The Role of Calcium in Magnesium Alloys
Magnesium alloys are widely used in the manufacture of automotive components, as well as in medical, aerospace and industrial applications. These light weight alloys are among the lightest structural materials available. This makes them popular for applications where strength and lightness is important, such as in aircraft and car bodies. Magnesium alloys are known for their corrosion resistance and good castability, making them ideal for a variety of casting processes.
Calcium is a key component of many magnesium alloys, primarily for its ability to improve mechanical properties such as hardness, tensile strength and fatigue resistance. In addition, calcium is often added to magnesium alloys in order to improve their castability. Calcium has a strong affinity for magnesium and forms an insoluble precipitate of MgCa2O4 upon contact with magnesium in the melt. This insoluble precipitate acts as a heterogeneous nucleant, helping to refine the magnesium grains in the solidifying alloy. This grain refinement helps to reduce porosity and improve the mechanical properties of the alloy.
Calcium is also added to magnesium alloys to reduce the amount of hydrogen gas that is released during the casting process. Hydrogen gas can cause porosity in the alloy, reducing its strength and reliability. Calcium reduces the amount of hydrogen gas released by combining with the dissolved hydrogen in the melt, forming molecular hydrogen and calcium hydroxide. This reduces the amount of hydrogen gas in the alloy, minimizing its formation of porosity.
Lastly, calcium is added to magnesium alloys to help improve their corrosion resistance. Calcium has a strong affinity for oxygen, thus, when added to magnesium alloys, it combines with oxygen in the molten alloy to form a thin protective layer of calcium oxides and hydroxides. This layer serves to form a barrier against corrosive agents, thus helping to protect the substrate from corrosion.
In conclusion, calcium is an important alloying element in magnesium alloys for a variety of reasons. Its ability to improve mechanical properties and castability, reduce hydrogen gas formation, and improve corrosion resistance makes calcium a valuable component in the manufacture of magnesium alloys.
