Microstructure and Mechanical Properties of Ring-mash-welded Powertrain Parts

The components of the powertrain that transmits power to an engine drive have been fabricated with various welding techniques, such as laser welding and gas metal arc welding. To reduce the weight of these components and hence the energy consumption of automobiles, the authors propose ring-mash welding as a component-joining method, which works by solid-phase bonding. The specimens were raw SCM415H chromium molybdenum steel, an alloy steel provided for machine structural use. Temperature and pressure are important parameters of joining. The proposed ring-mash welding relies on Joule heat generation. The bonding area softens during heating, facilitating solid-phase bonding. To clarify the bonding mechanism of ring-mash welding, the bonding condition was investigated under different applied pressures and electric currents. Although spatter was generated during bonding under excessive heat conditions, it was suppressed by increasing the applied pressure. The bonding strength depended more on the current than on the applied pressure. A small continuous gap appeared at the bonding interface under low current, which became intermittent, and eventually disappeared as the current increased. The bonding area was quenched by the temperature rise and rapid quenching during the joining process and an altered microstructure with increased hardness was formed. The optimal bonding conditions were determined.