铝合金厚板静止轴肩搅拌摩擦焊接头组织及性能

采用8.5 mm厚度2A14-T4铝合金和自主研制搅拌工具进行静止轴肩搅拌摩擦焊（stationary shoulder friction stir welding，SSFSW）实验，探讨焊接工艺参数对接头组织和力学性能的影响规律。结果表明：只有在低转速工艺参数范围内（转速ω=400~600 r/min与焊接速率v=60~120 mm/min）可获得焊缝表面光滑、无缺陷厚板铝合金SSFSW焊接接头。SSFSW焊缝区主要由焊核区（NZ）组成，周围热力影响区（TMAZ）及热影响区（HAZ）宽度明显减小，焊核区与搅拌针形状类似且由两种不同尺寸细小等轴晶构成，前进侧NZ晶粒比后退侧NZ更为细小。接头显微硬度呈"W"状分布，NZ硬度值可达到母材硬度80%~90%，TMAZ与HAZ交界处存在软化区，硬度最低为母材硬度72%左右。在给定ω=500 r/min，v=140 mm/min焊接参数下，SSFSW接头抗拉强度可达到母材的88%，断裂位置多位于后退侧TMAZ与HAZ交界处软化区，具有韧性断裂特征。

Microstructure and properties of stationary shoulder friction stir welded joints for aluminum alloy thick-plate

The stationary shoulder friction stir welding (SSFSW) processes for 2A14-T4 aluminum alloy with the thickness of 8.5 mm were performed by using the self-developed tools, and the influences of welding process parameters on the microstructure and mechanical properties of SSFSW welded joints were investigated. The results show that the SSFSW joints with smooth weld surface and defect-free for aluminum alloy thick-plate can only be obtained under the process parameter condition of lower rotational speed (rotational speed ω=400-600 r/min and welding speed v=60-120 mm/min).The weld zone of SSFSW joints mainly consists of nugget zone (NZ), and the widths of thermo-mechanically affected zone (TMAZ) and the heat affected zone (HAZ) around the NZ are obviously reduced; the NZ is similar with the shape of tool pin and it is composed of two kinds of fine equiaxed grains with different sizes, the grains on the advancing side are more finer than that of retreating side. The profiles of microhardness across the weld section present the "W" shape, the hardness values of NZ reach the 80%-90% of the base metal of hardness value, the softened region is produced between interfaces of TMAZ and HAZ, and its hardness is the lowest with the 72% of the base metal of hardness value. The tensile strengths of SSFSW joints reach the 88% of base metal under the welding parameters of ω=500 r/min, v=140 mm/min, and the fractured sites are always located at the softened zones between TMAZ and HAZ on the retreating side, exhibiting the toughness fracture features.