搅拌摩擦增材制造(friction stir additive manufacturing，FSAM)是一种先进的固相成形技术，目前研究主要集中在对铝合金、镁合金等的FSAM成形工艺进行参数优化以减少缺陷，从而替代传统有热源的成形方式，但对于成形过程中材料的微观组织演变研究相对较少。本工作以2 mm厚的6061铝板为基材，采用FSAM技术在垂直方向成功实现了多层无孔洞缺陷材料的构建。通过微观表征及性能测试研究了成形件沿构建方向的组织演变和力学性能变化规律。结果表明，成形区发生了动态再结晶，获得了细小的等轴晶粒，界面过渡区经历搅拌头的二次搅拌作用后晶粒进一步细化。成形区整体抗拉强度为母材强度的47.7%~55.2%，延伸率提高到母材的144.6%~148.8%，上、下板重叠界面由于经历多次热循环，力学性能较差。球状的α-Al(MnCrFe)Si在基体中起强化作用，FSAM过程中强化相的大量溶解是成形试样力学性能大幅下降的主要原因。经过520 ℃固溶1 h和165 ℃时效18 h热处理后，成形试样的力学性能显著提高，硬度略高于母材，抗拉强度恢复到母材的87.2%~91.9%。

Friction stir additive manufacturing (FSAM) is an advanced solid-phase forming technology based on the principle of friction stir. As no heat source is required, the FSAM process can avoid metallurgical defects during melting and solidification of the material. The FSAM also conserves energy and protects the environment. To replace the traditional forming technology with a heat source, current research aims to optimize the forming process parameters of aluminum and magnesium alloys. Similarly to the friction stir welding process, increasing the temperature in the FSAM process will dissolve part of the strengthening phase, coarsening the particles and softening the welding core area. In addition, during layer-by-layer stacking in FSAM, the stir tool will re-stir the previously formed area, introducing a new thermal cycle during the stirring process. Because the changes in the temperature and stress field are more complex in the FSAM process than in the friction stir welding process, the influence of microstructure evolution on the mechanical properties of materials in the FSAM process is worthy of investigation. In this study, a multilayer defect-free FSAM material was fabricated from 2-mm-thick 6061 aluminum alloy sheets. The microstructural evolution along the building direction was observed during the FSAM process to investigate its effect on the microhardness and tensile properties. Dynamic crystallization formed fine equiaxed grains in the stir zone, which were further refined after re-stirring in the overlapping interface regions. The tensile strength and elongation of the FSAM material were 47.7%-55.2% and 144.6%-148.8% those of the base material, respectively. Multiple thermal cycling weakens the performance of the overlapping interface regions. The spherical α-Al(MnCrFe)Si phase plays a strengthening role in the matrix. Extensive dissolution of the strengthening phase during the FSAM process is mainly responsible for the performance deterioration of the FSAM material. After heat treatment at 520 ^oC for 1 h and at 165 ^oC for 18 h of aging, the properties of the FSAM material were largely improved: the hardness slightly increased from that of the base material and the tensile strength reached 87.2%-91.9% that of the base material.