The widespread adoption of electric vehicles (EVs) depends on several e-mobility market factors. Foremost, it will require drivers’ concerns that the charging and range equation has been reasonably solved. The answer requires more charging stations, faster charging times and increased vehicle range.
Range can be increased by increasing the battery capacity, although that adds vehicle weight at the expense of range and vehicle cost. It could also be increased with minimizing electrical needs of other systems, like air conditioning or other features.
As a result, manufacturers have determined that the most palatable way, for drivers and OEMs alike, to increase range is to focus efforts on lightweighting the EV.
name="_i3nkzpg9fxnl">Comparing mass
While the days of 2.5 tons of “Detroit iron” are coming to a close, and with them the heavy, cast iron, block engines, EVs have their own weight problems. Most of the weight in an EV is in the battery pack, followed by the electric motors.
Ultimately, the choice in battery materials is determined by chemistry, and weight reduction for this system is secondary to energy density, safety and reliability. Although there are certainly efforts to reduce the weight of li-ion EV batteries, such as with lithium-sodium types, those power storage mediums remain in development. Manufacturers have largely found it more practical to look at present technologies to decrease weights in modern EVs, knowing that other improvements are on the horizon.
Table 1. Comparison of common automotive alloys.
At first glance, magnesium alloys have a slight disadvantage in strength to density ratios, meaning they are not as strong for their mass as their aluminum counterparts. However, this chart only tells part of the story. Unfortunately, both aluminum alloys and magnesium alloys drop in strength in response to temperature, so the exact nature of the application will dictate material suitability. In applications where weight reduction is important and temperatures are predictable and moderate, such as in certain brackets, housings, fittings, the low density of the magnesium alloys is an advantage.
Magnesium alloys have a few other benefits. They have good fatigue strength, meaning they can be used in applications where repeated stresses are encountered. Vibrations, even at low stress, can be the source of fatigue failure for aluminum alloys, where a magnesium alloy will be more durable. Magnesium alloys also tend to attenuate vibrations, which can be leveraged in things like seats to dampen vibrations.
name="_yl3u0zvdsnh5">If magnesium is so great…
Why hasn’t magnesium been a more popular automotive material to date?
Foremost, magnesium is a precious resource. Most of North American supplies come from China, with a geopolitical and economic situation that is uncertain. Domestic supplies include the Great Salt Lake in Utah, but recovery is an environmentally damaging process.
Even though the magnesium alloys are lighter weight, they suffer from a few problems as compared to other more traditional alloys. Magnesium alloys are not isotropic, meaning their properties are directional. This is because of the crystal structure of aluminum, which is hexagonal close packed (HCP) instead of the more commonly encountered Face Centered Cubic (FCC) found in steels. Magnesium alloys end up slightly stronger in compression than in tension.
As a result, today’s magnesium alloys can’t be used in structural issues without additional chemistry research and materials development. Although they can be used in stiffen beams and many of the parts already mentioned, materials innovations are required.
Magnesium, once ignited, burns extremely hot. Magnesium burns quickly and cannot be extinguished with water. Manufacturers need to be prepared for this during production, but more importantly, first responders will need training and new equipment.
Magnesium supplies for automotive needs may also serve a higher calling. Magnesium-ion batteries remain in the development stage, but initial research suggest is can have a charge density that is threefold of li-ion.
All of the above factors taken together means one more thing: magnesium raw materials are expensive to acquire.
name="_ahqgqzlgy2ez">Final Thoughts
Its easy to get distracted by the significant challenges facing magnesium’s wide significance. They are indeed significant.
However, to find all of the opportunities afforded by the e-mobility movement, engineers must take a step back and realize that EVs are fundamentally different from ICEs, and so some of the traditional auto materials used or ignored need to be reconsidered.
Electric motors are another high-weight component where the simple physics require some heavy materials. There may be an advantage to replacing the motor housings with lighter alloys, but windings, magnets, stators and other components will remain heavy.
Therefore, the two systems most critical to an EV, are unlikely to lose much weight in the near future. However, there are plenty of gains to be made in lots of other components. This is where EV engineers can learn a few tricks from internal combustion engine (ICE) vehicles, whose weights have seen significant cuts in the past decade. Things like seat frames, mounting brackets, hardware and plenty more have been re-engineered over the past decade to meet more stringent fuel efficiency requirements.
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Employing magnesium
The driving force for using magnesium alloys in any e-mobility applications is the ability to reduce overall weight. Magnesium is 75% lighter than steel and 33% lighter than aluminum. For an EV, even a small weight reduction can mean a few extra miles on a charge.
Automobile manufacturers have been using small amounts magnesium alloys to drop weight for a long time. Before automobile manufacturers started using magnesium alloys, airplane manufacturers were developing these alloys to reduce weight in the aircraft. Early development of magnesium components for aircraft began in the 1930s, with full prototypes available in the 1940s.
In the 2000s, automobile manufacturers started to recognize the advantages of magnesium alloys. GM, Audi, VW, Ford, Daimler Chrysler and others were swapping components of aluminum and steel for magnesium alloys. GM even developed a way to make sheet metal components from magnesium alloys, meaning body panels could be produced in a more cost-effective manner than ever before.
Other parts best suited for magnesium are those that tend to have light loads and are best created as single-piece, thin-walled, die-cast workpieces. Think instrument panels, steering wheels, engine cradles, seats, transfer cases and different housings.
Magnesium alloys could have potential for replacing other components that traditionally were made of aluminum alloys, such as motor housings, transmission and gearbox housings, and other such components. In ICEs, these components needed to have a higher temperature resistance. In an EV, these materials do not have the same concerns, and can be more easily converted to magnesium alloys.
