AZ91D

AZ91D is a die-cast magnesium alloy in the magnesium-aluminum-zinc family. It contains about 9% aluminum and 1% zinc, with manganese added in small amounts and the balance magnesium. The D suffix denotes a refined composition intended to improve ductility and castability compared with earlier AZ-series alloys. AZ91D is widely used for high-volume die cast parts where light weight is advantageous.

The alloy's microstructure typically consists of a magnesium-rich α-Mg matrix with intermetallic compounds containing aluminum, such as Mg17Al12, distributed within the grains and along grain boundaries. Manganese additions help refine the microstructure and improve corrosion resistance. This combination provides a balance of strength, ductility, and creep resistance for a cast alloy.

In terms of processing and properties, AZ91D offers good castability and dimensional stability, making it suitable for complex shapes. It can be used in the as-cast state, and it may undergo solution heat treatment followed by aging (a T6-type process) to increase strength. The alloy has a relatively low density compared with non-metal alternatives and demonstrates a favorable strength-to-weight ratio for magnesium alloys.

Corrosion behavior is a key consideration; while aluminum content improves corrosion resistance relative to some other Mg alloys, AZ91D remains susceptible to galvanic corrosion in certain environments. Protective coatings, anodizing, or paints are commonly applied for outdoor or corrosive service. Limitations include relatively lower high-temperature performance and wear resistance, requiring lubrication or coatings for some applications.

Common applications include automotive engine and transmission components, housings for electrical and home electronics, sporting goods, and other lightweight structural parts produced by die casting.