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Na2SiF6 was used as surface activating flux for laser welding of TC4 titanium alloy.The effect of Na2SiF6 on TC4 titanium alloy laser welding was determined by observing the weld surface.The morphological characteristics of the high temperature plasma above the workpiece was observed and analyzed by using high-speed digital camera system.The variation of weld depth,width and microstructure were analyzed by optical microscope.The experimental results show that laser weld of TC4 titanium alloy has good appearance with activat-ing flux of Na2SiF6,weld penetration increases by about 0.8％-12％,while weld surface width decrease by about 10％-29％,the depth to width ratio is effectively improved.The inhomogeneity of weld microstructure was improved,and the crystallization direction of β columnar crystals on the upper part of the weld was changed,the grain size and microstructure of the weld were refined by Na2SiF6.