Abstract
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.
Highlights
Powder metallurgy (PM) technology has been of interest to several industrial sectors for decades
For the AA7075-M powder, the particles have taken the shape of micrometric flakes about 1 μm thick and with lateral dimensions in the range 10–100 μm, which is a typical morphology for milled soft metals for a short time (≤ 5 h), as reported in previous works [34,35]
The increase in particle size after 1 h of grinding in an aluminum alloy (AA6061) was observed by Rana et al [36]. They showed that the particle size increased from 10–12 μm to 60–65 μm, and attributed this increase to cold welding between the particles, which results in the formation of agglomerates in which the particles are weakly joined at the point of contact
Summary
Powder metallurgy (PM) technology has been of interest to several industrial sectors for decades. The manufacture of aluminum alloy parts commonly uses powder metallurgy processes, such as cold isostatic pressing (CIP), hot isostatic pressing (HIP), hot pressing (HP), hot extrusion and hot rolling. These are competitive with respect to casting and extrusion, but it involves the degassing of the powder for several hours and several more hours (1–5 h) at relatively high temperatures [6,7], which makes the process expensive [1,2,8]. The long cycle time and high temperatures lead to the growth of the grains, to the detriment of the final properties
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