Light alloy castings for automotive applications: The case of Al vs Mg

The economical and environmental effects of mass reduction through Al and Mg primary alloys substitutions for cast iron and steel in automotive components are discussed using MF. Ashby's penalty functions method The viability of Mg alloy substitutions for existing Al alloy cast components is also considered. The cost analysis shows that direct, equal-volume, Al alloy substitutions for cast iron and steel are the most feasible in terms of the CAFE liability, followed by substitutions involving flat panels of prescribed stiffness. When the creation of CO2 associated to the production of Al and Mg is considered, the potential gasoline savings over the lifespan of the car compensate for the intrinsic environmental burden of Al in all applications, while electrolytic Mg substitutions for cast iron and steel are feasible for equal volume and panels only. Magnesium produced by the Pidgeon thermal process appears to be too primary energy intensive to be competitive in structural applications. Magnesium substitutions for existing Al alloy beams and panels are generally unviable. The current higher recycling efficiency of Al casting alloys confers Al a significant advantage over Mg alloys.

The effect of Cu addition and milling contaminations on the microstructure evolution of ball milled Al-Pb alloy during sintering

Al-10 wt.%Pb and Al-10 wt.%Pb-x wt.%Cu (x = 0-7.0) bulk alloys were prepared by sintering the mechanically alloyed powders at various temperatures. The microstructure changes of the as consolidated powders in the course of sintering were analyzed by differential scanning calorimetry, scanning electron microscopy, X-ray diffraction analysis and transmission electron microscopy. It has been found that, with respect to the Al-10 wt.%Pb-x wt.%Cu alloy, CuAl2 and Cu9Al4 phases formed in the milling process, and the amount of CuAl2 phase increased while the Cu9Al4 phase disappeared gradually in the sintering process. In both Al-10 wt.%Pb and Al-10 wt.%Pb-x wt.%Cu alloys, the sintering process results in the coarsening of Pb phase and the growth rate of Pb phase fulfills the Lifshitz-Slyozov-Wagner equation even though the size of the Pb phase was in nanometer range. The Pb particle exhibits cuboctahedral morphology and has a cubic to cubic orientation relationship with the Al matrix. The addition of Cu strongly depressed the growth rate of Pb. Contamination induced by milling has apparent influence on the microstructure of the sintered alloys. Al7Cu2Fe and aluminium oxide phases were identified in the sintered alloys. The cuboctahedral morphology of Pb particles was broken up by the presence of the oxide phase. (c) 2006 Elsevier B.V. All rights reserved.

Determination of strontium segregation in modified hypoeutectic Al-Si alloy by micro X-ray fluorescence analysis

Analysis of intra- and inter-phase distribution of modifying elements in aluminium-silicon alloys is difficult due to the low concentrations used. This research utilises a mu-XRF (X-ray fluorescence) technique at the SPring-8 synchrotron radiation facility X-ray source and reveals that the modifying element strontium segregates exclusively to the eutectic silicon phase and the distribution of strontium within this phase is relatively homogeneous. This has important implications for the fundamental mechanisms of eutectic modification in hypoeutectic aluminium-silicon alloys. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A new zirconium-rich master alloy for the grain refinement of magnesium alloys

A new zirconium-rich magnesium-zirconium master alloy (designated AM-cast) has been developed by the CRC for Cast Metals Manufacturing in collaboration with Australian Magnesium Corporation for use as a grain refiner for magnesium alloys that do not contain aluminium. This work describes the microstructural characteristics of this new grain refiner and its grain refining ability when added to different magnesium alloys under various conditions (alloying temperature from 680 °C to 750 °C; weight of melt from 1 kg to 150 kg and sample thickness from 7 mm to 62 mm). Owing to its highly alloyable microstructure, AM-cast can be readily introduced into molten magnesium at any temperature when assisted by a few minutes of stirring or puddling. Little sludge has been found at the bottom of the alloying vessel in these trials due to the fine zirconium particles contained in the master alloy. The recovery of zirconium is normally in the range from 40% to 60% with respect to 1% zirconium addition as the master alloy. It is shown that this new master alloy is an excellent grain refiner for aluminium-free magnesium alloys.