Study on the Influence Mechanism of Porosity Defects in Laser-TIG Hybrid Welded Joints of New Al-Mg-Zn Alloy

LIU Fuyun; QI Weining; ZHOU Xiaohui; LIN Danyang; TAN Caiwang; HAN Xiaohui; SONG Xiaoguo

doi:10.7512/j.issn.1001-2303.2026.07.02

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Study on the Influence Mechanism of Porosity Defects in Laser-TIG Hybrid Welded Joints of New Al-Mg-Zn Alloy
Vol. 56, Issue 7, Pages: 10-16(2026)
Received：26 December 2025，

Revised：2026-01-19，

Published：20 July 2026
DOI： 10.7512/j.issn.1001-2303.2026.07.02
稿件说明：

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刘福运，亓蔚宁，周晓辉，等.新型高强Al-Mg-Zn合金激光-TIG复合焊接头气孔抑制及力学性能研究［J］.电焊机，2026，56（7）：10-16. DOI： 10.7512/j.issn.1001-2303.2026.07.02.

LIU Fuyun, QI Weining, ZHOU Xiaohui, et al.Study on the Influence Mechanism of Porosity Defects in Laser-TIG Hybrid Welded Joints of New Al-Mg-Zn Alloy[J].Electric Welding Machine, 2026, 56(7): 10-16. DOI： 10.7512/j.issn.1001-2303.2026.07.02.

摘要

新型Al-Mg-Zn合金是轨道交通车体轻量化的核心候选材料，但其熔焊接头的气孔缺陷与软化问题尚未得到系统研究。本研究采用激光-TIG复合焊接方法对4 mm厚T6态Al-7Mg-3Zn合金开展焊接试验，通过金相观察、ImageJ图像分析、显微硬度测试及室温拉伸试验，系统研究激光功率（2.0、2.4、2.8 kW）对接头焊缝成形、气孔行为及力学性能的影响规律。结果表明，焊缝熔宽与熔深随激光功率增大而单调递增，熔宽从4.4 mm增至4.9 mm、熔深从2.8 mm增至3.5 mm。气孔率随激光功率增大呈现先降后升的非单调变化：2.0 kW时为0.87%，2.4 kW时降至最低值0.66%，2.8 kW时急剧升至2.28%。低功率阶段熔池体积扩大和冷却速率减缓促进气泡逸出，高功率阶段Mg、Zn等低沸点元素剧烈蒸发引发匙孔失稳坍塌。接头力学性能与气孔率呈负相关，2.4 kW时接头综合力学性能最优，抗拉强度达298.32 MPa，延伸率为10.23%，热影响区软化程度最低为16.9%。研究结果可为新型Al-Mg-Zn合金在轨道交通领域的焊接工艺优化提供理论依据。

Abstract

The new-type Al-Mg-Zn alloy is a core candidate material for lightweight rail transit car bodies

yet the porosity defects and softening issues of its fusion-welded joints remain insufficiently investigated. In this study

laser-TIG hybrid welding was applied to 4 mm thick T6-tempered Al-7Mg-3Zn alloy. The effects of laser power (2.0

2.4

2.8 kW) on weld bead formation

porosity behavior

and mechanical properties were systematically investigated by means of metallographic observation

ImageJ image analysis

microhardness testing

and room-temperature tensile testing. The results show that both the weld width and penetration depth increase monotonically with laser power

from 4.4 mm to 4.9 mm and from 2.8 mm to 3.5 mm

respectively. The porosity exhibits a non-monotonic trend of first decreasing then increasing with laser power: 0.87% at 2.0 kW

dropping to a minimum of 0.66% at 2.4 kW

and then sharply rising to 2.28% at 2.8 kW. This non-monotonic porosity variation is governed by the competing mechanism between molten pool dynamics and keyhole stability — at lower power levels

the enlarged molten pool volume and reduced cooling rate facilitate bubble escape

while at higher power levels

severe evaporation of low-boiling-point elements (Mg

Zn) induces keyhole instability and collapse. The mechanical properties of the joints are significantly and negatively correlated with porosity. At 2.4 kW

the joint achieves the best comprehensive performance

with an ultimate tensile strength of 298.32 MPa

an elongation of 10.23%

and the minimum HAZ softening degree of 16.9%. The findings can provide theoretical guidance for welding process optimization of the new Al-Mg-Zn alloy in rail transit applications.

关键词

Keywords

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