Compression deformation behavior of semisolid Al 2 O 3np reinforced 7075 aluminum matrix composites with high solid frac
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Semisolid forging is a type of semisolid metal processing with high solid fraction. However, the presence of nanosized particles has strong influences on flow behavior of the composites in the semisolid forging process. In this study, the compression deformation behavior of nanosized Al2O3 particles (Al2O3np) reinforced 7075 aluminum matrix composites with high solid fraction was investigated by conducting semisolid isothermal compression experiment. The microstructures after semisolid compression were characterized. The results showed that the true stress decreased with the increase of the deformation temperature and size of Al2O3np, the decrease of the strain rate and mass fraction of Al2O3np. After semisolid compression, deformation degree in large deformation zone was larger than that in free deformation zone. Besides, the solid grains in large deformation zone showed evidence of having undergone different degrees of plastic deformation under different deformation conditions. Simultaneously, the deformation mechanisms during the semisolid compression process were discussed.
I. INTRODUCTION
Semisolid forging is a typical technological route of semisolid metal processing, which involves forming of alloys in the semisolid state to near-net shaped products.1 For semisolid forging, it is necessary to have a fine globular microstructure with high solid fraction in a semisolid range.2 Semisolid forging has been recognized as a new technique offering significant advantages over forging or casting process, such as a low forming pressure, the reduction of segregation and porosity.3–5 In addition, semisolid forging basically consists of three procedures: feedstock production, reheating, and semisolid forming.6,7 Among them, the compression deformation behavior with high solid fraction must be well understood because it embodies the abilities of semisolid forging and mold filling, which has a significant effect on the properties of the shaped components. In recent years, more attention has been paid to compression deformation behavior in semisolid state. Lu et al. 8 mentioned an isothermal compression of Al–4Cu–Mg alloy in semisolid state. They found that the deformation temperature and the strain rate had great impacts on the peak flow stress and the flow stress decreased with the increase of the deformation temperature and the decrease of the strain rate. Chen et al.9 Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.407
investigated the compressive deformation behavior of Ti14 alloy in semisolid state. They concluded that the decrease in the amount of solid bridges between grains resulted in a sharp decrease in stress at a solid fraction between 0.96 and 0.98. Li et al.10 studied the microstructural evolution and flow stress of type 304 steel in semisolid state. They observed that flow stress curves around solidus temperature exhibited abrupt change, which was related to the phase change. Thanh et al.11 reported a compression experiment in semisoli
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