Magnesium alloys require strict control of charge cleanliness, melt protection, refining, modification, temperature, and pouring. Oxidation can accelerate quickly when the liquid surface is disturbed, while moisture, corrosion products, and nonmetallic contamination can reduce melt quality.
This article reorganizes the most important information from the supplied technical pages into a publishable guide to the Magnesium Alloy Melting Process. It focuses on flux and fluxless ZM-5 melting and summarizes the zirconium-bearing ZM-1 process.
Charge and Crucible Preparation
New crucibles are inspected for leakage and defects. Used crucibles are cleaned after residue and oxide removal, and localized damage is repaired before stress-relief treatment. Charge materials and tools must be clean, dry, and free from corrosion, oil, and oxide scale.
- Preheat additions to approximately 120–200°C where specified.
- For fluxless ZM-5, Grade II and III returns should not exceed 40%, with Grade III limited to 20%.
- The flux-melting charge described in the source contains about 20–40% fresh material and 60–80% returns.
Flux Preparation
| Component | Proportion |
|---|---|
| Carnallite | 10% |
| Boric acid | 5% |
| Water glass | 4% |
| Water | Balance |
The mixture is heated to approximately 120–150°C, dried to around 70–80°C, and used after preheating at approximately 120–200°C.
Flux Melting of ZM-5 Alloy
The crucible is heated to dark red and coated with RJ-2 or RJ-1 flux. Preheated charge is loaded, and the exposed metal is covered with RJ-2 flux equal to approximately 1–2% of charge weight.
At 700–720°C, master alloy and zinc are added. After complete melting, the bath is stirred for 5–8 minutes and sampled for spectrometric analysis. The melt is raised to about 730°C, skimmed, and protected with fresh RJ-2 flux.
Modification and Refining
Magnesite modifier is added at approximately 0.4% of charge weight in two or three foil-wrapped packets. The stated treatment time is 6–12 minutes and not less than five minutes.
| C2Cl6 treatment item | Value |
|---|---|
| Addition | 0.5–0.8% of charge weight |
| Temperature | 740–760°C |
For refining, the melt is held at 710–730°C and stirred for 5–8 minutes while RJ-2 flux is added. Refining flux equals about 1.5–2.0% of charge weight. The bath is then heated to 760–780°C and held for 10–20 minutes.
Fluxless ZM-5 Melting
The fluxless system uses SF6 and CO2 protection, C2Cl6 modification/refining, and optional argon washing.
Protective gas requirements
| Material | Requirement |
|---|---|
| SF6 | Moisture ≤30 ppm; CF4 ≤0.1%; air ≤0.1%; acidity as HF ≤5 ppm; hydrolyzable fluoride as HF ≤15 ppm |
| CO2 | Purity ≥99.9% |
| Argon | Purity ≥99.9% |
| C2Cl6 | Industrial Grade I |
Fluxless-tool coating
| Component | Proportion |
|---|---|
| Chalk powder | 18% |
| Iron oxide | 5% |
| Graphite powder | 5% |
| Boric acid | 6.5% |
| Water glass | 2% |
| Water at about 60°C | Balance |
SF6 flow
| Melt condition | SF6 flow | Delivery |
|---|---|---|
| Surface stationary | 0.015–0.1 L/min | 2–3 min every 15–20 min |
| Cover open; surface disturbed | 0.1–0.2 L/min | Continuous |
SF6 + CO2 mixed-gas flow
The stated SF6:CO2 ratio is 1:100.
| Condition | SF6 | CO2 | Pressure |
|---|---|---|---|
| Surface stationary | 0.04–0.05 L/min | 4–6 L/min | 0.3–1.0 kg/cm² |
| Surface disturbed | 0.2–0.3 L/min | 20–30 L/min | 0.3–1.0 kg/cm² |
Fluxless Process Sequence
At 700–720°C, the melt is stirred for 2–5 minutes, skimmed, and sampled. At 730–750°C, it is treated with 0.1% self-sinking C2Cl6 refining-modifier.
| Argon-washing item | Value |
|---|---|
| Flow | 1–2 L/min |
| Time | 2–4 min |
| Temperature | 730–750°C |
| Final holding | 760–780°C for 10–15 min |
Self-Sinking Modifier Formulations
| No. | C2Cl6 | Graphite | Zinc |
|---|---|---|---|
| 1 | 30 g | 3 g | 14–18 g |
| 2 | 50 g | 5 g | 23–28 g |
| 3 | 100 g | 10 g | 45–55 g |
ZM-1 Alloy with Zirconium
ZM-1 uses Mg-Zr master alloy containing at least 25% zirconium. Mg-Al charge and tools must not be mixed with those used for ZM-1. The charge is approximately 10–20% fresh metal and 80–90% returns, with Grade I return material at least 60%.
| Process item | Value |
|---|---|
| Zirconium-addition start | 720–740°C |
| Master-alloy addition range | 780–810°C |
| Refining temperature | 750–760°C |
| Stirring time | 4–6 min |
| Refining flux | 1.5–2.5% |
| Final heating | 780–820°C |
| Total settling when required | 30–50 min |
| Maximum post-refining holding | 2 h |
Temperatures below about 780°C promote zirconium settling, while temperatures above 820°C increase oxidation, hydrogen absorption, and iron dissolution.
Pouring Control
The source recommends pouring under reducing protection at the lowest practical temperature, normally around 720–780°C. The ladle is kept close to the sprue, flow remains stable, and the sprue cup is maintained about two-thirds full. Tools are washed, preheated, and protected before entering the melt.
Conclusion
The magnesium alloy melting process depends on coordinated control of material preparation, melt protection, refining, modification, temperature, settling, and pouring. Flux-based ZM-5 melting relies on RJ-series covering and refining fluxes, while the fluxless route uses controlled SF6/CO2 protection and C2Cl6 treatment. ZM-1 requires segregated tools and tightly controlled Mg-Zr addition.
Technical and safety note: This article is translated and reorganized from historical technical pages. Molten magnesium, SF6, chlorinated compounds, and reactive fluxes present severe fire, toxic-exposure, greenhouse-gas, and environmental hazards. Historical data are not stand-alone operating instructions. Current regulations, safer approved alternatives, emissions controls, qualified supervision, and validated plant procedures are required.
