Friction Stir Welding (FSW) is one of the most used solid-state welding processes in the aeronautical, aerospace, ground transportation and naval fields. Stationary Shoulder Friction Stir Welding (SSFSW) is a recently introduced variant of the process allowing lower heat input into the joints, with beneficial effects in terms of joint mechanical properties, microstructure and top surface finish. In the paper, lap joints produced by SSFSW and made out of AA6082-T6 aluminum alloy sheets have been analyzed with the aim to investigate the effect of the stationary shoulder on the lap joints surface, metallurgical, and mechanical properties. The lap joints produced by SSFSW have been compared to the ones produced by “conventional” FSW in order to highlight the differences between the two processes. The top surface of the joints obtained with the two processes has been quantitatively evaluated. Finally, a dedicated numerical model has been utilized to highlight the causes of the observed differences through the distributions of the main field variables, namely temperature, strain and strain rate. It was found that SSFSW results in narrower weld nugget and smaller areas involved by micro hardness reduction caused by smaller peak temperature and high temperature zone. Additionally, better surface quality was found for the joint welded by SSFSW with lower heights and flash, allowing to avoid subsequent finishing operations needed for most industrial applications.

搅拌摩擦焊（FSW）是航空，航天，地面运输和海军领域中最常用的固态焊接工艺之一。固定式肩部搅拌摩擦焊（SSFSW）是该工艺的最新推出，允许向接头输入较少的热量，在接头机械性能，微观结构和顶面光洁度方面具有有益效果。本文研究了由SSSFW生产的，由AA6082-T6铝合金薄板制成的搭接接头，旨在研究固定肩部对搭接接头表面，冶金学和机械性能的影响。将SSFSW生产的搭接接头与“常规” FSW生产的搭接接头进行了比较，以强调这两个过程之间的差异。这两个过程获得的关节的顶面已被定量评估。最后，一个专用的数值模型已被用来通过主场变量的分布，即温度，应变和应变率来突出观察到的差异的原因。已发现，SSSFW会导致焊接熔核变窄，并且由于较小的峰值温度和高温区域而导致显微硬度降低，从而导致较小的面积。另外，发现SSFSW焊接的接头具有较低的高度和溢料，从而具有更好的表面质量，从而避免了大多数工业应用所需的后续精加工工序。一个专用的数值模型已被用来通过主要场变量（即温度，应变和应变率）的分布来突出观察到差异的原因。已发现，SSSFW会导致焊接熔核变窄，并且由于较小的峰值温度和高温区域而导致显微硬度降低，从而导致较小的面积。此外，发现SSFSW焊接的接头具有较低的高度和飞边，从而具有更好的表面质量，从而避免了大多数工业应用所需的后续精加工工序。一个专用的数值模型已被用来通过主要场变量（即温度，应变和应变率）的分布来突出观察到差异的原因。已发现，SSSFW会导致焊接熔核变窄，并且由于较小的峰值温度和高温区域而导致显微硬度降低，从而导致较小的面积。此外，发现SSFSW焊接的接头具有较低的高度和飞边，从而具有更好的表面质量，从而避免了大多数工业应用所需的后续精加工工序。