Clustered Shrinkage Pores in Ill-Conditioned Aluminum Alloy Die Castings

The geometric features of clustered shrinkage pores (CSP) in ill conditioned aluminum alloy die castings were revealed and their effect on the fatigue strength was discussed To obtain the geometric features of CSP an observation using a commercial microfocus X ray computed tomography (X ray CT) system was carried out and the position and size of CSP were confirmed However the detailed geometry of the CSP could not he clearly observed by X-ray CT because each pore in the CSP was too small to observe owing to the insufficient resolution of the CT image We developed a serial sectioning system with a polishing machine and an optical microscope Observation using the serial sectioning system clearly showed that a CSP consists of many interconnected small pores which formed an extremely complicated shape The CSP was thought to grow from relatively large gas pores which connect to small pores and consequently generate a cavity with a huge volume and a complicated geometry The complex geometry of CSP resulted in the concentration of stress around CSP and significantly undermines mechanical properties such as tensile strength and fatigue strength [doi 10 2320/matertrans MAW201032]