The cracked Z-arm was tested by direct reading spectrometer

tensile tester

Brinell hardness tester and scanning electron microscope.The results show that the composition

structure and performance of Z-arm meet the technical requirements.The micro-morphology of the fracture presents cellular crystal

dendrite

pore and equiaxed dimple.The Z-arm is not fully fused in the casting process

resulting in the formation of cold shut

which is also the main reason of the cracking.Through the control measures of limiting pouring time

measuring pouring temperature and adding riser

effective improvement could be achieved.