RU2634402C1 - Friction welding method with aluminium wrought alloys mixing - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: welding tool with a pin with the length of 5.8…11.8 mm, cylindrical in shape, with left-hand thread and support collar with the diameter of 18…28 mm is used. Before welding, sheet parts with the thickness of 6…12 mm are fixed in the vice and the welded edges are milled along the plane. The rotary tool is immersed into the joint of the parts to be connected to the predetermined depth equal to 95-98% of the thickness of the welded parts. The tool is immersed into the joint of the parts to be connected with a minimum speed of vertical movement 10…16 mm/min and a high speed of rotation 300…500 rpm, while the tool angle is changed with respect to the vertical axis from 0° to -1.0°…-2.0°. The immersion depth of the tool is adjusted in accordance with the axial force values obtained from the machine feedback sensors. Then, while maintaining the angle and speed of rotation, the tool is moved along the joint line at a speed of 300…400 mm/min with constant axial force of 23…34 kN. On completion of the welding, the rotary tool is raised and removed from the joint.

EFFECT: method allows to increase the hardness of the welded seam.

9 dwg, 1 tbl, 1 ex

Description

The invention relates to the field of technology of one-piece connection (welding) and can be used in aircraft, rocket, shipbuilding and other engineering industries to obtain compounds of panel structures made of aluminum alloys.

A specific defect in joints made by friction stir welding (STF) is called "kissing bonds" ("non-fusion" at the root of the seam). The defect is eliminated by selection of the welding mode. The destruction of the samples during the test takes place on this defect, which is the reason for reducing the tensile strength of the welded joint.

A known method of friction welding of sheet joints of aluminum alloy AA2024-T4 (heat-treated and naturally aged) with a thickness of 4 mm with a rotation speed of 800 rpm and a feed speed of 87 mm / s, providing an average grain size of the core of the weld 4.9 μm [Y.S. Sato, S. Kurihara and N. Kokawa. Systematic examination of precipitation phenomena associated with hardness and corrosion properties in friction stir welded aluminum alloy 2024 // Welding in the world. 2011. Vol. 55. No. 12. pp. 39-47]. A tool with a diameter of a support collar of 15 mm, a pin diameter of 5 mm and a length of 3.8 mm and an inclination angle of 3 ° is used. The hardness of the base material (region A) varies between 130 HV and 140 HV and is comparable with the hardness of the thermomechanical influence zone (ZTMV) 140 ... 145 HV. The hardness of the core of the weld (region B) in the STP process is reduced to 120 HV. In ZTMV (region C), the hardness of 115 HV in the STP process also decreases to values lower than the hardness of the base material.

A disadvantage of the known method of friction stir welding with 4 mm thick plates with a minimum feed of 87 mm / s and a high speed of 800 rpm of tool rotation is the increased heat input to the weld, which leads to a significant decrease in hardness in ZTMV (region C), due to an increase in grain size . The geometry of the tool in combination with an angle of inclination equal to 3 ° leads to a thinning of the weld in the center. Welding without control of effort leads to a change in grain size over the cross section and gradient of the properties of the weld.

The closest to the same purpose to the claimed invention in terms of features is a method of friction welding with stirring 6 mm thick plates of AA2024-T351 (heat-treated, cooled and naturally aged to a substantially stable state) alloy, in which a tool with a threaded pin with a diameter of 6 mm and 5.5 mm long and a diameter of a support collar of 16 mm. A pin rotating at a speed of 850 rpm is immersed in the joint of the parts to be joined until a predetermined depth of 95 ... 98% of the thickness of the parts to be welded is reached. The tool is moved in the welding direction at a speed of 120 mm / min parallel to the rolling direction. At the end of welding, a rotating tool is raised and removed from the joint.

The heat affected zone (HAZ) experiences a peak temperature from 250 to 350 ° C, which leads to a sharp drop in hardness at the HAZ / ZTMV boundary from 140-155 HV to 115-120 HV (Fig. 1). In this zone, plastic deformation is absent or insufficient to change the initial granular structure. The hardness of ZTMV is minimum 115-120 HV, where the granular structure rotates and partially recrystallizes near the core. The largest plastic deformation occurs in the core, where the microstructure is completely dynamically recrystallized, an average grain size of 4 microns with a hardness of 130-140 HV (Fig. 2) [C. Genevois, A. Deschamps, A. Denquin, B. Doisneau-cottignies. Quantitative investigation of precipitation and mechanical behavior for AA2024 friction stir welds // Acta Materialia 53 (2005) 2447-2458]. The hardness of the base metal corresponds to 145-160 HV. This method is adopted as a prototype.

