**3. Magnesium for weight-saving and lowering energy for transportation**

Nowadays, the transportation sector impacts around 25% of direct CO2 emissions from fossil fuel combustion. Among the variety of transportation means, road vehicles, particularly passenger cars and freight vehicles such as heavy trucks, busses, and two-wheelers, are estimated by the International Energy Agency (IEA), accounting for nearly three-quarters of transport CO2 emissions. Although CO2 emissions from aviation and shipping have been increasing in the last decade, the road share of total transport sector emissions has fluctuated around 75% of total transport emissions for two decades. If several efforts and advancements have been made in road-vehicle electrification, otherwise larger (and heavier) vehicles are still preferred by lots of consumers. The worldwide market share of SUVs has increased in the last two decades, and in 2019, before the pandemic crisis, it represented nearly half of the global light-duty vehicle market in several countries. Growing demand for the urban transport of goods is rising, adversely affecting air quality, noise, safety, and liveability in the city. The automotive sector has been putting efforts for reversing CO2 emissions growth by several strategies; one of those strategies focuses on energy efficiency countermeasures that would be implemented in the form of:

managing/rationalizing travel habits to reduce the frequency and/or distance switching from high-energy-intensity modes (e.g., private car and or air) to most efficient methods (i.e., train for traveling long distances plus rented new efficient vehicles on local base).

deploying energy-efficient technologies for vehicles and fuels.

more stringent requirements on vehicle efficiency, namely, power consumption per km.

The latter strategy is thought a valuable approach for accompanying market migration from heavy vehicles powered by combustion engines fueled by gasoline toward cleaner electrified cars that could be likely powered by near-zero-emission electricity. During vehicle operation, the fuel consumption rate can be approximated as the sum of a linear function of the vehicle mass and—as a second contribution the loss in aerodynamic drag; both of them through coefficients that depends on several vehicle characteristics. Strategies approaching weight reduction are actually most effective during transient driving cycles; instead, during constant speed traveling, the vehicles' fuel efficiency mostly depends on aerodynamic drag forces. Global average fuel consumption of new cars has been too slowly decreased, less than 2% per year, setting around 7 L gasoline equivalent per 100 km (Lge/100 km). To get on track with 2030 targeted 4.5 Lge/100 km, expected standards will become significantly more stringent to achieve efficiency goals. In 2021 the European Commission proposed new CO2 emissions targets for 2030 and 2035 that require CO2 emissions reductions of half actual emissions for cars and vans.

Despite wide literature on life cycle assessment of on-road vehicles considers fossil fuel-powered vehicles, a similar approach is being deployed in the case of electric motor-powered vehicles (considering the energy efficiency of kWh per km traveled) or hydrogen-gas fueled road vehicles (considering hydrogen gas supplied to fuel cell unit per km traveled). Precisely for fully electric cars, the weight of full-electric vehicles is a sum of the mass of the vehicle's architecture and the mass of battery packs. Thus, its common sense considering that the travel range represents for the consumers the independence from the plug-in commences with battery size. That's the Achille's heel of plugged-in vehicles for fossil-fueled vehicle buyers. On the one hand, travel range increases with battery capacity, but on the other hand, larger battery capacity means a heavier vehicle to travel.

While vehicle downsizing improvements in fuel efficiency could be achieved, it appears in contrast with buyers' needs; thus, reducing size for reducing mass could not target a competitive strategy for automakers.

For this reason, a weight-saving strategy primarily implemented by extensive use of lightweight materials—better to say, by higher specific strength—is, therefore, most promising for pursuing consumers' satisfaction. Meanwhile, environmental aspects are successfully addressed, as they cannot be deferrable. It has been estimated that a 10% of vehicle weight curbing increases the vehicle's fuel efficiency by nearly 7%. But the ability to introduce new lightweight materials into vehicles is not a simple remove-and-replace process. Concerns about the impact of material changes on manufacturing lines, supplying network reliability, material cost stability, secure material availability in the marketplace are the main drivers in the material-shift decision process as they all could be more important for automakers than the percentage of weight saved. The potentiality of any lightweight scenarios steered by material replacement rates is based on the actual capability of lighter but weaker materials to safely replace heavier but stronger ferrous alloys, like steels and cast irons. As shown in **Table 3**, the weight-saving potentialities of lighter material depends on the specific substitution factor for the specific function, and it's a fact that the materials substitution factor strongly depends on: the physical properties of the material (e.g., its density and its elastic module as key-factor impacting on stiffness-limited design), the shaped part mechanical properties that are strongly dependent on the shaping process employed (e.g., fatigue limit obtained by cold pressure die-casting operations is different from fatigue limit obtained with low-pressurized die-casting), the geometrical constraints fixed by design (e.g., limited space of fixed boundaries to frame architecture).

As it is usual for any comparative analysis, we need a baseline and parameter to use in the calculation of data output to compare. The fuel consumption reduction coefficient is conventionally used as a measure of fuel-mass correlation. It provides the saving in specific consumption achieved through a 100 kg weight-saving. Recent literature set in the range 0.3–0.5 L/(100 km × 100 kg), varying with modeling assumptions, such as vehicle class, car model, driving cycle, the fuel consumption reduction coefficient for internal combustion engine vehicles [19], and values in the range of 0.47–1.17 kWh/(100 km × 100 kg) for electric vehicles [20].
