Microporosity control and thermal-fatigue resistance of A319 aluminum foundry alloy

The objective of this work was to gain a quantitative and qualitative understanding of the degree to which porosity influences thermal-fatigue performance and other mechanical properties of A319 aluminum casting alloy over ranges of commercial interest. The number of cycles to failure for each test was recorded. An increase in porosity content caused degradation in thermal-fatigue life and other mechanical properties. The fractographic examinations identified the pores and some intermetallics as the key microstructural features which promote damage and thermal-fatigue crack initiation sites in the specimens. Crack initiation and propagation is expected to occur sooner in regions of higher defects such as pores and large intermetallics. Progressive cyclic plastic deformation was also observed in constrained thermal-fatigue specimens. In the absence of other defects, thermal-fatigue crack initiation is dominated by accumulation of the local plastic deformation in the α-Al in constrained thermal-fatigue fracture surfaces.