The Temperature of Melting Aluminum Alloys

In sand casting foundries, aluminum is typically melted at around 660°C (1220°F). However, the pouring temperature of aluminum is usually higher, often around 750°C (1382°F), to ensure proper flow and filling of the mold.

Overheating the metal in special cases does have some advantages.  Pouring the metal at a higher temperature will help if there are thin walls, intricate coring, not enough room for necessary gating, etc.

• Thin walls – Sections of a casting that have a smaller cross-sectional thickness. These are typically challenging to fill with molten metal because they cool rapidly and can solidify before the mold is completely filled. By pouring the metal at a higher temperature, it remains in a liquid state longer, improving its ability to flow into and fill these narrow spaces. This reduces the risk of incomplete filling or cold shuts, where the metal cools too quickly and creates weak points in the casting.
• Intricate Cores – Complex internal cavities or shapes within the casting using sand cores. These cores can have narrow passages or intricate designs that are difficult for the molten metal to penetrate and fill completely. Overheating the metal can help it flow more easily into these complex cores, ensuring that the intricate details are captured and that the final casting has the desired shape and internal structure.
• Gating – Gating refers to the system of channels through which molten metal flows into the mold. In some designs, there might be limited space to create an optimal gating system, which can hinder the smooth flow of metal into all parts of the mold. When the gating system is less than ideal, overheating the metal can help compensate by allowing it to flow more freely and fill the mold despite potential restrictions in the gating channels. This can reduce the likelihood of defects such as misruns, where the metal fails to fill the entire mold.

Of course, overheating some alloys can also destroy their chemical properties and adds to the possibility of introducing porosity and other imperfections into the castings.

• Oxidation Risks – When aluminum is heated to high temperatures, especially when overheated, it becomes more susceptible to oxidation. This can form an oxide layer on the surface of the molten metal, which can lead to inclusions in the final casting if not properly managed.
• Dross Formation – At higher temperatures, aluminum is more prone to forming dross, a byproduct that consists of impurities and oxide particles. This can reduce the yield of usable metal and negatively affect the quality of the cast.
• Grain Structure – The pouring temperature can influence the grain structure of the final product. A higher pouring temperature may lead to a coarser grain structure, which can impact the mechanical properties of the casting.
• Alloy-Specific Considerations – Different aluminum alloys, such as 356 Alloy and 319 Alloy, have varying optimal melting and pouring temperatures. Precision Enterprises has been casting aluminum alloys for 70+ years and is very familiar with each specific alloy’s properties of the final casting.

Precision is dedicated to maintaining a consistent melting and pouring temperatures that are within the recommended range of industry standards. This attention to detail not only results in a better end product for our customers, it can improve energy efficiency in our foundry, reduce costs and minimize waste.