铝合金熔焊微气孔的三维同步辐射X射线成像

发布时间：2018-07-17 09:14

【摘要】：基于同步辐射X射线成像技术,对激光复合焊7020-T651铝合金接头内部的微气孔进行了研究,对气孔的体积、圆整度、扁平度及气孔形心至自由表面的距离等三维特征参数进行了统计分析与拟合.结果表明,铝合金熔焊微气孔主要为近球形的冶金型气孔,圆整度在0.65以上,以焊缝中心近似呈现对称分布,且焊缝上部气孔尺寸较大,热影响区和下部气孔密集且尺寸较小.等效直径在20 mm范围内的气孔,在接头上部和下部的频率分别高达65%和85%,并且100 mm以上的大尺寸气孔较少见.此外,由于熔池的下塌倾向和快速凝固,残留于枝晶网络间液相导致焊缝下部形成垂直于焊缝且层叠分布的形状复杂的热裂纹,少部分气孔之间以及气孔和热裂纹之间存在着连通现象,从而使得下部微气孔的圆整度平均值变小.此外,焊接速率越大,整个接头内部气孔体积分数越小,但对气孔形貌和位置的分布影响并不明显.
[Abstract]:Based on synchrotron radiation X-ray imaging technology, the micropores in 7020-T651 aluminum alloy joint were studied. The volume and roundness of the pores were measured. Three dimensional characteristic parameters, such as flatness and distance between pore center and free surface, were statistically analyzed and fitted. The results show that the micropores of aluminum alloy welding are mainly metallurgical pores of near spherical shape with the roundness above 0.65. The distribution of pores in the center of the weld is approximately symmetrical, and the size of the pores in the upper part of the weld is larger, and the pores in the heat affected zone and the lower part are dense and smaller. When the equivalent diameter is in the range of 20 mm, the frequencies of the pores in the upper and lower parts of the joints are as high as 65% and 85%, respectively. In addition, due to the sloughing tendency of the molten pool and the rapid solidification, the residual liquid phase in the branch crystal network leads to the formation of complex hot cracks in the lower part of the weld seam, which are perpendicular to the weld seam and are stacked and distributed. There is connectivity between a small number of pores and between pores and hot cracks, which makes the average roundness of micropores in the lower part smaller. In addition, the larger the welding rate, the smaller the porosity volume fraction in the whole joint, but the effect on the distribution of pore morphology and location is not obvious.
【作者单位】：西南交通大学牵引动力国家重点实验室;European
【基金】：国家自然科学基金项目51005068 中央高校基本科研业务专项资金项目2682013CX030 高速铁路基础研究联合基金重点项目U1234208资助~~
【分类号】：TG457.14

【参考文献】