Abstract:

Magnesium alloy castings can be produced by nearly all of the conventional casting methods, namely, sand, permanent, and semi permanent mold and shell, investment, and die-casting. The choice of a casting method for a particular part depends upon factors such as the configuration of the proposed design, the application, the properties required, the total number of castings required, and the properties of the alloy. Magnesium castings of all types have found use in many commercial applications, especially where their lightness and rigidity are a major advantage, such as for chain saw bodies, computer components, camera bodies, and certain portable tools and equipment. Magnesium alloy sand castings are used extensively in aerospace components.

Magnesium alloy castings can be produced by nearly all of the conventional casting methods, namely, sand, permanent, and semi permanent mold and shell, investment, and die-casting. The choice of a casting method for a particular part depends upon factors such as the configuration of the proposed design, the application, the properties required, the total number of castings required, and the properties of the alloy. Magnesium castings of all types have found use in many commercial applications, especially where their lightness and rigidity are a major advantage, such as for chain saw bodies, computer components, camera bodies, and certain portable tools and equipment. Magnesium alloy sand castings are used extensively in aerospace components.

The benefits of using magnesium components in today's automobiles are compelling. It's 75% lighter than steel, 33% lighter than aluminum, offers component and feature integration and provides a high dimensional stability that improves fit and finish.

Of course, the medium is only as good as the artist using it, and with manufacturing facilities in 5 countries driven by industry-leading design and engineering prowess, Meridian magnesium die casting continues to demonstrate that they are - indeed - masters of magnesium die casting.

1. What is magnesium?
2. Where is it found?
3. How much magnesium is produced?
4. What are the major benefits of magnesium?
5. How do you choose an alloy?
6. What alloy should be used in a high temperature application?
7. What are the material property comparisons of these alloys?
8. Magnesium vs Competing Materials?
9. Can magnesium castings be painted?
10. Are there special fasteners for magnesium castings?
11. How do you protect against galvanic corrosion?
12. What are the tooling and prototype options?

Q. What is magnesium?
The lightest structural material (1.8g/cm3), magnesium is the 8th most abundant element in the earth's crust. It occurs naturally in Dolomite, Magnesite, Carnallite and Chloride (sea water).

Q. Where is it found?
Magnesium is produced from sea water, brines and magnesium-bearing minerals which offer unlimited reserves.

Q. How much magnesium is produced?
350,000 metric tons in 1990; 2005 estimated at 500,000 metric tons.

Q. What are the major benefits of magnesium?

· Lightest of all structural materials
· 75% lighter than steel
· 33% lighter than aluminum
· High impact resistance
· High strength to weight ratio
· Can be cast to net shape
· Excellent dimensional stability/repeatability
· Abundant material supply
· 100% recyclable

Q. How do you choose an alloy? The alloy is selected based on the environment the part will function in the performance requirements of the component.

AZ91D: Most commonly used alloy for high pressure die casting. Offers good strength to weight ratio, very good corrosion resistance and excellent castability. This alloy is typically used for power-train and mechanical components where toughness is more important than deformation capability.

AM60B: Commonly used for automotive die castings for safety components such as instrument panel structures and seat frames. This alloy offers excellent ductility, energy absorbing properties, strength and castability.

AM50: With a lower aluminum content than AM60 this alloy offers a further increase in ductility but at a slightly reduced strength and a slight reduction in castability. It is typically used where the performance requirements demand elongation properties beyond that of AM60.

Q. What alloy should be used in a high temperature application? For applications such as power-train components where the operating temperature is above 120 degrees C (example; automatic transmission housing) there is a large selection of magnesium alloys available. These alloys are designed to operate in the higher temperatures without "creep" so that bolt tension and sealing surface flatness is maintained. Meridian recommends discussing this with our engineering group to review the options available.

Q. What are the material property comparisons of these alloys? Please refer to this specification sheet (PDF format)

Q. Magnesium vs Competing Materials?

Vs. Aluminum:
· 33% Lighter
· Superior Machining
· Greater Die Life
· Large thin-walled near net shape casting
· Similar or greater mechanical properties
· Greater general corrosion resistance

Vs. Steel:
· 75% Lighter
· Component consolidation/integration (No welding costs & less assembly costs)
· Significantly lower tooling costs
· High heat conductivity
· Complicated thin-walled near net shape
· Superior dimensional stability/repeatability

Vs. Plastic:
· Stronger
· Superior stiffness
· Greater energy absorbing capabilities
· Higher temperature applications
· Large thin-walled near net shape casting

Q. Can magnesium castings be painted?
Yes, die cast magnesium components can be painted using e-coat or powder coat processes. The parts require a pre-treatment to ensure adhesion. There are several body structure applications in production that are painted as well as first surface interior components.

Q. Are there special fasteners for magnesium castings?
Some fasteners used are standard fasteners that are used with other materials such as push nuts, and U nuts. For thread forming or self threading screws there are fasteners designed specifically for magnesium that allow multiple insertions with no loss of clamp torque.

Q. How do you protect against galvanic corrosion?
Galvanic corrosion occurs when there is a dissimilar metal in contact with the magnesium casting and there is an electrolyte present (such as salt water). There is no issue with interior components but for body, chassis or power-train castings there is a likelihood that galvanic corrosion protection will be required. The approach is to isolate the dissimilar metals either by coating one of the components or using an isolating material as a washer to eliminate the galvanic effect. Meridian is very experienced in designing to protect for galvanic corrosion and have many successful designs of galvanic protection in production.

Q. What are the tooling and prototype options?
There are several options for tooling and prototype parts depending on the intended use of the parts. For certain applications sand castings may be used with great success. Where die castings (and die cast mechanical properties) are needed there are several options for tooling with various lead times and tool life available to meet all program schedules. These include rapid tools, soft prototype tools and production tools.