Investigations On Friction Stir Welding Process Of Dissmilar Metals Of 2024 Aluminum To Q235 Steel

In this paper,the friction stir welding(FSW)process was used to join the 3mm thick2024 aluminum and Q235 steel with butt joint.The impacts of process parameters on microstructure and mechanical properties of the weld were investigated.The interface characteristics and the elements distribution of aluminum and steel interface were examined by scanning electron microscopy(SEM)and X-ray energy dispersive spectroscopy(EDS).Meanwhile,the fracture mechanism of joint was further explored by investigating the fracture behavior.In the process research of friction stir welding of aluminum and steel,the effects of different process parameters(parent metal location,penetration depth,pin offset,traverse speed and rotational speed)on weld formation,microstructure,mechanical properties and interface characteristics were investigated.The results show that,when the aluminum was put on the advancing side,the tunnel defects formed on the surface and in the interior of the joint.When the steel was put on the advancing side,the formation of the joint turned to be good,and the tensile strength increased obviously.With the increasing of the penetration depth,the flash on the joint’s surface and the number of steel particles scattered in the weld nugget increased distinctly.The Fe/Al interface turned to be curved,the thickness of the IMCs increased slightly,and the tensile strength increased first and then decreased,and the maximum tensile strength of the joint was obtained at the penetration depth of 0.3mm.With the increasing of the pin offset,the formation of the joint’s surface went bad.The number of steel particles scattered in the weld nugget increased,the tunnel defect formed in the interior at the pin offset of 0.8mm.The thickness of the IMCs increased,the tensile strength increased first and then decreased,and the maximum tensile strength of the joint was obtained at the pin offset of 0.4mm.With the increasing of the traverse speed,the formation of the surface and interior of the joint turned to be worse,and the tunnel defect formed in the interior at the traverse speed of 85mm/min.The thickness of the IMCs decreased,the tensile strength increased first and then decreased,and the maximum tensile strength of the joint was obtained at the traverse speed of 44mm/min.With the increasing of the rotational speed,the formation of the surface and interior of the joint turned to be well,and the Fe/Al surface turned to be curved from straightness.The thickness of the IMCs increased,the tensile strength increased first and then decreased,andthe maximum tensile strength of the joint was obtained at the rotational speed of 420 rpm.Appropriate welding parameters were obtained from the experiment,the steel was put on the advancing side,the penetration depth was 0.3mm,the pin offset was 0.4mm,the traverse speed was 44mm/min and the rotational speed was 420 rpm.On this condition,the maximum tensile strength was about 334 Mpa,which was about 74.2% of the tensile strength of aluminum matrix.The mechanism of fracture of the joint was studied on the basis of process research of the aluminum/steel joint with FSW.The transient temperature and the stress distribution of the weld in different rotational speed were obtained with the physical experiment,and the internal relationship with the microstructure of the joint and the fracture behavior was studied on this basis.The results show that,the thickness and continuously level of IMCs and the stress state was the most important factor to affect the quality of the joint.When the IMCs had small thickness,the crack was difficult to expand at the Fe/Al interface,but to expand at the aluminum beside the interface with the high residual stress.When the IMCs had big thickness,the crack was easily to expand at the Fe/Al interface.And because of the continuously distribution of the IMCs,the crack expanded at the IMCs of the Fe/Al interface.