Mechanical properties of laser-welded cast titanium and titanium alloy

Yun, Mi Kyung; Kim, Hyun Seung; Yang, Hong So; Vang, Mong Sook; Park, Sang Won; Park, Ha Ok; Lee, Kwang Min

Abstract

PURPOSE: The purpose of this study was to investigate the effect of the output energy(voltage) of laser welding on the strength and properties of joint of cast titanium(CP Gr II) and titanium alloy(Ti-6Al-4V). MATERIAL AND METHOD: Cast titanium and its alloy rods(ISO6871) were prepared and perpendicularly cut at the center of the rod. After the cut halves were fixed in a jig, and the joints welded with a laser-welding machine at several levels of output voltage of 200V.280V. Uncut specimens served as the non-welded control specimens. The pulse duration and pulse spot size employed in this study were 10ms and 1.0mm respectively. Tensile testing was conducted at a crosshead speed of 0.5mm/min. The ultimate tensile strength(MPa) was recorded, and the data(n=6) were statistically analyzed by one-way analysis of variance(ANOVA) and Scheffe's test at alpha=0.05. The fracture surface of specimens investigated by scanning electron microscope(SEM). Vickers microhardness was measured under 500g load of 15seconds with the optimal condition of output voltage 280V.
RESULTS
The results of this study were obtained as follows, 1. When the pulse duration and spot size were fixed at 10ms and 1.0mm respectively, increasing the output energy(voltage) increased UTS values and penetration depth of laser welded to titanium and titanium alloy. 2. For the commercial titanium grade II, ultimate tensile strength(665.3MPa) of the specimens laser-welded at voltage of 280V were not statistically(p>0.05) different from the non-welded control specimens(680.2MPa). 3. For the titanium alloy(Ti-6Al-4V), ultimate tensile strength(988.3MPa) of the specimens laser-welded at voltage of 280V were statistically(p<0.05) different from the nonwelded control specimens(665.0MPa). 4. The commercial titanium grade II and titanium alloy(Ti-6Al-4V) were Vickers microhardness values were increased in the fusion zone and there were no significant differences in base metal, heat-affected zone.