Microstructure And Mechanical Property Of TLP Bonded Joints Of Steel/aluminum Dissimilar Metal

S355 steel has high strength,good low temperature impact toughness and excellent weldability.6005 A aluminum alloy has advantages of low density,high specific strength,good corrosion resistance,etc.Due to significant differences in the chemical and physical properties between steel and aluminum alloy,the weldability of steel and aluminum is very poor,which seriously affects the performance of the joint.In order to improve the above problem,transient liquid phase?TLP?diffusion bonding of S355 steel and 6005 A aluminum alloy was studied with Al-Cu-La foil and nickle coating /Zn foil as interlayers respectively.Effects of joining parameters on microstructure and mechanical properties of joints were also studied.When Al-Cu-La interlayer was applied,TLP joints had obvious layered structure,which consisted of Fe2Al5,Fe4Al13 and Al-Cu-Fe layer.Al solid solution and Al2 Cu eutectic formed in the Al-Cu-Fe layer,as well as minor Fe4Al13 intermetallic compounds.With the increase of the temperature for 30 min,the joint reacted more sufficiently,and its diffusion zone became wider.At 580°C,grain boundary penetration occurred evidently in the joint and even voids formed.When the holding time rose from 15 min to 60 min at 570°C,the width of the diffusion zone,especially the width of Fe-Al layer,increased significantly.The diffusion zone was almost composed of Fe-Al intermetallic compounds for 60 min.At 570°C and 30 min,the shear strength of joints reached to 76 MPa.Joints fractured in the Al-Cu-Fe layer.?Fe,Cu?2Al5 and?Fe,Cu?4Al13 formed adding Cu element,which could reduce the brittleness of Fe-Al intermetallic compounds and improve the strength of joints.The addition of La can play an important role in inhibiting the formation and growth of Fe-Al intermetallic compounds.When nickle coating and Zn foil were employed as a composite interlayer,the diffusion zone was composed of Al-Zn solid solution layer,Al-Ni layer and nickle coating.Al3 Ni and AlNi were formed in the Al-Ni layer,in which AlNi compound continuously distributed along the nickel coating.The nickel coating completely prevented the formation of Fe-Al intermetallic compounds.When the heating temperature or the holding time increased,the amount of Al-Zn solid solution grew and the width of Al-Zn layer increased.Also,with the increase of temperature or holding time,the amount of Al3 Ni increased and its microstructure became coarse,and the width of nickel coating decreased gradually.At 440°C for 30 min or at 420°C for 60 min,cracks occured in the Al-Zn layer.The shear strength of the joint reached 61 MPa at 420°C for 30 min.Because of great differences between Al-Zn and Al-Ni compound in their microstructure and properties,it had an adverse effect on the joint property.Joint fractured along the interface between Al-Zn and Al-Ni layer in most areas,while in some local areas,it fractured in the Al-Ni layer,just between AlNi compound layer and Al₃Ni layer specifically.