Statistical assessment of fatigue crack initiation from sub-surface hydrogen micropores in high-quality die-cast aluminum

It has recently been discovered that micropores on the order of a few microns agglomerate in a high density in the sub-surface layer of aluminum alloys that have been produced in a high-quality die-casting process. It is known that fatigue behavior is dominated by the existence of the micropores. In the present study, geometrical parameters defining the relationship between fatigue crack initiation and micropores have been investigated using high-resolution X-ray microtomography, combined with two kinds of statistical analysis. It has been revealed that consideration of micropore pairs is necessary, and a number of parameters for paired micropores that may be strongly associated with fatigue crack initiation have been extracted and statistically evaluated. It is concluded that the mean diameter between paired micropores, and the mean distance to the casting surface, are predominant in fatigue crack initiation.