Microstructual and Thermal Analysis of AlSi and MgAl Alloys Subjected to High Cooling Rates
Abstract
This thesis is an examination of the effects of varying cooling rate on the solidification properties of AlSi and MgAl alloys. Rapid cooling accessories for the Universal Metallurgical Simulator and Analyzer Technology Platform (UMSA) were developed that enabled quenching up to peak rates of 520°C/s. Samples from four automotive production alloys (aluminum A356 and a Sr-modified Al-20wt.%-Si alloy as well as magnesium AM60B and AE44) were resolidified under a range of cooling rates. Resultant micrographs revealed improvements to the microstructure, especially for the modified hypereutectic alloy. The AM60B microstructure also indicated invariance to cooling rate. Thermal data from the magnesium alloys was used in the development of baseline and fraction solid calculations that are extensible to higher cooling rates. Though these techniques cannot yet be applied to the highest cooling rates, excellent phase composition data for the AM60B alloy was generated for cooling rates of approximately 20°C/s (peak).