{"id":3182,"date":"2026-04-15T11:36:09","date_gmt":"2026-04-15T03:36:09","guid":{"rendered":"https:\/\/www.c-adtech.com\/?p=3182"},"modified":"2026-04-15T15:23:11","modified_gmt":"2026-04-15T07:23:11","slug":"what-flux-to-use-when-melting-aluminum-complete-selection-and-application-guide","status":"publish","type":"post","link":"https:\/\/www.c-adtech.com\/tr\/what-flux-to-use-when-melting-aluminum-complete-selection-and-application-guide\/","title":{"rendered":"Al\u00fcminyum Eritirken Hangi Flux Kullan\u0131lmal\u0131: Eksiksiz Se\u00e7im ve Uygulama K\u0131lavuzu"},"content":{"rendered":"

When melting aluminum, the correct flux depends on your specific metallurgical objective: use degassing flux (KCl-NaCl-fluoride granular formulations) to remove dissolved hydrogen and prevent casting porosity<\/a>, apply drossing flux (powder-form chloride-fluoride salts)<\/a> to separate and recover metallic aluminum trapped in surface dross, specify covering flux (granular KCl-NaCl mixtures) to protect the melt surface from atmospheric oxidation during holding periods, and choose refining flux (fine powder chloride-fluoride blends)<\/a> to coagulate and float fine non-metallic inclusions \u2014 with AdTech’s complete aluminum flux product range covering all four functions in formulations optimized for temperatures of 680\u2013780\u00b0C across automotive die casting, foundry gravity casting, secondary aluminum smelting, and continuous casting operations.<\/p>\n

If your project requires the use of Aluminum Fluxes, you can contact us<\/a>\u00a0for a free quote.<\/span><\/p>\n

At AdTech, we field this question constantly from foundry metallurgists, plant managers at secondary smelters, and engineers setting up new aluminum casting lines. The difficulty is that “what flux to use when melting aluminum” is not one question \u2014 it is four or five different questions depending on what problem you are trying to solve. We have seen foundries applying drossing flux when their real problem was dissolved hydrogen porosity, and operations spending heavily on premium refining flux when their fundamental issue was moisture in the charge material. Selecting the wrong flux type wastes money and fails to address the actual metallurgical problem.<\/p>\n

\"Aluminium
Aluminium Alloy Casting Degassing Refine Flux<\/figcaption><\/figure>\n

Why Aluminum Needs Flux Treatment: The Core Metallurgical Problems<\/h2>\n

Before selecting a flux, understanding precisely why aluminum melt treatment is necessary prevents the common mistake of treating symptoms rather than root causes.<\/p>\n

Dissolved Hydrogen: The Porosity Problem<\/h3>\n

Molten aluminum absorbs hydrogen from multiple sources \u2014 atmospheric moisture, wet charge materials, humid furnace gases, and contaminated scrap. The solubility of hydrogen in aluminum drops dramatically at solidification: liquid aluminum at 660\u00b0C holds approximately 0.69 ml H\u2082 per 100g, while solid aluminum at the same temperature holds only 0.036 ml\/100g. This 20-fold solubility drop forces dissolved hydrogen to nucleate as gas bubbles during solidification, creating porosity in the finished casting.<\/p>\n

The acceptable hydrogen content for most structural aluminum castings is below 0.10\u20130.15 ml H\u2082 per 100g Al. Secondary aluminum (recycled scrap) routinely contains 0.30\u20130.60 ml\/100g before treatment \u2014 three to six times the acceptable level. Degassing flux addresses this specific problem.<\/p>\n

Dross and Metal Loss: The Yield Problem<\/h3>\n

Every time molten aluminum contacts air, a surface oxide film forms instantly. Turbulence during melting, charging, and stirring folds these films into the melt body and accumulates them as dross on the melt surface. In secondary aluminum operations, dross generation commonly represents 3\u20138% of total charge weight, with metallic aluminum comprising 40\u201370% of that dross mass \u2014 representing direct revenue loss. Drossing flux addresses this yield problem.<\/p>\n

Surface Reoxidation: The Contamination Problem<\/h3>\n

Between treatment cycles and during holding periods before casting, exposed aluminum melt surfaces continuously form new oxide. Each new oxide layer that forms on the melt surface and is subsequently disturbed creates new bifilm inclusions. Covering flux prevents this reoxidation.<\/p>\n

