Behaviour of spreading molten metal drops deposited by fusion

Liquid droplet deposition on solid surfaces has an important role in the industrial and research activities. The behaviour of such deposit is influenced by volume and interfacial phenomena and involves a large number of mechanisms such as gravity effect, mass transfer, capillary forces, and wetting. For the case of metal deposition the analysis of the problem is more complex because of the importance of thermal effects, involving steep gradients and phase changes. A unique experimental approach is presented in order to study the evolution of the spreading of a large drop of liquid metal called “macro-drop”. The objective of this work is to supply qualitative and quantitative information during the deposit of liquid metal in relation with process parameters. The overall shape of the macro-drop, especially its spreading and contact angles are studied in detail. The gradual spreading of the macro-drop is mainly governed by mass and heat transfers. The initial rapid spreading is due to kinetic energy of depositing droplets and direct arc heating on the solid target. All experimental results are analysed in the light of process parameters to identify the physical mechanisms involved and appreciate their effects on the behaviour of such a macro-drop.

► A unique experimental approach has been designed for studying arc processes.
► The spreading of static weld pool passes through three stages.
► An over-fusion time has been measured during the solidification of the deposited metal.
► Initial heat content and plasma nature affect a lot the wetting of studied system.
► Surface tension and thermal effects have been identified as major phenomena.