Magnesium HM21A-T8，UNS M13210,E FOUR

*Product Introduction: Magnesium Alloy HM21A-T8 (UNS M13210)** **Magnesium Alloy HM21A-T8** is a high-temperature, heat-treatable wrought magnesium alloy strengthened by thorium and manganese. The **T8 temper** indicates that the material has been solution heat-treated, then cold worked, and finally artificially aged. This specific thermomechanical processing is designed to achieve a superior combination of tensile strength, creep resistance, and structural stability at elevated temperatures, making it a premier choice for demanding aerospace applications. HM21A belongs to the "H" series of magnesium alloys and is particularly renowned for its exceptional performance in the 290°C to 400°C (550°F to 750°F) range. --- #### **1. Chemical Composition** The chemical composition of Magnesium HM21A conforms to the following specifications, as per major international standards. | Element | Composition (%) | | :--- | :--- | | **Magnesium (Mg)** | Balance | | **Thorium (Th)** | 1.5 - 2.5 | | **Manganese (Mn)** | 1.0 - 1.7 | | **Zinc (Zn)** | ≤ 0.30 | | **Silicon (Si)** | ≤ 0.10 | | **Copper (Cu)** | ≤ 0.10 | | **Nickel (Ni)** | ≤ 0.01 | | **Iron (Fe)** | ≤ 0.05 | | **Other Impurities** | ≤ 0.30 (each) | **Key Role of Alloying Elements:** * **Thorium (Th):** The primary strengthening element. It forms stable intermetallic compounds (e.g., Mg₂₃Th₆) that provide excellent creep resistance and long-term strength retention at high temperatures. * **Manganese (Mn):** Improves corrosion resistance, particularly against saltwater, by removing iron and other heavy metal impurities from the melt. It also contributes to solid solution strengthening. --- #### **2. Physical Properties** The following table outlines the key physical properties of Magnesium HM21A alloy. | Property | Value | | :--- | :--- | | **Density** | 1.78 - 1.79 g/cm³ (0.064 - 0.065 lb/in³) | | **Melting Point** | ~ 649 °C (~ 1200 °F) | | **Thermal Conductivity** | 125 W/m·K (at 25°C) | | **Coefficient of Thermal Expansion** | 26.7 µm/m·°C (20 - 100°C) | | **Modulus of Elasticity (Tension)** | 45 GPa (6.5 x 10⁶ psi) | | **Specific Heat Capacity** | ~ 1046 J/kg·K | --- #### **3. Mechanical Properties (Typical for HM21A-T8 Temper)** The T8 temper provides the optimal balance of room temperature and high-temperature strength for this alloy. Properties can vary with product form (sheet, plate, extrusion). **Room Temperature Properties (Typical for Sheet/Plate):** * **Ultimate Tensile Strength:** 234 MPa (34,000 psi) * **Tensile Yield Strength (0.2% Offset):** 172 MPa (25,000 psi) * **Compressive Yield Strength:** 117 MPa (17,000 psi) * **Elongation:** 6% (in 2 inches) **Elevated Temperature Performance:** HM21A-T8 excels where other magnesium alloys weaken. Its strength retention is a key feature: * At **205°C (400°F)**: Tensile Yield Strength ≈ **145 MPa (21,000 psi)** * At **315°C (600°F)**: Tensile Yield Strength ≈ **90 MPa (13,000 psi)** * At **425°C (800°F)**: Tensile Yield Strength ≈ **45 MPa (6,500 psi)** * It offers outstanding **creep resistance** and microstructural stability under sustained load at high temperatures. --- #### **4. Product Applications** Magnesium HM21A-T8 is a specialized aerospace alloy chosen specifically for its high-temperature capabilities and light weight. * **Aerospace & Defense:** * **Missile & Rocket Skins:** Body skins, fins, and structural components subjected to aerodynamic heating. * **Aircraft Engine Components:** Compressor casings, accessory gearboxes, and housings in gas turbine engines. * **Aircraft Wheels:** Primarily used in the forged form for wheel hubs. * **Gas Turbine Engines:** Components operating in the hot section where temperatures are elevated but full superalloy strength is not required. * **High-Speed Aircraft:** Structural parts in areas experiencing kinetic heating. --- #### **5. International Standards** Magnesium HM21A-T8 is covered by the following key international and aerospace standards. | Standard Organization | Standard Designation & Title | | :--- | :--- | | **ASTM International** | **ASTM B90 / B90M** - Standard Specification for Magnesium-Alloy Sheet and Plate | | **Aerospace Material (AMS)** | **AMS 4386** - Sheet and Plate, Magnesium Alloy HM21A-T8 | | **UNS Number** | **M13210** | | **SAE** | **AMS 4388** - Extruded Bars, Rods, and Shapes, HM21A-T8 (Covers extruded product forms) | --- #### **Key Advantages & Considerations** * **Advantages:** * **Superior High-Temperature Performance:** Offers the best creep resistance and strength retention in the 315°C - 425°C (600°F - 800°F) range among conventional Mg alloys. * **Excellent Strength-to-Weight Ratio:** Provides significant weight savings over aluminum at elevated temperatures. * **Good Weldability:** Can be readily welded using gas tungsten arc welding (GTAW/TIG) methods. * **Good Damping Capacity:** Inherent ability to absorb vibration and shock, typical of magnesium alloys. * **Considerations:** * **Thorium Content:** Thorium is a low-level radioactive element. This requires special handling, machining (controlling pyrophoric chips), and disposal protocols, increasing cost and complexity. * **Corrosion Resistance:** While manganese improves it, the alloy still requires robust protective coatings (e.g., chemical conversion coatings, anodizing, paint) for service in corrosive environments. * **Modern Substitutes:** Due to the handling concerns of thorium, newer rare-earth containing alloys like **WE43 (Mg-Y-Nd-Zr)** are often preferred for new designs, offering similar high-temperature performance without the radioactivity. **Conclusion** Magnesium HM21A-T8 (UNS M13210) represents a high-performance material solution for extreme thermal environments where minimum weight is critical. Its exceptional strength and creep resistance at temperatures up to 425°C have made it a historical choice for the most demanding missile, rocket, and jet engine applications. While its use is now more selective due to its thorium content, it remains a benchmark for high-temperature magnesium alloy performance.

Packing of Standard Packing: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 3336 gallon liquid totes Special package is available on request.