船用5083铝合金变极性等离子焊接头组织和性能

Microstructure and Mechanical Properties of Variable Polarity Plasma Arc Welded Joints of 5083 Aluminum Alloy for Shipbuilding

采用变极性等离子焊接工艺实现了5mm厚船用A5000系铝合金立向上位置焊接,并分析了接头的组织和力学性能。力学试验显示:接头抗拉强度达到295MPa,延伸率达到10%,断裂位置在熔合线附近;焊缝区和热影响区的显微硬度均低于母材,且焊缝中心处最低。接头金相观察发现:熔合线附近的焊缝为粗大的等轴晶组织,但焊缝区大部分为胞状树枝晶组织,从两侧呈对称生长并在焊缝中心处相遇,热影响区为再结晶组织。利用电子探针分析了拉伸断裂位置附近的成分,发现该区域Mg含量偏低且分布不均匀,固溶强化效果下降,组织和成分的不均匀导致该区域成为接头的薄弱部位。

A5000 series（Al-Mg） aluminum alloy with a thickness of 5 mm for shipbuilding was successfully welded by a variable polarity plasma welding process in a vertical-up position. The microstructure and mechanical properties of the joint were investigated. The ultimate tensile strength of the joint is 295 MPa, the elongation is 10%, and the location of fracture is near the fusion line. The micro hardness of the weld zone and heat affected zone is lower than that of the base metal, and the lowest hardness appears at the center of the weld. The optical micrographs of the joint show that the weld microstructure near the fusion line is a coarse equiaxed grain structure, and most of the weld region is a cellular dendritic structure growing from the two sides to the center, while the microstructure of the heat affected zone is a typical recrystallized structure. The composition around the tensile fracture was analyzed by EPMA, and the results reveal that the content of Mg is low and heterogeneously distributed. The lack and segregation of Mg and non-homogeneous microstructure decrease solution strengthening, resulting in weak areas of the joint.