Microstructure and mechanical properties of 2A12 aluminum alloy VPPA welded joint with Ar-He mixed shielding gas
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摘要:
研究二元混合保护气变极性等离子弧(variable polarity plasma arc,VPPA)焊接技术,获得厚度为12 mm 2A12铝合金接头. 焊后通过金相显微镜、扫描电子显微镜(scanning electron microscope,SEM)、能谱仪(energy dispersive spectrometer, EDS)、万能液压试验机等,分析焊接接头的焊缝成形、微观组织、界面元素分布和力学性能. 相比氩弧, 氩氦混合电弧有效截面积更小,使其具有更高的能量和更为集中的阳极功率密度. 焊接接头各区域的焊接热循环有所不同,而热量影响组织特征,进而影响力学性能. 结果表明,相比一元保护气焊接接头,焊缝区微观组织多出现麦穗状树枝晶,更加细小且致密,母材到焊缝中心区EDS分析显示,热影响区的Mg元素增多,焊缝中心区的Cu元素增多;接头平均抗拉强度为317 MPa,达到母材强度的75.8%,屈服强度相比母材降低65 MPa;断口呈现典型的韧窝断裂;同时接头显微硬度呈现“W”形分布,最低值为95.5 HV. 混合保护气VPPA焊接技术具有良好的应用前景.
Abstract:The variable polarity plasma arc(VPPA) welding technology of binary mixed shielding gas was studied, and the joint of 2A12 aluminum alloy with 12 mm thickness was obtained. After welding, the weld formation, microstructure, interface element distribution and mechanical properties of the welded joint were analyzed by metallographic microscope, scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and universal hydraulic testing machine. Compared with argon arc, the effective cross-sectional area of argon-helium mixed gas arc was smaller, which made it have higher energy and more concentrated anode power density. The welding thermal cycle of each region of the welded joint was different, and the heat affected the microstructure characteristics, which in turn affected the mechanical properties. The results showed that compared with the one-dimensional shielding gas welded joint, the microstructure of the weld zone appeared more wheat-like dendrites, which were finer and denser. The EDS analysis from the base metal to the seam center showed that the Mg element in the heat-affected zone increased, and the Cu element in the weld center increased. The average tensile strength of the joint was 317 MPa, which was 75.8 % of that of the base metal, and the yield strength was 65 MPa lower than that of the base metal. The fracture showed typical dimple fracture; at the same time, the microhardness of the joint presented a “W” shape distribution, and the minimum value was 95.5 HV. Hybrid shielding gas VPPA welding technology had a good application prospect.
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Keywords:
- mixed protective gas /
- welded joints /
- microstructure /
- mechanical properties
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表 1 母材及焊丝的化学成分(质量分数,%)
Table 1 Chemical composition of base metal and welding wire
材料 Si Fe Cu Mn Mg Ni Zn Ti Al 2A12-T4 0.15 0.25 4.58 0.68 1.63 <0.10 <0.20 <0.10 余量 ER5356 0.25 0.40 0.01 0.20 4.50 ~ 5.50 — 0.10 0.06 ~ 0.20 余量 表 2 焊接接头的拉伸性能
Table 2 Tensile properties of welded joints
试样 屈服强度
Rel/MPa抗拉强度
Rm/MPa断后伸长率
A(%)断裂部位 母材 303 418 19.2 — 100%Ar 260 308 6.0 焊缝 80%Ar + 20%He 238 317 5.7 焊缝 -
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