Technical Study of Exhaust Valve Overlaying Based on Micro-Plasma Arc Welding

The micro-plasma arc welding technology（MPAW） was used to remanufacture the exhaust valve of W615 engine. The ST6 Co alloy powder was selected as overlaying material, the processing parameters of overlaying was optimized considering the geometry demand of deposited layer, and the current downslope method was adopted to weaken the arc crater. The microstructure characteristics and the micro-hardness of the weld were investigated, no defects were found in the deposited layer or at the interface, and the heat-affected zone among joint was not evident. The maximum hardness situated at the top layer being 657.8HV, with a slight decrease towards the bottom layer and fusion zone.