AZ31 Mg machined chips were recycled by extrusion at 673 K with a low extrusion ratio of 45:1 and a high extrusion ratio of 1600:1. Oxide contaminants were dispersed more uniformly in the recycled specimen with the high extrusion ratio than in that with the low extrusion ratio. In tensile tests, the recycled specimens with the high extrusion ratio showed about 50% higher 0.2% yield stress and about 20% higher tensile strength compared with those of the reference specimens, which were the extruded AZ31 Mg blocks under the same conditions as the recycled specimens. The improvement of the tensile properties was attributed not only to the small grain size, but also to the dispersed oxide contaminants.

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Machined chips of a magnesium ally were repeatedly recycled by hot extrusion at 673 K, and mechanical and corrosion properties of the recycled specimens were investigated. At room temperature, the recycled specimen with a high repeated number showed high 0.2% yield stress and high tensile strength but low elongation at room temperature. The main strengthening mechanism of the repeatedly recycled specimen was grain refinement strengthening. Inhomogeneous distribution of oxide contaminants adversely affected the elongation. At elevated temperature, the recycled specimen showed low strength and low elongation as the recycling was repeated. The recycled specimen by a single extrusion exhibited a superior corrosion resistance to the reference specimens. On the other hand, the repeatedly recycled specimen showed poor corrosion properties even though a large amount of oxides is contaminated. The deteriorated corrosion properties are caused by the excessive iron contamination which promotes pitting sites resulting from localized galvanic corrosion sites.

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