Metallurgical Constants - Specific Gravity
Definition
Specific gravity is the weight of volume of material compared to an equal volume of water:
- Pounds, inches system: Density is the weight in pounds of 1 cubic inch of material.
- Metric system: Specfic gravity and density are the same - 1 cubic centimeter of water weighs 1 gram.
Specific Gravity/Density and Welding Flux
As a fundamental physical property, specific gravity/density enters into many considerations concerning the use and fabrication of metal. One example is the choice of flux when welding magnesium or aluminum using a fluxing welding process. The wrong choice of flux results in a slag with a higher specific gravity than the metal being welded, so that the slag sinks to the bottom of the weld puddle. This denies the cleansing effect of the slag to the metal ahead of the torch, which can result in a poor weld.
Specific Gravity/Density of Some Materials
The specific gravities of some materials important in metallurgy are listed in the following table.
| Element or Compound | Specific Gravity (g/cc) |
|---|---|
| Alumina (Aluminum oxide, Al2O3) | 4.0 |
| Aluminum | 2.7 |
| Carbon | ~2.0 (amorphous); 2.25 (graphite) |
| Chromium | 7.19 |
Copper |
8.96 |
| Iron | 7.9 |
Magnesium |
1.7 |
Manganese |
7.43 (alpha), 7.29 (beta), 7.18 (gamma) |
Mercury |
13.5 |
Molybdenum |
10.2 |
Nickel |
8.88 |
Silica (SiO3) |
2.3 |
Tungsten |
19.3 |
Vanadium |
6.15 |