CN106001863B - Improve the hot-working method of heat-treatable strengthened aluminum alloy joint made by flame welding elongation percentage - Google Patents

Abstract

The hot-working method for improving heat-treatable strengthened aluminum alloy joint made by flame welding elongation percentage, belongs to welding technology field.Two heat-treatable strengthened aluminum alloy workpiece to be welded are fixed on the welding tooling of no backing plate first, then backing welding is carried out with the TIG welderings of direct current heliarc, first layer cosmetic welding is carried out with Variable Polarity pulse TIG welding again, second layer cosmetic welding is finally carried out with Variable Polarity pulse TIG welding, to complete the welding of two heat-treatable strengthened aluminum alloy workpiece.Invention increases second layer cappings to make the tensile strength at the welding point after increase second layer capping be effectively improved, elongation percentage improves 40% by design technology and dimensional parameters.

Description

Thermal processing method for improving elongation of heat-treatable aluminum alloy welded joints

Technical field:

The invention relates to a thermal processing method, in particular to a thermal processing method for increasing the elongation rate of heat-treatable and strengthened aluminum alloy welded joints, and belongs to the field of welding technology.

Background technique:

The core tank of my country's launch vehicle is made of heat-treatable aluminum alloy, such as 2A14, 2219 and other models. The weld seam is welded by single-sided two-layer automatic TIG welding. The shape of the weld seam is shown in Figure 1. TIG welding is used to realize the bottom weld, and the second layer adopts variable polarity TIG welding to realize the cover weld.

The advantages are mainly reflected in:

1) The pores and inclusions in the bottom welding process are easy to overflow, which reduces welding defects and improves welding quality;

2) The welding speed of bottom welding can reach more than 12m/h, which significantly improves the welding efficiency;

3) While maintaining a large welding speed, the welding current is significantly reduced, the heat input of the weld is reduced, and the welding deformation of the product is reduced;

4) The linear energy density is high, the welding penetration is large, and the medium-thickness plate can be welded once without opening the bevel.

The direct current TIG welding process without a backing plate has the above obvious advantages, but it also has certain process limitations. The dense line energy and concentrated heat input cause the elongation of the welded joints of heat-treatable aluminum alloys to be low, about 3%. Under the action of force, the seam may be brittle.

The reason is that after TIG welding of 2219 aluminum alloy, due to different degrees of Cu element segregation in the weld (WZ) and partially melted zone (PMZ), the structure of the overaging zone (OAZ) and heat-affected zone (HAZ) will also occur to a certain extent. The change of the welded joint reduces the mechanical properties of the welded joint. The distribution of each area is shown in Figure 1. In order to make up for the lack of weld strength, a certain weld reinforcement is usually reserved. The presence of reinforcement makes the joint a geometric discontinuity, and stress concentration will appear at the weld toe when loaded. The weld toe is usually located at the junction of the weld and the partially melted zone, and the microstructure and mechanical properties of the partially melted zone are highly non-uniform, and the closer to the fusion line, the worse the strength and plasticity. When the non-defective joint with reinforcement is stretched transversely, the crack initiation position is generally near the weld toe, and the fracture path may be in the weld or partially melted zone.

Invention content:

The technical problem of the present invention is: to overcome the deficiencies of the prior art, to provide a thermal processing method for increasing the elongation of heat treatable strengthened aluminum alloy welded joints, effectively improving the elongation of heat treatable strengthened aluminum alloy welded joints and the weld seam strength.

The technical solution of the present invention is: a thermal processing method for improving the elongation rate of a heat-treatable and strengthened aluminum alloy welded joint, comprising the following steps:

(1) Fix the two heat-treatable strengthened aluminum alloy workpieces to be welded on the welding tool without backing plate;

(2) Backing welding with DC helium arc TIG welding;

(3) Perform the first layer of cover welding with variable polarity pulse TIG welding;

(4) The second layer of cover welding is performed with variable polarity pulse TIG welding to complete the welding of two heat-treatable aluminum alloy workpieces.

In the step (2), the process parameters of back welding with DC helium arc TIG welding are: welding speed is 13-23m/h, welding current is 160-300A, and arc voltage parameter is 13-18V.

In the step (3), the process parameters of the first layer of capping welding with variable polarity pulse TIG welding are: the welding speed is 6-14m/h, the duty cycle is 45-70%, and the base value current is 200- 300A.

In the step (4), the shielding gas for the second layer of cover welding is argon, the welding speed is 5-10m/h, the welding current is 80-150A, and the gas flow rate is 8-16L/min.

