Finally, there is the interesting study by Wang and Crepeau at General Motors and their colleagues at Nemak.43


They pre-


sented a case study of the successful pilot plant development of an engine block, which experienced quality problems after it went into production. A detailed investigation then began, and changes were made to melting and casting practices in order to realize an improvement in fatigue strength.


Concluding Remarks


In this review we have tried to establish a scientific basis to evaluate the quality of net-shaped castings. This approach to quality is important, because it allows a foundry engineer or


casting user to establish a value for the absolute or relative quality of a casting, and to know whether further improve- ments are possible.


Experimental information and theoretical equations show that even small quantities of defects result in a significant loss of ductility and tensile strength. This observation places a special emphasis on maintaining the highest metal quality, in order to reduce the presence of oxide films, porosity, and brittle intermetallic phases in castings.


The fatigue life of a casting is also strongly affected by the presence of defects. A number of excellent studies have


Figure 17. Weibull plot for fatigue life of Sr-modified 356 alloy containing different defects.40


Figure 18. Weibull plot for fatigue life of 356 alloy castings.42


(Maximum applied stress was 240 MPa, R=0.1) 20 International Journal of Metalcasting/Winter 11


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