In this study, the potential applications of Al-Mn-Mg 3004 alloy at elevated temperature have been evaluated through the systematic study of the precipitation behavior of α-Al(MnFe)Si dispersoids and their effect on material properties during precipitation treatment and long-term thermal holding. The results demonstrate a significant dispersion strengthening effect caused by the precipitation of fine uniformly distributed dispersoids during precipitation treatment. The peak compression yield strength (YS) at 300°C of the experimental 3004 alloy can reach as high as 78 MPa due to a large volume fraction (~2.95 vol. %) of α-Al(MnFe)Si dispersoids. The dispersoids are found to be thermally stable at 300°C for up to 1000 h of holding, leading to consistently high mechanical performance and creep resistance. The superior and stable YS and creep resistance at 300°C enables the 3004 alloy to be applied to weight-sensitive applications at elevated temperatures.
The present work investigates the influence of adding Mo to an Al-Mn-Mg 3004 alloy on elevated-temperature properties as well as their thermal stability during longterm thermal holding at 350°C and 400°C. In as-cast and heat-treated conditions, both microhardness and yield strength increase with increasing Mo contents and reach peak values at 0.3 wt. % followed by a plateau. With an optimized Mo content (0.3 wt. %), the volume fraction of dispersoids is increased while the volume percentage of the dispersoid-free zone is greatly reduced compared to the base alloy free of Mo, resulting in the remarkable increases in elevated-temperature strength and creep resistance. The results of the long-term thermal holding show that compared with the rapid drop of elevated-temperature strength and creep resistance in the base alloy, the Al-Mn-Mg alloy with 0.3% Mo is thermally stable up to 350°C, exhibiting a slight decrease of stability at 400°C. The combination of high elevated-temperature properties and their excellent thermal stability at 350-400°C with Mo addition makes Al-Mn-Mg 3xxx alloys the promising candidates for elevated-temperature applications.
The iron-rich intermetallics in A206 type cast aluminum alloy (Al-4.5Cu-0.3Fe) were investigated using thermal analysis, interrupted quenching testing, and differential scanning calorimetry (DSC). An optical microscope with image analysis and scanning electron microscopy were used to identify and quantify the iron-rich intermetallics. Basically, two kinds of ironrich intermetallics, Chinese script Al 15 (FeMn) 3 (SiCu) 2 (a-Fe) and platelet Al 7 Cu 2 (FeMn) or Al 7 Cu 2 Fe (b-Fe), are found in the final microstructures of the A206 cast alloys. All the possible solidification reactions, precipitation temperatures, and nucleation mechanisms for the iron-rich phases were investigated systematically. It is found that both a-Fe and b-Fe phases can precipitate on the oxide films. The a-Fe can also nucleate on Al 6 (FeMnCu) and Al 3 Ti particles. In addition, the previously formed a-Fe phase is also favorable for the nucleation of the b-Fe phase formed subsequently. These nucleation events were not only observed metallographically but also supported by the calculated planar disregistries. A possible nucleation hierarchy has been suggested.
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