Microstructure modification and corrosion resistance enhancement of die-cast Mg-Al-Re alloy by Sr alloying

The effects of Sr additions on the microstructure and corrosion performance of a Mg-Al-RE alloy in 3.5 wt.% NaCl saturated with Mg(OH)2 have been investigated. Microstructure examination reveals that the Sr addition introduces additional intermetallic phases, refines intermetallic networks and dendritic grains, and improves the network continuity. More Al and rare earth elements can be identified in the intermetallics and grain boundaries or inter-dendrite regions under a transmission electron microscope and secondary electron microscope, respectively. On the Sr-containing intermetallic phases and the refined microstructure, the oxide films become more protective, resulting in more corrosion resistant boundary areas and thus dendrite grain grooves. Hence, the presence of large amounts of intermetallics and boundaries can enhance the corrosion performance of the Mg-Al-RE alloy containing Sr .