The Interface Characteristics And Quality Control Of The Friction Welded Turbocharger Transmission Shaft

The turbocharger is an important component of the engine. It can improve theengine power, increase fuel economy and improve engine emissions. It is usually madefrom the joining of nickel-based superalloy K418and42CrMo alloy steel, which is atypical dissimilar welding technique. However, there is a distinct difference between thechemical composition and mechanical properties of the two materials. Although thejoining of the two materials can be achieved by laser welding and electron beamwelding, but the two methods have high cost and poor extension. Currently one of themost commonly used methods to realize the welding of K418/42CrMo is the inertiafriction welding. This method has advantages such as high efficiency and low cost.Problems such as the uneven distribution of the heat in the weld and uncontrollablewelding quality exist in the same size inertia friction welding. The present studyproposed a method to improve the properties of K418/42CrMo dissimilar inertia frictionwelded joints and control welding quality through interface. The microstructuralobservation, energy spectrum analysis, tensile tests and microhardness tests wereconducted on the obtained joint. The specific research content and the primaryconclusions are summarized as follows:①The macroscopic deformation and microstructure characteristics of the weldunder rotational speed of3000rpm, friction pressure of4MPa, forge pressure of15MPaand interface constraint of1mm,2mm,3mm,4mm and4.4.5mm were analyzed. Inaddition, the interacting mechanism between interface constraints and material flowduring welding is also analyzed.②The microhardness profile of the K418/42CrMo inertia friction weldingexhibits as a Z-shape characteristic. The maximum microhardness value appears at thedeformation zone, while the minimum appears at the heat affected zone. The width ofthe hardness increasing zone has an increment trend as the interface constraint increasesfrom1mm to4.4.5mm. The variation of the microhardness has different characteristicsat the two sides of the interface. Dynamic recrystallization took place at the42CrMoside, so the refined grains result in an increased microhardness. At the K418side, theincreased microhardness is caused by a quenching-like effect.③The problem of non-uniform interface joining on the dissimilar K418/42CrMoinertia friction welded joints was analyzed. When the interface constraint is4mm, this problem did not appear since the material flow became gentle and the welding heat wasincreased.④Elements diffusion has occurred in joint interface under different kinds ofconstraint. The elements diffusion width increases with the length of interface constraint.When it’s3mm, the elements diffusion width will decrease due to disorder material flowand the heat reducing stored in the seam.⑤The material flow pattern of42CrMo and the deformation pattern of K418during the welding process were analyzed. The material flow model under two differentinterface constraints was proposed. The effect mechanism of interface constraints onmaterial flow during inertia friction welding was revealed.