Friction stir processing (FSP) is a solid-state processing method, which recently gained wide popularity to modify the microstructure of metallic surfaces and to produce surface composites. For the past decade, composites of different materials such as aluminum, copper, magnesium, titanium, and their alloys were successfully produced by FSP. The amount of secondary phase that is dispersed at the surface of the workpiece during FSP and the level of dispersion depend on many factors such as tool design, processing parameters, and type of material. Recently, the method of secondary phase incorporation into the surface metals was also considered as an important factor in developing surface composites by FSP. A few strategies such as groove filling, holes filling, sandwich method, direct method, and surface coating followed by FSP methods have been developed as promising ways of secondary phase incorporation into the surface of the materials during FSP. The aim of this review paper is to give a comprehensive summary of different methods developed to disperse the secondary phase into the surface of the workpiece during FSP to produce surface composites. The strategies have been explained, compared, and discussed to suggest an appropriate method based on the requirement to adopt in developing surface composites.

中文翻译：

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显影表面复合材料中通过摩擦搅拌工艺将次级相掺入金属薄板的不同策略

摩擦搅拌处理（FSP）是一种固态处理方法，最近在修饰金属表面的微观结构和生产表面复合材料方面广受欢迎。在过去的十年中，FSP成功地生产了不同材料的复合材料，例如铝，铜，镁，钛及其合金。FSP期间分散在工件表面的次级相的数量和分散程度取决于许多因素，例如工具设计，加工参数和材料类型。近来，第二相结合到表面金属中的方法也被认为是通过FSP开发表面复合材料的重要因素。一些策略，例如凹槽填充，孔填充，夹心法，直接法，表面涂层和随后的FSP方法已被开发为在FSP期间将第二相掺入材料表面的有前途的方法。本文的目的是对在FSP生产表面复合材料时将次级相分散到工件表面的不同方法进行全面总结。已对策略进行了解释，比较和讨论，以根据开发表面复合材料的要求提出合适的方法。