Global Macrosegregation
Concentration gradients spanning large regions of an ingot, caused by convective currents and gravity during solidification, necessitating subsequent homogenization heat treatments.
Macrosegregation means: During solidification, alloying elements and impurities migrate. The center of the component then has a different composition than the edge. This is due to convection in the melt and the fact that lighter components rise. For you when welding, this means: The material is not homogeneous. If you stir it, you get varying hardness and strength, and it can lead to cracks. Before welding, only diffusion annealing helps to redistribute the elements evenly. The exact temperature and time depend on the alloy; you have to check the data sheet. If the part has not been annealed, don't weld it.