Analysis of spatial distribution characteristics and ejection behavior of plasma in deep penetration laser welding process of Ti6Al4V titanium alloy

Abstract

The spatial distribution characteristics and ejection behavior of the plasma is vital to complete understanding of the underlying physical mechanism of deep penetration laser welding process. Existing works concerning the dynamic behavior of the plasma mostly encounters challenges in direct detection and high temporal resolution detection. In this paper, an electrical detection approach based on the passive dual-probe sprayed by high-temperature-resistant and electrically insulating coating was proposed. This method was used to study the spatial distribution characteristics and ejection behavior of the plasma during deep penetration laser welding process of Ti6Al4V titanium alloy. The results indicated that within the laser power range of 1200–1500 W, the plasma temperature and electron density with the peak probability density exhibited the trend of firstly increasing and then decreasing along the axial direction of the plasma. Additionally, the ejection velocity with the peak probability density presented a tendency of increasing with the increasing laser power. Moreover, the relationship between the ejection velocity and maximum plasma temperature detected by the lower probe was analyzed in the view of the peak probability density. By quantitative statistical analysis, it was found that when the ejection velocity (or the maximum plasma temperature) had the peak probability density, the corresponding data points of the maximum plasma temperature (or the ejection velocity) mainly fell within one standard deviation. Finally, the linear regression model between the logarithms of the ejection velocity and plasma temperature variation rate detected by the lower probe was established for the ejection behavior analysis. Based on the linear regression model, the plasma ejection behavior could be reasonably analyzed using plasma temperature variation rate.