Grain refinement method based on double-pulse waveform fine modulation

Abstract

The invention provides a grain refinement method based on double-pulse waveform fine modulation, and belongs to the technical field of welding. The method comprises the steps that different average currents are obtained by changing current base values of a strong pulse train and a weak pulse train, and different heat inputs in the welding process are formed; the maximum value of the current base value is limited according to the diameter of the welding wire; and through circulation of the strong pulse train and the weak pulse train, grains at the bottom of a weld pool formed in the welding process are refined. And through circulation of the strong pulse train and the weak pulse train, a stirring effect is generated on the bottom of a weld pool formed in the welding process, so that the growth process of grains is continuously broken, and grain refinement of the electric arc welding weld microstructure is not achieved.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and more specifically, relates to a grain refinement method based on dual-pulse waveform fine modulation. Background Technology

[0002] When welding aluminum alloys, the strong and weak pulse groups each have a relatively long duration, allowing them to reach a stable state under their respective heat inputs. Therefore, the molten pool size during the strong pulse group is significantly larger than that during the weak pulse group. Due to the different heat inputs during the strong and weak pulse stages, the final weld contour morphology also differs. Numerical simulations were used to compare the effects of pulsed welding and constant current welding on weld formation. Although pulsed welding significantly reduces the heat input compared to constant current welding, it still produces the same weld contour. During the current peak-base transition, the molten pool undergoes alternating "expansion-contraction" changes, and the grain size of the fusion zone also changes accordingly.

[0003] Therefore, the technology of improving weld microstructure, especially refining weld grain size, through dual-pulse fine modulation still needs further exploration. Summary of the Invention

[0004] The main objective of this application is to provide a grain refinement method based on dual-pulse waveform fine modulation, which can achieve grain refinement of the microstructure of arc welding welds.

[0005] To achieve the above objectives, this application proposes a grain refinement method based on dual-pulse waveform fine modulation, comprising: Different average currents are obtained by changing the current base values ​​of strong and weak pulse groups, resulting in different heat inputs during welding. The maximum value of the current base value is limited according to the diameter of the welding wire. Through the cycle of strong and weak pulse groups, the grains at the bottom of the weld pool formed during welding are refined.

[0006] Furthermore, the number of pulses in the strong pulse group is the same as that in the weak pulse group.

[0007] Furthermore, the maximum value of the current base value is 30A-110A.

[0008] Furthermore, the heat input conforms to: P=ηUI, Where P is the heat input, η is the thermal efficiency, U is the welding voltage, and I is the welding current.

[0009] Furthermore, the current phase difference between the strong pulse group and the weak pulse group is zero.

[0010] Furthermore, the pulse base time in the strong pulse group and the weak pulse group is 8ms-12ms.

[0011] Furthermore, the peak pulse time in the strong pulse group and the weak pulse group is 1ms-3ms.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: through the cycle of strong pulse groups and weak pulse groups, a stirring effect is generated at the bottom of the weld pool formed during the welding process. When the current is changed to a weak pulse and the outline becomes shallower, that is, during the process of the upward slope, after the molten droplet impacts the bottom of the weld pool, under the constraint of the solid base material in front of the weld pool, it continuously impacts and stirs the previous solidification zone during its backward and downward movement, so that the grain growth process is continuously interrupted, thus preventing it from growing into columnar crystals. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of adjusting the average current by changing the pulse base value, provided in Embodiment 2 of the present invention. Figure 2 This is a waveform diagram of a dual-pulse system with variable pulse count provided in Embodiment 3 of the present invention; Figure 3 This is a schematic diagram of the frequency-modulated dual-pulse current-voltage waveform provided in Embodiment 3 of the present invention; Figure 4 This is a schematic diagram of the microstructure of different samples provided in Embodiment 3 of the present invention. Detailed Implementation

[0014] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0015] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0016] Example 1 This embodiment provides a grain refinement method based on dual-pulse waveform fine modulation, including: obtaining different average currents by changing the current base values ​​of strong pulse groups and weak pulse groups to obtain different heat inputs, thus forming different heat inputs during the welding process; and limiting the maximum value of the current base value according to the diameter of the welding wire; and refining the grains at the bottom of the weld pool formed during the welding process by cycling through strong pulse groups and weak pulse groups.

[0017] In this process, the number of pulses in the strong pulse group and the weak pulse group are the same, generally ranging from 1 to 30. The current phase difference between the strong pulse group and the weak pulse group is zero, which enables stable welding with less spatter, reduces the increase in welding arc interruption, and improves weld formation.

[0018] Specifically, the pulse base time in strong and weak pulse groups is 8ms-12ms, and the peak time is 1ms-3ms. To ensure that the welding wire does not experience droplet spraying during the base current, the maximum base current is 110A, and the typical base current is 30A-110A. The calculation of heat input conforms to: P=ηUI. Where P is the heat input, η is the thermal efficiency, U is the welding voltage, and I is the welding current.

