Controlling the microstructure of welds is important to assess the structural integrity of joint. The microstructure is controlled by different factors such as heat and mass transfer occurring in the weld pool. Different parameters as welding speed and current waveform lead to different microstructure morphologies. Experimental tests with different parameters were conducted on CuNi plate with in situ observation around the solidifying interface to evaluate the microstructure evolution. This setup allows to observe and to investigate the dendritic growth around the semi-solid zone. Some EBSD maps were performed for different process parameters and are used for comparison. To model microstructure generation, cellular automaton (CA) have proven its versatility. It can model complex phenomena of solidification such as grain growth, grain competition, nucleation and Columnar to Equiaxed Transition. One of the main ingredient to model the microstructure morphology is the dendritic growth model that is linked to the undercooling. The objective of this paper is to compare experimental results with some cellular automaton results and to discuss the modelling of dendritic growth model under different solidification conditions.