*Magnesium Alloys for Sustainable Weight-Saving Approach: A Brief Market Overview, New… DOI: http://dx.doi.org/10.5772/intechopen.102777*

But there is always a "but"; light-weighting is not a stand-alone measure whether its motivation is pollution curbs [21]. The extractive metallurgy (mining and refining) of nonferrous structural metals that are highly reactive toward oxygen like aluminum, titanium, and magnesium is complicated due to their low grade. The high complexity of the ore extraction and the energy-intensive pyrometallurgical or hydrometallurgical processes employed for pure metal refining are critical stages for the potential release of gas, liquid, and solid emissions (i.e., direct pollutant emissions) and for a large amount of CO2 emissions correlated to lots of energy consumed (i.e., indirect pollutant emissions). In the next sections, we'll go into details, but for the moment, we can summarize by this way:


Therefore, a broad vision must encompass the net CO2 emissions over the road vehicle lifespan.

A qualitative scheme representing the green ability of light alloys against heavier metal, such as steel, is depicted in **Figure 7**. The baseline case (1) represents a reference, for example, a body panel made of galvanized plain carbon steel. For the steel-made product, the total CO2 emitted over the product's lifespan is the sum of the CO2 (direct and indirect) emitted during the manufacturing stage and the usage phase (traveling). By replacing steel-made products with lighter metal alloy (2), we shall consider more pollutant emissions in the fabricating stage. For this reason, the break-even point T1 versus the baseline scenario (1) could be targeted at the T1 traveled distance. The beneficial effect of weight saving is visible by the gray shaded area from T1 to the expected vehicle lifespan representing the net CO2 curb by lightweight solution. Case (3) represents the use of much lighter material (due to the reduced slope of the line), but with higher CO2 emitted in the manufacturing stage as per the higher linear coefficient of the line (3). In this second scenario, the break-even point switches to the higher T2 mileage. The difference between the two shaded areas represents the net CO2 cut for alternative weight-saving scenarios (2) and (3) compared to the baseline scenario (1).

We refer again to **Table 3**. On average, you may consider 0.5 the aluminum substitution factor applicable in structural engineering applications, thus 100 kg of steel (that accounts for around 230 kgCO2 for the manufacturing stage) would be potentially replaced by approximately 50 kg of aluminum, which accounts for about 700 kgCO2eq emitted in the manufacturing phase. On the other hand, referring to the schematic representation in **Figure 7**, aluminum onboard would potentially save 50 kg. Now you

### **Figure 7.**

*Three qualitative scenarios for addressing the environmental impact of automotive body panels over the product lifespan.*

can account for nearly 0.2 gramCO2, the pollution cut per kg of weight saved and per each km traveled. Putting onboard an internal combustion engine-powered vehicle 50 kg aluminum to replace steel, we would cut around 5.95 gCO2 per km traveled.

Now, we can proceed with a further step.

The net CO2 emissions from the aluminum-steel switch account for around 470 kgCO2eq emitted in the "cradle-to-gate" phase (including extractive, refining, alloying, and manufacturing stages). Aluminum bodies shall travel onboard around 78,000 km to achieve the break-even point, namely the traveling distance necessary to offset the 470 kgCO2 extra emissions over the steel-made bodies (the baseline scenario). The environmental sustainability of the lighter solution is therefore strongly influenced by the environmental impact of the raw material fabrication phase, mostly the extractive stage. For that reason, intensive use of recycled patterns to limit the use of primary (virgin) metal for such energy-intensive lightweight alloys is the key to excellent sustainable use of light alloys on-road vehicles. And what about magnesium products? Former data about the carbon footprint of magnesium production have indicated an extensive range of 37–47 kgCO2eq/kg of magnesium [22]. With such numbers, many still consider magnesium from a technical point of view an exciting opportunity to implement lightweight strategies but an unsound option for a crosscutting greening approach. It would be effortless to calculate whether 37 kgCO2eq is the carbon footprint per kg of magnesium to put onboard for replacing 1.6 kg of steel, the CO2 emitted for the manufacturing phase could be "absorbed", traveling for a lot, above 200,000 km. What are the reasons for such a high carbon footprint of magnesium metallurgy? And shall we consider those numbers still valid today? We'll try to get an answer to those questions in the following sections.