[0019] Example 2 To obtain different heat inputs, the average current is varied by changing the base value of the pulse current, thereby obtaining weld seams under different heat inputs. A schematic diagram of pulse current adjustment is shown below. Figure 1 As shown.

[0020] To more accurately capture the changes in weld contour during welding, this scheme further refines the base current range of 50A-90A with increments of 10A. Specific parameters, including average current and heat input, are shown in Table 1. To ensure that the 1.2 mm diameter welding wire does not experience droplet spraying transition at the base current, the maximum base current is set to 110A.

[0021] Example 3 Based on Examples 1 and 2, experiments were conducted on double pulses with different numbers of frequency modulations, and their waveforms are shown below. Figure 2 As shown, the parameters of a single pulse in the strong and weak pulse groups are B30 and B70 in Table 1, respectively. In order to accurately compare the effects of the strong and weak pulse groups on the weld contour and microstructure and to eliminate interference from other factors as much as possible, the number of pulses in the strong pulse group and the weak pulse group are the same, i.e., N1 = N2. The longitudinal contour of the weld corresponding to the double pulse current is shown below. The specific current waveform process parameters used in this paper are shown in Table 1.

[0022] Welding experiments were conducted using a dual-pulse method with varying numbers of pulses within strong and weak pulse groups. Figure 3 The image shows the current and voltage waveforms acquired using a wavelet analyzer with different numbers of pulses (1, 2, 3, 4, 5, 7, 11, 13, 15, 20, and 30), where the number of pulses within a pulse group gradually increases from 1 to 30. Figure 3 As can be seen, both current and voltage have good repeatability, and neither current nor voltage has a zero value, indicating that the welding process can be carried out stably.

[0023] Figure 4 The figure shows the grain morphology at the bottom of the molten pool for different samples, among which... Figure 4 a) The microstructure of sample #15 located on both sides of the weld penetration valley. The contour where the weld penetration becomes shallower along the welding direction is defined as the "upper slope edge", and the opposite is defined as the "lower slope edge". Figure 4 b) and c) are magnified views of the grain morphology along the upper and lower slopes of Figure a). Comparing the two figures, it can be seen that the grain morphology differs significantly between the upper and lower slopes. Along the lower slope, the grains exhibit a distinct columnar morphology, while along the upper slope, the columnar morphology disappears, and the grains become significantly finer. This is because, as mentioned earlier, when the current transforms into a weak pulse and the contour becomes shallower (i.e., along the upper slope), after the molten droplet impacts the bottom of the molten pool, under the constraint of the solid parent material at the front of the molten pool, it continuously impacts and stirs the previously solidified zone as it moves backward and downward. This constantly interrupts the grain growth process, preventing it from growing into columnar crystals. Figure 4 As shown in c). When the welding current becomes a strong pulse, that is, during the falling edge, under the constraints of the solid base material wall and gravity, the upward flow intensity of the molten metal in the weld pool weakens. Therefore, the grains located above them on the rear side can continuously grow into columnar grains without impact stirring, such as... Figure 4 As shown in b). Other samples, such as 13# and 7#, also show this pattern. However, it should be noted that as the number of pulses within the pulse group decreases, this difference gradually diminishes. When the number of pulses decreases to 5 or even less, the difference in grain morphology gradually disappears because the melting depth at the bottom of the molten pool no longer exhibits a significant peak-valley difference. Figure 4 As shown in i)-j).

[0024] The above description is merely illustrative of the embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made without creative effort within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A grain refinement method based on dual-pulse waveform fine modulation, characterized in that, include: Different average currents are obtained by changing the current base values ​​of strong pulse groups and weak pulse groups, thus forming different heat inputs during the welding process; And the maximum value of the current base value is limited according to the diameter of the welding wire; By cycling strong pulse groups and weak pulse groups, the grains at the bottom of the weld pool formed during the welding process are refined.

2. The grain refinement method based on dual-pulse waveform fine modulation according to claim 1, characterized in that, The number of pulses in the strong pulse group is the same as that in the weak pulse group.

3. The grain refinement method based on dual-pulse waveform fine modulation according to claim 1, characterized in that, The maximum value of the current base value is 30A-110A.

4. The grain refinement method based on dual-pulse waveform fine modulation according to claim 1, characterized in that, The heat input conforms to: P=ηUI Where P is the heat input, η is the thermal efficiency, U is the welding voltage, and I is the welding current.

5. The grain refinement method based on dual-pulse waveform fine modulation according to claim 1, characterized in that, The current phase difference between the strong pulse group and the weak pulse group is zero.

6. The grain refinement method based on dual-pulse waveform fine modulation according to claim 1, characterized in that, The pulse base time in the strong pulse group and the weak pulse group is 8ms-12ms.

7. The grain refinement method based on dual-pulse waveform fine modulation according to claim 1, characterized in that, The peak pulse duration in the strong pulse group and the weak pulse group is 1ms-3ms.

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