Due to the emphasis on efficiency and reduction of CO2 emissions in the automotive industry, the potential for lightweight materials has become increasingly important [1]. Moreover, critical components such as gear wheels and brake discs cannot be replaced with lightweight materials like aluminium alloys because of their high strength requirements. Despite this, only certain parts of these components requires high strength, while other parts could be substituted with lighter materials. The joining of light and heavy materials can be achieved through rotary friction welding (RFW). RFW is predominantly used in the industry for similar material connections, such as steel-to-steel joints, where connections are formed because of high speed and pressures. Since the melting point is not reached during the process, it is possible to weld dissimilar alloys with significant differences in their chemical, thermal, and physical properties. This capability is currently the focus of ongoing research and has not yet been widely adopted in the industry [2].
During the RFW process of dissimilar materials, the significant influence of high temperature and time leads to the formation of intermetallic phases [3]. In the aluminium-iron system, the orthorhombic η and monoclinic θ phases are primarily formed. However, with the addition of silicon, a broader range of intermetallic phases, such as α and β, can develop, while the addition of manganese results in a more complex system. These intermetallic phases are crucial for achieving high joint quality due to their hardness and strength. However, they also possess low fracture toughness [4]. A literature review indicates that while intermetallic phases are necessary for high joint quality, excessive formation beyond a certain threshold adversely affects mechanical properties [5].
The influence of various RFW process parameters—rotational speed, friction time, friction and forging pressure—on the formation of intermetallic phases in the iron-aluminium system will be adressed. Focus is put on the formation of different intermetallic phases and their impact when using a precipitation-hardened aluminium alloy from the 6xxx series, which has higher silicon and manganese content. Finally, the effect of these parameters and intermetallic phases on the mechanical properties is demonstrated.