In the aerospace business welding must be performed by a qualified welder for aerospace products which has to take examination periodically to be able to permitted to weld aerospace products. Usually every aerospace company has its own procedures for qualifying and approving welders. The welder should be familiar with the base material and filler materials metallurgy and have all the information needed, otherwise he is probably not qualified by an aerospace company/industry.
You should consult a qualified welder for the surface and weld area preparations and dimensions. As the appropriate welding method for your product and its use purpose.
One of the best sources will be the ASM metal handbook series.
If you can comeback with more information about you proposed welding requirements and the thermal history of you casting it will help in getting more information.
