Design for Recycling - A Key to Sustainable Magnesium Application

"The increasing use of coated magnesium in consumer products results in creation of coated Mg scrap during product manufacture and after End-of-Life product treatment. Currently this material is generally not recycled, leaving a material resource unused. Closure of the magnesium cycle in a sustainable manner is necessary. In order to do so, the effect of coatings on the recycling process has to be quantified, predicted and minimized. For this purpose metrics have been developed, based on first principles supported by detailed understanding of the recycling process. The developed 3D metric enables quantitative assessment of the recyclability and links coating design, product design and recycling to each other in a visual manner. The parameters that form the metric can be measured and predicted, hence an engineering basis for Design for Sustainability of coated magnesium is provided.IntroductionEvery product progresses through the four phases of the product life cycle depicted by figure 1. In each phase residues are created. Their amount and composition is largely determined by the complex material combinations created/invented during product design in the manufacture phase. Compared to the ideal cycle the magnesium cycle is far from closed (fig. 2). Most noticeable is absence of the link between the EoL phase and raw materials production. A closed cycle only exists for class 1 scrap, which goes from the product manufacture phase directly to production from industrial material and returns to the manufacture phase as magnesium alloys. The four problematic streams are marked by ???. Coated semi-products are present in two of the four residues, namely in rejects and collected scrap. When these semi-products are recycled the amount and composition of the dross and salt slag residue is affected as well.During product design selection of the coating takes place, fixing the coating character¬istics and properties from this moment on for the rest of its life cycle. The choices made in the manufacturing phase are therefore critically linked to the recyclability of coated semi-products as well as the sustainability of the magnesium cycle as a whole. Sustainable closed life cycles, in which the quality of materials is preserved and residue creation and resource depletion are minimized, can be attained by selecting the appropriate alternative during product design. To realize this the effect of design choices on the life cycle and more specific the recycling process has to be known and quantified."