Influence of Fe and Mn on the Microstructure Formation in 5xxx Alloys—Part I: Evolution of Primary and Secondary Phases

The increasing demands for Al sheets with superior mechanical properties and excellent formability require a profound knowledge of the microstructure and texture evolution in the course of their production. The present study gives a comprehensive overview on the primary- and secondary phase formation in AlMg(Mn) alloys with varying Fe and Mn additions, including variations in processing parameters such as solidification conditions, homogenization temperature, and degree of cold rolling. Higher Fe alloying levels increase the primary phase fraction and favor the needle-shaped morphology of the constituent phases. Increasing Mn additions alter both the shape and composition of the primary phase particles, but also promote the formation of dispersoids as secondary phases. The size, morphology, and composition of primary and secondary phases is further affected by the processing parameters. The average dispersoid size increases significantly with higher homogenization temperature and large primary particles tend to fragment during cold rolling. The microstructures of the final soft annealed states reflect the important effects of the primary and secondary phase particles on their evolution. The results presented in this paper regarding the relevant secondary phases provide the basis for an in-depth discussion of the mechanisms underlying the microstructure formation, such as Zener pinning, particle stimulated nucleation, and texture evolution, which is presented in Part II of this study.

Limitation by iron and manganese on phytoplankton communities in the Drake Passage.

<p>The Southern Ocean (SO) accounts for over 40% of anthropogenically derived CO<sub>2</sub> uptake. It is the world’s largest High-Nutrient Low-Chlorophyll (HNLC) region and the scarcity of trace metals such as iron (Fe) drives phytoplankton composition and biomass build up. Besides Fe, manganese (Mn) is the second most abundant trace metal since it is present in the thylakoids. As dissolved manganese (dMn) concentrations in the Atlantic sector of the SO are very low (0.04 nM), phytoplankton growth may not only be limited by Fe but also by Mn availability, a theory previously described by Martin et al. (1990). However, mechanistic studies investigating the effects of multiple trace metals limiting or co-limiting on growth and photosynthesis are lacking. This study focuses on the identification of the Fe-Mn co-limitation of natural phytoplankton assemblages to elucidate the impact of different Fe and Mn additions on species composition. To this end, two shipboard Fe-Mn addition bottle incubation experiments were conducted during the ‘RV Polarstern’ expedition PS97 in the Western and Eastern Drake Passage (DP) in 2016. This study highlights the importance of Mn in the otherwise Fe-limited Drake Passage. From microscopy samples, the addition of Fe and Mn together triggered the highest abundance of the genus <em>Fragilariopsis sp.</em> in the Western DP. In the Eastern DP, the nanophytoplankton fraction, detected by flow cytometry, reached the highest abundance only when both trace elements were provided, confirmed by highest chlorophyll<em>-a</em> build up. Moreover, the distinct response of Mn depletion relative to the Fe depletion support the findings that Fe and Mn do not substitute to each other. This experimental study highlights that both trace elements act as drivers of the ecology across the Drake Passage.</p>

Effect of Small Additions of Cr, Ti, and Mn on the Microstructure and Hardness of Al–Si–Fe–X Alloys

The Al–Si–Fe system has drawn the attention of the scientific community due to its capacity to replace parts in several manufacturing industries, as this alloy system is very sensitive to small additions of transition metals. Therefore, the aim of this work is to study the effect of Cr, Ti, and Mn additions in the Al–20Si–5Fe (wt. %) alloy and to study the modification of the iron intermetallic and the microstructural refinement through the formation of secondary phases. Al–20Si–5Fe–X (X = Cr, Mn and Ti at 1.0, 3.0, and 5.0 wt. %) alloy ingots were prepared by arc melting furnace. The elemental chemical analysis was performed by X-ray fluorescence spectrometry (XRF). The microstructure of all samples was investigated by scanning electron microscopy and X-ray diffraction. Finally, microhardness was measured in order correlate the hardness with the formation of the different compounds. The highest hardness was found for the alloy with the 5 wt. % Cr. The addition of Ti and Mn raised the hardness by ~35 HVN (Vickers microhardness) when compared to that of AlSiFe master alloy. Important changes were also observed in the microstructure. Depending on the Cr, Ti, and Mn additions, the resulting microstructure was dendritic (CrFe), acicular (Ti5Si3), and “bone like” (Mn0.2Fe0.8), respectively.