The size parameters of the second layer of covering meet:

2δ+b‐3mm≤a≤2δ+b+3mm

1.5mm≤h≤2mm

Where a is the width of the front of the second layer of cover, b is the width of the back of the back welding, δ is the thickness of the workpiece to be welded, and h is the front reinforcement of the second layer of cover.

The realization method of carrying out the second layer cover welding with the variable polarity pulse TIG welding is as follows:

(6.1) Grinding and cleaning the two heat-treatable aluminum alloy workpieces to be welded and the first-layer cover weld seam;

(6.2) The welding torch starts arcing above the welding seam, and the welding torch moves along the position of the welding seam, swinging left and right, fully covering the original welding seam, and ensuring that the size parameters of the second layer of covering surface meet 2δ+b‐3mm≤a≤2δ +b+3mm, 1.5mm≤h≤2mm.

The thickness of the two heat-treatable strengthened aluminum alloy workpieces to be welded is greater than 4mm.

Compared with the prior art, the present invention has the following beneficial effects:

(1) On the basis of the existing welding seam adopting single-sided two-layer automatic TIG welding, the present invention increases the second layer of cover surface, and through the design process and size parameters, the weld seam after adding the second layer of cover surface ( The tensile strength of the welded joint) has been improved to a certain extent, and the elongation has been increased by 40%.

(2) The size of the second covering surface of the present invention satisfies 2δ+b-3mm≤a≤2δ+b+3mm, which effectively disperses the stress at the original welding toe and optimizes the fracture path of the welded joint, thereby increasing the strength and Elongation.

(3) The present invention realizes that the width dimension of the second-layer cover surface meets the requirement by swinging the welding torch from side to side, and overcomes the defect that the width dimension of the cover surface in the traditional welding torch welding method is relatively narrow.

Description of drawings:

Fig. 1 is a schematic diagram of the composite welding of two heat-treatable and strengthened aluminum alloy workpieces to be welded;

Fig. 2 is the composite welding schematic diagram of bottoming and cover surface of the present invention;

Fig. 3 is a schematic diagram of the swing of the welding torch during the welding of the second layer cover.

Detailed ways:

Aiming at the low elongation and strength of the welding seam caused by single-sided two-layer automatic TIG welding, the present invention proposes a thermal processing method for improving the elongation of heat-treatable and strengthened aluminum alloy welded joints, which includes the following steps:

(1) Fix the two heat-treatable strengthened aluminum alloy workpieces to be welded on the welding tool without backing plate, wherein the thickness of the two heat-treated strengthened aluminum alloy workpieces to be welded is greater than 4mm.

(2) Backing welding is performed by DC helium arc TIG welding. The process parameters are: welding speed is 13-23m/h, welding current is 160-300A, and arc voltage parameter is 13-18V.

(3) The first layer of capping welding is performed with variable polarity pulse TIG welding. The process parameters are: welding speed is 6-14m/h, duty cycle is 45-70%, and base current is 200-300A.

(4) The second layer of cover welding is performed with variable polarity pulse TIG welding to complete the welding of two heat-treatable aluminum alloy workpieces. The shielding gas during welding is argon, the welding speed is 5-10m/h, the welding current is 80-150A, and the gas flow rate is 8-16L/min. When the plate is thick, in order to ensure that the front of the weld is formed, the welding wire can be added appropriately.

As shown in Figure 2, the size parameters of the second layer cover satisfy:

2δ+b‐3mm≤a≤2δ+b+3mm

1.5mm≤h≤2mm

Among them, a is the front width of the second layer of cover, b is the back width of the back welding, δ is the thickness of the workpiece to be welded, h is the front reinforcement of the second layer of cover, and the unit is mm.

In order to achieve the above welding effect, after the weld seam of the product is polished and cleaned, it is fixed on the welding tool; the welding torch strikes the arc above the weld seam, providing heat to act on the front of the weld seam, and the welding torch moves along the weld seam position, covering it one after another.

During the movement of the welding torch along the position of the weld seam, it swings left and right to fully cover the original weld seam, as shown in Figure 3, and ensure that the shape of the weld seam meets the requirements of Figure 2. The left and right swing of the welding torch is realized by the automatic movement of the clamping welding torch mechanism, and it can also be realized by manual movement.

Using reasonable welding parameters, when the welding torch covers the remelted original weld, ensure that the frontal height of the remelted weld is 1.5mm-2mm.

