Segregation Behavior and Evolution Mechanism of Iron-Rich Phases in Molten Magnesium Alloys

A new method has been proposed to prepare Mg–Al–Si master alloys by utilizing scrap Al–Si–Fe alloys with higher Fe levels, which aims to segregate Fe from Al–Si–Fe alloys by Mg melt. The segregation behaviors, microstructure morphology and evolution mechanism of iron-rich phases in Mg–Al–Si alloy melts were studied, after Al–14Si–4Fe (wt%) alloys were added and dissolved completely. In the Mg–Al–Si alloys, iron has very little solubility and tends to combine with other elements to form intermetallic phases, which grow into a deposition layer due to the higher density. During the cooling and solidifying process of Mg–Al–Si melts, the needle-like Al5SiFe phase in Al–14Si–4Fe alloy evolved into blocky Al5Fe2 and Al0.7Fe3Si0.3 phases. Besides, the Fe levels of the Mg–Al–Si master alloys were reduced to 0.017 wt% from nominal content of 0.164 wt%. Based on the above results, this work carried out a semi-quantitative phase-compositions analysis for the deposition layer by relative intensity ratio (RIR) method, and evolution mechanism of the iron-rich phases had also been discussed. This study has paved a new way to regenerate the scrap Al–Si–Fe alloys, which has a great significance of promoting the recycling of aluminum resources.