Electric Arc Furnace Dust Recycled in 7075 Aluminum Alloy Composites Fabricated by Spark Plasma Sintering (SPS).

The reuse of industrial waste, such as electric arc furnace dust (EAFD) as reinforcement in aluminum matrix composites (AMC), is still little explored even though it has shown potential to improve the mechanical properties, such as hardness and mechanical strength, of AMCs. To propose a new alternative for EAFD recycling, AA7075-EAFD composites were produced by spark plasma sintering (SPS). The starting powders were prepared by high-energy milling with different weight fractions of EAFD in two particle size ranges added to an AA7075 matrix. SEM shows that the distribution of reinforcement particles in the matrix is homogeneous with no agglomeration of the particles. XRD patterns of initial powders and the SPS-sintered (SPSed) samples suggest that there was no reaction during sintering (no additional peaks were detected). The relative density of all SPSed samples exceeded 96.5%. The Vickers microhardness of the composites tended to increase with increasing EAFD content, increasing from 108 HV (AA7075 without reinforcement) up to 168 HV (56% increase). The maximum microhardness value was obtained when using 15 wt.% EAFD with a particle size smaller than 53 µm (called G1), showing that EAFD presents a promising potential to be applied as reinforcement in AA7075 matrix composites.

Microstructure and Mechanical Properties of AA7075 Aluminum Alloy Fabricated by Spark Plasma Sintering (SPS).

AA7075 aluminum alloy is widely used for several high-technology applications for its high mechanical strength to weight ratio but is still the subject of several studies seeking a further increase in its mechanical properties. A commercial powder is used, either as-received or after ball-milling. Dense AA7075 samples are prepared in one step by Spark Plasma Sintering, at 550 °C with a holding time of 15 min and a uniaxial pressure of 100 MPa. No additional heat treatment is performed. Laser granulometry, X-ray diffraction and optical- and scanning electron microscopy show that both grain size and morphology are preserved in the dense samples, due to the relatively low temperature and short sintering time used. The samples prepared using the ball-milled powder exhibit both higher Vickers microhardness and transverse fracture strength values than those prepared using the raw powder, reflecting the finer microstructure.