Analysis of fatigue crack initiation and S–N response of model cast aluminium piston alloys

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-09, Vol.528 (24), p.7331-7340
• Main Authors: Mbuya, Thomas O., Sinclair, Ian, Moffat, Andrew J., Reed, Philippa A.S.
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Applied sciences; Cast aluminium; Casting defects; Condensed matter: structure, mechanical and thermal properties; Crack initiation; Crack propagation; Exact sciences and technology; Fatigue; Fatigue (materials); Fatigue failure; Fractures; Intermetallics; Mechanical and acoustical properties of condensed matter; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Mechanical properties of solids; Metals. Metallurgy; Physics; Piston alloys; Pistons; Porosity; Tribology and hardness
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.06.007

► Hipping improves fatigue performance of a low Si (Al0.7Si) piston alloy but has no effect in a higher Si (Al7Si–Sr) alloy. ► Fatigue cracks initiate at intermetallic particles (e.g., Al 9FeNi) in both hipped alloys and sometimes from oxide particles in Al0.7Si alloy. ► Scatter in fatigue life is correlated with the size of fatigue crack initiating particles and the overall particle size distribution. Fatigue crack initiation and S–N fatigue behaviour of hipped model Al7Si–Sr and Al0.7Si piston alloys have been investigated after overaging at 260 °C for 100 h to provide a practical simulation of in-service conditions. The results show that hipping did not affect the S–N behaviour of Al7Si–Sr. This is attributed to the lack of significant change in porosity distribution in this alloy because of its low porosity levels even in the unhipped state. However, hipping profoundly improved the fatigue performance of alloy Al0.7Si due to the significant reduction in porosity. In this investigation, it was observed that porosity was rendered impotent as a fatigue crack initiator in both hipped alloys. Instead, fatigue cracks were observed to originate mainly from intermetallic particles (particularly the Al 9FeNi phase) in both alloys and sometimes from oxide particles in Al0.7Si alloy. Fatigue cracking was also frequently observed at intermetallic clusters in hipped Al0.7Si. The observed scatter in fatigue life is discussed in terms of the size of fatigue crack initiating particles and the overall particle size distribution which follows a power law distribution function.