Many obvious advantages offered by magnesium and its alloys are due to its special characteristics that put it out of comparison. The automotive industry has crossed the threshold from using magnesium in a protected environment, predominantly interior applications to an unprotected environment. Production magnesium components currently emphasize interior applications, such as steering column brackets, instrument panel, seat frames, steering wheel, and sunroof track assembly etc. However, some modern applications expand magnesium's domain to roof panels, hood, rear deck lid, wheels, intake manifold, cylinder head cover, oil pan, starter/alternator, and engine block.
Possibly the main technological reason that caused magnesium to be at a disadvantage with respect to some competitive materials (plastic and aluminum) in the automotive industry is its corrosion properties. The latest technical developments help to avoid many key-issues related to magnesium expansion in the automotive.
Considering its characteristics of low density, its extensive use in vehicles would obtain major reductions of weight and corresponding fuel savings. The data indicate that the overall weight savings could be of around 10%. In turn, this weight saving would lead to a fuel saving of the order of 20-30% without drastic changes in design. A new passenger car produces on average some 150 g/km exhaust gasses. With magnesium technology this value could be reduced to around 100-120 g/km. Considering the large number of vehicles around, this weight saving could lead to a significant reduction of carbon dioxide released to the atmosphere, reducing the impact on global warming in agreement with the Kyoto treaty. Magnesium is now the center of attention for the United States Automotive Materials Partnership (USAMP). This USCAR initiative investigates ways to develop a family car that can attain 2.9 L/100 km (80 mpg). The $10 million project involves the U. S. government, automakers, suppliers, universities, and national laboratories.
Australian Magnesium Company announced a strategic alliance with German-based VAW Aluminium, AG to assess the potential for the production of a magnesium engine block. The agreement aims to define an appropriate engine block alloy, to test prototypes and move to commercial production of a magnesium engine block. The annual demand for magnesium alloy in a typical mass-produced four-cylinder engine block is about 7000 t/a. AMC believes magnesium engine blocks will be used in a number of vehicles within the next 10 years.
The obvious advantages of magnesium over other materials are best seen in magnesium die castings. They offer a large number of economic advantages. Many of them cannot be realized using other materials and comparable manufacturing processes.
When the die casting process reaches such a high state of perfection, there is a tendency for some to think of future progress in terms of refinements. Such thinking is always fallacious, and especially so when applied to die-castings. Too many things are yet to be done: the development of satisfactory die materials for high-melting point alloys, for bigger and better casting machines, improved finishing techniques, casting of metals that have not yet been practical, and increases in size and intricacy of die cast parts - are but a few. Insofar as applications are concerned, the so-called limitations of the die casting process are nonexistent. They exist only in the minds of those who do not fully appreciate the potentials of this method of production.
This is an appropriate statement related not only to die casting in general, but it has special significance when applied to magnesium die casting, as we know it today.
Mostly the die casters are aware that magnesium is expensive, corrosive, and a fire hazard. But mostly these thoughts are exaggerated. In order to capture new markets and enhance the use of magnesium die castings, the leading producers as well as the material design engineers should be educated at the end-user level that these are misconceptions and myths about magnesium.
One of the most effective means of doing this is to educate these people on the positive advantages of die casting in magnesium. The best way of doing so is looking at the major economic advantages over other materials and similar processes.
Key advantages of magnesium and its alloys over other materials used in the die casting process are as follows:
1. Most alloys have high fluidity, which allows casting of intricate and thin-walled parts (e.g. 2 mm, or 0.08 in.);
2. Magnesium has a low volumetric specific heat compared with aluminum and zinc, which means that magnesium castings cool more quickly, allowing faster cycle times and reducing die wear;
3. Magnesium has a low density, which means that gate pressures can be achieved at moderate pressures;
4. Iron in the dies has very low solubility in liquid magnesium alloys, which reduces the sticking tendency encountered with aluminum. In addition, magnesium die casting alloys contain less heat per volume. As a result of these two factors, dies last two to three times longer than with aluminum.
Other Advantages
1. Parts Consolidation. Castability and dimensional stability of magnesium alloys allow structures to be made in one piece rather than assembled from several components. Among the benefits:
- Homogeneous design
- Improved reliability
- Fewer joints, parts and fasteners
- Lower assembly costs
- Less dunnage and scrap
- Lower intangible costs
- Improved warehousing
- Parts consolidation also provides for design simplification.
2. Design Simplification. Component consolidation allows for single shell, or monocoque, design. The principal advantage is simplified construction. The benefits of using thick-gage magnesium instead of a thin-gage construction requiring separate stiffening components are:
- Greater ruggedness for longer life and fewer repairs
- Greater stiffness
- Better denting resistance
- Greater cubic capacity for same overall size (no extra ribs needed)
- Greater cubic capacity per unit of structure weight
- Smoother surface for improved appearance and aerodynamics
3. Superior Dimensional Stability. Magnesium die castings exhibit consistent and predictable shrinkage rates during solidification. Magnesium parts eject from the die with minimum distortion and casting stress.
4. Higher Production Speeds. Magnesium's extremely low heat content produces fast chilling of molten metal. The low heat content of magnesium means less energy is required to reach casting temperature than for an equal amount of aluminum. In fact, depending on their size and configuration, some magnesium parts can be die cast up to 50% faster than the same parts in aluminum.
5. Longer Die Life. Magnesium's low heat content and low affinity for iron reduce the effect of thermal fatigue and die erosion. Dies last as much as two to three times longer, than those experienced with aluminum.
These factors, combined with the fact that magnesium is only two-thirds the weight of aluminum, account for the growing popularity of magnesium die casting, particularly in the automotive field.
For more information please see the sections comparing the major economic advantages of magnesium die cast parts to die cast aluminum, zinc, and polymers. |
