Abstract
Friction Stir Welding (FSW) is the most promising solid-state metals joining method introduced in this era. Compared to the conventional fusion welding methods, this FSW can produce joints with higher mechanical and metallurgical properties. Formerly, FSW was adopted for low melting metals like aluminum alloys. In recent years it has made significant progress in friction stir welding of steels since unfavourable phase transformations occurred in welds due to the melting of the parent and filler metals in fusion welding can be eliminated. The main advantage of FSW over traditional fusion welding is the reduction in the heat-affected zone (HAZ), and the joints exhibit excellent mechanical and corrosion resistance properties. This article reviews the progress in the relevant issues such as the FSW tool materials and tool profiles for joining steels, microstructure and mechanical properties of steels joints, special problems in joining dissimilar steels. Moreover, in-situ heating sources was used to overcome the main limitations in FSW of hard metals and their alloys, i.e., tool damages and insufficient heat generation. Different in-situ heating sources like laser, induction heat, gas tungsten arc welding assisted FSW for various types of steels are introduced in this review. On the basis of the up-to-date status, some problems that need further investigation are put forward.
Highlights
Friction Stir Welding (FSW), as a solid-state welding process, can achieve the joining of metals below the melting point or in the plastic stage of the metals with the aid of a non-consumable tool [1]
The results show that many factors affect the microstructure formation in friction stir welding of steels
This research shows that better steel joints can be fabricated by using friction stir welding [248]
Summary
Friction Stir Welding (FSW), as a solid-state welding process, can achieve the joining of metals below the melting point or in the plastic stage of the metals with the aid of a non-consumable tool [1]. Compared with the welds made by fusion welding processes, the friction stir welds have a more homogeneous grain structure and better mechanical properties like tensile strength, hardness, and toughness [2]. Friction stir welded specimens exhibit better corrosion resistance properties due to the homogeneous microstructure and narrow heat-affected zone. The feature of joining metals in the semisolids state helps this FSW method to join metals with different melting points like aluminium and copper. While considering hard metals like steel, FSW still does not accomplish the same feasibility in aluminium alloys [6, 7]. The limitations of friction stir welding on steels are as follows: (a)
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