The growing interest in environmental protection and the increased demand for fuel-efficient vehicles has created challenges for automobile producers all over the world. In order to decrease the effect of automobiles on climate change, automakers started considering substitutions of materials in the automobile parts with less harmful to the environment.
Understanding the use of magnesium and aluminum alloys in the automobile industry
Naturally, lighter vehicles are more fuel-efficient than heavier vehicles. According to research by Prof. Julian Allwood of the University of Cambridge, global energy use could be heavily reduced by using lighter cars, and an average weight of 500 kg has been said to be well achievable.
Thus, manufacturers have done numerous researches to find materials that are just as safe but not as heavy to replace certain parts in a vehicle. This practice does not lead to a decrease in the number of current vehicles, of course, but allows for the addition of more safety and luxury gadgets in automobiles without any additional penalties.
Lighter components also improve the crash characteristics of a vehicle. They reduce the amount of kinetic energy required for a vehicle’s movement. They also outperform other materials, such as steel, in the absorption of energy (through plastic deformation) in the case of a crash.
Apart from economic reasons, the viability and application of any material are determined based on its mass and environmental efficiency. The substitutions would usually take place at either constant volume or constant stiffness.
In the first case, this would be the substitution of a cast engine with aluminum, for example. And the second one would be applicable to certain structural panels or beams in the car body. Occasionally, some substitutions may be determined by strength considerations as is the case with cylinder heads.
The environmental efficiency of a component is determined by the CO2 footprint of the primary metal’s production. Even though iron and steel are considered “clean materials” due to their non-pollutant production, their high density marks them as “dirty” to use.
Magnesium vs. aluminum alloys: What we should know.
This is how a recent trend has emerged: to substitute steel and cast iron automobile components with magnesium (Mg) and aluminum (Al) lighter ones.
The characteristic properties of aluminum, high strength stiffness to weight ratio, good formability, and corrosion resistance, together with recycling potential have made it the ideal candidate to replace heavier materials in the automotive industry. Most of the aluminum is used for car parts such as cylinder heads, radiators, car’s body, and wheel rims.
It was found, however, that magnesium has several advantages over aluminum in terms of manufacturability due to its physical properties.
Due to the rising need for alternative materials, the interest in magnesium has been revived and the application of magnesium alloys has become more common. Today they are present in automotive components such as steering wheels, steering column parts, instrument panels, seats, gearboxes, and air intake systems.
Thanks to its physical and mechanical properties, magnesium has proved to be more preferable to aluminum. Even though aluminum alloys are widely used today, the market for magnesium alloys is predicted to develop and their applications will rapidly increase in the near future.
Contrary to iron and steel, however, light alloys such as aluminum and magnesium are energy-intensive to make even though they are very clean to use. Thus, these components already carry high amounts of energy prior to their installation in vehicles. Therefore, a significant amount of driving is required before we notice a certain positive environmental impact.
In their fleet analysis on the distribution of emissions, F. Field, R. Kirchain, and J. Clark indicate that it may take up to 15 years for any net environmental benefit to appear since the introduction of aluminum-intensive vehicles. The researchers state that if we consider the CO2 emissions of the production of aluminum, then we can say that aluminum vehicle body designs do not offer any environmental benefits in the short term. They say that it might take up to 32-38 years for an aluminum car to offset the CO2 emissions from the production of the metal.
The production methods of aluminum and magnesium vary across countries and this defines the differences in the environmental footprint they would have. Energy sources with low emissions, such as hydroelectricity, geothermal power, and nuclear power are most favorable for the production of these metals. Different methods and technologies used even in low-emission production, however, would still lead to uneven effects in footprint.
It is very hard, however, to determine the general environmental impact of the substitutions of iron and steel vehicle parts with aluminum or magnesium ones. The primary reason for this is the different amounts of metal and types of automobile components used in the new lighter bodies.
Thus, Carlos H. Cáceres took the initiative to develop a tool that is able to break down the time-dependent emissions pattern of light material alloys, based on the type of substitutions and materials involved. His model allows for the explaination of the overall emissions pattern into the upfront debits attached to each substitution, and to individually compare them with the emissions savings resulting from the increased fuel efficiency.
Through a series of case studies, where he explores the effects of both heavy and light materials, with reference to a standard family sedan, he reaches a conclusion for each of the 14 possible material substitutions and scenarios that he analyses.
Cáceres concludes that only two of these materials can be considered viable due to the small emission peaks they lead to. These are exactly aluminum and electrolytic magnesium castings with high recycling rates. The analysis indicates that environmental benefits of the aluminum and electrolytic magnesium castings, with high proportions of secondary metal, can be expected after relatively short times, approximately 4 years. The three least efficient ones seem to be the Pidgeon Mg beams, Pidgeon Mg panels, and Electrolytic Mg beams, where the increased fuel efficiency is not enough to offset the initial debit.
Thus, we can say that aluminum and magnesium castings are some of the most reliable automobile substitutions that the industry should continue to implement. Their short-term environmental benefits would increase fuel efficiency and reduce the impact on climate.
The industry, however, keeps on looking towards even lighter and more Eco-friendly materials. The best way to choose more efficient substitutes is to look at material use by major systems and then correlate it to its manufacturing process to evaluate its suitability and effectiveness.