As the most widely used thermal Power machine, the diesel engine plays a key role in today’s social and economic development. Its dynamic performance could effectively upgraded by one of its core components, the turbocharger, whose quality largely depends on welding technology for dissimilar materials.

    A research team led by Prof. Yu Gang in the Institute of Mechanics, CAS has made an encouraging progress in its study field of laser welding technology of dissimilar metals. Besides meeting the critical requirements of mechanical strength, the novel approach could greatly improve the welding efficiency, offering an important technical support for the development of diesel engine.

    The rotor, a key part of the turbocharger, is usually manufactured in China by welding the turbine disk which is made of cast Ni-based superalloy K418 to the shaft which is made of tempered middle carbon alloy steels 42CrMo. Because of the high content of Al and Ti in K418 and high carbon equivalent of the 42CrMo, there is a strong tendency of hardenability. In addition, the welding ability is rather poor. The conventional welding methods of these two materials are either electronic-beam method or friction welding method. However, building a large vacuum chamber to contain a huge component in order to carry on the electronic beam welding is not practicable. As for the friction welding method, low-stress destruction often occurs and welding defects are usually detected near the fusion zone and results in lower production efficiency. Therefore, this welding process is quite challenging.

    As the result of pioneering in-depth research for laser welding of dissimilar materials, Prof. Yu and his colleagues have come up with a solution to prevent hot cracks based on an analysis of their inherent mechanism. In addition they have solved a series of difficulties. For instance, via the optimization of process indices and post welding heat treatments, they have succeeded in avoiding the formation of laves phase noted fro low melting points and hard-brittleness. On the basis of the interaction mechanism between laser and dissimilar materials, they creatively put forward an associated heating resource to simulate the welding process. Experiments show that the optimal welding technique could ensure the strength of the welding seam higher than that of the base materials.