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等离子弧焊接铝合金厚板接头显微组织与力学性能沿厚度方向的梯度特征

Microstructural and mechanical property gradients along the thickness direction of plasma arc welded thick aluminum alloy joints

  • 摘要: 针对大厚度铝合金焊接头强度不足的问题,提出了变极性等离子弧-钨极氩弧焊(variable polarity plasma arc-tungsten inert gas, VPPA-TIG)复合焊接工艺. 为进一步验证VPPA-TIG复合焊的焊接质量,开展了厚度为17 mm的2219铝合金板焊接试验,详细研究了焊缝厚度方向上的微观组织和力学性能分布特征,并通过显微组织分析揭示了强度分布特征的机理. 结果表明,VPPA-TIG复合焊焊缝成形质量较好,内部冶金程度较高. 焊缝熔合区硬度分布均匀,平均值为67.6±2.7 HV0.2;抗拉强度达到了母材的62.83%,而断后伸长率仅为24.81%. 焊件厚度的增加扩大了熔池的散热面积,造成焊缝晶粒生长不充分,在界面区形成“蜿蜒”状微孔. 微孔在受到拉伸载荷作用时将会继续生长,是影响焊缝拉伸强度的主要原因. 进一步拓展了VPPA-TIG复合焊工艺应用范围,阐明了厚板焊接头强度失效的机理,为解决大厚度板材焊接提供理论和技术参考.

     

    Abstract: To address the issue of insufficient strength in thick aluminum alloy welding, a variable polarity plasma arc-tungsten inert gas(VPPA-TIG) composite welding process was proposed. This study further validates the welding quality of VPPA-TIG composite welding by conducting welding experiments on 2219 aluminum alloy plates with thickness of 17 mm, followed by a detailed analysis of the weld seam microstructure and mechanical properties. The mechanism of strength distribution characteristics is revealed by microstructure analysis. The results show that VPPA-TIG composite welding process produces high-quality weld seam formations with a superior degree of metallurgical bonding. The hardness distribution in the weld seam fusion zone is uniform, with an average value of 67.6±2.7 HV0.2. The tensile strength reaches 62.83% of the base material, while the elongation after fracture is only 24.8%. The increased thickness of the weldment expands the heat dissipation area of the weld pool, resulting in insufficient grain growth within the weld seam. This leads to the formation of "meandering" micropores in the interface region. These micropores will continue to grow when subjected to tensile loads, which is the main reason for affecting the tensile strength of the weld seam. This study further expands the application range of VPPA-TIG composite welding process, clarifies the mechanism of strength failure in thick plate weld joints, and provides a theoretical and technological reference for solving the welding of large-thickness plates.

     

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