Signs of the prototype, which coincides with the essential features of the proposed method is the immersion of a tool rotating at high speed, consisting of a pin and a support collar, in the joint of the parts to be joined until a predetermined depth of 95-98% of the thickness of the parts being welded is reached; tool movement along the connection line; lifting a rotating tool and removing it from the joint.

The disadvantage of this method, adopted as a prototype, is the increased heat input in the weld, which leads to a sharp decrease in hardness in ZTMV, due to an increase in grain size, a change in its crystallographic orientation and partial recrystallization. Welding without control of effort leads to a change in grain size over the cross section and gradient of the properties of the weld.

The problem to which the invention is directed is the development of a method of friction welding with stirring of butt joints 6 ... 12 mm thick from aluminum deformable alloys, which allows to increase the hardness of the weld.

The problem was solved due to the fact that in the known method of friction welding with stirring of butt joints of aluminum deformable alloys, comprising immersing a tool rotating at a high speed, consisting of a pin and a support collar, in the joint of the parts to be joined until a predetermined depth of 95- 98% of the thickness of the parts to be welded, moving the tool along the connection line, lifting the rotating tool and removing it from the joint, according to the invention, use a welding tool with a pin, made With a length of 5.8 ... 11.8 mm of a cylindrical shape with left-hand thread and a support collar with a diameter of 18 ... 28 mm, before inserting a pin into the joint of parts, sheet parts with a thickness of 6 ... 12 mm are fixed in a vise and milling the welded edges in a plane, immersing the tool the joint of the connected parts is carried out with a minimum speed of vertical movement of 10 ... 16 mm / min and a high speed of rotation of 300 ... 500 rpm, while the angle of the tool is changed relative to the vertical axis from 0 ° to -1.0 ° ... -2.0 ° the depth of immersion of the instrument is adjusted according to the value of the axial force derived from the feedback sensors of the machine, then, keeping the angle and speed of rotation, the tool is moved along the joint line at 300 ... 400 mm / min at a constant axial force of 23 ... 34 kN.

Signs of the proposed technical solution, distinctive from the prototype, - use a welding tool with a pin made of a length of 5.8 ... 11.8 mm of a cylindrical shape with left-hand thread and a support collar with a diameter of 18 ... 28 mm; before the pin is inserted into the joint of parts, sheet parts with a thickness of 6 ... 12 mm are fixed in a vice and milling of the welded edges in a plane; immersion of the tool in the joint of the parts to be connected is carried out with a minimum vertical movement speed of 10 ... 16 mm / min and a high rotation speed of 300 ... 500 rpm, while the tool angle is changed relative to the vertical axis from 0 ° to -1.0 ° ... -2, 0 °, the immersion depth of the tool is adjusted in accordance with the values of the axial force obtained from the feedback sensors of the machine; keeping the angle and speed of rotation, the tool is moved along the line of the joint at a speed of 300 ... 400 mm / min with a constant axial force of 23 ... 34 kN.

Distinctive features, together with the known ones, will eliminate porosity in the root of the seam, prevent coagulation of grains of different zones of the weld and increase the strength of the joint to values above 90% of the tensile strength of the base material. This will provide an increase in hardness in the weld zone.

The proposed method is illustrated by the drawings shown in FIG. 19.

In FIG. 1 shows the distribution of hardness in the cross section of a weld during welding by a known prototype method.

In FIG. 2 - the microstructure of the weld when welding in a known manner, the prototype.

In FIG. 3 is a graph of the change in axial force depending on the length of the weld.

In FIG. 4 is a graph of the change in depth depending on the length of the weld.

In FIG. 5 shows a diagram of fixing sheet blanks before friction stir welding. The drawing shows:

1 - supporting shoulder tool for STP;

2 - pin tool for STP;

3 - substrate;

4 - weld;

5 - parts to be welded;

6 - an example of the installation of machine clamps;

7 - joint line;

8 - axis of rotation of the tool;

9 - normal to the surface of the parts;

10 - axis installation side clamps;

11 - direction of welding;

12 - direction of rotation of the tool;

13 - the angle of the tool.

In FIG. 6 is a cross section of a weld.

In FIG. 7 - pole pattern inverted relative to the X-direction of the sample for the free side (EDX analysis).

In FIG. 8 is a pole drawing inverted relative to the X-direction of the sample for the runaway side (EDX analysis).

In FIG. 9 - averaged distribution of microhardness along the height of the weld. In FIG. 9 shown:

- верх шва;

- top of the seam;

- середина шва;

- the middle of the seam;

- дно шва;

- bottom of the seam;

NANOSECOND - the free side;

SS - runaway side;

OM is the main material.

The method is as follows.

