Effect of Holding Time and Temperature for Hypereutectic Al-Si Alloy on the Segregation of Primary Si Particles In Producing A Functionally Graded Material

In functionally graded composite materials the volume fraction of reinforcement particles varies continuously along specific directions, resulting in graded properties. These types of functionally graded materials (FGMs) are useful in applications where a combination of high surface wear resistance and high toughness of the interior bulk material is required. In the present study functionally graded Al-Si composites were prepared by holding Al-18wt.%Si hypereutectic samples at various temperatures within the freezing range of the alloy and the effect of holding time (0-15min) and temperature (590-650°C) on the distribution of primary Si particles and hardness of composites was quantified. The results showed that the structure of the samples in the upper part was hypereutectic identified by the presence of primary silicon particles. The number of primary Si particles and consequently the hardness of samples decreased gradually from the upper towards the lower parts of the samples. For the lower parts, a hypoeutectic structure with a relatively low hardness value was identified. These results were rationalized in terms of the variation in the microstructure due to segregation of Si towards the upper parts of the sample.