厚板铝合金搅拌摩擦焊接头组织及性能沿厚度方向的变化规律

Variations of the microstructure and mechanical properties for the thick aluminum friction stir welding joint along the thickness direction

通过分层法对30 mm厚7A05-T6铝合金搅拌摩擦焊接头焊核区不同位置的微观组织、力学性能进行了研究.结果表明,上表层附近的再结晶晶粒尺寸最大;当旋转频率为360 r/min,焊接速度为100 mm/min时,TI到T5层的抗拉强度分别为326,354,342,334和307 MPa,呈先高后低的趋势,且屈服强度和断后伸长率也呈一样的趋势;微观断口中存在大量的网状韧窝,其中分层切片T2上韧窝最深.显微硬度分布为焊缝上部高于下部,沿焊缝中心不对称分布.随厚度增加,轴肩产生的摩擦热自上到下不断降低,是造成中下部工件性能下降的主要原因.

Through the hierarchical method,microstructure and mechanical properties in different areas of the weld nugget zone for 30 mm thick 7A05-T6 aluminum alloy friction stir welding join have been studied. The results show that,the size of recrystallization grain in the near area of surface is largest.When the rotation speed is 360 r / min and the welding speed is100 mm / min,for the area of T1 to T5,the tensile strength separately is 326,354,342,334 and 307 MPa,the yield strength and elongation are also increased gradually. The fracture micrographs show that,there are a lot of mesh dimples in the fracture surface,and they are deeper on slicing T2 especially. The hardness profile is not central symmetric,and hardness value of top area is larger than that of lower area. Friction heat will decrease with the increase of thickness,and that is the reason why the performance decline at the middle and bottom of workpiece joint.