Fatigue of an aluminium cast alloy used in the manufacture of automotive engine blocks

The fatigue resistance of an aluminium alloy used for casting engine blocks was studied. The tests were carried out with specimens machined from the bulkheads of V8 engine blocks cast by the low pressure process. The samples were obtained from two different locations in the bulkheads to evaluate the effect of microstructural refining as the material was cut from regions in which the secondary dendrite arm spacing was within two different sizes, namely 30 and 45 μm. The samples were tested either in their as-cast and heat treating conditions in a computer controlled servohydraulic machine. The tests were fully reversible following staircase schedules. The specimens were fatigued to fracture or up to 107 cycles. The results show that fatigue cracks nucleate in pores located close to the surface of the specimen. It is concluded that the fatigue resistance is affected by heat treating and microstructural refining. The enhancement in fatigue resistance due to microstructural refining is documented. An analysis was carried out to predict the cycles to failure that the material is able to sustain.