Interfacial Bonding Mechanism and Fatigue Performance of Al/Steel Dissimilar Welds Fabricated via Friction Stir Brazing
Based on character of friction stir welding such as low temperature and severe plastic deformation,the tool only stir in the top Al alloy,which promotes thermodynamic couple,coupling with the interlayer of zinc coating on the steels to improve interfacial bonding and fatigue performance of Al/steel dissimilar welds.The investigation indicated that making use of thermodynamic couple mechanism,the zinc coating improved weldability of Al alloy and steel.As a brazing filler metal,the zinc coating layer avoides direct contact between Al alloy and steel,and thus avoides the formation of intermetallic compound.The zinc material gathered around the retreating side on the Al/steel interface,and typical eutectic structure of Al and Zn are formed on the advancing side at the Al/steel interface.The zinc material is squeezed outside of the stirring zone,where nano scaled Fe3Al Fe4Al13 are identified,which are formed during the hot-dipping process.Lap shear strength of the friction stir brazed Al/steel dissimilar welds are stable,the maximum lap shear strength and elongation reached 333.8 N/mm and 11.33％,respectively.Under the fatigue load,three different failure modes are observed:interfacial failure under higher load,mixed failure under medium load,base metal failure and interfacial failure under lower load.The cycle can reach 2×106 without failure under a load of 2.64 kN.
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