Abstract
Lightness and high specific strength make magnesium alloys ideal materials for the transportation industry, especially the automotive sector that is struggling to cope with the everyday more stringent regulations on emission of carbon dioxide. Wrought magnesium alloys are difficult to deform because of the few active slip systems characteristic of their hexagonal close-packed lattice. Consequently, most of the commercially available magnesium alloys are alloys based on the Mg-Al binary system used in casting processes. The improvement of the mechanical properties of these alloys cannot be achieved by means of grain refinement using Zr due to the formation of Zr aluminides. In this study we propose a novel chemical composition that can refine all types of Mg alloys as proved in the Al-containing AM50 Mg alloy. We demonstrate that Nb-B inoculation of Mg alloys promotes the formation of heterogeneously nucleated primary α-Mg grains leading to the reduction of the grain size and this is obtained over a wide range of cooling rates. We also show that the grain refinement achieved leads to the improvement of the properties of high pressure die cast Mg automotive components and has the potential to enhance the mechanical properties of cast Mg alloys.
Highlights
The interest for Mg as structural metal has increased in recent years [1] because of some of its physical, mechanical and technological characteristics such as low density, good damping behaviour, strength and stiffness as well as good castability and machinability [2]
Our study demonstrates that consistent grain refinement of Mg alloys is possible via Nb-B inoculation, which is effective over a great range of cooling conditions
We demonstrate that the refinement of the grain structure corresponds to increased mechanical performances
Summary
The interest for Mg as structural metal has increased in recent years [1] because of some of its physical, mechanical and technological characteristics such as low density (i.e. the lowest among metals, apart Be), good damping behaviour, strength and stiffness as well as good castability and machinability [2]. Mg alloys are generally divided on the basis of the presence of Al as major alloying elements; Al-free and Al-containing Mg alloys are available. The latter are preferred because of their low cost and good castability [4]. It has been proven that good combinations of strength/ductility are possible in fine-grained Mg alloys [9]
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