Spraying the surface of the die will help create a barrier to prevent soldering. Spraying also contributes to thermal shock and an increase in tensile stress build up that eventually leads to heat checking.
It is important to maintain good die lube retention by spraying. The spray wetting of the surface can, as long as present, help to maintain a barrier between the aluminum and iron
It is best to apply a diffusion process to create a compound layer at the surface that generates a non-contributing barrier that will not allow aluminum to interact with the iron. This will protect areas that receive inadequate spray wetting.
