Magnesium HM21A-T81,UNS M13210;,E FOUR

### **Product Datasheet: Magnesium Alloy HM21A-T81 (UNS M13210)** **Introduction** Magnesium Alloy HM21A-T81 is a high-temperature, heat-treatable wrought magnesium alloy known for its superior creep resistance and excellent strength-to-weight ratio at elevated temperatures. The "-T81" temper indicates that the material has been solution heat-treated, cold worked, and then artificially aged. This specific thermal-mechanical processing significantly enhances its strength, particularly its yield strength, compared to the as-fabricated (-F) temper, making it ideal for critical aerospace components operating under sustained thermal and mechanical stress. **Key Features** * **Enhanced Strength:** The T81 temper provides higher tensile and yield strength compared to the F temper. * **Excellent Creep Resistance:** Maintains mechanical integrity and dimensional stability at temperatures up to 315°C (600°F). * **Low Density:** Offers significant weight savings over aluminum and steel alloys. * **Good Fabricability & Weldability:** Can be formed (with heating) and welded using standard techniques for magnesium alloys. --- #### **1. Chemical Composition (Weight %)** The nominal composition of HM21A-T81 conforms to the following standard limits: | Element | Content (%) | | :---------------- | :---------------------------------- | | **Thorium (Th)** | 1.8 - 2.5 | | **Manganese (Mn)** | 0.45 - 1.0 | | **Magnesium (Mg)** | Remainder | | **Other Impurities** | ≤ 0.30 (total) | ***Important Note:*** *The thorium content classifies this alloy as a low-level radioactive material. This subjects it to specific handling, shipping, and disposal regulations. In many modern applications, it has been superseded by non-thorium, rare-earth containing alloys like WE43 (Mg-Y-RE) or Elektron 21.* --- #### **2. Physical Properties** | Property | Value | | :---------------------------- | :-------------------------------------------- | | **Density** | 1.78 g/cm³ (0.064 lb/in³) | | **Melting Point** | ~ 649°C (1200°F) | | **Thermal Conductivity** | 112 W/m·K (77 Btu·ft/(h·ft²·°F)) | | **Coefficient of Thermal Expansion** | 26.1 µm/m·K (14.5 µin/in·°F) at 20-100°C | | **Modulus of Elasticity** | 45 GPa (6.5 x 10⁶ psi) | --- #### **3. Mechanical Properties (Typical for Sheet, T81 Temper)** The T81 temper provides a significant increase in strength over the F temper. **Room Temperature Properties:** | Property | Value | | :----------------------------- | :-------------------------------------------- | | **Tensile Strength, Ultimate** | 255 MPa (37,000 psi) | | **Tensile Strength, Yield (0.2% Offset)** | 172 MPa (25,000 psi) | | **Elongation** | 5% | | **Compressive Yield Strength** | 138 MPa (20,000 psi) | **Elevated Temperature Properties:** HM21A-T81 is designed to retain its strength under thermal load. * **At 315°C (600°F):** * Tensile Strength: ~ 124 MPa (18,000 psi) * **Creep Strength:** Outstanding resistance to deformation under sustained stress at high temperatures. --- #### **4. International Standards** Magnesium HM21A-T81 is covered by several international and historical standards. * **ASTM:** **ASTM B90 / B90M** - Standard Specification for Magnesium-Alloy Sheet and Plate. * **AMS:** **AMS 4384** - Sheet and Plate, Magnesium Alloy HM21A, Solution Heat Treated, Cold Worked, and Artificially Aged (T81 Temper). * **UNS:** **M13210** * **SAE:** **AMS 4384** * **Federal Standard:** **QQ-M-56** (Covers various tempers) --- #### **5. Product Applications** The combination of light weight, high strength, and exceptional performance at elevated temperatures made HM21A-T81 a preferred material for critical aerospace systems, though its use is now often limited to legacy platforms. * **Aerospace & Defense:** * **Missile & Rocket Skin and Structures:** Withstands kinetic heating during flight. * **Aircraft Engine Components:** Engine cowlings, gearbox covers, and heat shields. * **Supersonic Aircraft Skin Panels:** Used in areas subject to aerodynamic heating. * **Spacecraft and Satellite Components:** Where weight savings are paramount. * **Gas Turbine Components:** Non-critical static parts in high-temperature environments. **Fabrication & Heat Treatment Notes:** * **The T81 Temper Process:** The material is typically solution heat-treated, cold worked (e.g., by stretching or rolling), and then artificially aged to achieve the specified mechanical properties. * **Welding:** Can be welded using Gas Tungsten Arc Welding (GTAW/TIG), but post-weld heat treatment may be required to restore properties in the Heat-Affected Zone (HAZ). * **Forming:** Requires hot forming techniques. --- **Disclaimer:** This information is for reference purposes only. Properties can vary based on manufacturing process, lot, and section thickness. The thorium content necessitates careful regulatory compliance. It is essential to consult the latest official material specifications from the relevant standards organizations (e.g., ASTM, SAE) for design, procurement, and manufacturing. The suitability of the material for any specific application must be evaluated by the user.

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 3338 gallon liquid totes Special package is available on request.