It is becoming increasingly evident that lightweight technology is vital for reducing demand on limited natural resources and to combat global warming. Thus, there is currently a growing interest in magnesium (Mg) and its alloys since they are the lightest structural metallic materials and can enable the design of lighter engineering solutions. Efforts are underway to replace iron-based alloys with Mg-based alloys. Still, the use of Mg-based alloys is restricted by a number of inherent limitations, including inherent vulnerability to environmental degradation, poor formability, low creep resistance and unstable price. However, with the latest breakthroughs in Mg technology, these major drawbacks are being gradually overcome. One solution to solve the corrosion issue in Mg alloys has been shown to be alloy development through controlling the solidification. Our efforts in developing a quantitative description of the alloys’ microstructure and the alloys’ corrosion behavior have now reached an interesting stage; the newly designed cast Mg alloys AZ91 and AM50 exhibit significantly better corrosion resistance than their commercial counterparts. This is achieved a through a fundamental understanding of the interplay between microstructural constituents and the Mg alloys’ corrosion process. We show that changing the alloy microstructure, with no new addition of alloying elements as compared to existing commercial alloys and no significant change in the manufacturing, improves the alloys’ corrosion resistance. In this presentation, we discuss the research strategy (from micron to nanometer scales) that results in an improvement in the corrosion behavior of Mg alloys. Besides, some previously unrecognized concepts in Mg corrosion phenomenon are also presented. We believe that the ideas presented here are generic and can be employed for other light alloys, when corrosion is an issue.