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The mechanical properties of cast aluminum alloys can be affected by the delay in time involved between the stages of rapid cooling after solubilization (quenching) and aging. This effect was studied on samples from three different Al-Si alloys that were cast with a wide range of microstructures. It was found that the parameter that exerts the highest influence on the mechanical properties is the degree of microstructural refining, which is referred to dendrite arm spacing, as a finer structure enhances the strength and ductility. It was found that the yield strength and total elongation, and to a lesser extend the ultimate tensile strength, are affected by the delay in time. The material that was treated to the peak-aged condition was found to be more susceptible to the reduction in mechanical properties with the increase in the delay in time.

The working conditions within the combustion chamber of engine blocks force the use of liners able to resist the pressure and wear caused by reciprocating pistons. Most liners are made from iron alloys and can be either inserted after the block has solidified, or can be cast-in the block. Cast-in liners promote residual stresses in regions such as cylinder bridges. These stresses arise from the differences in the thermal expansion coefficient of iron and aluminium and may promote the failure of the block if high enough. This work describes the procedure followed to measure the residual stresses in aluminium engine blocks with cast-in grey iron liners by means of extensometric measurements. The trials were conducted in blocks of I-4 and V-8 configuration that were either in the as cast or heat treated condition. It was found that the stresses can be .150 MPa in tension, depending on the geometry and size of the piece. Similar analyses were carried out in blocks that have pressed-in liners, which resulted to have compressive stresses. It is concluded that these analyses can provide for an early advice when changes take place in design, processing or material.

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