Method for eliminating friction welding root defect by liquid phase extrusion

Abstract

The invention discloses a method for eliminating a friction welding root defect by liquid phase extrusion. The method comprises the following steps: presetting brazing filler metal on a base plate under a weld pass or presetting brazing filler metal on a butt welding interface, and performing FSW welding by a tool with a needle; in the stirred range which the needle can touch, eliminating the original interface of a base material by "solid-phase plastic flowing" formed by needle stirring and forming a compact joint; and melting the brazing filler metal at the weld joint root which the needle cannot arrive at by friction heat and deformation heat, obtaining a liquid phase, filling the non-welded gap by the liquid phase through extrusion of the tool, dissolving the solid base material whichis deformed to a certain degree in a heating power influence region below the needle tip into the liquid phase so as to realize striping, brazing seam alloying and metallurgical bonding among the basematerials at the root and eliminate the defect that the root is not welded completely or is osculated. By the method, the fact that the influence on the tensile property of the FSW joint by the rootdefect is avoided is guaranteed, the plasticity of the joint is improved, the deformation ability and the crack initiation resistance of the joint are improved and the operation process is simple andtime-saving.

Description

technical field [0001] The invention relates to a friction stir welding method, in particular to introducing a liquid phase, using the mechanical action of a tool to squeeze the liquid phase into the root gap, and dissolving the solid base metal, so as to realize film removal, densification and alloying, and finally achieve metallurgical bonding. Elimination of friction stir weld root defects. Background technique [0002] Friction stir welding (FSW: friction stir welding) technology provides a solid-phase welding method for low-strength alloys such as aluminum, copper, and magnesium. Many characteristics such as arc light and splash, so it has been rapidly developed and industrialized. However, at the bottom of the FSW weld bead, there are prone to defects (root defects) caused by insufficient stirring and mixing caused by the needle length being slightly shorter than the plate thickness (usually the needle length is 0.1-0.5mm shorter than the plate thickness): one is unwe...

AI Technical Summary

Problems solved by technology

The second is that the FSW welding machine itself cannot pressurize from the side perpendicular to the welding interface (butt joint), which affects the direct and close contact of the base metal on both sides of the interface

[0005] Although the dual-shoulder friction stir welding can completely eliminate the incomplete penetration defect of the friction stir welding root, a series of problems will occur during the welding process, which makes the dual-shoulder friction stir welding technology have great limitations in eliminating root defects

For example: when the stirring pin enters the beginning of the welding interface from the lead-in plate, the moment generated by the forward thrust of the pin will make the base metal deflect in a "V", resulting in a larger gap at the front end, even greater than the diameter of the pin; when there is no lead-in plate, the weld bead "Herringbone"-shaped defects are easy to appear at the beginning; the stirring needle is easy to break; when the temperature is high, groove defects are prone to appear on the advancing side of the weld; a large number of flashes appear on the retreating side; when the welding temperature is low, the joint cannot form a continuous weld ; The stirring head is easy to stick to the base metal; and the welding process requires high control precision of the machine tool

[0006] Single-shouldered double-sided welding can also completely eliminate root defects of friction stir welding, but this welding method also has certain limitations

For example: it is necessary to weld the upper and lower surfaces of the weldment once, which reduces the welding efficiency; double-sided welding is more serious for the thinning of the base metal; some special-shaped components cannot be welded

[0007] Adding power to assist friction stir welding can improve root defects, but this method can only reduce the thickness of incomplete penetration defects in friction stir welding, and cannot completely eliminate incomplete penetration defects, and it is necessary to introduce auxiliary power to increase energy consumption in the welding process. The fixation of the weldment is also relatively troublesome

[0008] Possible ways to eliminate kiss bond defects and the problems they face: (1) Difficulty adjusting the needle length: Based on the premise that the needle length of a normal tool with a needle in FSW must be smaller than the plate thickness, it is difficult to change, so the needle length is smaller than the plate thickness. Stirring, film removal, and insufficient mixing at the root of the weld are difficult to achieve by adjusting the needle length

(2) Difficulty in lateral pressure: Since the workpiece is rigidly fixed to prevent rotation, even if it can be laterally pressured, it will be partially offset by the rigid fixation

(3) Increase the "vertical" forging pressure and strengthen the "horizontal" plastic flow under the needle end: this has limited potential for ordinary displacement-controlled FSW welding equipment or FSW equipment modified by milling machines

(5) Adding soft welding materials: If soft filling materials are inserted in the welding area, although it is possible to strengthen the flow of plastic metal at the lower part of the needle end, the soft filling materials will cause excessive softening of the entire stirring area and poor performance

[0015] In addition, methods such as pre-filling friction stir and filling repair are mentioned in existing patents (for example, CN107813044A, CN108941880A, CN101670483, CN106583916A), but it is mainly to repair welding after defects such as holes appear on the top of the weld, and it is unavoidable Or to repair root defects of relatively small size that occur in friction stir welding

Images