Materials Science Forum Vols. 828-829

Abstract: Research into magnesium die-cast alloys from the Mg-Al-(Zn), Mg-Zn-(Al), Mg-rare earth (RE) and Mg-Al-RE systems is discussed. Particular attention is paid to factors influencing mechanical properties and castability. The nature and level of alloy addition is in all cases an important determinant of castability (cracking and fluidity) and mechanical properties (strength, ductility and creep resistance). The interplay of these factors shows considerable variation between different alloy systems.

Abstract: In the present paper, we introduce the development of casting an industrial component with a newly developed high strength aluminium alloy for high pressure die casting, including the introduction of property requirement, and the simulation results of temperature distribution, air entrapment, air pressure and the porosity potential in the casting, overflows and gating system. The microstructure and mechanical properties of the casting with satisfied quality are described under as-cast and heat-treated conditions.

Abstract: Magnesium as the lightest structural metal offers significant potential weight saving compared with steel and aluminium. Cast magnesium components are widely used, e.g. as engine blocks or gear box housings. To open more opportunities for weight saving, it is necessary to widen the application fields to wrought products, such as large thin walled components for which sheets as semi-finished products are needed. The production and processing of magnesium sheets material is currently hampered by the limited formability of magnesium and high costs. The use of the twin-roll casting (TRC) as a cost-effective manufacturing process and the development of new calcium-containing alloys are leading to a decisive reduction of those obstacles.

Abstract: In this study, grain refinement efficiency of a new oxide master alloy based on MgAl₂O₄ was demonstrated in Al alloys. The grain size of the reference alloy was reduced by 50-60% with the addition of the master alloy and introduction of ultrasonic cavitation. While cooling rate has an influence on the grain size reduction, higher levels of addition of master alloy was found to be not effective in further reducing the grain size.

Abstract: The hypoeutectic Al-7Si-1Cu-0.5Mg (wt%) alloy was modified with micro-additions of Zr, V and Ti in order to improve its thermal stability. As revealed by a number of experimental techniques, Cu and Mg rich phases along with the eutectic Si dissolved in the temperature range from 300 to 500°C. At the same time, the (AlSi)_x(TiVZr) phases containing transition metals were present up to 696–705°C. During isochronal aging, the modified alloy exerted different aging characteristics than the reference A380 grade with a higher peak hardness and a lower temperature of alloy softening. Micro-additions of Ti, V and Zr positively affected the alloy strength during testing both in as-cast state and after T6 heat treatment. Improvements in tensile and compressive strength as compared to the reference alloy were preserved up to temperatures over 200 °C with more positive effect seen for the T6 state.

Abstract: Intensive melt shearing is a process that can be used for mixing ceramic particles into magnesium melt. It applies shear stress to the melt and can de-agglomerate nanoparticle additions to magnesium melts without the use of electromagnetic fields or ultrasound. A wrought magnesium alloy AM30 was selected for processing with intensive melt shearing and subsequent twin-roll casting. AM30 with additions of CaO and SiC were also processed by this route and the hardness and microstructure were investigated. Sheets were rolled and their tensile strength was determined. The work was done as part of the European Union research project ExoMet. Its target includes the production of high-performance magnesium-based materials by exploring novel grain refinement and nanoparticle addition in conjunction with melt treatment by means of external fields.

Abstract: With the increasing use of recycled aluminium alloys from the end-of-life products more and more iron is accumulated into the compositions of alloys. Sometimes, recycling causes the iron levels to increase beyond the set target levels for down-stream processing. The only way to deal with this impurity currently in industry is to increase the primary aluminium added to the furnace to dilute the melt and re-add all other elements or cast it for re-melting or extrude it for products that is not surface finish critical or required higher corrosion resistance. Formation of small well dispersed spherical a- or small b- Fe-bearing intermetallics, which can be homogenised for shorter times and has no negative effect on downstream processing, would be promising even if the iron levels are above the targeted compositional limits. In the present paper, fine and dispersed Fe-bearing intermetallics have been achieved by Melt Conditioned DC (MC-DC) casting technology, instead of coarser Fe-bearing intermetallics forming network like morphology in the DC castings with grain refiner additions (DC-GR). This suggests feasibility of an increased tolerance of iron levels by melt conditioned DC casting technology.

Abstract: This work is based on investigation of the influence of electromagnetic fields and ultrasonic vibrations and their combination on the resulting microstructure of an AA7449 aerospace aluminium alloy. The results demonstrate the application of the compound electro-magnetic and ultrasonic fields under optimum conditions delivers not only a refined microstructure but also consistent distribution of chemical composition. It suggests an alternative method for producing high strength aerospace alloys which could not be refined through conventional addition of chemical grain refiners.

Abstract: The effect of Al-5Ti-1B grain refiner addition on solidification microstructure, especially the formation of the binary eutectic (Al)+Al₁₅(Fe,Mn)₃Si₂ was investigated in Al-5Mg-2Si-0.7Mn-1.1Fe (wt.%) alloy. The experimental results showed that the solidification microstructure were consisted of primary α-Al phase, inter dendritic binary eutectic (Al)+Al₁₅(Fe,Mn)₃Si₂, and ternary eutectic (Al+Mg₂Si+Al₁₅(Fe,Mn)₃Si₂). The heterogeneous nucleation of the primary (Al) phase in the alloys was greatly enhanced by the Al-5Ti-1B grain refiner, refining the (Al) grains significantly. The subsequent binary eutectic was nucleated on these refined (Al) phase. Consequently, the size of Al₁₅(Fe,Mn)₃Si₂ phase with a Chinese script morphology in the binary eutectic was greatly refined, without much change in the secondary branch spacing.