Fine Inclusions and Alkali Metals: The Quality Problem<\/h3>\n

Even after effective degassing and drossing, aluminum melts contain fine oxide bifilms, spinel particles, and dissolved alkali metals (sodium, calcium, potassium from scrap contamination) that degrade casting mechanical properties. Sodium content above approximately 15 ppm in aluminum-silicon alloys causes eutectic modification to become excessive and can cause hydrogen absorption to accelerate. Refining flux removes these fine contaminants.<\/p>\n

The Four Main Types of Aluminum Melting Flux and What Each Does<\/h2>\n

Quick Reference: Flux Type vs. Problem Solved<\/h3>\n
\n\n\n\n\n\n\n\n\n\n\n
Flux Type<\/th>\nPrimary Problem Solved<\/th>\nSecondary Benefit<\/th>\nPhysical Form<\/th>\nWhen Applied<\/th>\n<\/tr>\n<\/thead>\n
Degassing flux<\/td>\nDissolved hydrogen \/ porosity<\/td>\nSome inclusion flotation<\/td>\nGranular powder<\/td>\nDuring or after complete melt<\/td>\n<\/tr>\n
Drossing flux<\/td>\nDross metal loss \/ surface oxide<\/td>\nCleaner skim line<\/td>\nFine powder<\/td>\nWhen dross accumulates<\/td>\n<\/tr>\n
Covering flux<\/td>\nSurface reoxidation during holding<\/td>\nH\u2082 absorption barrier<\/td>\nCoarse granular<\/td>\nAfter skimming \/ during holding<\/td>\n<\/tr>\n
Refining flux<\/td>\nFine inclusions \/ alkali metals<\/td>\nGrain refinement support<\/td>\nFine powder<\/td>\nBefore casting, after degassing<\/td>\n<\/tr>\n
Multipurpose flux<\/td>\nCombined functions<\/td>\nSimplified treatment<\/td>\nGranular powder<\/td>\nGeneral treatment<\/td>\n<\/tr>\n
Furnace cleaning flux<\/td>\nWall \/ hearth oxide buildup<\/td>\nMetal recovery from buildup<\/td>\nCoarse granular<\/td>\nMaintenance periods<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Understanding When You Need Each Type<\/h3>\n

The four-question diagnostic we use with new foundry clients:<\/p>\n

Are you seeing gas porosity or sponge porosity in castings?<\/strong>\u00a0\u2192 Primary need is degassing flux, combined with rotary degassing equipment if porosity is severe.<\/p>\n

Is your aluminum metal recovery below 93\u201395%?<\/strong>\u00a0\u2192 Primary need is drossing flux to reduce metal trapped in surface oxide.<\/p>\n

Is your casting hydrogen content rising during long holding periods?<\/strong>\u00a0\u2192 Primary need is covering flux to prevent atmospheric hydrogen absorption during holding.<\/p>\n

Are you seeing mechanical property scatter, elongation shortfalls, or machined surface inclusions?<\/strong>\u00a0\u2192 Primary need is refining flux to remove fine bifilm inclusions and alkali contamination.<\/p>\n

Many operations have multiple problems simultaneously \u2014 in these cases, a treatment sequence using dedicated fluxes in the correct order outperforms any single multipurpose product.<\/p>\n

Degassing Flux: When to Use It, How It Works, and Correct Dosing<\/h2>\n

The Mechanism of Hydrogen Removal<\/h3>\n

Degassing flux works through a physical bubble-transport mechanism rather than direct chemical reaction with hydrogen. When flux granules or powder contact molten aluminum, chloride salt components react with trace moisture and aluminum to generate very fine gas bubbles \u2014 primarily chlorine gas (Cl\u2082) and chloride vapors. These bubbles rise through the melt.<\/p>\n

As each rising bubble passes through the aluminum, dissolved hydrogen diffuses from the surrounding metal into the bubble interior, driven by the concentration gradient between the hydrogen-saturated metal and the essentially hydrogen-free bubble. The bubble carries this hydrogen to the melt surface where it escapes to the atmosphere.<\/p>\n

The process efficiency depends critically on bubble size (smaller bubbles have dramatically higher surface area per unit volume and collect more hydrogen) and bubble distribution (uniform distribution throughout the melt depth removes hydrogen from all zones, not just near the lance or injection point). This explains why rotary degassing units \u2014 which produce bubbles 2\u20135mm diameter distributed uniformly \u2014 outperform lance injection significantly.<\/p>\n

When to Specify Degassing Flux<\/h3>\n

Degassing flux is the correct choice when:<\/p>\n