Phase formation during solidification of Mg-Nd-Zn alloys: An in situ synchrotron radiation diffraction study

Mg-4Nd base alloys with Zn additions of 3, 5 and 8 wt % were investigated with in situ synchrotron radiation diffraction during solidification. This method enabled the investigation of phase formation and transformation in the alloys. The diffraction results were supported with TEM observations on the as-solidified samples. The results show the effect of increased Zn addition on stabilizing the Mg3RE phase (RE—rare earth). The experimental results agree only partially with the theoretical calculations indicating the need to improve the existing thermodynamic database on the alloy syste

Ultrasound assisted casting of an AM60 based metal matrix nanocomposite, its properties, and recyclability

An AM60 magnesium alloy nanocomposite reinforced with 1 wt % of AlN nanoparticles was prepared using an ultrasound (US) assisted permanent-mould indirect-chill casting process. Ultrasonically generated cavitation and acoustic streaming promoted de-agglomeration of particle clusters and distributed the particles throughout the melt. Significant grain refinement due to nucleation on the AlN nanoparticles was accompanied by an exceptional improvement in properties: yield strength increased by 103%, ultimate tensile strength by 115%, and ductility by 140%. Although good grain refinement was observed, the large nucleation undercooling of 14 K limits further refinement because nucleation is prevented by the formation of a nucleation-free zone around each grain. To assess the industrial applicability and recyclability of the nanocomposite material in various casting processes, tests were performed to determine the effect of remelting on the microstructure. With each remelting, a small percentage of effective AlN nanoparticles was lost, and some grain growth was observed. However, even after the third remelting, excellent strength and ductility was retained. According to strengthening models, enhanced yield strength is mainly attributed to Hall-Petch strengthening caused by the refined grain size. A small additional contribution to strengthening is attributed to Orowan strengthening

Effects of Er and Zr Additions on the As-Cast Microstructure and on the Solution-Heat-Treatment Response of Innovative Al-Si-Mg-Based Alloys

The microstructure of Al-Si-Mg alloys strongly depends on their chemical composition and the heat treatment they undergo during production. The influence of solution heat treatment (SHT) and the addition of Er and Zr on the microstructure of gravity-cast A356 (Al-7Si-0.4Mg) were examined. The reference as-cast microstructure is characterized by the grain size and morphology of eutectic Si, as well as the morphology, area fraction, and chemical composition of the intermetallic compounds. The morphology of eutectic Si is unstable during SHT; the evolution mechanisms can be described using thermodynamic and kinetic models and have been validated using optical and scanning electron microscope (SEM) micrographs. The effect of high-temperature exposure during SHT, on the other hand, plays a minor role on the quantity and morphology of the intermetallic compounds, as demonstrated by optical and SEM micrographs

Additive manufacturing of an Fe–Cr–Co permanent magnet alloy with a novel approach of in-situ alloying

Additive manufacturing has become increasingly important in the production of magnetic materials in recent years due to the great demands for miniaturization and complex-shaped magnet parts. In this study, the laser beam-powder bed fusion process (LPBF) has been used to develop an in-situ alloying process for the additive manufacturing of a permanent magnet material of the Fe–Cr–Co system. This novel method allows for the production of complex alloys with a chemical composition suited to each specific case of application, achieved by using elemental powders or simpler commercial alloy powders as base materials. The core focus of this study has been on the development and characterization of the printing process using a Fe-30.5Cr-15Co-1.5Mo alloy. The in-situ alloying process has been developed by performing melt pool tests on the two main component powders Fe and Cr and by conducting parameter studies using two different powder mixtures with different sphericity of their components. The influence of different printing parameters and post-printing treatments on the chemical homogeneity and magnetic properties has been studied for selected samples. In addition, magnetic measurements at different temperatures have been performed to investigate the temperature stability of the magnetic properties of the 3D printed material. Impact Statement As by today, the current amount of research done on the additive manufacturing of magnetic materials is rather low. Most of research is focused on rare- earth containing magnetic materials. In this work therefore, we are taking another direction in which we will show that LPBF combined with in- situ alloying is an ideal method for the production of a great variety of different rare- earth free magnetic materials. The positive results of our work can both have an influence on the the scientific community, as further research in the field on different promising rare- earth free magnetic materials is to be expected. Furthermore, a positiv economic impact may occur since the production of rare- earth free magnetic materials is dependent on different raw material sources which are both more cost- effectiv and less critical in terms of their supply chain. This effect is also accompanied by a positive environmental impact, since the mining of rare- earth metals usually comes with considerable environmental pollution

Characterization of localized corrosion of heat treated Er- and Zr-containing A356 alloys in 3.5 wt% NaCl aqueous solution

The influences of Er and Zr additions on the corrosion behavior of A356 (Al-7Si-0.4Mg) alloy are investigated. Electrochemical tests (potentiodynamic polarization and electrochemical impedance spectroscopy), gravimetric analyses, and microstructural investigations demonstrate that 0.3 wt% Er nominal addition is beneficial for the corrosion resistance of A356 alloy, due to a modified eutectic morphology and a low volume fraction of intermetallic compounds. The further addition of about 0.5 wt% Zr, on the other hand, partially reduces the corrosion resistance of Er-containing A356 alloy, possibly due to a higher amount of intermetallic compounds which promote corrosion localization

The Role of Zn Additions on the Microstructure and Mechanical Properties of Mg–Nd–Zn Alloys

Mg-rare earth alloys have improved yield strength and creep resistance compared to commercial alloys such as AZ91, AM60 or AS21. The influence of Zn additions in Mg–Nd alloys on intermetallic phases and the resulting changes in the macroscopic mechanical behaviour of the materials are not yet fully understood. The aim of this work is to identify the effect of Zn additions on the nature of the intermetallic phases and on the mechanical properties in a Mg–4Nd (wt%) alloy. The addition of 8 wt% Zn to a base Mg–4Nd wt% alloy marginally improved the tensile and compression properties at room temperature or at 200 °C with the exception of the 0.2% proof stress of Mg–4Nd–8Zn alloys when tensile- or compression-tested at 200 °C. Two intermetallic phases, a quasi-binary Mg$_3$(Zn, Nd) and ternary Mg$_{50}$Nd$_{8}$Zn$_{42}$, have been identified by the means of electron microscopy and synchrotron diffraction. These results indicate that there are some discrepancies in the current thermodynamic calculations, suggesting an update to the databases may be required

Corrosion and creep resistance of Thixomolded® magnesium alloys

German Ministry of Education and Researc