Before the welding process by friction with stirring, the edges of the parts to be welded are prepared 5. For this, the parts 5 are clamped in a vice with the edges to be welded up and milled in a plane without bevel edges. During welding, the tool is rotated 300 ... 500 rpm, the parts are deepened into the material at a speed of 10 ... 16 mm / min, while the angle of the tool relative to the vertical axis changes from 0 ° to -1.0 ° ... -2.0 ° , upon reaching the specified depth of 95 ... 98% of the thickness of the material, while maintaining the angle and speed of rotation, the tool begins to move along the joint line at a speed of 300 ... 400 mm / min, welding is carried out with a constant axial force of 23 ... 34 kN. In this mode, the depth of the tool is inconsistent and is regulated in accordance with the values of the axial force received from the feedback sensors of the machine.

At constant speeds and axial force, first of all, the coordinate (tool deepening) changes, as well as the torque of the machine engine. All parameters change in a certain interval, depending on the feedback of the installation. For example, during the welding process, a signal is received from the force sensor that the force has become greater than the set one and the installation drives slightly raise the tool from the welding zone. In case of lesser force of a given value, the unit drives increase the immersion depth of the tool. This regulation occurs with a high frequency and the graph of the axial force changes very quickly changes direction up and down, therefore, it looks very dense while maintaining changes within certain limits (Fig. 3). The non-linear graph of the coordinate, under other constant conditions, also changes discretely (Fig. 4).

Sheet blanks (parts) 5 are processed in pairs to prevent the appearance of a gap between them. The press of the side surfaces of the parts 5 is carried out in the plane of the bed perpendicular to the joint 7 to ensure the most complete contact of the welding edges. The clamping of parts 5 in a vertical plane by machine clamps 6 prevents the movement of parts 5 relative to the bed during the welding process and the occurrence of high cyclic loads and bending of the tool (Fig. 5), and also provides tight contact of parts 5 with the substrate 3. The substrate 3 is used in the form of a plate stainless steel without external defects and polished to a mirror finish to prevent the penetration of aluminum melt into the substrate material 3 and, as a result, adhesion of the welded parts to it 5. Substrate 3 to It is necessary to be of such a size as to completely overlap the weld 4 and the installation location of the clamps 6.

In addition to edge preparation and fastening, the formation of the joint and its quality are significantly affected by the shape and length of pin 2 and the diameter of the support collar 1 (Fig. 5). The use of pin 2 with a length of 5.8 ... 11.8 mm of a cylindrical shape with two-way left-handed threads and a support collar with a diameter of 18 ... 28 mm with two spiral "left" grooves allows for positive rotation of the tool to direct the plasticized metal to the center and down to the root of the weld, which will increase the hardness of the weld (Fig. 6).

The optimal constant axial force on the tool is 23-34 kN, the rotation speed is 300 ... 500 rpm, the minimum penetration speed is 10 ... 16 mm / min and the tool is informed by the longitudinal feed rate of 300 ... 400 mm / min, which leads to an increase in temperature in the core of the weld, increasing the degree of mixing of its material, grinding grain to 2 μm (Fig. 7-8), the formation of a symmetrical weld, the formation at the initial stage of aging of nanoscale Guinier – Preston – Bagaryatsky zones (GPB), and, ultimately, to increasing the hardness of the weld and minimized w hardness to its bottom (Fig. 9).

The hardness of the weld core 110-150 HV is reduced to 130 HV in ZTMV on the upstream side and to 80 HV in ZTMV on the downstream side. The HAZ hardness drops sharply to the hardness of the main non-heat-treated alloy AA2024 - 60 HV (Fig. 9). An advantage of the claimed invention is heat treatment with the used technological parameters of the STP of the material of the core of the weld.

For high-quality formation of joints without defects in the form of pores in the root part of the seam (Fig. 6), it is necessary to ensure that the metal of the joined parts in this zone is in a plastic state for a certain period of time. In this case, mixing of the metal parts in the root of the seam is ensured.

The rotation of the tool at the stage of deepening the pin into the material of the part at a speed of 300 ... 500 rpm promotes heating of the material of the parts to a plasticized state and avoids extreme conditions: milling of the groove, or melting of the material of the parts.

The penetration of pin 2 (Fig. 5) into the material of parts at a speed of 10 ... 16 mm / min at a tool rotation speed of 300 ... 500 rpm and reaching a predetermined pin depth, providing full contact of the surface of the parts with the support collar 1 of the tool, allows you to warm the material of the parts in the place of contact with the pin and to prevent the appearance of chips or excessive flaking, warm the root zone of the welded joint and keep its material in a plastic state for a certain period of time. This provides increased hardness of the weld.

