Norbert Hort

Effects of Gadolinium and Neodymium Addition on Young’s Modulus of Magnesium-Based Binary Alloys

In order to investigate the influence of solute atoms and particles on Young’s modulus of magnesium, series of binary Mg–Gd and Mg–Nd alloys were prepared using hot extrusion. With increasing Gd content from 0 to 2.654 at.% Young’s modulus of Mg–Gd alloys increases linearly from 44.0 to 45.3 GPa. Regarding Mg–Nd alloys, Young’s modulus firstly decreases to 42.5 GPa until 0.184 at.% Nd, and then increases to 43.4 GPa at Mg–0.628 at.% Nd. The different influences of solutes Gd and Nd on Young’s modulus of Mg are attributed to their different solid solution behaviors in magnesium, which can lead to the alterations of crystal cell parameters and/or different amount of second phases. For Mg–Gd alloys the lattice parameters increase and the axial ratio (c/a) decreases with Gd content increasing. In contrast, for Mg–Nd alloys they almost keep unchanged due to small solubility of Nd in Mg when Nd content increases.

Mg Alloys: Challenges and Achievements in Controlling Performance, and Future Application Perspectives

In recent years, Mg alloys have made inroads into applications for transport industries. The favorable property profile of Mg promotes increased usage. Despite magnesium alloys being used for years, there is still a lack of knowledge about the potential of Mg alloys. New or optimized alloys and processes are creating new ideas for substituting traditional materials. High-pressure die-casting (HPDC) is the predominant technology, while other casting and wrought processes are of secondary importance. Developments in the last decade have led to an improvement of the property profile and effectiveness of magnesium wrought alloys. Additive manufacturing has opened new opportunities for tailoring of the property profile and functionality. In addition, Mg as material for battery anodes adds a new field of application in the energy sector. This presentation will provide an overview of the status of modern process and alloy development, and discuss the challenges to extending the use of magnesium alloys in various applications.

3D Microstructural Evolution on Solidifying Mg–5Nd–5Zn Alloy Observed via In Situ Synchrotron Tomography

In situ synchrotron tomography is a unique technique to study 3D microstructure evolution during solidification due to the high brilliance of the beam and the short acquisition time of the detector systems. In this work, in situ synchrotron tomographic observations were performed during the solidification of Mg–5Nd–5Zn (wt%) alloy with a cooling rate of 5 °C/min. The experiment was performed at the TOMCAT beamline of the Swiss Light Source (Paul Scherrer Institute (PSI), Villigen, Switzerland). The sample was melted using a laser-based heating system and then cooled until completely solidified. 3D tomograms were acquired during solidification. The microstructural analysis starts after the coherency point until the end of solidification. A differential thermal analysis (DTA) experiment was performed to estimate the liquidus and solidus temperature of the alloy. These values were used to correct the measured temperature from the in situ solidification experiment. Different microstructural parameters such as the volume fractions of the phases, i.e. α-Mg dendrites, interdendritics and pores, as well as the interconnectivity and skeletonization results are discussed.

Influences of Yttrium Content on Microstructure and Mechanical Properties of as-cast Mg–Ca–Y–Zr Alloys

The microstructure and mechanical properties of as-cast Mg–Ca–Y–Zr alloys with different Y contents were investigated. The alloy containing 0.5 wt% Y exhibited finer grains compared to the alloys with higher Y content. All alloys had a dendritic microstructure with eutectics composed of α-Mg and Ca-rich intermetallic phases. Few Mg–Y-rich intermetallic particles were also found along grain boundaries. EDS analysis showed that the solute Y segregated at dendritic and grain boundaries. The amount of Y contained in eutectics remarkably increased with increasing Y. In addition, the eutectics volume fractions of all alloys were comparable but the morphology became less continuous at higher Y contents. Both the room temperature tensile and compressive strengths were largely improved with increasing Y content. Moreover, the elevated temperature compression tests showed that the compressive yield strength first decreased slightly when the temperature rose to 175 °C, but then remained stable as the temperature increased.

Intermetallic Phase Characteristics in the Mg–Nd–Zn System

Neodymium, a Rare Earth with low solid solubility in Mg is an ideal alloying element to improve the yield strength and creep resistance cost effectively. The addition of Zn achieves a further improvement; however, its influence on the intermetallic phases in the Mg–Nd–Zn ternary system is not yet fully understood. A Mg-5Nd alloy modified with 3, 5 and 7 wt% of Zn was investigated with in situ synchrotron radiation diffraction during cooling from the molten state to 200 °C in order to investigate the phase-formation and -transformation characteristics of the alloys. The synchrotron diffraction results have been complemented with TEM investigations on the as-solidified samples. The results suggest that Zn has a strong effect on the microstructure by stabilizing the Mg3Nd phase and accelerating the precipitation formation. The experimental results do not fully comply with the theoretical calculations, indicating the necessity of improving the thermodynamic databank for this alloy system.

Microstructure and Mechanical Properties of Mg-Gd Alloys as Biodegradable Implant Materials

Mg alloys attract more and more attentions for biomedical applications. Mg-Gd alloys were designed as biodegradable implant materials which combine favorable mechanical and corrosion properties. In this work, the microstructure and mechanical properties of binary Mg-2Gd, ternary Mg-2Gd-(Ag, Ca) and quaternary Mg-2Gd-2Ag-0.4Ca alloys were investigated. The alloys were prepared by permanent mould casting. The results show that the additions of Ag and Ca had significant influences on the microstructure and mechanical properties of Mg-2Gd alloy. Ag and Ca additions affect the formation of second phases. A quaternary Mg-Gd-Ag-Ca second phase was found in the quaternary alloy. Both the hardness and tensile yield strength were improved by adding Ag and Ca to 2 wt% Gd-containing alloys due to grain refinement and formation of different intermetallic phases (IMPs). Furthermore, the addition of Ag and Ca can apparently enhance the age hardening of Mg-2Gd alloy.

Magnesium Pistons in Engines: Fiction or Fact?

Magnesium alloys are already widely used in numerous applications in transportation and consumer products. Ways have been found to improve corrosion and creep resistance, formability in general, and processing routes have been optimized. But would Mg alloys also be suitable for use in an environment where friction, corrosion, thermal fatigue and creep resistance at elevated temperatures are issues? Due to lightweighting benefits, pistons would be an ideal application for Mg based materials. It is much more efficient to accelerate and to decelerate a lightweight material compared to a heavier one. Al alloy pistons are already fairly well established. But Mg could provide further benefits compared with Al due to its specific strength and mass. We will report the state of the art in Mg pistons, with our own and others approaches to improve properties and the challenges that Mg pistons have to face.

Magnesium-Based Metal Matrix Nanocomposites—Processing and Properties

It is well known that magnesium alloys reinforced with ceramic particles of micro-scale sizes give increased hardness and wear resistance. However, such particles need to be smaller to improve the strength, ductility and creep resistance of alloys. The optimum size of particles for Orowan strengthening is a diameter less than 100 nm. Not only the size of particles, but also their chemical composition and the composition of the alloy are important for the beneficial effect of nanoparticles. The mechanical properties can be tailored with much fewer nanoparticles compared to microparticles, because the interparticle spacing is much smaller. However, with large surface areas compared to their weight and low wettability, any deagglomeration of the nanoparticles in a magnesium melt is difficult to achieve and so requires additional processing, such as by electromagnetic or ultrasound-assisted stirring. This paper presents a short review and some original work on ceramic nanoparticle reinforced magnesium alloys and their properties.