Pulsed Nd:YAG laser beam welding (P-LBW) and pulsed tungsten inert gas (P-TIG) welding were used to prepare full penetration bead-on-plate weldments of 1.6 mm thick Ti-5Al-2.5Sn alpha titanium alloy sheet. The influence of welding phenomenon on the microstructure, micro-hardness, tensile properties, surface and sub-surface residual stress distribution and deformation and distortion of both the weldments were studied. Higher cooling rate in P-LBW resulted in complete ␣' martensitic transformation in fusion zone whereas in P-TIG weldment ␣' and acicular ␣ was formed within equiaxed ␤ matrix due to lower cooling rate. Hardness in fusion zone of P-LBW was higher than that of the fusion zone of P-TIG weldment due to faster cooling rate in P-LBW. The welded zone in both the weldments showed higher hardness and strength than that of the parent metal since a ductile fracture occurred in the un-welded section during tensile testing. Residual stresses in both P-LBW and P-TIG weldments showed similar trend but the distribution was much narrower in P-LBW due to less width of heat affected zone. P-LBW resulted in more nonuniformity in through thickness stress profile because of greater top to bottom width ratio. Less residual stresses, deformation and distortion and superior mechanical properties in P-LBW made the process more feasible than P-TIG for the welding of Ti-5Al-2.5Sn alloy sheet.

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Friction stir welding is a recently developed technique for joining low-melting metals and polymers. In the present work, friction stir welded joints of high-density polyethylene (HDPE) sheets were produced using a newly designed tool with a concave shoulder and a grooved conical pin. The joints were produced with and without the additions of ceramic particulates including silicon carbide (SiC), alumina, graphite, and silica. The effect of strain rate on the tensile properties of base material and plain welded joints was examined. In addition to tensile properties of composite joints, hardness profiles across the weld nugget were analyzed. It was observed that the increasing strain rate improved both the tensile strength and the ductility of the plain welded joints. The tool was able to yield a joint efficiency of around 84% in the plain welded samples. Although, in terms of joint efficiency, the composite joints were less efficient than the plain welded HDPE, SiC additions were found to yield better material properties relative to other reinforcements. Finally, it was concluded that an SiC–HDPE composite joint can be of practical importance in high strain rate applications, provided the optimum tool design and stir welding parameters are available.

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