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One-Stop Billet Production: Melting to Homogenizing
Today, we'll skip the formalities and go straight to the actual production sequence. We'll connect the smelting, refining, casting, sawing, and homogenizing production lines.
Apr 14th,2026
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Veterans in the aluminum billet business know they often face surface issues like extrusion cracks and coarse grains. These issues don't actually arise during the casting process. The seeds of problems are sown from the very first batch of material in the furnace.Today, we'll skip the formalities and go straight to the actual production sequence. We'll connect the smelting, refining, casting, sawing, and homogenizing production lines. In this article, we'll discuss things that are truly applicable.
I. Smelting: Don't Bring Bad Temper into the Molten AluminumThe biggest misconception in smelting is that "it's enough once it melts." In reality, the furnace charge ratio, the order of loading. And the control of the melting temperature all affect subsequent processes.Furnace Charge SelectionIf using a large amount of recycled material, the proportion must be carefully controlled. Otherwise, elements like magnesium and zinc are prone to exceeding limits, and there will be many oxide inclusions. It's best to use a mixture of standard aluminum ingots and some primary scrap.Furnace Loading SequenceFollow the principle of placing large pieces of material at the bottom and small, lightweight materials on top. Otherwise, the smaller materials will melt first, causing localized overheating and severe burn-off. Add aluminum ingots first, add the returned materials slowly after they melt, and finally add the intermediate alloy.Temperature Control
Maintain the furnace temperature within a suitable range during the melting period. High temperatures will absorb hydrogen, increase oxidation, and accelerate the dissolution of impurities such as iron and silicon.StirringMany people simply stir with a rake, which is ineffective. Stir thoroughly by moving up, down, left and right to ensure uniform composition, especially after adding the intermediate alloy. However, be careful not to stir the surface oxide film into the molten aluminum.
II. Refining and Degassing: Invisible Pores are the Most DangerousHydrogen and oxide inclusions are the hidden killers of aluminum rods. Later extrusion peeling and black lines on anodizing are most likely due to problems in this step.Rotary Blowing DegassingThis technology is now very mature; the key is to control the rotor speed and nitrogen flow rate.Flux Refining: Sodium-free refining agents are safer. Refining temperature must be well controlled, and slag removal must be thorough.Ceramic Filtration
Use filter plates of at least 30ppi, ideally 50ppi. The filter box must be properly preheated before introducing molten aluminum; otherwise. The cold plates will solidify instantly upon contact with the molten aluminum, causing blockages and cold shuts.
III. Casting: The Watershed for Surface QualityCasting is the most challenging part of the entire production line. Parameters vary greatly, but the core elements are few—lubrication, cooling, liquid level, and temperature.In actual production, the following adjustments are recommended:Crystallizer Lubrication
If using oil-air lubrication, more oil is not necessarily better. Too much oil will cause black spots on the surface, while too little will cause scratches.Cooling Water
The angle of the water inlet is crucial. Do not allow water to directly hit the newly formed shell of the aluminum rod. Soft water is best; hard water easily forms scale in the crystallizer water inlets.Liquid Level Control
Laser or eddy current sensors are now commonly used. Fluctuations should ideally be kept within a reasonable range. Even a slight fluctuation in liquid level can cause surface segregation, resulting in uneven lighting. Furthermore, level fluctuations can trap the surface oxide film, forming inclusions.Temperature and Speed Matching
High temperatures result in thicker segregation layers; slow speeds easily lead to surface scratches. A simple rule is: the larger the rod diameter, the lower the temperature and the slower the speed.The initial casting and final casting stages are high-risk periods for accidents. During initial casting, the ingot head should be preheated to a suitable temperature. And the graphite sealing ring should be tightened. During final casting, the speed and water volume should be gradually reduced; avoid shutting off the entire process abruptly.
IV. Sawing and InspectionPreventing Potential Problems Before the Next ProcessThe cast aluminum rods should not be immediately sent to the homogenizing furnace; they must undergo an inspection first.Sawing
Use a carbide circular saw or band saw. The key is to ensure adequate cooling and lubrication; otherwise. The saw cut will overheat, soften during annealing, and leave burrs on the end face.Surface Inspection
Visually inspect for scratches, cold shuts, and segregation nodules. Severe defects require immediate rejection. Minor defects can be treated with grinding.Low-Magnification AnalysisTake at least one rod from each batch, cut it under low magnification. And check its grain size, segregation layer thickness, porosity and inclusions.
V. Homogenization Treatment: Don't Let Intra-Granular Segregation Ruin Extrusion PerformanceMany people think homogenization is simply "heating" the rod to a suitable temperature. The quality of homogenization directly determines the extrusion speed and the surface quality of the finished product.Heating
Raise the temperature from room temperature to the homogenization temperature, controlling the heating rate within a reasonable range. Too rapid a heating will cause excessive thermal stress, leading to rod bending.Heating
The purpose is to dissolve the non-equilibrium eutectic phase. Ensure uniform distribution of Mg₂Si particles, and eliminate intra-granular segregation.Cooling
Rapid cooling is essential after homogenization. Slow cooling will cause Mg₂Si to precipitate again and coarsen. Easily resulting in coarse grains and peeling during extrusion, and hindering the extrusion speed.Results Verification
Metallographic analysis of the homogenized aluminum rods should not show obvious dendrite deviations.
VI. Lessons Learned: Especially degassing and filtration—these are small investments that save big money in the long run.Furthermore, don't wait until equipment breaks down to repair it. Disassemble and clean the crystallizer monthly, replace the graphite rings regularly, and replace the filter plates after each batch. These consumables may seem expensive, but compared to the scrap rate, they are negligible.
VII. A Final Remark: There are no shortcuts in aluminum rod production. From smelting to homogenization, every step is "accounting"—what's done in the past must be paid in the future. If you are currently experiencing unstable surface quality, coarse grains after extrusion, or streaks after anodizing. It is recommended that you review your process records from the beginning. The problem is most likely hidden in some detail within these five processes.
