Mechanical and Corrosion Properties of AZ31 Magnesium Alloy Repeatedly Recycled by Hot Extrusion

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.