Microstructures, Mechanical and Creep Properties of Rapidly Solidification/Powder Metallurgy Mg-6wt.%Zn Alloys with 5wt.%Ce and 1.5wt.%Ca Additions

Rapidly solidification/powder metallurgy (RS/PM) Mg-6Zn, Mg-6Zn-5Ce and Mg-6Zn-5Ce-1.5Ca (wt.%) alloys were produced via hot extrusion with RS powders, produced by atomization-twin roll quenching. Microstructures, mechanical and creep properties of the alloys were investigated. The results showed that for the Mg-6Zn alloys with 5wt.%Ce and 1.5wt.%Ca additions, the microstructures of the alloys were gradually refined, which caused the strength of the alloy at room temperature to increase remarkably, especially for the RS/PM Mg-6Zn-5Ce-1.5Ca alloy, exhibited a high compressive strength of 394MPa at room temperature. At elevated temperatures, due to the fine and stable intermetallic compounds i.e. MgxZnyCez and MgxZnyCez-(Ca) phases were formed for the Mg-6Zn-5Ce alloy and Mg-6Zn-5Ce-1.5Ca alloys, respectively, and the thermal stability of the ternary phase was a little lower than that of the quaternary phase because of the dissolving of Ca into the MgxZnyCez phase, the mechanical and creep properties at elevated temperatures increased remarkably with Ce and Ca additions, especially for the RS/PM Mg-6Zn-5Ce-1.5Ca alloy, which exhibited a high compressive strength of 258MPa at 200°C, and the minimum creep rate was decreased about 2 times, compared with that of the Mg-6Zn-5Ce alloy.

Dilatometer Study of Aluminium-Silicon Based Alloys with Metastabile Structures

Aluminum-Silicon alloys are sought in a large number of automotive and aerospace applications due to their low coefficient of thermal expansion and high wear resistance. The fine structure of Si precipitates is controlled by forced solid solution structure obtainable by rapidly solidification techniques [1, 2, 3]. Present study focuses on precipitation of silicon in Al88Si12 as a function of temperature by dilatometer analysis. Different structures out of equilibrium have been obtained after casting in sand, black-lead and steel mould and by melt spinning. The average value of the activation energy for the precipitation of Si in steel mould casting of eutectic composition was found to be 47 kJ/mol. Our dilatometer studies were complemented by metallographic microscopy and XRD measurements.

Rapidly Solidified AZ31 Magnesium Alloy Ribbons Used in Rechargeable Batteries

Better properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries. However, the magnesium alloy thin sheets used in rechargeable batteries were produced by ingot casting and rolling. That technology was so complex and the cost was high. Rapidly solidification by melt spinning is an effect way to solve that problem. In this paper, the technology of rapidly solidified (RS) ribbons in Mg-3%Al-1%Zn-0.2%Mn alloy has been investigated using melt spinning technique. The effect of wheel speed on thickness and microhardness of the ribbons is presented. Microhardness is found to increase with the wheel speed. Rapidly solidification leads to small grains (1~2 µm). The plasticity of the ribbons was well. The quantity of Mg17Al12 decreases with the increase in wheel speed. When the wheel speed reaches 1600 rpm, no Mg17Al12 phase precipitates. As the increase of the wheel speed, the corrosion resistance of the ribbons changes better.

Evolution of intrinsic coercivity in Pt-Co-B alloys

New permanent magnets based on Pt-Co-B ternary alloys have been developed by rapidly solidification with subsequent heat treatments. The coercivity achieved in the Pt-Co-B ternary alloys is more than double the highest coercivity observed in the Pt-Co binary system. Good thermal stability of the coercivity produced by annealing provides a basis for consolidation processes such as hot isotropic pressing to produce bulk magnets from the rapidly solidified Pt-Co-B materials. Increased coercivity coupled with special properties such as high Curie temperature, corrosion resistance and ductility may expand the potential applications for these alloys. The evolution of microstructure and its effect on coercivity from annealing the as-quenched materials are investigated to understand the magnetic hardening mechanism and optimize the magnetic properties.