Intermetallic Compound Layer Morphology and Distribution in Friction-Welded Steel–Aluminum Components

In this study, the morphology, distribution, and local thickness of the intermetallic compound layer (IMC-layer) in friction-welded steel-aluminum hybrid components used for Tailored Forming applications are investigated. By friction-welding of steel and aluminum, which is the first step in the Tailored Forming process chain, an IMC-layer in the joining zone is formed. In this study, the influence of friction-welding parameters, such as rotational speed, friction pressure, friction length, upsetting pressure, and upsetting time, on local IMC-layer thickness and distribution is examined. For characterization, a detailed analysis over the whole joining surface by means of scanning electron microscopy and a thorough statistical evaluation are employed. In the results, it is indicated that lower rotational speeds (700 rpm) in the friction phase result in more uniform and thinner IMC-layer (<0.5 μm), while higher speeds (1600 rpm) produce a thicker and more heterogeneous IMC- layer (up to 0.9 μm). Tensile tests show that specimens with thinner mean IMC-layer (0.17 μm) feature a higher tensile strength (244 MPa). The morphology and distribution of the IMC-layer over the cross section of the friction-welded specimen have a significant effect on the mechanical properties of the joint, with a uniform thin layer improving the tensile strength.