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Magnesium Sheet Metal Could Be Key to Better Fuel Economy


GM's Thermo-formed Magnesium Trunk Lid PrototypeModern auto manufacturers have a number of objectives they need to achieve in order to build and market a successful vehicle. At times, some of these objectives seem to be at odds with each other. Engine Power and Occupant Space are always at odds with Fuel Economy. Fuel Economy is always at odds with Occupant Safety and Body Rigidity. These are just a couple of considerations that can make or break a vehicle in the modern automobile market.

Magnesium isn’t new in automobile manufacturing, having found its way into die-cast parts such as steering wheel frames and engine cradles, but General Motors [GM] is the first to apply the material to thermo-formed sheet metal parts.

The various metal parts that form the vehicle body, frame, safety cage, and other parts need to be strong enough to be safe in an accident, as well as rigid enough to give a comfortable ride and maintain precise road handling. Steel has been the material of choice because its strength and flexibility offer safety and rigidity.

The only problem is that steel is heavy. Various formulations of steel have enabled manufacturers to reduce weight by using thinner steel parts that have the same strength characteristics, but still fight with the overall weight of steel. Aluminum parts have been increasingly used to replace heavier steel panels. GM recently pioneered a new aluminum spot welding process which will give vehicles more aluminum parts.

GM’s new magnesium thermo-formed panels are three or four times more expensive, but are 75% lighter than steel panels and 33% lighter than aluminum panels. “Every gram of weight reduction matters when it comes to improving fuel economy,” said Greg Warden, GM executive director for global vehicle body engineering. “Being able to replace heavier metals with one of the lightest will help us deliver better fuel economy to customers around the world while also still providing the safety and durability they expect.”

The US Automotive Materials Partnership estimates that by 2020, 630 pounds of steel and aluminum could be replaced by just 350 pounds of magnesium. This could realize maybe a 12% increase in fuel economy.

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