With high productivity,easy adjustment of welding parameters and free of weld defects,the micro-plasma arc welding technology is used successfully to remanufacture the exhaust valve of W615 engine.The ST6 Co alloy powder is selected as overlaying material.Considering the geometry of deposited layer and economy,the processing parameters of overlaying is optimized,which include welding current,the rotate velocity of exhaust valve,the speed of feeding metal powder,etc.An current downslope method is developed to weaken the arc crater when arc flameout.The microstructure characteristics of the weld are investigated by the optical microscope and X-ray diffraction.The micro-hardness and the internal stress of the deposited layer are also measured by the instrument.The results show that the deposited layers have a fine dendrite structure at the top layer,and coarse columnar/cellular grain structures in the middle and at the bottom of the deposited layer.The fusion zone displays epitaxial grains structure,and the heat-affected zone within joint is not evident.