The microstructure evolution during dissimilar friction stir welding of copper with stainless steel 316L is studied. The welding is performed in transparence configuration using tools of two different geometries. The joints are characterized by optical microscopy, scanning and transmission electron microscopy, electron backscattered diffraction, and microhardness. The microstructure and crystallographic texture of base metals are significantly affected. The joint produced using a shoulder of 8 mm in diameter is characterized by a copper nugget with refined grains. The texture of copper is dominated by component of the shear texture. The steel beneath the tool shows a grain refinement with grains of sub‐micron size and a texture which is close to the ideal simple shear texture. For the joint produced by the 16 mm diameter tool shoulder, the nugget consists of large grains of copper, while the steel beneath the tool shows small recrystallized grains of micrometer size. The texture in the steel is dominated by the component of the shear texture. The Cu/316L interface in both types of joint is of very good quality. In a detailed study of the interface, it is revealed that the welding of metals is achieved by mutual intense mechanical interlocking without formation of any intermetallic compounds.

Macrostructure, microstructure, and distribution of phases through the interface were analyzed for friction-stir-welded joints 5083 aluminum alloy and 316L steel. Several analytical techniques, including light microscopy, transmission and scanning electron microscopy, elemental analysis using X-ray spectroscopy, and electron diffraction, were used to thoroughly analyze the weld interface. The interface is characterized by a significant reduction in grain size for both aluminum alloy and stainless steel. New compounds, not corresponding to thermodynamically stable phases in the binary Al–Fe phase diagram, were found in the stirred zone (SZ) as dispersed particles. On the steel side of the welding, thin slabs of new compounds were found, as well, being interlaced with the stainless steel. The observations support that the grain refinement of stainless steel is likely due to a continuous dynamic recrystallization. The intermetallic compounds present as a layer at the interface, exhibiting nanometric grain size, were identified by electron diffraction as Al 13 Fe 4 and Al 5 Fe 2 phases. Concerning the intermetallic compound formed in SZ, the elemental analysis showed a compound containing principally Al and Fe, with admixture of Si and Mn. It was concluded that it is a pseudo-ternary compound with body-centered cubic structure, Im -3 space group, which is for the first time reported in this kind of dissimilar assembly, and is known as α-Al(Fe,Mn)Si.

Microstructure changes in dissimilar friction stir welding of 316L and Al 5083 were investigated using electron microscopy techniques. The results showed that there is a refinement of the structure in both base metals. The change in aluminum structure is governed by a dynamic recrystallization. The low temperatures of the process and the microstructure changes on the structure of the steel allows us to deduce that the grain refinement of the steel is governed by a continuous dynamic recrystallization. Different intermetallic compound were identified by electron diffraction in the welded region. At the interface, in the steel side of the weld, the studies allowed to identify two Al–Fe intermetallic compounds, namely Al 13 Fe 4 with monoclinic structure and Al 5 Fe 2 with orthorhombic structure. In the stirred zone, a new intermetallic was observed, in the form of particles identified as α–Al(Fe,Mn)Si with a bcc structure. Graphical abstract

In this work, Friction Stir Welding (FSW) was applied to join a stainless steel 316L and an aluminum alloy 5083. Ranges of rotation and translation speeds of the tool were used to obtain welding samples with different heat input coefficients. Depending on the process parameters, the heat generated by FSW creates thin layers of Al-rich InterMetallic Compound (IMC) mainly composed of FeAl3, identified by energy dispersive spectrometry. Traces of Fe2Al5 were also depicted in some samples by X-ray diffraction analysis and transmission electron microscopy. Monotonous tensile tests performed on the weld joint show the existence of a maximum mechanical resistance for a judicious choice of rotation and translation speeds. It can be linked to an affected zone of average thickness of 15 µm which encompass the presence of IMC and the chaotic mixing caused by plastic deformation in this area. A thickness of less than 15 µm is not sufficient to ensure a good mechanical resistance of the joint. For a thickness higher than 15 µm, IMC layers become more brittle and less adhesive due to high residual stresses which induces numerous cracks after cooling. This leads to a progressive decrease of the ultimate shear stress supported by the bond.

Lap joining configuration for Friction Stir Welding process is a methodology mostly dedicated to heterogeneous bonding. This welding technology was applied to join pure titanium with 1050 aluminum alloy by varying the rotation speed and the movement speed of the tool. Regardless of the process parameters, it was found that the maximum strength of the junction remains almost constant. Microstructural observations by means of Scanning Electron Microscopy and Energy Dispersive Spectrometry analysis enable to describe the interfacial join and reveal asymmetric Cold Lap Defects on the sides of the junction. Chemical analysis shows the presence of one exclusive intermetallic compound through the interface identified as TiAl3. This compound is responsible of the crack spreading of the junction during the mechanical loading.