design stress limit for brittle material

[UkraineTrain]

I am working on a design for a die cast aluminum part, alloy EN AC-Al Si9Cu3(Fe) in as-cast condition. I am wondering what stress level to use as a limit for fatigue failure. I have read that because the material is so brittle that it is acceptable to just use the ultimate tensile strength of the material (240MPa) because there is no clearly discernible transition from elastic to plastic deformation. However, the yield strength listed in the material spec is 140Mpa. Elongation at break is 1%. So what's the preferred approach? The lifetime load cycles in my application are low, only a couple million near peak load.