Modification of Eutectic Si in Hypoeutectic Al-Si Alloys with Erbium Addition

Effect of erbium (Er) on the eutectic Si morphologies in hypoeutectic Al-Si based alloys was investigated using thermal analysis and microstructure examination. The microstructural observations show that the addition of Er causes significant modification of the eutectic silicon morphology from a coarse plate-like to a fine fibrous one. Furthermore, the results of thermal analysis reveal that the addition of Er decreased the temperatures of eutectic nucleation and growth, and increased the eutectic undercooling. The eutectic undercooling caused by the presence of Er plays an important role in the modification of eutectic silicon.</jats:p

Primary Si refinement and eutectic Si modification in Al-20Si via P-Ce addition

Abstract Enhancing the mechanical properties of hypereutectic Al-Si alloys by refining the primary and eutectic Si morphology is very challenging. In this study, the refinement mechanism of primary and eutectic Si morphologies via the simultaneous addition of P-Ce into the Al-20Si alloy was studied. Microstructural analysis revealed that the primary and eutectic Si morphologies were significantly refined, which increased the tensile strength. Furthermore, the addition of Ce, up to 0.6 wt%, can result in the formation of Ce-rich intermetallic phases, which may lead to a significantly increased tensile strength while retaining the ductility of the alloy. The ultimate tensile strength of the Al-20Si alloy increased from 96 to 175 MPa, and the elongation increased from 1.0% to 1.7% with the addition of P-Ce. Moreover, the wear resistance of the alloy improved. The added P and Ce did not react with each other to form an intermetallic compound; therefore, this method can simultaneously refine primary and eutectic Si.</jats:p

Effect of post-processing treatments on surface roughness and mechanical properties of laser powder bed fusion of Ti–6Al–4V

This study focuses on enhancing the surface characteristics of Ti–6Al–4V alloy fabricated through laser powder bed fusion (LPBF), a prominent additive manufacturing technique. The primary objective is to assess the impact of post-processing surface treatments on the surface roughness, microstructure, and mechanical properties of LPBF Ti–6Al–4V. As-built specimens with fully dense structures underwent sandblasting (SB), chemical etching (CE), and a combination of sandblasting and chemical etching (SB + CE). The investigation reveals significant variation in the surface morphology of as-built samples, primarily influenced by factors such as spattered particles, powder adhesion, and the stair-step effect. In the as-built condition, the down-skin exhibited the highest particle adhesion, covering 11.9 % of the surface. Sandblasting proved particularly effective in removing adhered particles, reducing surface roughness to 5.1 μm from an initial value of 17.8 μm for the down-skin surface. Furthermore, combining sandblasting and chemical etching was more effective than chemical etching alone in achieving uniform surface profiles. Tensile testing indicated that while the ultimate tensile strength remained unchanged, the strain at break significantly improved from 4.8 % to 11.5 %, representing a noticeable increase in ductility in post-processed samples compared to as-built conditions. These findings underscore the influence of post-processing treatments in mitigating surface roughness and enhancing ductility without compromising mechanical strength

The improvement of deformability in AA7075 alloy through cryogenic treatment and its correlation with microstructural evolution and FE modelling

Abstract Cryogenic treatment has high potential for improving the deformation behavior through the recrystallization at a low temperature. In this work, true stress–strain curves were obtained via compression tests to understand the deformation behavior of an AA7075 under cryogenic conditions. Results showed a significant improvement in the flow stress of AA7075, increasing from 260 to 560 MPa at the yield point. The strain hardening exponent (n) also increased from 0.25 to 0.35 after deformation at cryogenic temperatures. The presence of Al2CuMg phase influenced the deformation texture of the tested aluminum alloy, resulting in more elongated grains and fine sub-grains after deformation at cryogenic temperatures, due to the hindered recrystallization. Microstructure evolution after deformation at room and cryogenic temperatures was investigated using EBSD technique to characterize texture and recrystallized grains. The results indicated that the spacing of the high-angle grain boundaries (HAGBs) in the sample deformed at room temperature was slightly larger than in the cryogenically treated sample. The alloy deformed at the cryogenic temperature exhibited a higher strain hardening exponent (n = 0.35) compared to room temperature deformation (n = 0.25). Furthermore, finite element analysis supported the experimental findings, showing that the Plastic Equivalent Strain (PEEQ) of the model tested at cryogenic temperature was higher than at room temperature, attributed to grain refinement during low-temperature deformation. The calculated effective stress responses at cryogenic temperatures for the investigated flow stress aligned well with the experimental results. These new aspects and mechanisms of deformation of aluminum alloys at cryogenic temperatures can improve the formability of high-strength alloys in the future production of more complex and integrated lightweight components