Study On Axial Friction Welding Quality Of Turbocharger Rotor Under Interface Constraints

Turbocharger has been widely applied in shipbuilding industry and automobile industry,and its core component is the rotor with high-speed rotation in high temperature environment.Turbocharger rotor is connected by K418 B superalloy and 40 CrNiMoA alloy steel,usually by laser welding and axial friction welding.The main disadvantages of laser welding are stress concentration and lack of penetration,so it is not suitable for the welding of large diameter turbocharger rotor.The axial friction welding is applicable for both large and small diameter turbocharger rotors.It has obvious advantages in comparison with laser welding because of its high welding efficiency and reliable quality.Edge part of turboshaft suffers the largest stress when turbocharger rotor is working because it bears torque.But the disadvantage of the axial friction welding is that the edge area lost a lot of plastic material,leading to low pressure in upsetting stage and poor welding quality at edge area than core area.In order to improve the welding quality at the edge area,this paper proposed the axial friction welding under interface constraints to study the influence of different interface constraint conditions on macro morphology,microstructure,mechanical properties and the element diffusion of the welding joint.The main results are as follows:In macro morphology aspects: weld interface temperature,axial burn-off length,interface axial depth and horizontal expansion of flash first increase and then decrease on the whole with the increase of interface constraints.There are a lot of splashes at first and then splash disappeared in the welding process.There are a lot of cracks on the surface of flash and then the surface of flash becomes smooth.The welding interface has experienced a "U" shape curve at first and then change to a straight line.In microstructure aspects: at core area of 2 # and 5 # joint,the material is single flow mode and formed the shape of unimodal bump.At core area of 1 #,3 # and 4 # joint the material is distribution mode and formed a double-peak shape;At the edge of the area,2# and 5# joint interfaces are almost straight line,and 1 #,3 # and 4 # joint interfaces are irregular shape and formed island-shape structure,but at the core areas all joints formed thorn-shape structure;Compared with 4 # joint,whose interface temperature is higher,the DZ is more wide at both edge area and core area of 5 # joint,whose interface temperature is lower,but the DRZ decreases,and the martensite in DRZ and TMAZ become dilute and bigger.In mechanical properties and the element diffusion aspects: peak microhardness of joint、the tensile strength of tensile samples at the edge area、Fe element diffusion width at both edge area and core area increase at first and then decrease on the whole with the increase of interface constraints.