The element magnesium (Mg) has a specific
gravity of 1.74, making it the lightest commonly used structural
metal. When used as a base for die casting alloys, magnesium is
alloyed with various combinations of elements from a group
including aluminum, zinc, manganese and silicon. Other elements
present in the alloys are generally regarded as impurities, and
maximum limits (expressed as single numbers) are specified.
The magnesium industry offers several alloys that are widely used
for die casting. They are most commonly designated by a system
established by ASTM for all magnesium alloys, which covers both
chemical compositions and tempers. The first two positions in the
ASTM designation are capital letters representing the two major
alloying elements, and arranged in decreasing percentages. The
letters are followed by numerals indicating the respective
percentages rounded off to whole numbers. A letter in the next
position indicates a slight variation in composition not reflected
in the preceding characters, such as a minor alloying element
variation. Temper designations, which normally follow, are not
used for die casting alloys because porosity in the die casting,
even in relatively small amounts, can cause blistering at heat
treating temperatures.
