Effect of cooling rate on solidification characteristics of aluminium alloy AA 5182

Abstract

Microstructural reactions during solidification of aluminium alloy AA 5182 were investigated using cooling curve analysis to determine the start temperature of the various transformations and the overall evolution in solid fraction. Three cooling rates were studied: 0.5 K s^-1, 1 K s^-1 and 2 K s^-1. The key finding of the study is that the main eutectic reaction and subsequent reactions, including Mg₂Si formation, occur at much lower temperatures and higher solid fractions than previously published. The primary eutectic was found to precipitate between 575 and 588 °C, which corresponds to a solid fraction between 0.87 and 0.91, and Mg₂Si was found to precipitate between 551 and 560 °C, which corresponds to a solid fraction between 0.96 and 0.97. Increasing cooling rate was observed to result in a slight increase in solid fraction for primary eutectic precipitation from 0.87 - 0.88 at the low cooling rate to 0.89 - 0.91 at the intermediate cooling rate and 0.91 at the highest cooling rate. The highest cooling rate also resulted in a drop in solidus temperature to 461 °C from 500 - 510 °C (at the low and intermediate cooling rates) that led to an increase in the solidification interval from 123 K to 151 K.