Prediction of porosity characteristics of aluminium castings based on X-ray CT measurements

ABSTRACT

Porosity is a main factor limiting the fatigue performance of aluminium castings. Using micro X-ray computed tomography, size and morphology characteristics of porosity distributions are analysed for material from a cast Al–8Si–3Cu–(Sr) crankcase as well as from cast Al–8Si–3Cu–(Sr), Al–7Si–0·5Cu–Mg–(Sr) and Al–7Si–0·5Cu–Mg–(Na) cylinder heads. Correlations are developed between the porosity volume percentage and mean and maximum pore sizes. Two characteristic size measures of the porosity distribution are identified: the volume weighted spherical mean diameter and the volume weighted mean envelope diameter. Both correlate linearly with the corresponding diameters of the largest pore. The pore morphology is described by a volume weighted mean sphericity. This mean sphericity and the local amount of porosity are used to predict the mean and maximum pore sizes of the porosity distributions. These correlations will find applications in integrated computational materials engineering.

KEYWORDS:

• Aluminium casting
• X-ray computed tomography
• microporosity
• pore size distribution
• sphericity