Abstract
Microstructural and mechanical behaviors of semi-solid 7075 aluminum alloy were investigated during semi-solid processing. The strain induced melt activation (SIMA) process consisted of applying uniaxial compression strain at ambient temperature and subsequent semi-solid treatment at 600–620 °C for 5–35 min. Microstructures were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). During the isothermal heating, intermetallic precipitates were gradually dissolved through the phase transformations of α-Al + η (MgZn2) → liquid phase (L) and then α-Al + Al2CuMg (S) + Mg2Si → liquid phase (L). However, Fe-rich precipitates appeared mainly as square particles at the grain boundaries at low heating temperatures. Cu and Si were enriched at the grain boundaries during the isothermal treatment while a significant depletion of Mg was also observed at the grain boundaries. The mechanical behavior of different SIMA processed samples in the semi-solid state were investigated by means of hot compression tests. The results indicated that the SIMA processed sample with near equiaxed microstructure exhibits the highest flow resistance during thixoforming which significantly decreases in the case of samples with globular microstructures. This was justified based on the governing deformation mechanisms for different thixoformed microstructures.
Highlights
Semi-solid metal processing is a single step fabrication method for production of near net shape metallic parts [1,2,3]
It is worth noting that Zn, Cu, and Mg are the main alloying elements in 7075 alloy which play an important role in the formation of precipitates
The strain induced melt activation (SIMA) process consisting of applying uniaxial compression strain at ambient temperature and subsequent semi-solid treatment in the range of 600–620 ̋ C for 5–35 min was investigated
Summary
Semi-solid metal processing is a single step fabrication method for production of near net shape metallic parts [1,2,3]. The cast products show poorer mechanical properties than wrought alloys e.g., 2xxx, 6xxx, and especially 7xxx series This restricts their applicability in the high strength applications such as aerospace and automotive. Yong et al [15] prepared an appropriate 7075 semi-solid feedstock by 50% swaging of the specimens at room temperature and heat treating at 590 ̋ C They investigated the properties of the thixoforged part. Previous studies on the semi-solid processing of 7075 aluminum alloy were mainly restricted to investigations in the field of thixotropic feedstock preparation criteria and producing some thixoformed parts. The present work aims to investigate the phase evolution and kinetics of partial remelting during isothermal treatment in the mushy zone and the semi-solid deformation behavior of AA7075 alloy
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