Yb: YAG laser welding of Ti6Al4V sheet using conventional and annular power density distribution: microstructure mechanical properties relationship

Development of high power laser beams with increasing beam quality and decreasing purchase cost lead to a strong development of laser welding techniques. Narrow weld beads, high welding speed, and low heat input are the main advantages of this reliable and repeatable joining process. The aim of this study is to investigate properties of weld seam obtained by Gaussian and annular power distribution, on butt joints of 0.9 mm annealed Ti6Al4V sheet by mean of an experimental design varying power level, spot size and shape, welding speed, and face gaseous protection flow. Examined characteristics of the weld seams are geometrical (Fusion Zone FZ and Heat Affected Zone HAZ shapes and dimensions, defects like porosities, undercut and underfill, distorsions of welded plates), microstructural (FZ and HAZ nature and morphology) and mechanical (tensile test, hardness filiations). Major features concerning the use an annular power distribution concern the flawless weld seam geometry and fair mechanical properties, with relatively low levels of distortions due to residual stresses.