Porosity suppression of Nickel-based superalloy by modulated base temperature in laser welding and mechanism analysis

This paper investigates the distribution pattern of welding porosity defects in annular weld seams of superalloy during laser welding. The results reveal that the initial portion of the annular weld seam exhibits a higher density and larger size of porosity defects compared to the ending portion. At a laser power of P=360 W, the numerical simulation combination showed that the A1 region's average cooling rate is 8.767×103 °C/s and the A2 region is 8.151×103 °C/s that the thermal conduction effect at the initial welding position leads to an elevation in the base metal temperature in the subsequent unwelded region, thereby reducing the solidification rate of the molten pool in the latter half of the weld seam and effectively decreasing the porosity rate at the weld seam. Furthermore, the study demonstrates that elevating the base metal temperature can effectively modify the cooling rate of the molten pool, thereby influencing the formation of porosity defects. At a laser power of P=360 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 8.767×103 °C/s at a base metal temperature of T=20 °C to 7.451×103 °C/s, leading to a decrease in the porosity rate from 3.357% to 0.022%. At a laser power of P=672 W, increasing the base metal temperature to 600°C reduces the cooling rate of the molten pool from 6.781×103 °C/s at a base metal temperature of T=20 °C to 5.056×103 °C/s, leading to a decrease in the porosity rate from 8.214% to 0.002%. The increase in laser power brings more heat input, so the solidification rate of the molten pool decreases, but the porosity increases significantly. However, increasing the base temperature can effectively suppress the porosity defects under different laser powers. The research further reveals the relationship between welding porosity rate and cooling conditions, providing a control strategy for achieving low porosity rate welds.