mm/s, and the pressing amount is 1-2 times the depth of the groove of the selected tool head; after the pressing is completed, The dwell time of the tool head rotating continuously is 0-10s;

In some embodiments, the diameter D _s of the tool head is in the range of 10-30mm, and the adjustable range of the groove depth d in the end face of the shoulder is 1/10-1/5 of the thickness of the metal plate, about 0.1-1mm (with 1-5mm The metal plate is for reference), the adjustable range of D _c diameter is 1/2-2/3 of the shoulder diameter, about 5-20mm;

The present invention will be further described in detail below with reference to specific embodiments. It should be pointed out that the specific embodiments are intended to explain rather than limit the present invention.

Example 1

A process method for strengthening metal and carbon fiber reinforced composite friction stir point joints based on concave shoulders, comprising the following steps:

Step 1, processing and preparing a needleless concave stirring tool head, as shown in FIG. 1 . Among them, the diameter dimensions of the shoulder and the end face groove are D _s and D _c respectively, and the groove depth is d.

In step 2, the metal surface is cleaned with alcohol, and the overlapping area is coated with silane-coupling gold. Clamp the workpiece and fix the center position of the stirring tool head, as shown in Figure 2. The metal is in the upper layer of the lap joint structure, and the upper surface is fixed and pressed with a clamp to prevent rigid slippage.

Step 3: Set the rotational speed, pressing speed and time of the tool head; after moving the tool head downward to contact the upper surface of the metal, record the original position of the friction end face of the tool head through the welding machine displacement sensor; after starting the welding procedure, the tool head touches the upper surface of the metal Then record the change of the pressing amount, and keep the horizontal position after reaching the set pressing time; the resin matrix on the upper surface of CFRP melts to form a thin molten layer, which forms a dense contact with the lower surface of the metal (as shown in Figure 2).

In step 4, the tool head continues to rotate, and after the residence time is completed, the tool head is pulled upwards; the molten resin base cools and solidifies, and forms mechanical anchoring, physical bonding and chemical bonding with the upper surface of the metal (as shown in Figure 2) .

In this embodiment, the metal material used is 6061 aluminum alloy with a thickness of 2 mm, and the carbon fiber reinforced thermoplastic composite material is short-range discontinuous carbon fiber reinforced nylon six (CF-PA6) with a thickness of 3 mm.

In this embodiment, the metal surface is coated with a silane coupling agent with a concentration of 5%, and the temperature is maintained at 120° C. for 50 minutes.

In this embodiment, the shoulder diameter is 20mm, the groove diameter and depth are 12mm and 0.2mm, and the material is SKD steel.

In this embodiment, the rotational speed of the tool head is 1500 rpm, the pressing speed is 0.1 mm/s, the pressing time is 3 s, and the pressing amount is 0.3 mm.

In this embodiment, a needle-free concave shoulder tool bit is used. During the pressing process, the plastic deformation of the metal plate is characterized by a high outer side and a small inner side, and at the same time, the internal heat generation is reduced; The free flow of the solid resin base to the outside increases its contact time with the lower surface of the metal relatively, which is conducive to strengthening the micro-mechanical anchoring effect and physical bonding. The principle is shown in Figure 3.

In this example, a needle-free flat shoulder tool head with a diameter of 20 mm is used as a reference. Under the condition that other process conditions remain the same, the tensile shear strength and interface fracture morphology of the two mixing tool heads are compared, as shown in Figure 4 ; Using the concave shoulder tool head, the concave area on the aluminum alloy side is annular, and the CFRP side adhered to the metal surface after breaking has more residual fibers and resins, indicating that the use of the needle-free concave mixing tool head strengthens the interface bonding state , the joint tensile shear strength results also proved the above findings.

Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will still Modifications may be made to the technical solutions described in the foregoing embodiments, or equivalent replacements may be made to some of them. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A friction stir point connection process based on concave needleless shoulders to strengthen the connection strength of light alloy/thermoplastic composite materials, is characterized in that, comprising: A cylindrical tool head is prepared from steel or ordinary alloy steel material for the mold. The inner side of the shoulder end face of the tool head is designed with a groove surface with a certain degree of concavity, and the connection between the groove surface and the original end face adopts a 45° chamfer transition form; The tool head is fixed in the welding equipment stirring tool head holder; The workpiece is pretreated and clamped and fixed, and the workpiece is a metal plate to be welded and a CFRP plate to be connected; The workpiece is welded by the needle-free shoulder stirring point connection process, that is, it is obtained. 2. The friction stir point joining process based on the concave needle-free shoulder to strengthen the connection strength of the light alloy/thermoplastic composite material as claimed in claim 1, wherein the metal plate to be welded and the CFRP plate to be connected are stacked on top of each other. Together they form a lap area with a metal sheet on the upper side and a CFRP sheet on the lower side. 3. The friction stir point joining process based on the concave needle-free shoulder to strengthen the connection strength of the light alloy/thermoplastic composite material as claimed in claim 1, wherein the tool head diameter D _s is in the range of 10-30mm, wherein the shoulder end face The adjustable range of the depth d of the inner groove is 1/10-1/5 of the thickness of the metal plate, and the adjustable range of the diameter of D _c is 1/2-2/3 of the diameter of the shaft shoulder. 4. The friction stir point connection process based on the concave needle-free shoulder to strengthen the connection strength of light alloy/thermoplastic composite material as claimed in claim 1, it is characterized in that, the material of described metal plate to be welded is titanium alloy, aluminum alloy Or magnesium alloy, preferably, the plate thickness is 1-5mm; Or, the carbon fiber reinforced thermoplastic composite material CFRP is short-range or continuous carbon fiber reinforced polyether ether ketone, polyphenylene sulfide or nylon 6. Preferably, the thickness of the composite material is 2-5 mm. 5. The friction stir point joining process based on the concave needle-free shoulder to strengthen the connection strength of the light alloy/thermoplastic composite material according to claim 1, wherein the surface of the metal plate to be welded is pretreated, and the method comprises the following steps: : Surface micro-texture preparation, silane coupling agent coating, mechanical polishing. 6. The friction stir point joining process based on the concave needle-free shoulder to strengthen the connection strength of light alloy/thermoplastic composite material as claimed in claim 5, it is characterized in that, microtexture adopts femtosecond, picosecond or nanosecond laser processing Process preparation, the texture is composed of an elliptical groove array structure, the spacing is 80-200 μm, and the depth is 200-450 μm; Or, the silane coupling agent coating is completed at 100-120°C for 40-60min. 7. The friction stir point connection process based on the concave needle-free shoulder to strengthen the connection strength of light alloy/thermoplastic composite material as claimed in claim 1, it is characterized in that, the concrete step of described welding is: setting friction stir point connection Then, start the friction stir point connection process, the tool head presses down and contacts the metal plate, and then pulls out after reaching the predetermined amount of pressure or keeps it for a certain period of time and then pulls out; after cooling for a period of time, unload the speed and remove the Tooling to complete the welding process. 8. The friction stir point joining process based on the concave needle-free shoulder to strengthen the connection strength of light alloy/thermoplastic composite material as claimed in claim 1, it is characterized in that, the connection process parameters are as follows, and the rotational speed of the tool head is 250-2000rpm, and the The pressing speed is 0.05-0.2mm/s, and the pressing amount is 1-2 times the depth of the groove of the selected tool head; after the pressing is completed, the dwell time of the continuous rotation of the tool head is 0-10s. 9. The light alloy/thermoplastic composite material prepared by the method of any one of claims 1-8. 10. A needle-free shoulder tool head based on a friction stir point connection process for strengthening the connection strength of a light alloy/thermoplastic composite material based on a concave needle-free shoulder, characterized in that the tool head is cylindrical, and the shoulder end face is The inner side is designed with a certain concave groove surface, and the connection between the groove surface and the original end surface adopts a 45° chamfer transition form.

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