Benefits of Magnesium in Metal Parts Manufacturing
In the realm of die casting, one of the first questions that comes to mind is, “Why magnesium?” This is a good question, but that thought really should be, “What are the many facets of magnesium?” – or maybe it is both? Why is that you ask yourself this? This is the question that we will try and answer in the following article.
Two characteristics that always come to the forefront about magnesium are “lightweight” and “fire hazard”. While both are true, they are not the only areas that we should be aware of about magnesium.
The Two Most Common Characteristics of Magnesium
It is true that magnesium is lightweight and has the best strength to weight ratio of the common die castable metals. As far as safety goes, magnesium does burn under the right conditions and two great examples are fireworks (the bright white light that you see) and flares (they even burn underswater). However, newer dosing melting furnaces, fire fighting equipment, detection devices (hydrogen sniffers in machining areas), chip and dust control, and good housekeeping have improved the safety aspect of die casting magnesium.
Now that we have determined that die casting magnesium is manageable from a safety standpoint with the right equipment, training and good housekeeping, we are back to the same two questions. But magnesium is so much more than that.
But There’s More to Magnesium...
Magnesium is the lightest structural material (1.8 grams per cubic centimeter or for those of who prefer 0.065 pounds per cubic inch), and is the eigth most abundant element in the earth’s crust. It is produced from sea water, brines(chloride) and magnesium bearing minerals ( it occurs naturally in dolomite, magnesite and carnallite), which offer unlimited reserves. It is also 100% recyclable.
Magnesium’s die cast tooling life, while not as good as zinc, is substantially better than aluminum and can last up to three times longer. There are also several options for tooling and prototyping, which include rapid tools, soft prototype tools and production tools, all with various lead-times and tool life to meet all programs, schedules, and number of parts needed.
Magnesium offers great versatility. It can be run in both hot (conventional and multi-slide machines) and cold chamber die cast machines. This makes is suitable for castings that are small in size (less than an ounce) to very large (up to sixteen pounds or larger).
Magnesium offers a great array of alloy choices. There are many available alloys for magnesium die casting. The most common of which are AZ91D and AM60B. AZ81, AM50A AM20, AE42, and AS41B are also available, but are usually used for a specific desired property such as creep resistance or higher temperature usage.
AZ91D Magnesium is the most commonly used alloy for high pressure die casting. It offers good strength to weight ratio, very good corrosion resistance and excellent castability. This alloy is typically used for mechanical components where toughness is more important than deformation.
AM60B Magnesium is commonly used for safety applications or where ductility is desired. Applications include automotive components such as seat frames, instrument panel structures, steering wheels (frames or armatures) or where possible cold forming applications are needed.
With lower aluminum content than AM60B, AM50 Magnesium offers further increase in ductility but at a slightly reduced strength and a slight reduction in castability. It is typically used where elongation requirements are beyond that of AM60B.
AE and AS series alloys are Rare Earth Alloys and are used where creep resistance or higher temperature requirements are needed.
Thin Wall Capabilities
As far as thin wall capabilities go, some of the new cast alloys for zinc are slightly better than magnesium, but for overall wall thickness, magnesium can compete with zinc. With typical cast wall thickness at around 2mm (.078 in.), it is not uncommon to see wall thickness down to .5mm (.020 in.) being achieved. It is much better than average aluminum at 2.5mm to 3mm (.090 to .120 inches). As a side note, it is important to note that if the component is designed for magnesium with the right wall thickness, some of the cost difference between aluminum and magnesium can be offset as well. In the United States, this is very important because of the current tariff on imported magnesium.
Galvanic Corrosion IssuesGalvanic corrosion occurs when there are two dissimilar metals in contact with each other and there is an electrolyte present (such as salt water). There should be no issue with galvanic corrosion components that are not exterior components. If there is a likelihood of galvanic corrosion, the approach should be to coat one of the materials or to use an isolating material (for example a washer) to eliminate the galvanic effect. With the proper design considerations, galvanic corrosion protection should be achievable.
Magnesium parts can be Powder Painted, E-Coated and even Plated if ther eis a need for greater corrosion resistance or for a decorative finish. It is important to note that magnesium parts require a pre-treatment to ensure adhesion.
Special Fasteners for Magnesium
Standard fasteners are available that can be used with several materials such as push nuts. For thread forming and self threading type applications there are fasteners made just for magnesium that allow multiple insertions.
SummaryTo re-cap some of the major benefits of Magnesium Die-Casting:
- Lightest of all structural materials
- 33% lighter than aluminum
- 75% lighter than steel
- High Strength to weight ratio
- Excellent dimensional stability and repeatability
- High Impact resistance
- Large alloy selection
- Abundant Material supply
- 100% recyclable