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

Microstructural reactions during solidification of aluminium alloy AA 5.182 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), I K s-1 and 2 K s-1. The key finding of the study is that the main eutectic reaction and subsequent reactions, including M92Si formation, occur at much lower temperatures and higher solid fractions than previously published. The primary eutectic was found to precipitate between 575 and 588degreesC, which corresponds to a solid fraction between 0(.)87 and 0(.)91, and M92Si was found to precipitate between 551 and 560degreesC, 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 461degreesC from 500-510degreesC (at the low and intermediate cooling rates) that led to an increase in the solidification interval from 123 K to 151 K.