ZA-8 ductility

[grouse1]

What might cause a significant reduction in the ductility of ZA-8 diecasting ? We have noticed a significant reduction in ductility that results in cracking during a staking operation. The chemistry looks good with very low lead, cadmium and tin. The castings are water quenched and there does not appear to be significant variation in quench bath temp between good part lots and bad part lots. I did notice a 10 point hardness difference between good parts (HRB 60) and lower ductility parts (HRB 70)

Thanks

 

[CoryPad]

Porosity, inclusions