The deviation of the tool relative to the vertical axis from 0 ° to -1.0 ° ... -2.0 ° is necessary to seal the weld behind the tool and reduce the likelihood of defects in the weld.

The tool rotation speed of 300 ... 500 rpm during the friction stir welding process remains constant to maintain the solid-phase welding process. Saving the angle and speed of rotation of the tool during its movement along the line of the junction allows you to get a dense fine-grained structure of the weld and achieve a weld strength of more than 90% of the strength of the base material.

Maintaining the welding speed or longitudinal feed of the tool 300 ... 400 mm / min allows for other specified parameters to carry out the welding process of parts without external and internal defects, as well as without significant grain growth in various zones of the weld.

Welding with a constant axial force of 23 ... 34 kN allows you to ensure a uniform structure of the weld without defects and porosity in the root of the weld. In this case, welding with constant effort and feedback control, in contrast to welding with a constant level of penetration, eliminates defects that occur when the substrate, the machine bed, and the parts themselves deviate from the flatness. With a decrease in force, there is a risk of lack of penetration at the root of the seam and the occurrence of defects in the form of a “wormhole” (tunnel defect). As the force increases, the tool will penetrate deeper into the material of the parts, thereby leading to a thinning of the weld, the appearance of stress concentrators at the boundaries of the movement of the support collar, as well as mixing of the substrate material into the weld, deformation of the substrate and the risk of tool destruction.

The proposed method performed experimental welding of samples with a thickness of 12 mm from a deformable aluminum alloy AA2024. For welding, a tool with a pin in the form of a cylinder with a left-side double-thread was used with a pitch of 2.8 mm, a length of 11.8 mm and a support collar with a diameter of 25.4 mm with a spiral groove. The pin material is chromium-nickel-cobalt alloy MP 159 (USA), the supporting collar is tool steel H13 (USA). When welding the tool, a rotation of 300 rpm is imparted, deepening into the workpiece material is carried out at a speed of 12 mm / min, while the angle of the tool relative to the vertical axis changes from 0 ° to -1.5 °, upon reaching the specified depth of 11.8 mm, while maintaining the angle and speed of rotation, the tool begins to move along the line of the joint at a speed of 300 mm / min, welding is carried out with a constant axial force of 34 kN. In this mode, the depth of the tool is inconsistent and is regulated in accordance with the values of the axial force received from the feedback sensors of the machine.

The results of research and testing are shown in FIG. 6-9. A metallographic study of the structure of the weld in its cross section (Fig. 6), estimation of grain size and their preferred direction in all zones of the weld on the upstream (Fig. 7) and recession sides (Fig. 8) using EDX analysis and the study of the averaged distribution microhardness along the height of the weld (Fig. 9) as a result of mechanical tests suggest that the developed method contributes to an increase in temperature in the core of the weld, increase the degree of mixing of its material, and grind the grains to 2 10 .mu.m, forming a symmetrical weld formation in the initial stage of aging nanoscale zones Guinier - Preston - Bagaryatskogo and, ultimately, increasing core firmness and ZTMV weld hardness and the minimum reduction in its bottom part.

Analysis of the test results shown in FIG. 9 shows that in the proposed method, the hardness of the core of the weld is 50 ... 90 HV higher than the hardness of the base material (AA2024-0). In the prototype, the hardness of the core and the HAZ of the weld is lower than the hardness of the base material (AA2024-351) by 15 ... 20 HV and 30 ... 40 HV, respectively, which indicates a lower strength of the weld.

Claims (1)

A method of friction welding with stirring of butt joints of aluminum deformable alloys, comprising immersing a rotating tool consisting of a pin and a support collar in the joint of the parts to be joined until a predetermined depth of 95-98% of the thickness of the parts to be welded is reached, moving the tool along the connection line, raising the rotating tool and removing it from the joint, characterized in that they use a welding tool with a pin made of a length of 5.8 ... 11.8 mm of a cylindrical shape with left-hand thread and a support collar m with a diameter of 18 ... 28 mm, before introducing a pin into the joint of parts, sheet metal parts with a thickness of 6 ... 12 mm are fixed in a vise and milling the edges to be welded along the plane, the tool is immersed in the joint of the joined parts at a speed of vertical movement of 10 ... 16 mm / min and a speed rotation 300 ... 500 rpm, while the angle of the tool is changed relative to the vertical axis from 0 ° to -1.0 ° ... -2.0 °, the immersion depth of the tool is adjusted in accordance with the values of the axial force received from the feedback sensors of the machine, then ins the pipe is moved along the joint line at a speed of 300 ... 400 mm / min with constant angle, rotation speed and axial force of 23 ... 34 kN.

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