Magnesium Alloys
Magnesium alloys are noted for low weight, high strength to weight ratio, exceptional damping capacity, and ease of machining. Casting temperatures are about the same as aluminum, and both hot chamber and cold chamber machines are used to produce castings.
Casting rates for magnesium are high because of its low heat content which produces rapid solidification. For the same reason, less energy is required to heat the metal to casting temperature.
AZ91HP (high purity) alloy has been developed for die casting parts subject to corrosive environments. Because of lower levels of nickel, iron, copper and silicon versus AZ91B, this alloy is finding applications in automobiles, computers and peripheral equipment, and in other applications where paint or coatings are either undesirable or expensive. the high cost of surface finishing this alloy is a major issue and elecroplating is impractical. surface defects casting yeilds are low adn many parts are rejected
Two new magnesium die casting allowys AM-lite and AM-HP2 have been developed to address the market needs for a light weight die casting alloy with high quality surface finish. it improves many of the limitations of AZ91D and it compestes with xinc and aluminum die casting alloys and plastics. AM-lite has more than double the limit of linear elsatic befavior of the AZ91D This means that the stiffenss of critical parts is considerably higher. AM-HP2 has been specially developed to provide highly diecastable creep resistant alloy this is suitable for powertrain components such as engine blocks, structural sumps, engine covers and automatic transmission housings. AM-HP2 has the similar die castability of AZ91D and has a creep resistance similar to the aluminum allys commonly used in these components. It is been specially adapted for high pressure die casting process. It can be realily electorplated
| Property | AM-lite | AZ91D |
| Yield stress (0.2% proof), MPa | 160-170 | 120-150 |
| Ultimate tensile strenght, MPa | 230-250 | 180-205 |
| Young's modulus, GPa | 45 | 44 |
| Elastic limit, MPa | ~100 | ~40 |
| Tensile elongation, % | 3-4 | 3-4 |
Although magnesium die castings are used uncoated, they can be finished in a variety of ways to give increased protection against corrosion, wear and abrasion resistance, and to improve appearance. Common inorganic treatments include chemical dips, anodizing and plating. Organic coatings -- oil, wax, resin or paint -- are usually applied over chemical treatments or anodizing to seal the surface, increase corrosion protection and provide an attractive appearance.