Papers by Keyword: Eutectic Phases

Abstract: The impact of cooling rates on the microstructural evolution of an Al-Sr eutectic alloy was investigated. Two distinct cooling rates, 0.02 and 57.12 °C/s, were employed during the solidification process. To elucidate the characteristics of phase transformations and microstructural evolution during solidification, thermal analyses were conducted on the recorded cooling curves. Both the first and second derivatives of these curves were examined. At the slower cooling rate, the microstructure predominantly consisted of the eutectic Al phase and the eutectic Al-Sr phase, as identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Conversely, at the higher cooling rate of 57.12 °C/s, primary Al phases were observed, indicating a significant departure from equilibrium solidification conditions. Additionally, a substantial quantity of nanosized eutectic Al-Sr particles was detected, resulting in a markedly refined microstructure.

Abstract: The effects of cooling rates on the microstructure development of an Al-Fe eutectic alloy were studied. Two different cooling rates of 0.03 and 61.00 °C/s were applied to the solidifying alloys. To unfold the characteristics of phase changes and the microstructure evolution taking place during solidification, the recorded cooling curves based on temperature measurements were analyzed by thermal analyses, in which the first and second differences of the cooling curves were derived. The slow cooling resulted in the formation of only the eutectic Al phase and the eutectic Al-Fe phase in the microstructure identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). With the cooling rate increasing to 61.00 °C/s, the primary Al phase appeared, as the solidification became strongly non-equilibrium. A large quantity of the nanosized eutectic Al-Fe particles were detected. Overall, the microstructure refined substantially.

Abstract: Forging processes, such as liquid forging, rheoforging and thixoforging process, were used in this study as an effective method for manufacturing high-strength, finely-dispersed and highly-uniform AZ91D alloy parts. It has been found that although the microstructures of the three forging parts are all composed of α-Mg and β-Mg₁₇Al₁₂ phases, their shapes, sizes, numbers and distributions are all different, which also influences their mechanical properties. The tensile fracture morphologies were observed and their energy spectrums were analyzed by scanning electron microscopy. The results show that the cracks are mainly originated from the brittle fracture of the β-Mg₁₇Al₁₂ eutectic phases, whereas their fracture morphologies are greatly different, which indicate the direction for providing a reasonable forging process.

Abstract: Aluminum-Lithium alloys were developed as major replacements for existing aluminum alloys to reduce the weight of aircraft and aerospace structures. Mechanical properties of Al-Li alloys greatly depend on solidification conditions. Other than reducing the microsegregation, homogenization treatment has other effects on the microstructure of Al-Li ingots. In this research, effects of homogenization treatment at constant temperature (500°C) on the precipitation in the microstructure of Al-1Li-3Cu-0.1Zr (wt %) and Al-2Li-3Cu- 0.1Zr (wt %) specimens have been investigated. Results show that homogenization at 500°C for 24 hours not only increases the hardness and phases precipitating in grain but also reduces microsegregation of Fe in grain boundaries.

Abstract: The formation of eutectics in Al–Zn–Mg–Ni and Al–Zn–Mg–Si systems is studied by means of metallography, DSC, EPMA, X-ray spectroscopy and thermodynamical calculations. Polythermal sections of the corresponding phase diagrams are constructed. The concentrations and temperatures of binary eutectic reactions L → (Al) + Al3Ni and L → (Al) + Mg2Si in quaternary alloys are determined. Nonequilibrium solidification in Al–7% Zn–3% Mg-based alloys ceases at approximately 480 °C. The alloys close by composition to binary eutectics have considerably improved casting properties as compared to the base Al–7% Zn–3% Mg composition. In particular, hot tearing susceptibility is much less in alloys with Al3Ni or Mg2Si. These results are corroborated by measurements of thermal contraction during solidification. The alloys containing binary eutectics exhibit much lower temperatures of contraction onset and less thermal strain is accumulated in the solidification range. Fine eutectic morphology enables fragmentation and spheroidization of intermetallic particles during annealing. The presence of Al3Ni and Mg2Si particles does not decrease the precipitation hardening effect associated with precipitation of the T′ (AlMgZn) phase. Improved casting properties and good mechanical properties of castings allow the application of Al–Zn–Mg alloys with binary eutectics formed by Al3Ni or Mg2Si as foundry alloys.