A solid-state recycling method for Mg–4Y-3RE alloy scraps incorporating spark plasma sintering and friction stir processing

The low density of Mg alloys makes them advantageous in lightweight structures for transportation, reducing energy costs and CO 2 emissions. However, the production of Mg alloys is energy intensive and produces large amounts of waste, weakening the advantage of Mg alloys as a green material. A solid-state recycling method incorporating spark plasma sintering (SPS) and friction stir processing (FSP) has been proposed to recycle Mg–Y-RE alloy scraps produced during the machining process. In the first step, SPS rapidly turned scraps into a consolidated disk, with coarse grains, second phases and large pores. In the following FSP step, dynamic recrystallisation refined grains to about 1.2-3.0 μm. Large second phases were partly re-dissolved into the matrix and redistributed. Pore size and fraction were reduced and a more densified disk was then obtained. The FSPed disk exhibited a yield strength (YS) of 190.3 MPa and an elongation (El) of 3.8%. Further ageing increased the YS to 226.5 MPa, whilst decreasing the El to 2.2%. The mechanical properties of the recycled material are comparable to cast and additively manufactured counterparts. It offers a possibility of the combination use of powder metallurgy and plastic deformation to achieve solid-state recycling of Mg alloys.