Magnesium HK31A-O，UNS M13310;,E FOUR

Product Introduction: Magnesium Alloy HK31A-O (UNS M13310)** **Magnesium Alloy HK31A** is a high-strength, heat-treatable magnesium alloy primarily strengthened by the addition of thorium. It is renowned for its exceptional high-temperature stability, maintaining useful mechanical properties at temperatures up to 315°C (600°F) and higher. The "O" temper designation indicates the annealed (softest) condition, which offers optimal formability and is the standard condition prior to age-hardening. This alloy is part of the "H" series of magnesium alloys, which are specifically designed for elevated temperature service. --- #### **1. Chemical Composition** The typical chemical composition of Magnesium HK31A, as per ASTM and other international standards, is provided in the table below. | Element | Composition (%) | | :--- | :--- | | **Magnesium (Mg)** | Balance | | **Thorium (Th)** | 2.5 - 4.0 | | **Zirconium (Zr)** | 0.45 - 1.0 (Min. 0.45) | | **Zinc (Zn)** | ≤ 0.30 | | **Manganese (Mn)** | ≤ 0.15 | | **Silicon (Si)** | ≤ 0.01 | | **Copper (Cu)** | ≤ 0.10 | | **Nickel (Ni)** | ≤ 0.01 | | **Other Impurities** | ≤ 0.30 (each) | **Key Role of Alloying Elements:** * **Thorium (Th):** The primary strengthening element. It forms stable intermetallic compounds that provide excellent creep resistance and strength retention at high temperatures. * **Zirconium (Zr):** Acts as a powerful grain refiner, which enhances the alloy's strength, ductility, and castability. --- #### **2. Physical Properties** The following table outlines the key physical properties of Magnesium HK31A alloy. | Property | Value | | :--- | :--- | | **Density** | 1.79 g/cm³ (0.065 lb/in³) | | **Melting Point** | ~ 649 °C (~ 1200 °F) | | **Thermal Conductivity** | 112 W/m·K (at 25°C) | | **Coefficient of Thermal Expansion** | 26.1 µm/m·°C (20 - 100°C) | | **Electrical Resistivity** | ~ 82 nΩ·m | | **Modulus of Elasticity (Tension)** | 45 GPa (6.5 x 10⁶ psi) | --- #### **3. Mechanical Properties (Typical for HK31A-O Condition)** The "O" temper is the as-fabricated and annealed condition. For high-strength applications, this alloy is typically heat-treated to the **H24 (Strain-Hardened and Partially Annealed)** or **T6 (Solution Heat-Treated and Artificially Aged)** temper. **Typical Room Temperature Properties (Sheet/Plate - H24 Temper):** * **Ultimate Tensile Strength:** 241 MPa (35,000 psi) * **Tensile Yield Strength (0.2% Offset):** 172 MPa (25,000 psi) * **Compressive Yield Strength:** 138 MPa (20,000 psi) * **Elongation:** 9% (in 2 inches) **High-Temperature Performance:** A key advantage of HK31A is its ability to retain strength at elevated temperatures. For example, at **315°C (600°F)**, it can maintain a tensile yield strength of approximately **110 MPa (16,000 psi)**. --- #### **4. Product Applications** Magnesium HK31A is primarily specified for aerospace and military applications where its unique combination of light weight and high-temperature performance is critical. * **Aerospace Structures:** Skin and structural components for missiles, rockets, and high-speed aircraft. * **Engine Components:** Gearboxes, compressor housings, and accessory casings operating at elevated temperatures. * **Missile and Spacecraft Components:** Body skins, fins, and frames that experience aerodynamic heating. * **Nuclear Industry:** Shielding and structural components due to thorium's neutron absorption characteristics. --- #### **5. International Standards** Magnesium HK31A is covered by several prominent international and national standards. | Standard Organization | Standard Designation | | :--- | :--- | | **ASTM International** | **ASTM B90 / B90M** (Standard Specification for Magnesium-Alloy Sheet and Plate) | | **Aerospace Material (AMS)** | **AMS 4383** (Sheet and Plate, Magnesium Alloy HK31A-H24) | | **UNS Number** | **M13310** | | **SAE** | **AMS 4385** (Extruded Shapes and Bars, HK31A) | --- #### **Key Advantages & Considerations** * **Advantages:** * Excellent strength-to-weight ratio at elevated temperatures. * Good creep resistance. * Superior stability and retention of properties after long-term exposure to heat. * Good weldability and fabricability in the "O" temper. * **Considerations:** * **Thorium Content:** The presence of thorium, a low-level radioactive element, requires special handling, machining, and disposal procedures to manage the fine, pyrophoric chips and dust. This has led to its replacement by newer, non-radioactive alloys like WE43 or Elektron 21 in many modern applications. * **Corrosion Resistance:** Like most magnesium alloys, it requires protective coatings or a clad layer (e.g., with Alclad) for use in corrosive environments. **Conclusion** Magnesium HK31A-O (UNS M13310) is a specialized, high-performance alloy engineered for the most demanding high-temperature, lightweight applications, particularly in the aerospace sector. While its use is now more selective due to its thorium content, it remains a benchmark material for its proven performance in extreme conditions.

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 3334 gallon liquid totes Special package is available on request.