Example 1:

For products with a model thickness of 8mm, the implementation parameters are shown in Table 1:

Table 1 Welding parameters of products with a thickness of 8mm

Wherein, the size parameter of the second layer of cover satisfies a=2δ+b+3mm, h=1.5mm, a is the front width of the second layer of cover, b is the back width of bottom welding, and δ is the thickness of the workpiece to be welded , h is the frontal reinforcement of the second layer of covering, and the unit is mm.

The elongation of the first layer after welding is 3.5%, and the strength is 280‐290MPa. The elongation rate of the second layer cover after welding is 5.0%, and the strength is 320MPa.

Example 2:

For products with a model thickness of 10mm, the implementation parameters are shown in Table 2:

Table 2 Welding parameters of products with a thickness of 10mm

Wherein, the size parameter of the second layer of cover satisfies a=2δ+b-3mm, h=2mm, a is the front width of the second layer of cover, b is the back width of the bottom welding, δ is the thickness of the workpiece to be welded, h is the frontal reinforcement of the second layer of covering, in mm.

The elongation of the first layer after welding is 3.5%, and the strength is 280‐295MPa. The elongation rate of the second layer cover after welding is 5.5%, and the strength is 310MPa.

Example 3:

For products with a model thickness of 12mm, the implementation parameters are shown in Table 3:

Table 3 Welding parameters of products with a thickness of 12mm

Wherein, the size parameter of the second layer of cover satisfies a=2δ+b+2mm, h=1.8mm, a is the front width of the second layer of cover, b is the back width of the bottom welding, and δ is the thickness of the workpiece to be welded , h is the frontal reinforcement of the second layer of covering, and the unit is mm.

The elongation of the first layer after welding is 3.0%, and the strength is 290‐300MPa. The elongation rate of the second layer cover after welding is 5.5%, and the strength is 330MPa.

It can be seen from the above three embodiments that according to the method of the present invention, the mechanical properties of the joint of the workpiece to be welded are significantly improved, the tensile strength is increased from 280-300MPa to 310-330MPa, and the elongation is increased from 3.0% to 5.5%.

Parts not described in detail in the present invention belong to the common knowledge of those skilled in the art.

Claims (6)

1. improving the hot-working method of heat-treatable strengthened aluminum alloy joint made by flame welding elongation percentage, it is characterised in that including following step Suddenly：

(1) two heat-treatable strengthened aluminum alloy workpiece to be welded are fixed on the welding tooling of no backing plate；

(2) backing welding is carried out with the TIG welderings of direct current heliarc；

(3) first layer cosmetic welding is carried out with Variable Polarity pulse TIG welding；

(4) second layer cosmetic welding is carried out with Variable Polarity pulse TIG welding, to complete the weldering of two heat-treatable strengthened aluminum alloy workpiece It connects；

The dimensional parameters of the second layer capping meet：

2δ+b‐3mm≤a≤2δ+b+3mm

1.5mm≤h≤2mm

Wherein a is the frontal width of second layer capping, and b is the back side width of backing welding, and δ is the thickness of workpiece to be welded, h the The topside height of two layers of capping.

2. hot-working method according to claim 1, it is characterised in that：In the step (2) with direct current heliarc TIG weld into The technological parameter of row backing welding is：Speed of welding is 13-23m/h, and welding current 160-300A, arc voltage parameter is 13-18V.

3. hot-working method according to claim 1, it is characterised in that：With Variable Polarity pulse TIG welding in the step (3) Carry out first layer cosmetic welding technological parameter be：Speed of welding is 6-14m/h, duty ratio 45-70%, background current 200- 300A。

4. hot-working method according to claim 1, it is characterised in that：Second layer cosmetic welding welds in the step (4) When protection gas be argon gas, speed of welding 5-10m/h, welding current 80-150A, gas flow 8-16L/min.

5. hot-working method according to claim 1, it is characterised in that：It is described to carry out second with Variable Polarity pulse TIG welding Layer cosmetic welding implementation method be：

(4.1) two heat-treatable strengthened aluminum alloy workpiece to be welded and first layer cap weld grinding process are clean；

(4.2) the welding gun square starting the arc in welded joints, welding gun is moved along position while welding, in a manner of swinging, is covered comprehensively original Weld seam, and ensure that the dimensional parameters of second layer capping meet the 2 δ+b-3mm≤δ of a≤2+b+3mm, 1.5mm≤h≤2mm.

6. hot-working method according to claim 1, it is characterised in that：Two heat-treatable strengthened aluminium to be welded Alloy workpiece thickness is more than 4mm.