Fatigue failures in low pressure die cast AlSi10Mg cylinder heads

Abstract

Exposed to both high and low cycle fatigue, the modern automotive cylinder head is certainly a demanding application for aluminium alloys. AlSi10Mg cylinder heads were investigated to identify the material issues which impact their performance. Fatigue cracks occurred at or very near the water jacket surface, shown to experience the highest residual stresses after quenching. The majority of these cracks were linked with either extensive porosity, insufficient level of modification or with Fe based intermetallic platelets. The predominance of such features near the water jacket surface is accounted for by the relatively slower solidification near the water jacket surface. Fatigue cracks were almost completely avoided by keeping the density index below 2 to control porosity, by improving the solidification rate to achieve SDAS smaller than 35 micrometres, by limiting the Fe level to a maximum of 0˙12 wt-%, by using a higher quality sand for the manufacture of water jacket cores and, finally, by adopting polymer water quenching practice during heat treatment.

Keywords:

• ALUMINIUM ALLOYS
• CASTING
• CYLINDER HEADS