2219-T87/T852铝合金异质接头力学性能弱化及断裂机制

Weakening Mechanism and Fracture Behavior of Dissimilar Joint of 2219-T87/T852 Aluminum Alloy

开展了航天贮箱用2219-T87和2219-T852铝合金变极性钨极氩弧焊接研究,通过拉伸试验确定了接头力学强度薄弱区,对接头焊缝晶粒特征、晶界偏析及强化相分布等微观组织分析,阐明接头力学性能弱化及断裂机制。结果表明,接头在-196℃低温条件下平均抗拉强度为314 MPa,平均延伸率为5.68%,接头力学强度薄弱区为2219-T852侧熔合区。在拉伸过程中,接头背部焊缝打底层边缘首先发生起裂,沿熔合区向上扩展,最终断口呈现混合断裂模式。微观组织分析表明,在接头力学强度薄弱区,组织为非均匀过渡混合晶粒特征,晶界偏析造成的沿晶共晶相呈粘连网状分布,基体强化相大量溶解与粗化,共同导致了接头强度和塑性的显著下降。

Dissimilar joint between 2219-T87 and 2219-T852 alloys were produced by VPTIG. The weakened zone of the joint was determined by tensile test, and the weakening mechanism and fracture behavior of joints were discussed after observing of the grain size, element segregation and precipitates distribution. The results showed that the average ultimate tensile strength and elongation of VPTIG joints at -196℃ reached up to 314 MPa and 5.68% , respectively. All joints were broken from the heat affected zone of 2219-T852 side, where showed the worst segregation of the Cu element, dissolving and coarsening of precipitates, non-uniform grain sizes, and the strain localization caused by the joint deformation. The fracture originated at the edge of the weld seam from the joint bottom surface, and propagated along the heat affected zone to the top surface, showed a mixed fracture mode.