Experimental study on the keyhole dynamic evolution and porosity formation during laser welding of Ti-6Al-4V alloy

Abstract

Keyhole dynamic evolution significantly affects laser welding quality. For observing the keyhole’s dynamic behaviors directly, a sandwich workpiece that consists of a piece of quartz glass and a piece of  Ti-6Al-4V alloy is used in experiments of this study, and the dynamic behaviors of the keyhole are recorded with a high-speed camera. The experimental results show that, in the first 5 ms of welding, the depth and width of the keyhole increase linearly and, at about 70 ms, a relatively stable keyhole is formed. A keyhole typically exhibits the shape of a “7” character in a short period after it forms. At this stage, the laser beam is reflected by the wall of the keyhole repeatedly until it reaches the bottom, which results in some tiny pore formations in the middle part of the keyhole. In subsequent welding, the collapsing and rebuilding process of the keyhole are observed, and big pores are formed at the bottom of the keyhole. The results of this research are helpful to understand the mechanism of the keyhole dynamic evolution and porosity formation during titanium alloy laser welding.