ZC71 is not a casting alloy.  You have discovered a problem - the current magnesium alloys (developed 50 years ago) have poor mechanical properties.  If you intend to use a magnesium (or aluminium) casting alloy, you will need to redesign your part to accomodate the different properties.  Good luck.

I agree, although Aluminium properties are lower, new alloys are being developed that over come some of these problems. You do not say what properties you are after, but new alloys like KO1 with silver has potential to expand the aluminium market into higher strength components. this has the disadvantage of being expensive.

Well that's interesting to know there is a alloy K01, I did'nt know about. I'll have to look that one up, is it similar to A201 ? I know 201 has silver in it. My problem is I have a part that was cast from Ductile cast iron.  Trying to remake in a non ferrous lite weight alloy,problem is it was engineered in Japan by someone very sharp, and has been made to fit the application it serves like a glove. The way all the bolt holes are arranged and the way various componets fit, there is really no way to reengineer.It would be perfect if I could find a NF Alloy I could just substitute for the Fe. Very limited to what I could change other than just increase the wall thickness in certain areas. Wanted to use Mg at first but have ruled it out due to strength requirements. Have looked very serious at using A206 and possible increasing wall thickness to strengthen part where possible. Getting headache from thinking to much about it, and how good a job the person who designed did in the first place. Back to the drawing board for another day of fun.