Effect of Aluminium Content on the Tensile Properties of Mg-Al-Zn Alloys

ABSTRAC

Greenhouse Gas Emissions Payback for Lightweighted Vehicles Using Aluminum and High-Strength Steel

In this article we consider interactions between life cycle emissions and materials flows associated with lightweighting (LW) automobiles. Both aluminum and high-strength steel (HSS) lightweighting are considered, with LW ranging from 6% to 23% on the basis of literature references and input from industry experts. We compare the increase in greenhouse gas (GHG) emissions associated with producing lightweight vehicles with the saved emissions during vehicle use. This yields a calculation of how many years of vehicle use are required to offset the added GHG emissions from the production stage. Payback periods for HSS are shorter than for aluminum. Nevertheless, achieving significant LW with HSS comparable to aluminum-intensive vehicles requires not only material substitution but also the achievement of secondary LW by downsizing of other vehicle components in addition to the vehicle structure. GHG savings for aluminum LW varies strongly with location where the aluminum is produced and whether secondary aluminum can be utilized instead of primary. HSS is less sensitive to these parameters. In principle, payback times for vehicles lightweighted with aluminum can be shortened by closed-loop recycling of wrought aluminum (i.e., use of secondary wrought aluminum). Over a 15-year time horizon, however, it is unlikely that this could significantly reduce emissions from the automotive industry, given the challenges involved with enabling a closed-loop aluminum infrastructure without downcycling automotive body structures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79236/1/j.1530-9290.2010.00283.x.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/79236/2/JIEC_283_sm_SuppMatS1.pd

Energy and carbon audit of a rooftop wind turbine

Abstract: Microgeneration is being promoted as a means of lowering carbon dioxide (CO2) emissions by replacing electricity from the grid with production from small domestic genera-tors. One concern over this drive is that the use of smaller plant could lead to the loss of econ-omies of scale. Partly, this relates to cost but also in terms of energy consumed and CO2 emitted over the life cycle of the microgenerator. Here, an analysis is presented of a life-cycle audit of the energy use and CO2 emissions for the ‘SWIFT’, a 1.5 kW rooftop-mounted, grid-connected wind turbine. The analysis shows that per kilowatt-hour of electricity generated by the turbine, the energy intensity and CO2 emissions are comparable with larger wind turbines and significantly lower than fossil-fuelled generation. With energy and carbon intensities sensitive to assumed levels of production, assessments were carried out for an annual production range of 1000–4000 kWh, representing capacity factors of 8–31 per cent. For the manufacturer’s estimated production of 2000 to 3000 kWh and, giving credit for component recycling, the energy payback period was found to be between 17 and 25 months, whereas the CO2 payback was between 13 and 20 months. Across the full production range, the energy and carbon payback periods were 13–50 months and 10–39 months, respectively. A key outcome of the study is to inform the manufacturer of the opportunities for improving the energy and carbon intensities of the turbine. A simple example is presented showing the impact of replacing one of the larger aluminium components with alternative materials

Pyrolysis and ignition of a polymer by transient irradiation

Pyrolysis is the thermochemical process that leads to the ignition of a solid fuel and a key mechanism in flame spread and fire growth. Because polymer materials are flammable and ubiquitous in the modern environment, the understanding of polymer pyrolysis is thus essential to tackle accidental fires. In this paper, we used transient irradiation as an external source of heat to study the process of pyrolysis and ignition of a polymer sample. While previous ignition studies use constant irradiation, transient irradiation is the most frequent condition found in accidental fires, but it lacks a theoretical framework since it has been largely ignored in the literature. Moreover, transient irradiation is a more comprehensive case for the understanding of pyrolysis where nonlinear heat transfer effects challenge the validity of solid-phase criteria for flaming ignition developed previously. We propose here that transient irradiation is the general problem to solid fuel ignition of which constant irradiation is a particular solution. In order to investigate how this novel heat source in uences polymer pyrolysis and flammability, numerical simulations and experiments have been conducted on Poly(methyl methacrylate) (PMMA) samples 100mm by 100mm and 30mm deep exposed to a range of parabolic pulses of irradiation. The 1D model, coded in GPyro, uses heat and mass transfer and single-step heterogeneous chemistry, with temperature dependent properties. The predictions are compared to experiments conducted in the Fire Propagation Apparatus using both constant and transient irradiation conditions. The experiments validate the temperature predictions of the model and also provide the time to ignition. The model then complements the experiments by calculating the mass loss rate. A series of 16 parabolic pulses (including repeats) are investigated with a range of peak irradiation from 25 to 45 kW/m2, while the time to peak ranges from 280 to 480s. For these pulses, the time to ignition measurements range from 300 to 483s. The model can predict the in-depth temperature profiles with an average error lower than 9%. Model and experiments are then combined to study the validity of the solid-phase criteria for flaming ignition found in the literature, namely critical temperature, critical mass loss rate, critical energy and critical time-energy squared. We find that of these criteria, the best predictions are provided by the critical mass loss rate followed by the critical temperature, and the worst is the critical energy. Further analysis reveals the novel concept of simultaneous threshold values. While the mass loss rate is below 3g/m2 and the surface temperature is below 305ºC, ignition does not occur. Therefore these threshold values when exceeded simultaneously establish the earliest time possible for ignition

Strength-ductility behaviour of Al-Si-Cu-Mg casting alloys in T6 temper

A comparative study of the mechanical properties of 20 experimental alloys has been carried out. The effect of different contents of Si, Cu, Mg, Fe and Mn, as well as solidification rate, has been assessed using a strength-ductility chart and a quality index-strength chart developed for the alloys. The charts show that the strength generally increases and the ductility decreases with an increasing content of Cu and Mg. Increased Fe (at Fe/Mn ratio 0.5) dramatically lowers the ductility and strength of low Si alloys. Increased Si content generally increases the strength and the ductility. The increase in ductility with increased Si is particularly significant when the Fe content is high. The charts are used to show that the cracking of second phase particles imposes a limit to the maximum achievable strength by limiting the ductility of strong alloys. The (Cu + Mg) content (at.%), which determines the precipitation strengthening and the volume fraction of Cu-rich and Mg-rich intermetallics, can be used to select the alloys for given strength and ductility, provided the Fe content stays below the Si-dependent critical level for the formation of pre-eutectic alpha-phase particles or beta-phase plates