Studies on the weldability, microstructure and mechanical properties of flux assisted Nd:YAG laser welds of AISI 904L
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School of Mechanical & Building Sciences, VIT University, Vellore – 632014, Tamil Nadu, India (Received 16 May 2015; accepted 25 June 2015)
This research article investigates the effect of SiO2 flux on Nd:YAG laser welding of 5 mm thick plates of super-austenitic stainless steel, AISI 904L. Microstructure studies revealed multidirectional grain growth comprising columnar and cellular dendrites along with a prominent, fine equiaxed dendritic growth at the centerline of the fusion zone. Tensile studies showcased the fracture at the fusion zone in all the trials. The average tensile strength reported for the flux assisted laser weldments was found to be 587 MPa which was slightly lower than the parent metal. The impoverishment of tensile strength could be attributed to the formation of centerline equiaxed grains. Similarly the impact toughness of the joints was found to be 58 J. The studies demonstrated the possibility of using a 2 kW Nd:YAG laser welding machine to weld 5 mm thick plate with the use of SiO2 flux. A detailed study on the structure–property relationship of flux assisted Nd:YAG laser weldment was carried out using the combined techniques optical microscopy, scanning electron microscopy, and energy dispersive x-ray analysis.
I. INTRODUCTION
Improving the depth of penetration capability is one of the primary goals of the welding processes adopted in industries. In the recent past, activated flux assisted welding has been one of the promising, notable techniques for joining various metal combinations, with a focus on maximizing the depth of penetration. In general, the fluxes such as sulphides, halides, and/or oxides which are dissolved in the solvents, such as carbinol, ethanol, or acetone. This flux is precoated on the plates to be joined using a paint brush or dispenser. Researchers addressed that the arc constriction and marangoni convection are the underlying mechanisms, contributing for the improved depth of penetration. Although a deep weld penetration could be obtained from activated flux tungsten inert gas (A-TIG) welding process, the oxidization of the tungsten electrode often occurs simultaneously. It was proven that the penetration capability of A-TIG welding had been increased to 200–300% compared to conventional TIG welding. Similarly, several researchers have addressed the use of laser welding for joining versatile materials. Some of the typical advantages include the narrow beads with lesser or nil heat affected zone (HAZ), lower distortion, improved mechanical properties, and higher productivity. However, the use of low kW capacity laser welding
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.209 J. Mater. Res., Vol. 30, No. 15, Aug 14, 2015
machine for joining high thickness materials is cumbersome task. Kuo et al.1 performed the flux assisted laser welding of mild steel, austenitic, and duplex stainless steels. The authors used a 3 kW CO2 laser welding equipment for carrying out the studies. According to the authors,
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